11institutetext: Institute for Particle Physics and Astrophysics, ETH Zürich,
Wolfang-Pauli-Strasse 27, 8093 Zürich, Switzerland 22institutetext: Max-
Planck-Institut für Extraterrestrische Physik (MPE), Giessenbachstrasse 1,
D-85748 Garching bei München, Germany 33institutetext: European Space Agency
(ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1,
2201 AZ Noordwijk, The Netherlands 44institutetext: Citizen Scientist,
Zooniverse, Astrophysics Sub-department, University of Oxford, Keble Road,
Oxford, OX1 3NP, UK 55institutetext: Max-Planck-Institut für Astrophysik
(MPA), Karl-Schwarzschild-Straße 1, D-85748 Garching bei München, Germany
66institutetext: European Space Agency (ESA), European Space Astronomy Centre
(ESAC), Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid,
Spain

# Hubble Asteroid Hunter

II. Identifying strong gravitational lenses in HST images with crowdsourcing

Emily O. Garvin e-mail<EMAIL_ADDRESS>Sandor Kruk e-mail:
<EMAIL_ADDRESS>Claude Cornen 44 Rachana Bhatawdekar 33 Raoul
Cañameras 55 Bruno Merín 66

(Received April 9, 2022; revised June 10, 2022; accepted June 28, 2022)

###### Abstract

Context. The Hubble Space Telescope (HST) archives constitute a rich dataset
of high resolution images to mine for strong gravitational lenses. While many
HST programs specifically target strong lenses, they can also be present by
coincidence in other HST observations.

Aims. We aim to identify non-targeted strong gravitational lenses in almost
two decades of images from the ESA Hubble Space Telescope archive (eHST),
without any prior selection on the lens properties.

Methods. We used crowdsourcing on the Hubble Asteroid Hunter (HAH) citizen
science project to identify strong lenses, alongside asteroid trails, in
publicly available large field-of-view HST images. We visually inspected 2 354
objects tagged by citizen scientists as strong lenses to clean the sample and
identify the genuine lenses.

Results. We report the detection of 252 strong gravitational lens candidates,
which were not the primary targets of the HST observations. 198 of them are
new, not previously reported by other studies, consisting of 45 A grades, 74 B
grades and 79 C grades. The majority are galaxy-galaxy configurations. The
newly detected lenses are, on average, 1.3 magnitudes fainter than previous
HST searches. This sample of strong lenses with high resolution HST imaging is
ideal to follow-up with spectroscopy, for lens modelling and scientific
analyses.

Conclusions. This paper presents an unbiased search of lenses, which enabled
us to find a high variety of lens configurations, including exotic lenses. We
demonstrate the power of crowdsourcing in visually identifying strong lenses
and the benefits of exploring large archival datasets. This study shows the
potential of using crowdsourcing in combination with artificial intelligence
for the detection and validation of strong lenses in future large-scale
surveys such as ESA’s future mission Euclid or in JWST archival images.

###### Key Words.:

Gravitational lensing: strong – Galaxies: general – Galaxies: individual

##  1 Introduction

Strong gravitational lensing is a powerful tool that has multiple applications
in astrophysics and cosmology. Strong lenses are used to study the dark matter
content and distribution in galaxies (Koopmans et al. 2006; Barnabè et al.
2009; Sonnenfeld et al. 2015; Oldham & Auger 2018) and clusters (Richard et
al. 2010; Jauzac et al. 2015; Caminha et al. 2019), to study distant galaxies
(Marshall et al. 2007; Dessauges-Zavadsky et al. 2015; Swinbank et al. 2015;
Cañameras et al. 2017), and to constrain cosmological parameters such as the
Hubble constant and the dark energy equation of state from time delay
observations (e.g. Suyu et al. 2010, 2014; Sereno & Paraficz 2014; Courbin et
al. 2018; Wong et al. 2020; Millon et al. 2020). With the help of strong
gravitational lensing of massive clusters, we have also been able to probe
galaxy evolution through Ultra-Violet luminosity functions (UV LF) (Atek et
al. 2014; Livermore et al. 2017), stellar mass functions (Bhatawdekar et al.
2019; Kikuchihara et al. 2020), and UV slopes (Bhatawdekar & Conselice 2021),
well into the epoch of reionisation. Strong gravitational lensing is a rare
phenomenon which relies on the chance alignment of a foreground object with a
large surface mass density (lens) with a bright background object (source)
such as a galaxy, a quasar or a supernova (Kelly et al. 2015). Recently, other
lensed sources have also been reported, such as magnified stars and stellar
complexes (Welch et al. 2022; Vanzella et al. 2021). Overall, since the
discovery of the first gravitational lens (Walsh et al. 1979) only
approximately one thousand strong lenses have been confirmed.

Finding strong gravitational lenses is a difficult outlier detection problem.
So far, numerous automated algorithms have been developed for the detection of
strong lenses in large-scale surveys, for example through the identification
of arcs and rings in multiband imaging (e.g. Alard 2006; Marshall et al. 2009;
Gavazzi et al. 2014; Sonnenfeld et al. 2018), or through the blended
signatures of lens and source galaxies in fibre spectroscopy (e.g. Bolton et
al. 2008; Brownstein et al. 2012; Holwerda et al. 2015; Shu et al. 2017;
Talbot et al. 2021). With the latest developments of artificial intelligence,
machine learning algorithms, and in particular convolutional neural networks
(CNNs), have had an increasing number of applications in astronomy, from
galaxy classification (Dieleman et al. 2015; Huertas-Company et al. 2015;
Walmsley et al. 2020, 2022) to estimating quantities such as photometric
redshifts (Samui & Samui Pal 2017; D’Isanto & Polsterer 2018; Schuldt et al.
2021). Strong lens searches have largely benefited from the use of CNNs (e.g.
Bom et al. 2017; Schaefer et al. 2018; Petrillo et al. 2019; Jacobs et al.
2019; Cañameras et al. 2020; Huang et al. 2020). The Bologna strong
gravitational lens finding challenge has extensively compared the performance
of these methods on simulated data resembling future ground- and space-based
imaging surveys such as LSST and Euclid (Metcalf et al. 2019). While automated
search algorithms are generally highly efficient on real data, they remain
affected by false-positives, and they are typically complemented by visual
inspection to increase the sample purity (for instance, only $\simeq$1$-$3% of
candidates selected by arc-finders and CNNs are highly-probable lenses;
Sonnenfeld et al. 2018; Petrillo et al. 2019).

One distributed method that has been proven successful in the visual
identification of strong lenses is citizen science. The general public has
been involved in the classification of astronomical data through projects such
as Galaxy Zoo (Lintott et al. 2008). The Space Warps project (Marshall et al.
2016) pioneered the crowdsourced identification of strong gravitational lenses
in surveys such as CFHTLS (More et al. 2016) and HSC-SSP (Sonnenfeld et al.
2020). Using the Zooniverse framework, Space Warps display images on a web-
based interface and ask volunteers whether a gravitational lens is present in
the images. To assess the completeness and uncertainty of the classifications,
Space Warps measures the performance of each user on a training set of
simulated lenses, and weights the individual user contributions based on their
‘skill’.

These various lens search methods typically focus on specific lens
configurations. On the one hand, galaxy-scale strong lens candidates
identified from unresolved fibre spectra have massive foreground elliptical
and Einstein radii limited by the fibre aperture sizes (e.g. Bolton et al.
2008; Brownstein et al. 2012). On the other hand, searches using multiband
images from wide-field, ground-based surveys are preferentially selecting
candidates with wider image separations ($\geq$2″ from the lens centre)
ensuring robust lens and source deblending, and are therefore spanning both
galaxy-scale and more massive group-, cluster-scale foreground halos (e.g.
Belokurov et al. 2009; Sonnenfeld et al. 2018; Cañameras et al. 2020).
Moreover, the visual grades assigned by strong lens expert and volunteers show
large scatter due to the difficulty in distinguishing strong lenses from
rings, spirals, mergers, and other contaminants in seeing-limited images (e.g.
More et al. 2016; Rojas et al. 2021).

In this study, we employed a crowdsourced approach to detect strong lenses in
archival images from the Hubble Space Telescope (HST), in order to benefit
from the higher angular resolutions, and to cover a broader range of lens and
source galaxy types, lens potentials, and multiple image configurations.
Instead of showing volunteers postage stamps of galaxies, we displayed cutouts
of HST images sufficiently large to contain tens of objects. Although the
original project was not designed for the detection of lenses but for the
detection of asteroids, we asked the volunteers on Hubble Asteroid Hunter
111www.asteroidhunter.org (HAH) to tag possible lenses on the forum of the
project, and the science team inspected all the tagged lenses. Several square
degrees of HST imaging have been previously searched for the presence of
lenses, for example in the HST AEGIS survey (Moustakas et al. 2007), the GEMS
survey (More et al. 2011), the COSMOS survey (Jackson 2008; Faure et al. 2008;
Pourrahmani et al. 2018), and over 7 deg2 of archival observations (Pawase et
al. 2014). We extended the systematic morphological selection of strong lenses
from the HST archive to a much larger area, without colour, brightness, and
redshift cuts, in order to provide a statistically-significant and diverse
sample of robust lens candidates for future spectroscopic follow-up and
detailed modelling.

The structure of this paper is as follows. In Sect. 2, we present the input
data set, and in Sect. 3 we describe the inspection, classification, and light
profile fitting. The results and properties of strong lens candidates are
given in Sect. 4. Finally, we compare with other search methods in Sect. 5,
and we summarise in Sect. 6. Throughout the paper we adopted the WMAP Seven-
Year Cosmological parameters (Jarosik et al. 2011) with ($\Omega_{\rm
M},\Omega_{\Lambda},h)=(0.27,0.73,0.71)$.

##  2 Data

We analysed archival HST images from the Advanced Camera for Surveys Wide
Field Channel (ACS/WFC) and Wide Field Camera 3 Ultraviolet and Visible
(WFC3/UVIS) and Near-infrared (WFC3/IR) channels. These instruments and
detectors have the largest field-of-views, thus the highest chance of
containing serendipitously observed strong lenses. The observations were taken
between 30 April 2002 (when the ACS camera was installed) and 24 April 2020
for ACS/WFC, and between 25 July 2009 (when the WFC3 obtained first light) and
24 April 2020 for WFC3/UVIS. This data is presented in the Kruk et al. (2022)
paper. The WFC3/IR images were uploaded later to the project, after the
analysis of ACS and WFC3/UVIS data was completed, and consisted of
observations taken between 25 July 2009 and 1 June 2020.

The analysis is complete with data taken and publicly available in the HST
archives up to 1 June 2020. Observations based on general observer (GO)
proposals are available in the HST archive one year after they were taken,
therefore the last GO observation analysed were taken before June 2019. HST
Snapshot observations are available in the archive immediately after they are
acquired and they were analysed up to June 2020. One of the authors, citizen
scientist Claude Cornen inspected the data released in the HST archives after
June 2020 and found 12 new strong lens candidates. These were not included in
the main analysis but presented separately in Appendix C.

In the Hubble Asteroid Hunter (HAH) project, volunteers inspected the single-
band HST composite images in PNG format available from the European Hubble
Space Telescope (eHST) archive (the same images are also available in MAST).
These images were created from the FITS images by first applying autoscaling,
which scales the image linearly from the 0.5% pixel level to the 99.5% pixel
level (using autoscale=99.5, which is the default), and then applying a
trigonometric asinh scaling.222More details on the parameters used can be
found at https://hla.stsci.edu/fitscutcgi_interface.html.

The composite HST images were obtained by stacking individual HST dithered
exposures, processed using the standard HST data processing pipeline by STScI:
the exposures were aligned and processed with DrizzlePac333https://hst-
docs.stsci.edu/drizzpac (Gonzaga et al. 2012) for geometric distortion
corrections and cosmic ray removal.

In order to optimise the presentation of the images for the visual inspection
of citizen scientists, we split the HST ACS/WFC and WFC3/UVIS composite images
into four equal parts, of sizes 101″ $\times$ 101″ and 80″ $\times$ 80″,
respectively. For the WFC3/IR images we used the full frame with size 127″
$\times$ 137″ for the search. We selected all the composite HST images
available in the archive based on the following criteria: an exposure time
greater than 300 seconds, and a field-of-view greater than 7 arcmin2 to
exclude sub-frames (only for ACS/WFC and WFC3/UVIS). Occasionally, the same
field was observed multiple times by HST. We showed all the images available,
even though observations overlapped in the targeted region of the sky.

In total, 145 396 cutouts were inspected, corresponding to 45 784 unique
observations. The inspected images were in grey-scale, without colour
information. The total area imaged by HST and inspected in this project is
about 27 deg.2. This includes the HST Cosmic Evolution Survey (COSMOS;
Koekemoer et al. 2007; Scoville et al. 2007), as well as the CANDELS survey
(Grogin et al. 2011). The estimate of the total area imaged takes into account
the overlap between the HST pointings of the approximately same region of the
sky with different instruments and filters. These overlapping observations
were nonetheless inspected individually by the volunteers. Details on the
images inspected are shown in Table 1.

Table 1: HST archival images inspected while searching for strong
gravitational lenses in the Hubble Asteroid Hunter project.

HST Instr. | FoV | Scale | Images | Cutouts
---|---|---|---|---
|  | (″/pix) |  |
ACS/WFC | 202″ $\times$ 202″ | 0.05 | 22 940 | 91 760
WFC3/UVIS | 160″ $\times$ 160″ | 0.04 | 10 326 | 41 118
WFC3/IR | 123″ $\times$ 136″ | 0.13 | 12 518 | 12 518

Notes. The search contains HST observations taken and released between 2002
and June 2020, with exposure times larger than 300s. Images follow the
standard HST processing pipeline and are single-band. ACS/WFC and WFC3/UVIS
images were divided into 4 equal quadrants (cutouts) in order to maximise the
detection of smaller arcs. WFC3/IR images were presented as they are.

##  3 Method

###  3.1 Visual identification by citizen scientists

We identified gravitational lenses in the Hubble Asteroid Hunter citizen
science project (Kruk et al. 2022), launched on 20 June 2019 and which ran
until August 2020. The primary purpose of the project was to identify
serendipitously observed asteroid trails in HST images while the telescope was
observing targeted objects, proposed by astronomers. In total, 11 482
volunteers inspected the 145 396 cutouts, each image being inspected by ten
people. The project also had a dedicated forum,
Talk444https://www.zooniverse.org/projects/sandorkruk/hubble-asteroid-
hunter/talk, where the volunteers could tag cutouts containing interesting
objects (with #) and discuss about them.

In contrast to other citizen science projects that are specifically designed
to identify strong lenses (such as Space Warps) or projects that have the
strong lens classification as part of their workflows (e.g. Galaxy Zoo),
Hubble Asteroid Hunter did not provide a classification option for strong
lenses. Instead, we asked the volunteers to specifically tag observations
containing strong gravitational lenses on Talk, including individual strong
lenses (with #gravitational_lens) and clusters of galaxies with arcs
corresponding to strong lensing (with #cluster_lens). For training, we
provided several examples of strong gravitational lenses, based on previously
identified lenses in HST images and targeted lenses, both in the Tutorial and
the Field Guide of the project. The science team inspected and assessed all
gravitational lenses as the project progressed, instead of analysing the
classifications when the project was completed. Finally, it is worth
mentioning that some of the citizen scientists on the project who tagged
lenses participated in Space Warps and, therefore, have prior training and
familiarity with the appearance of strong lenses.

###  3.2 Visual identification by authors

In total, 2 354 cutouts were tagged as containing individual strong lenses
(with #gravitational_lens). Members of the science team (EOG, SK, CC)
inspected all the cutouts, selected 417 unique gravitational lens candidates
and added them to our catalogue.

The initial catalogue contained the position of the lens, the instrument and
filter used. We used the ESASky555https://sky.esa.int/ portal (Giordano et al.
2018) to retrace the sky coordinates of the lenses in the images. ESASky also
reports the objects which appear in previous publications, matching their
positions in the HST images with astronomical catalogues and papers from the
CDS Simbad database. This eased our work to establish which lenses have been
previously published. We also double-checked with other databases such as NED.
We classified the objects as being ‘targeted’ (in the case where the strong
lenses were the target of the observations, judged based on the corresponding
HST proposal), previously ‘published’ (whether they appeared in other
publications) or ‘unpublished’. A number of 165 strong lenses were the target
of the HST observations, for example by the Sloan Lens ACS Survey (SLACS,
Bolton et al. 2008), the CFHTLS-Strong Lensing Legacy Survey (SL2S, More et
al. 2012), the CASSOWARY survey (Stark et al. 2013), or the BOSS Emission-Line
Lens Survey (BELLS, Shu et al. 2016). These targeted lenses were excluded from
our analysis. The remaining 252 strong lenses were not the primary targets of
the HST observations. We searched for these objects on ESASky, NED, and
enquired with the 96 Principal Investigators of these HST observations whether
they appear in previous publications. 54 have been previously identified and
appear in other publications. Hence, we are left with 198 unknown, new lens
candidates distributed on the sky according to Fig. 1.

Figure 1: Map in galactic coordinates showing the sky position of the newly
discovered lenses serendipitously observed with HST (red points), over the
densities of the parent sample of HST pointings analysed in the HAH project
(in tiles of $\sim$215 deg.2 each). The sky distribution of the HST
observations with strong lens candidates is roughly isotropic, excluding the
Galactic Plane. The grey dotted line represents the ecliptic.

Three members of the science team (EOG, SK, CC) assigned a grade to each lens,
based on: the morphology, the shape of the source image and the quality and
availability of a colour image. We discussed each object and agreed on a final
grade. The criteria used for the classification are inspired by the convention
of More et al. (2016), and define the likelihood of each object to be a strong
lens. Grades A are almost certainly lenses. They are the most promising
candidates based on the configuration of the lens, and the morphology in the
colour- or grey-scale images. Their identification is based on the presence of
an image and counter image, and on a clear colour separation between the lens
and image (if colour information was available). Grades B are highly probable
lenses. These are also high-quality candidates showing probable lensing
features, but with typically fewer clear and bright counter-images, and less
colour information available than grades A. Their confirmation requires
spectroscopic follow-up or lens modelling. Grades C are maybe lenses. These
possible strong lens systems mostly have single arcs without clear counter-
images. They are more difficult to distinguish from non-lens contaminants, and
some could be tidal tails, compact groups, or weakly lensed arcs.

We further classified the morphology of the source images into ‘Arc’, which is
the most common class, ‘Double’ (two images), ‘Triple’ (three images), ‘Quad’
(four images), and ‘Ring’ or ‘Cross’ for the rarest Einstein ring and Einstein
cross configurations. Additionally, we classified the morphology of the lenses
into ‘elliptical’, ‘disc’ and ‘edge-on disc’.

###  3.3 Measuring the arc radii

A measurable parameter for the strong lenses in our sample is the arc radius,
which can be used as a proxy for the Einstein radius. For the strong lenses
made of a single arc, we measured the radius of the circle centered on the
brightest pixel of the lensing galaxy and tangent to the arc, using both the
DS9 and the Aladin ‘circle’ tool. For the other configurations, we drew a
circle, or the best matching ellipse, as a substitute for the outer tangential
critical curve in the lens plane and measured its radius.

###  3.4 Galfit modelling of the lenses

In this subsection, we describe the fitting process using GALFIT (Peng et al.
2002) to determine the parameters of the lenses: the magnitudes, effective
radii, axis ratios, and position angles. These parameters are important for
future tasks, such as lens modelling and source reconstruction, which are not
covered in this work.

We fitted a total of 252 lenses with GALFIT, including the 198 previously
unknown systems, and the 54 which were already identified and published, as
discussed above. We used the sky position of the lenses to create cutouts with
square sizes of 10″, centered on the objects, from the single-band composite
HST images available in eHST. If multiple bands were available, we used the
reddest band available, which was F814W in the majority of cases. The band
used for fitting is shown in Table LABEL:tab:unpublished and Table
LABEL:tab:rediscoveries.

To ensure that only the lenses are fitted, we masked out the other objects in
the cutouts, including the arcs and any other background image, with
SExtractor (Bertin & Arnouts 1996). We created images of the HST Point Spread
Function (PSF) using TinyTim (Krist 1995), for the band corresponding to each
image and the position of the object in the corresponding image, which we use
for the fitting. We fitted the lenses with a single Sérsic profile (Sersic
1968) described by the following equation:

$\sum(r)=\sum_{\rm e}\exp\Bigg{\\{}-k\left[(\frac{r}{r_{\rm
e}})^{\frac{1}{n}})-1\right]\Bigg{\\}},$ (1)

where $\mathrm{\sum(r)}$ is the surface brightness at radius r, $r_{\rm e}$ is
the half-light radius, $\sum_{e}$ is the effective surface brightness, k is a
normalisation coefficient and n is the Sérsic index. As starting parameters,
we used a magnitude of 20, an axis ratio of 0.9, and an effective radius of
0.5″.

We used a fixed De Vaucouleurs profile ($n=4$) for the majority of the lenses
(243 galaxies), which we classified as being elliptical galaxies. We fitted
the remaining 23 galaxies which we classified as being discs with an
exponential Sérsic index ($n=1$). We note that in the case of group-scale
lenses, we fitted multiple galaxies which we deemed to be the lenses, hence
the total number of galaxies fitted is higher than the number of strong lens
candidates. We show the GALFIT models and residuals of the A grade lenses in
Fig. 11 and Fig. 12.

To determine the magnitudes, we calculated the zero points based on the
quantities provided in the FITS headers,
using666https://www.stsci.edu/hst/instrumentation/acs/data-
analysis/zeropoints:

$\displaystyle m_{\rm AB}=$ $\displaystyle-2.5\log_{10}(F)-2.5\log_{10}({\tt
PHOTFLAM})$ (2) $\displaystyle-2.5\log_{10}({\tt PHOTPLAM})-2.408,$

where PHOTFLAM is the inverse sensitivity and represents the scaling factor
necessary to transform an instrumental flux in units of electrons per second
to a physical flux density, and the PHOTPLAM is the pivot wavelength provided
in the FITS header and used to derive the instrumental zero point magnitudes.
For consistency, we also measured the magnitudes of the lenses with SExtractor
($\mathrm{mag}_{\rm AUTO}$ and $\mathrm{mag}_{\rm ISO}$). We compare the
magnitudes estimated with GALFIT and SExtractor in Figure 13 and find that the
measurements are consistent between the different methods.

##  4 Results

We present the results on the 198 newly identified lens candidates (which we
henceforth call ‘discovered’) in Table LABEL:tab:unpublished, and on the 54
previously published lenses (which we henceforth call ‘rediscovered’) in Table
LABEL:tab:rediscoveries. The lenses in the tables are grouped by grades, and
postage stamps of the Grade A, Grade B, and Grade C lenses are shown in
Figures 2, 3, and Figure 4, respectively. In the tables we provide the IAU
name, the $\mathrm{RA}$ and $\mathrm{Dec}$ coordinates of the candidate, the
instrument corresponding to the HST observation in which the lens was found,
and the filter used for light fitting. We also provide our measurements of the
arc radii, $r_{\mathrm{arc}}$, as well as the magnitude, the effective radius,
$r_{\rm e}$, the axis ratio, $q$, and the position angle, PA, measured using
GALFIT. We also list our classification into Arc, Double, Ring, and Quad
configurations.

While the sample mainly consists of galaxy-galaxy lens configurations, some of
the lens galaxies may be part of a cluster, in which case the strong lensing
effect can be enhanced by the mass distribution of the cluster. In addition,
the presence of a structure along the line-of-sight, either in front or behind
the main lens plane, will also perturb the light deflection. Firstly, we
identify the lens candidates that are associated with known foreground galaxy
clusters (from, e.g. MACS, Abell, RELICS catalogues) using the target name of
the HST observations. Secondly, to get a more comprehensive overview of the
lens candidates located in possible cluster fields, we also cross-match with
the positions of cluster candidates selected (1) from SDSS DR8 data with the
redMaPPer algorithm (the SDSS catalogue from Rykoff et al. 2016), and (2) in
the footprint of DESI legacy imaging surveys based on a photometric redshift
clustering analysis (DR8, Zou et al. 2021). Both surveys cover a significant
fraction of the line-of-sights towards our HAH lenses. We use a maximal cross-
match radius of 3′ corresponding to $\simeq$1 Mpc at $z\sim 0.5$. Tables
LABEL:tab:unpublished and LABEL:tab:rediscoveries indicate whether each lens
matches the position of a cluster, and Table LABEL:tab:clusters gives
additional information on the cluster names and angular separation. In total,
124 out of the 198 new lens discoveries and 32 out of the 54 rediscoveries are
within 3′ from the centroid position of a candidate or confirmed cluster.

Finally, we search for redshifts available for the lens galaxies. We provide
either the photometric or spectroscopic redshift, if available, retrieved from
NED or from the SDSS-IV DR16 (Ahumada et al. 2020). Additionally, the last
column of Table LABEL:tab:rediscoveries lists the reference papers for the
candidates previously published.

Figure 2: The 78 grade A HAH lenses identified in this study, with green
triangles indicating the 33 ‘rediscovered’ lenses. The lenses are indicated
using the sequence part of their name. Postage stamps are $10\arcsec\times
10\arcsec$. The orientation of the images is North up and East is to the left.
Figure 3: The 89 grade B HAH lenses identified in this study, with green
triangles indicating the 15 ‘rediscovered’ lenses. The lenses are indicated
using the sequence part of their name. Postage stamps are $10\arcsec\times
10\arcsec$. The orientation of the images is North up and East is to the left.
Figure 4: The 85 grade C HAH lenses identified in this study, with green
triangles indicating the 6 ‘rediscovered’ lenses. The lenses are indicated
using the sequence part of their name. Postage stamps are $10\arcsec\times
10\arcsec$. The orientation of the images is North up and East is to the left.
Figure 5: The first sub-figure on the left shows a histogram distribution of
the redshifts retrieved with SDSS and NED (both photometric and
spectroscopic). The middle sub-figure uses a violin plot to show the
respective empirical distributions of discovered and rediscovered lenses. The
right sub-figure shows violin plots per grade groups. The violin plots were
fitted using a Gaussian kernel, with the software R. Figure 6: The left panel
shows a histogram distribution of the apparent magnitudes as measured with
GALFIT (in the filter mentioned in Table LABEL:tab:unpublished and Table
LABEL:tab:rediscoveries). The middle panel shows violin plots as the
respective empirical distributions of discovered and rediscovered lenses. The
right panel shows empirical distributions of magnitudes for each grade group.
Figure 7: The first sub-figure on the left shows a histogram distribution of
the measured arc radii. The middle sub-figure uses violin plots to show the
respective empirical distributions of discovered and rediscovered lenses. The
right sub-figure shows empirical distributions of arc radii per grade groups.
The distributions are all skewed to the right. Figure 8: The first sub-figure
on the left shows a histogram distribution of the effective radii measured
with GALFIT. The middle and right sub-figure shows empirical Gaussian kernel
distributions of lenses, separated per discovery (middle panel) and per grade
(right panel). Figure 9: The mosaic plot shows the discovery groups and grades
in a visual representation of a contingency table. The widths of the stacked
boxes represent the fraction of each grade in the sample, while the heights of
the boxes represent the proportion per discovery group. All the grades have
been assigned by three members of the science team (EOG, SK, CC) after
consensus following the individual evaluations. We observe that in the
discovery group, we have a higher fraction of C grades compared to A grades.
In the rediscovery group, there is a higher fraction of A grades compared to
both B and C grades. Hence, the mosaic plot indicates that, overall, our
grading scheme is rather conservative towards newly discovered lenses.

###  4.1 Distribution of lens properties

In the previous sections, we described how the gravitational lenses were found
and reported into discovered and rediscovered lenses and we explained how we
fitted them in order to retrieve the lens parameters. In this subsection, we
describe the results, namely the distributions of properties such as arc
radii, and lens redshifts, magnitudes, and effective radii. The properties are
grouped by either discovered or rediscovered lenses, and by visual grade.

In Figure 5, we plot the distribution of photometric and spectroscopic
redshifts from SDSS and NED for the lens galaxies for which this information
was available. The median redshift of our sample is $z=0.41$, and the
distribution is skewed to higher redshifts, up to $z=1.3$. The discovered and
rediscovered lenses show similar distributions, while Grade A lenses are, on
average, at lower redshifts compared to Grade B or C. The redshift
distribution of the lenses in our sample is also broadly consistent with the
lens galaxy redshifts from previous ground-based searches (e.g. Bolton et al.
2008; Stark et al. 2013).

Figure 6 shows the distribution of magnitudes over all instruments and
filters. We find that the magnitude of reported objects are distributed around
an average value of $m=20.6$. Although our sample contains lenses observed
with WFC3/IR, which are typically brighter, our average magnitude is 1.3
magnitudes fainter than the average magnitude $m=19.3$ of the sample of lenses
found by Pawase et al. (2014) in a previous search in ACS images. The violin
plots in Figure 6 show that the magnitudes of the discovered lenses are
fainter than those of rediscoveries ($m=20.8$ vs. $m=20.1$). Indeed, the
faintest lens found has a measured magnitude of $m=26.4$ compared to $m=23.6$
in the rediscovered group. Moreover, a quarter of the rediscovered objects
were detected above $m=21$, while a quarter of the new discoveries have a
magnitude above $m=21.9$. Interestingly, Grade C lenses are brighter than
Grade B or Grade A, showing that we did not assign the grade based on
brightness, but on the morphology. It is important to note that the magnitudes
are plotted together for both the ACS and WFC3 instruments and some are
measured in different filters (see Table LABEL:tab:unpublished for the filters
used).

As for the arc radii of the lenses, the distribution is right skewed, with a
median of $r_{\mathrm{arc}}=1.58\arcsec$ and a mean of
$r_{\mathrm{arc}}=1.94\arcsec$. Although it is consistent with the
distribution of arc radii presented in Pawase et al. (2014), we notice from
the plot on the left in Figure 7 that our detected lenses include more extreme
arc radii than their sample. Indeed, a few of the newly discovered arc radii
range up to $r_{\mathrm{arc}}=4.5\arcsec$, which corresponds to group-scale
lenses. In addition, for our newly discovered lenses, the median arc radius is
$r_{\mathrm{arc}}=1.23\arcsec$ and the smaller arcs we find have a radius of
only $r_{\mathrm{arc}}=0.33\arcsec$. This shows a relative improvement in
finding smaller separation arcs in comparison to previously reported lenses
(in the rediscovered group), for which median $r_{\mathrm{arc}}=1.67\arcsec$
and the smallest arcs have radii $r_{\mathrm{arc}}=0.61\arcsec$. Furthermore,
a quarter of the rediscovered objects were found to have $r_{\mathrm{arc}}\leq
0.88\arcsec$ while a quarter of our newly discovered objects have
$r_{\mathrm{arc}}\leq 0.82\arcsec$. This observed difference in the median arc
radii and their distribution (shown in the central plot in Figure 7) indicates
that citizen science as a strong lens detection method has a potential to
unveil arcs with smaller angular separations from the source. This potential
deserves to be further investigated and quantified in future studies.

The distributions of lens galaxy effective radii (Figure 8) show a median
$r_{\mathrm{e}}=0.66\arcsec$ and are consistent across discovered and
rediscovered groups, as well as with the distribution in Pawase et al. (2014).

Finally, the mosaic plot from Figure 9 shows a visual representation of a
proportion test on the contingency table of the grades assigned by members of
the science team (EOG, SK, CC) to the discovered and rediscovered lenses. We
can see that the C grades are relatively larger in proportion than the B grade
and A grade lenses in the discovery group, while the A grades are more
frequent than both the B and C grades in the rediscovery group.

Overall, the results we presented in this sub-section highlight the interest
and importance of the contribution of citizen scientists and detection by
human eye in order to continuously cross validate and improve the performance
of classical algorithms.

###  4.2 Properties of the high-quality candidates

The morphological search conducted in this paper results in strong lenses with
high diversity of image configurations and lens potentials, and their future
spectroscopic follow-up and detailed modelling will enable a range of valuable
studies. In Sect. 4.2.1, we illustrate possible applications with the highest-
quality, newly-discovered, grade A candidates in Fig. 2. In Sect. 4.2.2, we
further describe the lensing configurations and we highlight the properties of
few individual lenses.

####  4.2.1 Prospects for scientific studies

Strong lenses with distant, isolated foreground galaxies are promising to
improve our understanding of the total mass-density slope, $\gamma_{\rm tot}$,
of early-type galaxies. While it is firmly established that $\gamma_{\rm tot}$
is nearly isothermal at low redshift (e.g. Treu & Koopmans 2004; Koopmans et
al. 2006; Cappellari et al. 2015), its evolution at $z<1$ remains debated,
with strong lensing studies suggesting a mild increase from $z\sim 1$ to
$z\sim 0$ (Koopmans et al. 2006; Bolton et al. 2012; Sonnenfeld et al. 2013;
Li et al. 2018), and Jeans dynamical modelling and cosmological simulations
favouring nearly constant $\gamma_{\rm tot}$ over this period (e.g. Wang et
al. 2019; Derkenne et al. 2021). Measurements are mainly restricted to early-
type galaxies at $z\lesssim 0.6$ and need to be extended to higher redshifts
in order to further test galaxy evolution models. Systems with the most
distant, isolated deflectors (e.g. HAH J083420.3$+$452506.9 at $z_{\rm
spec}=0.65$) are very useful in that regard, as well as future spectroscopic
follow-up of lenses with $z_{\rm phot}>0.6$ (e.g. HAH J005403.4$+$394712.1,
HAH J125709.5$+$282239.7).

Double source plane lenses are beneficial to infer tight constraints on the
foreground total mass-density profiles (e.g. Tu et al. 2009). Multiple images
covering different angular separations from the lens centre, as for instance
in HAH J121653.9$-$121104.2, and HAH J132824.5$-$313204.6, break parameter
degeneracies in the lens models. Together with multiband photometry or stellar
kinematic measurements, such lensing configurations enable to characterise the
lens dark-matter distributions. Moreover, when the background sources lie at
distinct redshifts, measuring the two Einstein radii can provide valuable and
independent constraints on the equation of state of dark energy (Collett et
al. 2012). Only a handful of double source plane lenses are known to date
(e.g. Gavazzi et al. 2008; Tanaka et al. 2016), and in our sample, HAH
J002753.2$-$753730.0 and HAH J132824.5$-$313204.6 are good candidates. The
former shows two opposite blue, thin arcs surrounding a foreground elliptical
galaxy, and a broad fuzzy ring that could be a distinct background source.
Possible applications to cosmology make these strong lenses well-suited for
spectroscopic follow-up.

In addition, systems with isolated lens galaxies and bright, extended, and
structured lensed arcs are typically prioritised to search for the presence of
foreground dark-matter sub-halos and line-of-sight halos (e.g. Vegetti &
Koopmans 2009; Ritondale et al. 2019). Due to their arc surface brightness
distributions, HAH J025659.9$-$163059.5, HAH J105722.7$+$580046.5, and HAH
J113158.4$-$195451.5 have the potential to put valuable constraints on
foreground mass perturbations.

####  4.2.2 Strong lensing configurations

While Tables LABEL:tab:unpublished and LABEL:tab:clusters indicates the
presence of galaxy clusters along the lines-of-sight towards several
candidates, the image separations and the morphologies in Fig. 2, 3 and 4 show
that in fact, most have galaxy-galaxy strong lens configurations. In
particular, the light deflection is dominated by a single member or line-of-
sight galaxy for 20 out of 21 newly-discovered grade A with foreground
confirmed or candidate clusters. Only HAH J025241.6$-$150025.5 shows an
extended arc and is located within 0.5′ from the centroid position of a
cluster candidate listed in Zou et al. (2021). Three grade A have $r_{\rm
arc}>3$″, suggesting a major contribution from an extended group- or cluster-
scale mass component to the external convergence and shear and, for instance,
HAH J093325.2$+$284348.6 comprises a compact group of three foreground
galaxies. These three systems are nonetheless absent from our compilation of
cluster candidates selected from shallower ground-based imaging. In addition,
Fig. 2 shows a compact group at $z_{\rm spec}=0.1895$ towards HAH
J234106.5$-$000007.5, but this system has smaller image separation ($r_{\rm
arc}\simeq 2.3$″), and the associated candidate from Zou et al. (2021) is
$>2$′ away. Towards the low-end of the image separation distribution, several
grade A candidates have very compact configurations with sub-arcsec Einstein
radii, as best shown by HAH J042044.0$-$403607.2 with $r_{\rm arc}\simeq
0.4$″. This extends current samples of compact, galaxy-scale strong lenses
(e.g. SLACS, Bolton et al. 2008), and illustrates the new discovery space that
will be unlocked by the Euclid survey with comparable, high-resolution imaging
over $\simeq$15,000 deg2.

The sample contains a majority of extended, distorted arcs and rings, which
are much less ambiguous than configurations with more compact lensed sources.
HAH J001538.4$-$390435.0, HAH J005403.4$+$394712.1, and HAH
J024329.8$-$593102.7 are examples of systems with pairs of blue lensed arcs
while HAH J061345.7$-$562750.4 shows a single, but particularly elongated arc,
and HAH J033603.9$-$451223.1 or HAH J100141.8$+$021424.2 exhibit near-complete
Einstein rings. The difficulty in identifying doubles is coming from their
similarity with compact groups and other non-lens contaminants in the grey-
scale HST images seen by volunteers during the first stage of the
classification. HAH J100251.8$+$691959.3 is the only new grade A candidate
firmly identified as a blue, doubly-imaged source from the inspection of
colour images by the science team. HAH J002348.6$-$244149.6 also shows compact
images, but in a quadruple configuration.

In terms of morphological types, our sample contains interesting classes of
foreground lens galaxies. While traditional selection methods are mainly
restricted to massive elliptical lens galaxies, the angular resolution reached
from space is key to extend to less common lens galaxy types, and to
asymmetric, or more exotic configurations which are particularly difficult to
identify from the ground. Firstly, the new A grade HAH J002348.6$-$244149.6
comprises a moderately inclined lens spiral galaxy with a bright, blue point-
like image in the north and three images distributed evenly along a southern
thin arc. This system extends the small number of known spiral deflectors with
prominent discs (see also, the SWELLS survey, Treu et al. 2011) and, due to
the relative positions of multiple images, its modelling has the potential to
tightly constrain the galaxy bulge mass. Secondly, HAH J100251.8$+$691959.3
and HAH J143811.5$+$464007.6 show edge-on disc galaxies with $r_{\rm
arc}\simeq 0.6$–0.7″. Thirdly, the flexibility of the crowdsourced
classification is demonstrated by the complex structure of the previously
published A grade lens HAH J133235.0$+$503237.3 (Ragozzine et al. 2012). A
background galaxy is lensed into a thin elongated arc by a spectacular
foreground environment, where an edge-on jellyfish galaxy and nearby
ellipticals are embedded within the merging cluster A1758N $z=0.279$ (Ebeling
& Kalita 2019).

Most candidates with SDSS spectroscopic follow-up have large image separations
(e.g. HAH J111337.4$+$221249.2), which limits the contribution from the lensed
sources to the emission collected in the 2″ diameter aperture fibres. This
limits the number of candidates with spectroscopic redshift measurements for
both the lens and source. We nonetheless inspected the SDSS spectra of all
grades A, and identified multiple emission lines inconsistent with the lens
redshift of 0.6495 for HAH J083420.3$+$452506.9 ($\sigma_{*}=269\pm 48$ km
s-1). Our estimate $r_{\rm arc}\simeq 0.6\arcsec$ suggests that the lens and
source galaxies are blended in the SDSS spectrum, and that the background
source is a star-forming galaxy with detections of CIV-$\lambda 1549$,
HeII-$\lambda 1640$, OIII-$\lambda 1664$, and CIII]-$\lambda 1908$ emission
lines (see Fig. 10). The [OII]$\lambda\lambda 3727$ doublet is also
tentatively detected at 9942.6 $\AA$ and 9949.47 $\AA$. By fitting the
smoothed spectrum, we inferred a probable source redshift of $\approx$1.667.
Higher signal-to-noise ratios are nonetheless needed to confirm this estimate.

Figure 10: BOSS spectrum of the newly-discovered grade A candidate HAH
J083420.3+452506.9 showing multiple emission lines inconsistent with the
spectroscopic of the foreground early-type galaxy of 0.6495. The blue and
orange lines show the observed spectrum and the best-fit SDSS model for the
central lens galaxy, respectively. The vertical lines mark the positions of
the CIV-$\lambda 1549$, HeII-$\lambda 1640$, OIII-$\lambda 1664$, and
CIII]-$\lambda 1908$ emission lines at $z\approx 1.667$, from left to right.

##  5 Discussion

###  5.1 Citizen science for lens finding

Previous strong lens searches have relied on dedicated citizen science
projects, the most well-known example being the Space Warps project (Marshall
et al. 2016), which was also built within the Zooniverse framework. Space
Warps has demonstrated that the visual inspection of volunteers is an
efficient data mining tool for strong lenses. It has been successfully applied
to the CFHT Legacy Survey finding 29 promising (and 59 total) new lens
candidates (More et al. 2016). More recently, Sonnenfeld et al. (2020) used a
dedicated algorithm, YATTALENS (Sonnenfeld et al. 2018) and a citizen science
approach on Space Warps to find lenses in the HSC survey, finding 14 definite
lenses (grade A), 129 probable lenses (grade B), and 581 possible (grade C)
lenses in total. Citizen science approaches have also been implemented for
lens modelling (Küng et al. 2015).

Our citizen science project and Space Warps employ different approaches for
the inspection of images. Space Warps shows to the volunteers postage stamps
of objects, generally pre-selected with some criteria (for example, objects
within a redshift and mass range), in order to maximise the chances of
detecting strong lenses and minimise the required volunteer effort. They also
inserted simulated lenses in order to calibrate the response of the volunteers
and measure the completeness.

In contrast, in our project we show large fields-of-view to the volunteers and
ask them to tag on ‘Talk’ if they think the image contains a strong lens.
While the Space Warps approach provides a measure of completeness, which is
difficult to assess in our case, our project provides an unbiased search for
strong lenses (since our images were not pre-selected with some criteria),
being able to find more exotic/interesting lenses. Sonnenfeld et al. (2020)
also mention in the Space Warps project that there were candidates flagged on
the ‘Talk’ section of the Space Warps project that would have otherwise been
missed using the main workflow of the project.

Additionally, using large fields-of-view (corresponding to 80″$\times$ 80″ or
larger) allowed us to explore the HST images much faster than showing
individual postage stamps of galaxies. Finally, this is the first time the HST
images are explored with a citizen science approach, showing the benefit of
asking volunteers to inspect space-based images spanning decades in time.

###  5.2 Comparison to previous $HST$ studies

Previous visual searches for strong gravitational lenses in HST images has
been undertaken by Faure et al. (2008) and Jackson (2008) in the 1.64 deg2
COSMOS field and Pawase et al. (2014) on 7 deg2 of archival ACS/WFC I-band and
WFC3/IR in the near-infrared channel F160W HST images taken until 31 August
2011. Additionally, Pourrahmani et al. (2018) trained a convolutional neural
network on classifications by Faure et al. (2008) to identify strong lenses in
COSMOS.

In a first dedicated exploration of the COSMOS field, Faure et al. (2008)
identified 67 low-grade strong galaxy-lens candidates with 20 of them
displaying multiple images or obvious arcs. Their searches were limited to
massive early-type lenses only with arcs at radii smaller than 5″. Jackson
(2008) visually explored all galaxies in COSMOS that are brighter than 25 mag
finding two more certain and one probable lens, in addition to the lenses
presented in Faure et al. (2008). Pourrahmani et al. (2018) identified 11 more
candidate strong lenses in COSMOS, using the automated LensFlow machine
learning algorithm. Nine of the lenses we identified were reported in
previously lens searches in COSMOS (shown in Table LABEL:tab:rediscoveries).
We recover two more lenses in COSMOS (HAH J100142.8+015448.1, HAH
J100222.3+023220.0) which were not previously reported.

In the only other archival search for gravitational lenses in HST images,
Pawase et al. (2014) explored 7 deg.2 ACS/WFC I-band and WFC3/IR F160W HST
images taken until 31 August 2011. They found 40 lens candidates in ACS and 9
in the WFC3/IR images. Even though the images we inspected overlap, we only
recovered seven strong lenses (four secure cases) in common between the two
studies (see Table LABEL:tab:rediscoveries). There are 12 cases labelled by
Pawase et al. (2014) as secure lenses not recovered in this study. In
addition, eight of our grade A lenses (HAH J054707.0-390516.3, HAH
J145250.0+580135.3, HAH J045413.1+025733.8, HAH J171314.9+602207.7, HAH
J005403.4+394712.1, HAH J084833.4+444431.9, HAH J025241.6-150025.5, HAH
J100108.4+024029.9) observed by HST before 31 August 2011 were not recovered
by Pawase et al. (2014). This relatively low overlap between the two samples
is due to the different approaches: postage stamp inspection by experts (in
the case of Pawase et al. 2014) and large cutout inspection by an army of
citizen scientists (in our case). It also shows the difficulties in the visual
inspection searches of strong lenses, as studies differ in how liberal or
conservative are in the definition of lenses.

###  5.3 Comparison to automated lens search

Strong lens candidates in this paper were drawn from the largest and most
extensive search of 27 deg2 archival HST images taken until June 2020. The
selection is purely based on morphological criteria, and relies on the
systematic inspection of HST images without colour, brightness, or redshift
pre-selections. This type of crowdsourced classification is expected to
recover the majority of lensing configurations, as long as multiple images are
spatially-resolved (see, e.g. Sonnenfeld et al. 2020), and Sect. 4 illustrates
that candidates indeed cover a large variety of lens and source galaxy types,
image multiplicity and angular distributions, including exotic lenses.

This approach differs from automated searches in several aspects. Firstly,
robots are generally run on wide-area, ground-based imaging and spectroscopic
surveys, and focus on massive foreground early-type galaxies due to their high
lensing cross-section (e.g. Oguri & Marshall 2010), and to their smooth light
distributions and typical rest-frame optical spectra facilitating the
identification of signatures from background lensed images. This allows to
deal with memory limitations but restricts automated classifications to
relatively small pre-selected samples (Bolton et al. 2008; Belokurov et al.
2009; Shu et al. 2017; Sonnenfeld et al. 2018). Similarly, despite the
significant boost in classification accuracy offered by CNNs, recent lens
searches on multiband imaging using machine learning have also focused on the
population of elliptical lens galaxies (e.g. Jacobs et al. 2019; Petrillo et
al. 2019; Cañameras et al. 2020). Secondly, automated algorithms based on
supervised neural networks reach the best classification performance (Metcalf
et al. 2019), but they are strongly dependent on the content of the ground
truth data set, and require substantial examples of each morphological class
and lens configuration for training. While deep residual networks are able to
identify strong lenses with various image separations (e.g. Huang et al.
2020), this poses challenges in developing machine learning pipelines reaching
high completeness over broad ranges of lens halo masses ($\simeq$ 1011–1015
M⊙, from isolated galaxies to clusters).

Knabel et al. (2020) compare the citizen science classification of galaxy-
scale lenses with automated deep learning and spectroscopic selections over a
common footprint covered by the Galaxy and Mass Assembly and Kilo Degree
surveys. Interestingly, the independent crowdsourced and machine learning
searches result in essentially distinct sets of lens candidates. Despite
substantial differences in the parent samples, these findings highlight the
complementarity between the two approaches for ground-based searches.

Regarding space-based data, automated lens searches in optical and near-
infrared imaging are currently also suffering from limitations. For instance,
due to the lack of colour information, the deep learning search conducted in
HST data by Pourrahmani et al. (2018) is restricted to the most massive lens
ellipticals. The minor overlap with our present sample illustrates again that,
even though machine learning reaches higher performance for specific
classification tasks (Metcalf et al. 2019), citizen science projects remain
key in accessing the broad diversity of strong lenses.

###  5.4 Future prospects

Given the comparable angular resolution and sampling of Euclid and HST images,
our results highlight the range of strong lensing studies that will become
accessible with the wide Euclid survey. Given the large variety of lens
configurations targeted in our archival search, and given the in-homogeneous
selection process involving images with different depths and taken in
different filters, we can not robustly measure the sample completeness. It is
nonetheless interesting to note that our overall number of strong lens
candidates is comparable to the re-scaled Euclid forecasts. Collett (2015)
predicted that 170 000 galaxy-scale strong lenses will be discoverable from
the final stack of the Euclid survey, for lens early-type galaxies and various
assumptions on the source population and detectability criteria. This
corresponds to $\simeq$300 strong lenses discoverable over our 27 deg2
footprint, while we found $\simeq$240 non-targeted candidates from the ACS and
WFC3/UVIS classifications, including a few group-, cluster-scale and more
exotic lenses which are not considered by Collett (2015).

This adds further evidence that Euclid will be able to find large samples of
$>$100 000 strong lenses, while covering much broader ranges in lens redshifts
and extending robust mass measurements to $z>1$. Strong lens searches in
Euclid will likely benefit from joining CNN and crowdsourced classifications,
for instance by involving citizens to assemble representative training sets,
or to clean the contaminants from CNN selections in order to increase the
sample purity.

##  6 Conclusion

We present a sample of 198 new, high-quality strong lens candidates identified
in 18 years of HST archival data. We performed a systematic search for non-
targeted strong gravitational lenses in the entire HST archive, by inspecting
observations taken with the ACS and WFC3 instruments between 2002 and 2020
with crowdsourcing.

We find 252 strong gravitational lens candidates appearing serendipitously in
HST observations, after excluding targeted observations of known lenses. 54 of
them have been previously mentioned in other studies, as presented in Table
LABEL:tab:rediscoveries. A total of 198 strong lens candidates were not
previously reported in the literature. We categorised them into 45 grade A, 74
grade B, and 79 grade C based on their morphology, the shape of the source
image, and the quality and availability of an HST colour image. Our selection
purely based on morphological criteria results in strong lenses with various
lens and source galaxy types, and various image multiplicities and angular
distributions. This shows the potential of citizen science in accessing the
broad diversity of strong lenses, and the complementarity with automated
classification algorithms.

The sample contains a majority of extended, distorted arcs and rings, which
are less ambiguous than compact lensed sources. While 124 (63%) of the new
strong lenses are associated with foreground spectroscopically-confirmed or
candidate galaxy clusters, most of them have galaxy-scale configurations, with
the light deflection dominated by a single member or line-of-sight galaxy. For
instance, only three new grade A show a major contribution from the cluster-
scale mass component. In addition, while we find a majority of lenses being
ellipticals, $\lesssim$10% of the foreground lens galaxies have light profiles
consistent with exponential discs, corresponding either to edge-on or to
moderately inclined spirals. Finally, a few systems have exotic configurations
such as possible double source plane lenses.

In terms of distributions, the newly detected lenses are, on average, 1.3
magnitudes fainter than previous HST searches. The angular separations between
multiple images are typically smaller than for lenses found in ground-based
data. A quarter of our newly discovered systems have arc radii $\leq$0.82″,
showing the advantage of combining high-resolution of HST imaging with
crowdsourcing to select the most compact, galaxy-scale strong lenses for
galaxy evolution studies. The redshift distribution of the lens galaxies in
our sample is consistent with the lens redshifts from previous ground-based
searches.

Since we did not restrict our search to postage stamps of massive elliptical
galaxies, as commonly done in strong lens searches, our study constitutes an
unbiased search for lenses with the highest resolution currently possible with
HST. This overall sample of 252 strong lenses is a useful benchmark for future
lens searches in high-resolution images, such as those with Euclid, JWST or
Roman.

This paper shows that crowdsourcing is a robust method to perform visual
detection of strong lenses. Indeed, after receiving proper training and
knowledge transfer, the volunteers demonstrated their ability to detect
classical lenses as well as outliers such as exotic lens configurations.
Although inspecting large field of view images might lead to a decrease in
completeness, this approach has the advantage of considerably speeding up the
detection process compared to inspecting postage stamps, where a pre-selection
of the targets is often necessary. In addition, providing metadata for the
images, such as the coordinates and links to ESASky, enabled the volunteers to
perform further analysis and identify the objects in the archives. While using
colour images for the inspection might have led to a larger number of lenses
being identified, multiple bands were only available for a fraction of the
Hubble images in the archives. Nevertheless, the volunteers demonstrated that
they are able to identify strong lenses in grey-scale images, which is an
important lesson for Euclid, where only a single optical band is available. It
is important to note that, while it is significantly faster for thousands of
citizen scientists to inspect the images than for a handful of professional
astronomers, it still took one year of volunteer effort to explore more than
45 000 HST observations. Given the scale of Euclid, a citizen science approach
to explore the entire Euclid dataset of $\simeq$15 000 deg2 is not feasible on
its own. Combining artificial intelligence methods and crowdsourcing for the
detection of strong lenses, for example through iterative training and
validation, has thus a strong potential to produce reliable catalogues in
shorter timescales and detect outliers such as exotic lenses. Our study also
demonstrates the potential for using crowdsourcing to explore the growing JWST
archives of images for strong gravitational lenses, as the high-resolution,
infrared and multi-wavelength JWST observations will reveal even higher
redshift lenses and with smaller Einstein radii.

To conclude, this series of Hubble Asteroid Hunter papers reaffirmed the
importance of crowdsourcing in visually detecting complex objects such as
strong gravitational lenses and Solar System objects. It also showed the
benefits of exploring large archival datasets spanning decades in time to
expand the horizons of future research.

###### Acknowledgements.

We acknowledge the tremendous work made by the citizen scientist volunteers on
the Hubble Asteroid Hunter project. Their contributions are individually
acknowledged on https://www.zooniverse.org/projects/sandorkruk/hubble-
asteroid-hunter/about/results.

We thank the anonymous referee for their detailed and insightful comments, as
they greatly contributed to enhance the quality of our paper. We thank Stella
Seitz and Sherry Suyu for insightful discussions on the sample of strong
gravitational lenses.

This work has been conducted by EOG as part of the European Space Agency (ESA)
student internship. SK and RB gratefully acknowledge support from the ESA
Research Fellowship.

This paper is based on observations made with the NASA/ESA Hubble Space
Telescope, obtained from the data archive at the Space Telescope Science
Institute. STScI is operated by the Association of Universities for Research
in Astronomy, Inc. under NASA contract NAS 5-26555. Based on observations made
with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy
Archive, which is a collaboration between the Space Telescope Science
Institute (STScI/NASA), the Space Telescope European Coordinating Facility
(ST-ECF/ESA) and the Canadian Astronomy Data Centre (CADC/NRC/CSA).

The new strong lens candidates (Table LABEL:tab:unpublished) were found in the
following HST programs: 9405, 9414, 9427, 9458, 9476, 9483, 9500, 9722, 9753,
9770, 9822, 9836, 10096, 10134, 10152, 10200, 10207, 10325, 10326, 10334,
10395, 10420, 10491, 10496, 10503, 10504, 10505, 10521, 10523, 10569, 10626,
10635, 10816, 10825, 10861, 10875, 10880, 10881, 10997, 11142, 11588, 11597,
11613, 11697, 11734, 12063, 12064, 12104, 12166, 12195, 12209, 12238, 12253,
12286, 12313, 12319, 12362, 12476, 12477, 12515, 12546, 12549, 12555, 12575,
12591, 12756, 12884, 12898, 12937, 13023, 13024, 13307, 13352, 13364, 13393,
13412, 13442, 13495, 13496, 13514, 13641, 13657, 13695, 13698, 13711, 13750,
13845, 13942, 14096, 14098, 14118, 14165, 14199, 14594, 14662, 14766, 14808,
15063, 15117, 15121, 15183, 15212, 15230, 15275, 15287, 15307, 15320, 15378,
15446, 15495, 15608, 15642, 15644, 15654, 15696, 15843, 16025. We are
extremely grateful to the PIs of the HST observations for their positive
feedback and responses in including the objects in our catalogue and for the
useful conversations.

This publication uses data generated via the Zooniverse.org platform,
development of which is funded by generous support, including a Global Impact
Award from Google, and by a grant from the Alfred P. Sloan Foundation. Funding
for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation,
the Participating Institutions, the National Science Foundation, the U.S.
Department of Energy, the National Aeronautics and Space Administration, the
Japanese Monbukagakusho, the Max Planck Society, and the Higher Education
Funding Council for England. The SDSS Web Site is http://www.sdss.org/.

The SDSS is managed by the Astrophysical Research Consortium for the
Participating Institutions. The Participating Institutions are the American
Museum of Natural History, Astrophysical Institute Potsdam, University of
Basel, University of Cambridge, Case Western Reserve University, University of
Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the
Japan Participation Group, Johns Hopkins University, the Joint Institute for
Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and
Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences
(LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for
Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico
State University, Ohio State University, University of Pittsburgh, University
of Portsmouth, Princeton University, the United States Naval Observatory and
the University of Washington.

This research made use of NASA’s Astrophysics Data System Bibliographic
Services. This work made extensive use of Astropy777http://www.astropy.org/, a
community-developed core Python package for Astronomy (Price-Whelan et al.
2018) and of the Tool for Operations on Catalogues And Tables
(TOPCAT888http://www.star.bris.ac.uk/~mbt/; Taylor 2005). This publication
used GALFIT (Peng et al. 2002) and SExtractor (Bertin & Arnouts 1996) for the
lens fitting and parameter retrieval, as well as the software tool R (R Core
Team 2020) and its packages vioplot (Adler & Kelly 2020) and Hmisc (Harrell Jr
& Harrell Jr 2019) for preparation of the tables and data visualisation. This
work also made use of Xmatch (Budavari & Lee 2013) and TOPCAT to perform
cross-matching of the lenses with nearby clusters.

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##  Appendix A List of strong lens candidates

Table 2: Newly discovered lenses. IAU Name | ID | RA | Dec | $r_{\rm arc}\,(\arcsec)$ | instru. | filter | $mag$ | $r_{\rm e}\,(\arcsec)$ | $q$ | $PA$ | class | clust. | $z$
---|---|---|---|---|---|---|---|---|---|---|---|---|---
A grade Lenses |  |  |  |  |  |  |  |  |  |  |  |  |
HAH $J001538.4-390435.0$ | $1$ | $3.91007$ | $39.07643$ | 0.79 | UVIS | f475w | $25.4$ | $0.06$ | $0.93$ | $-81.9$ | Arc |  |
HAH $J002348.6-244149.6$ | $2$ | $5.95275$ | $-24.69702$ | 1.07 | ACS | f814w | $20.1$ | $1.45$ | $0.56$ | $89.1$ | Quad | DClust1 |
HAH $J002753.2-753730.0$ | $3$ | $6.97150$ | $-75.62500$ | 1.71 | ACS | f606w | $19.6$ | $1.10$ | $0.93$ | $-112.6$ | Ring | DClust2 |
HAH $J004924.3-205729.8$ | $4$ | $12.35113$ | $-20.95829$ | 0.78 | ACS | f606w | $20.3$ | $0.80$ | $0.77$ | $-19.7$ | Arc | DClust3 |
HAH $J005403.4+394712.1$ | $5$ | $13.51445$ | $39.78661$ | 2.05 | ACS | f814w | $20.2$ | $0.85$ | $0.81$ | $155.8$ | Arc |  | 0.73 P
HAH $J015949.3-084906.0$ | $6$ | $29.95549$ | $-8.81828$ | 1.17 | ACS | f606w | $21.1$ | $0.35$ | $0.92$ | $128.6$ | Arc | DClust4 | 0.39 P
HAH $J021706.2-051318.0$ | $7$ | $34.27592$ | $-5.22168$ | 1.14 | ACS | f814w | $21.7$ | $0.54$ | $0.68$ | $-9.8$ | Arc |  | 0.59 P
HAH $J024329.8-593102.7$ | $8$ | $40.87441$ | $-59.51759$ | 0.63 | UVIS | f200lp | $23.1$ | $0.35$ | $0.81$ | $95.4$ | Arc | DClust5 |
HAH $J024533.6-530203.5$ | $9$ | $41.39015$ | $-53.03433$ | 0.73 | ACS | f814w | $20.1$ | $0.39$ | $0.88$ | $-24.2$ | Ring | DClust6 |
HAH $J024932.8+334635.5$ | $10$ | $42.38714$ | $33.77651$ | 0.55 | ACS | f775w | $25.1$ | $0.32$ | $0.39$ | $89.7$ | Arc |  |
HAH $J025241.6-150025.5$ | $11$ | $43.17305$ | $-15.00712$ | 3.23 | ACS | f814w | $21.3$ | $0.36$ | $0.90$ | $-111.1$ | Arc | DClust7 |
HAH $J025659.9-163059.5$ | $12$ | $44.24984$ | $-16.51655$ | 1.48 | ACS | f606w | $18.8$ | $2.08$ | $0.71$ | $-164.4$ | Arc | DClust8 | 0.31 P
HAH $J033603.9-451223.1$ | $13$ | $54.01630$ | $-45.20642$ | 0.63 | ACS | f814w | $22.6$ | $0.31$ | $0.79$ | $-176.5$ | Ring |  |
HAH $J034445.2-642133.8$ | $14$ | $56.18856$ | $-64.35941$ | 1.42 | ACS | f606w | $24.2$ | $0.10$ | $1.00$ | $153.0$ | Arc | DClust9 |
HAH $J042044.0-403607.2$ | $15$ | $65.18326$ | $-40.60200$ | 0.42 | UVIS | f814w | $22.7$ | $0.48$ | $0.84$ | $152.3$ | Ring |  |
HAH $J054707.0-390516.3$ | $16$ | $86.77923$ | $-39.08786$ | 0.74 | ACS | f814w | $19.7$ | $0.40$ | $0.80$ | $139.2$ | Ring | DClust10 |
HAH $J061345.7-562750.4$ | $17$ | $93.44050$ | $-56.46400$ | 1.2 | ACS | f606w | $18.9$ | $1.08$ | $0.42$ | $68.7$ | Arc | DClust11 |
HAH $J072221.9+072326.7$ | $18$ | $110.59159$ | $7.39076$ | 0.59 | ACS | f814w | $20.3$ | $0.74$ | $0.91$ | $-99.5$ | Arc | DClust12 |
HAH $J081334.8+254518.3$ | $19$ | $123.39489$ | $25.75509$ | 1.6 | IR | f140w | $19.1$ | $1.04$ | $0.83$ | $52.6$ | Arc |  |
HAH $J083420.3+452506.9$ | $20$ | $128.58462$ | $45.41860$ | 1.04 | ACS | f814w | $21.2$ | $0.65$ | $0.61$ | $-107.9$ | Arc | DClust13 | 0.65 S
HAH $J084833.4+444431.9$ | $21$ | $132.13930$ | $44.74220$ | 1.2 | ACS | f814w | $22.5$ | $0.27$ | $0.81$ | $120.9$ | Arc |  | 0.19 P
|  |  |  | 1.2 | ACS | f814w | $24.2$ | $0.22$ | $0.13$ | $-174.1$ | Arc |  | 0.19 P
|  |  |  | 1.2 | ACS | f814w | $23.6$ | $0.20$ | $0.46$ | $-158.5$ | Arc |  | 0.19 P
HAH $J093325.2+284348.6$ | $22$ | $143.35520$ | $28.73018$ | 3.27 | ACS | f606w | $20.6$ | $0.10$ | $0.77$ | $-130.3$ | Arc |  | 0.4 P
|  |  |  | 3.27 | ACS | f606w | $19.7$ | $1.38$ | $0.84$ | $-103.8$ | Arc |  | 0.4 P
HAH $J100141.8+021424.2$ | $23$ | $150.42410$ | $2.24010$ | 1.46 | ACS | f814w | $23.7$ | $0.26$ | $0.80$ | $-104.2$ | Ring |  | 0.34 P
HAH $J100251.8+691959.3$ | $24$ | $150.71567$ | $69.33316$ | 0.7 | ACS | f606w | $22.0$ | $1.21$ | $0.22$ | $133.9$ | Double |  | 0.56 P
HAH $J102914.8+262207.0$ | $25$ | $157.31170$ | $26.36860$ | 0.64 | ACS | f475w | $23.6$ | $0.36$ | $0.69$ | $108.2$ | Arc | DClust14 | 0.57 P
HAH $J105722.7+580046.5$ | $26$ | $164.34460$ | $58.01290$ | 0.46 | ACS | f814w | $22.7$ | $0.32$ | $0.75$ | $-105.9$ | Arc | DClust15 | 0.54 P
HAH $J111337.4+221249.2$ | $27$ | $168.40564$ | $22.21368$ | 2.11 | UVIS | f350lp | $18.8$ | $1.94$ | $0.74$ | $-135.1$ | Arc | DClust16 | 0.41 S
HAH $J113158.4-195451.5$ | $28$ | $172.99340$ | $-19.91430$ | 1.66 | ACS | f814w | $18.8$ | $1.25$ | $0.65$ | $114.5$ | Arc |  |
HAH $J114938.4+222107.7$ | $29$ | $177.41020$ | $22.35200$ | 0.8 | ACS | f814w | $20.8$ | $0.38$ | $0.66$ | $58.8$ | Arc | DClust17 | 0.42 P
HAH $J121653.9-121104.2$ | $30$ | $184.22457$ | $-12.18464$ | 1.12 | ACS | f814w | $19.2$ | $0.54$ | $0.97$ | $-57.9$ | Ring |  |
HAH $J125709.5+282239.7$ | $31$ | $194.28970$ | $28.37770$ | 0.88 | ACS | f475w | $26.4$ | $1.48$ | $0.05$ | $140.0$ | Arc |  | 0.78 P
|  |  |  | 0.88 | ACS | f475w | $24.6$ | $0.17$ | $0.55$ | $-93.9$ | Arc |  | 0.78 P
HAH $J130124.0-113114.6$ | $32$ | $195.34996$ | $-11.52072$ | 0.91 | ACS | f814w | $19.1$ | $1.13$ | $0.67$ | $-29.2$ | Ring |  |
HAH $J131953.6+700420.8$ | $33$ | $199.97339$ | $70.07245$ | 1.16 | ACS | f606w | $20.0$ | $0.46$ | $0.85$ | $-157.0$ | Ring | DClust18 |
HAH $J132824.5-313204.6$ | $34$ | $202.10207$ | $-31.53468$ | 1.4 | UVIS | f475w | $22.0$ | $0.94$ | $0.69$ | $179.8$ | Arc |  |
HAH $J133525.9+405952.4$ | $35$ | $203.85800$ | $40.99790$ | 0.95 | ACS | f814w | $18.9$ | $1.49$ | $0.74$ | $102.6$ | Arc | DClust19 | 0.29 P
HAH $J135955.7+143820.4$ | $36$ | $209.98235$ | $14.63882$ | 0.56 | UVIS | f390w | $22.9$ | $0.55$ | $0.94$ | $44.7$ | Arc |  |
HAH $J141139.2+565200.9$ | $37$ | $212.91351$ | $56.86694$ | 0.51 | UVIS | f475x | $21.2$ | $0.74$ | $0.45$ | $92.6$ | Ring | DClust20 |
HAH $J141900.1+524249.0$ | $38$ | $214.75050$ | $52.71360$ | 1.12 | ACS | f814w | $20.9$ | $0.44$ | $0.94$ | $-136.8$ | Arc |  | 0.46 P
HAH $J143811.5+464007.6$ | $39$ | $219.54794$ | $46.66877$ | 0.57 | ACS | f435w | $22.1$ | $0.46$ | $0.46$ | $-118.5$ | Ring |  |
HAH $J163124.5+124304.3$ | $40$ | $247.85224$ | $12.71771$ | 2.31 | UVIS | f814w | $22.5$ | $0.52$ | $0.92$ | $-45.1$ | Arc |  | 0.64 S
HAH $J163417.6+703107.0$ | $41$ | $248.57350$ | $70.51860$ | 1.13 | IR | f140w | $19.1$ | $0.46$ | $0.93$ | $138.3$ | Arc |  |
HAH $J171314.9+602207.7$ | $42$ | $258.31200$ | $60.36890$ | 0.94 | ACS | f814w | $21.2$ | $0.27$ | $0.62$ | $-17.9$ | Ring |  | 0.26 P
|  |  |  | 0.94 | ACS | f814w | $24.6$ | $1.95$ | $0.00$ | $-28.7$ | Ring |  | 0.26 P
HAH $J214817.6-484350.5$ | $43$ | $327.07301$ | $-48.73045$ | 1.12 | UVIS | f200lp | $23.1$ | $0.39$ | $0.89$ | $98.0$ | Arc | DClust21 |
HAH $J215849.5-223159.7$ | $44$ | $329.70656$ | $-22.53325$ | 3.27 | ACS | f775w | $19.2$ | $2.38$ | $0.68$ | $-23.8$ | Arc |  |
HAH $J234106.5-000007.5$ | $45$ | $355.27743$ | $-0.00210$ | 2.31 | UVIS | f390w | $19.9$ | $1.43$ | $0.92$ | $-50.2$ | Arc | DClust22 | 0.19 S
B grade Lenses |  |  |  |  |  |  |  |  |  |  |  |  |
HAH $J001419.9-302600.7$ | $46$ | $3.58309$ | $-30.43355$ | 1.3 | ACS | f814w | $18.6$ | $0.93$ | $0.67$ | $177.1$ | Arc | DClust23 |  0.29 $\star$
HAH $J002706.3+170313.5$ | $47$ | $6.77622$ | $17.05375$ | 0.8 | ACS | f814w | $21.5$ | $0.72$ | $0.67$ | $-174.9$ | Arc | DClust24 |
HAH $J003350.8-074959.9$ | $48$ | $8.46170$ | $-7.83330$ | 0.88 | ACS | f814w | $22.1$ | $0.45$ | $0.65$ | $-95.4$ | Arc | DClust25 | 0.16 P
HAH $J004426.2-403941.4$ | $49$ | $11.10937$ | $-40.66150$ | 0.55 | ACS | f606w | $23.9$ | $0.44$ | $0.71$ | $-120.6$ | Ring | DClust26 |
HAH $J004859.0+401706.7$ | $50$ | $12.24571$ | $40.28517$ | 1.05 | ACS | f606w | $24.6$ | $0.30$ | $0.29$ | $69.4$ | Arc |  |
HAH $J005141.6+272001.5$ | $51$ | $12.92343$ | $27.33376$ | 1.3 | IR | f110w | $17.6$ | $0.81$ | $0.97$ | $-1.4$ | Arc | DClust27 | 0.36 P
HAH $J011138.3-454015.1$ | $52$ | $17.90972$ | $-45.67088$ | 0.93 | IR | f105w | $19.4$ | $0.29$ | $0.82$ | $146.2$ | Arc | DClust28 |
HAH $J013723.7-082852.2$ | $53$ | $24.34861$ | $-8.48115$ | 1.87 | ACS | f606w | $20.1$ | $0.43$ | $0.88$ | $-178.1$ | Arc | DClust29 | 0.52 P
HAH $J015256.3-135416.3$ | $54$ | $28.23476$ | $-13.90454$ | 0.59 | ACS | f814w | $21.9$ | $0.55$ | $0.73$ | $-86.4$ | Arc |  |
HAH $J022056.4-033332.1$ | $55$ | $35.23505$ | $-3.55899$ | 1.46 | ACS | f850lp | $21.5$ | $0.33$ | $0.56$ | $-130.1$ | Arc |  |
HAH $J023951.1-013205.9$ | $56$ | $39.96294$ | $-1.53500$ | 1.1 | ACS | f814w | $19.8$ | $0.45$ | $0.68$ | $0.2$ | Arc | DClust30 | 0.48 P
HAH $J024535.7-530125.5$ | $57$ | $41.39911$ | $-53.02377$ | 0.86 | ACS | f814w | $20.0$ | $0.61$ | $0.48$ | $-11.2$ | Arc | DClust31 |
HAH $J025735.5-220928.5$ | $58$ | $44.39802$ | $-22.15791$ | 0.84 | ACS | f814w | $18.8$ | $1.84$ | $0.74$ | $-161.8$ | Arc | DClust32 |
HAH $J025740.9-221027.3$ | $59$ | $44.42063$ | $-22.17426$ | 0.85 | ACS | f814w | $20.0$ | $0.29$ | $0.59$ | $168.8$ | Arc | DClust33 |
HAH $J032030.9+003242.8$ | $60$ | $50.12858$ | $0.54522$ | 2.91 | ACS | f775w | $19.4$ | $0.69$ | $0.53$ | $-102.5$ | Arc | DClust34 | 0.39 S
HAH $J033305.9-274744.8$ | $61$ | $53.27467$ | $-27.79577$ | 1.3 | ACS | f606w | $21.1$ | $0.37$ | $0.74$ | $-174.9$ | Arc |  |  0.35 P$\star$
HAH $J033530.7-540734.7$ | $62$ | $53.87735$ | $-54.12630$ | 3.23 | ACS | f814w | $20.2$ | $1.17$ | $0.34$ | $-4.0$ | Arc | DClust35 |
|  |  |  | 3.23 | ACS | f814w | $20.0$ | $15.49$ | $0.52$ | $-0.1$ | Arc |  |
HAH $J033645.9-535536.7$ | $63$ | $54.18759$ | $-53.92647$ | 1.21 | UVIS | f814w | $20.4$ | $0.33$ | $0.77$ | $-149.5$ | Arc | DClust36 |
HAH $J035851.7-295418.7$ | $64$ | $59.71560$ | $-29.90520$ | 1 | ACS | f814w | $20.1$ | $0.50$ | $0.76$ | $-28.2$ | Arc | DClust37 |  0.42 $\star$
HAH $J041631.5-240512.5$ | $65$ | $64.13140$ | $-24.08680$ | 1.23 | ACS | f814w | $21.1$ | $1.06$ | $0.34$ | $-116.5$ | Double | DClust38 |
HAH $J044208.3-281503.7$ | $66$ | $70.53440$ | $-28.25102$ | 4.4 | ACS | f814w | $19.9$ | $1.16$ | $0.58$ | $-103.0$ | Arc | DClust39 |
|  |  |  | 4.4 | ACS | f814w | $19.5$ | $1.62$ | $0.66$ | $-46.3$ | Arc |  |
HAH $J045430.7-030133.2$ | $67$ | $73.62796$ | $-3.02590$ | 1.47 | ACS | f814w | $20.3$ | $0.66$ | $0.77$ | $-97.0$ | Arc | DClust40 |
HAH $J045441.7-030319.9$ | $68$ | $73.67378$ | $-3.05553$ | 1.18 | ACS | f814w | $20.1$ | $0.51$ | $0.76$ | $-82.1$ | Arc | DClust41 | 0.61 P
HAH $J051850.3-431442.0$ | $69$ | $79.70954$ | $-43.24500$ | 1.56 | ACS | f814w | $21.4$ | $1.10$ | $0.80$ | $99.1$ | Arc | DClust42 |
HAH $J055326.6-334254.0$ | $70$ | $88.36070$ | $-33.71500$ | 2.65 | ACS | f814w | $20.0$ | $0.36$ | $0.77$ | $-18.5$ | Arc | DClust43 |
HAH $J065821.5-555711.5$ | $71$ | $104.58970$ | $-55.95316$ | 1.88 | ACS | f606w | $19.9$ | $0.87$ | $0.43$ | $-88.6$ | Arc |  |
HAH $J072218.2+072314.8$ | $72$ | $110.57599$ | $7.38745$ | 0.6 | ACS | f814w | $21.4$ | $0.44$ | $0.60$ | $146.3$ | Arc | DClust44 |
HAH $J072333.8-732550.9$ | $73$ | $110.89080$ | $-73.43080$ | 0.97 | ACS | f814w | $21.3$ | $0.42$ | $0.31$ | $139.8$ | Arc | DClust45 |
HAH $J074421.4+375400.0$ | $74$ | $116.08890$ | $37.89990$ | 1.27 | UVIS | f606w | $24.3$ | $0.40$ | $0.28$ | $-159.4$ | Arc |  |
HAH $J074531.3+195111.7$ | $75$ | $116.38083$ | $19.85327$ | 0.73 | UVIS | f606w | $22.4$ | $0.45$ | $0.79$ | $112.4$ | Double |  | 0.44 P
HAH $J083410.0+491332.2$ | $76$ | $128.54159$ | $49.22560$ | 0.85 | ACS | f606w | $23.0$ | $0.83$ | $0.46$ | $-8.7$ | Arc |  |
HAH $J084712.7+344910.9$ | $77$ | $131.80310$ | $34.81970$ | 0.69 | ACS | f814w | $22.9$ | $0.13$ | $0.84$ | $26.1$ | Arc | DClust46 |
HAH $J091503.8+581147.7$ | $78$ | $138.76580$ | $58.19660$ | 0.85 | UVIS | f350lp | $22.8$ | $0.50$ | $0.89$ | $134.8$ | Ring |  |
HAH $J094949.9+170614.4$ | $79$ | $147.45790$ | $17.10399$ | 2.3 | ACS | f814w | $19.8$ | $0.57$ | $0.40$ | $30.4$ | Arc | DClust47 | 0.39 P
HAH $J095549.0-100034.8$ | $80$ | $148.95441$ | $-10.00973$ | 1.16 | ACS | f606w | $24.5$ | $0.47$ | $0.34$ | $36.0$ | Arc |  |
HAH $J095633.6-100913.3$ | $81$ | $149.13990$ | $-10.15370$ | 1.31 | ACS | f606w | $17.6$ | $2.00$ | $0.86$ | $19.2$ | Arc |  |
HAH $J095712.5+690709.1$ | $82$ | $149.30206$ | $69.11924$ | 3.79 | ACS | f814w | $19.7$ | $0.96$ | $0.81$ | $145.4$ | Arc |  | 0.52 P
|  |  |  | 3.79 | ACS | f814w | $20.4$ | $1.01$ | $0.70$ | $-139.8$ | Arc |  | 0.52 P
HAH $J095803.9+653409.1$ | $83$ | $149.51620$ | $65.56920$ | 1.44 | ACS | f814w | $21.0$ | $1.66$ | $0.77$ | $4.4$ | Arc | DClust48 |
HAH $J100030.1+023716.7$ | $84$ | $150.12550$ | $2.62130$ | 0.84 | ACS | f814w | $25.6$ | $0.03$ | $0.41$ | $39.6$ | Arc | DClust49 | 0.52 P
|  |  |  | 0.84 | ACS | f814w | $24.8$ | $0.36$ | $0.27$ | $-103.8$ | Arc |  | 0.52 P
|  |  |  | 0.84 | ACS | f814w | $24.5$ | $2.60$ | $0.42$ | $-93.1$ | Arc |  | 0.52 P
HAH $J100124.2+555407.2$ | $85$ | $150.35080$ | $55.90200$ | 1.45 | ACS | f814w | $21.2$ | $0.13$ | $0.62$ | $-165.7$ | Arc | DClust50 | 0.36 S
|  |  |  | 1.45 | ACS | f814w | $20.8$ | $0.70$ | $0.35$ | $-169.3$ | Arc |  | 0.36 S
HAH $J103937.6-001421.5$ | $86$ | $159.92930$ | $-0.26555$ | 0.51 | ACS | f814w | $21.4$ | $1.10$ | $0.90$ | $-24.6$ | Arc |  | 0.23 P
HAH $J104001.6+474558.0$ | $87$ | $160.00670$ | $47.76612$ | 0.66 | ACS | f435w | $22.8$ | $0.53$ | $0.50$ | $60.0$ | Arc |  | 0.35 P
HAH $J104132.0+000125.0$ | $88$ | $160.38332$ | $-0.02360$ | 0.99 | ACS | f606w | $23.7$ | $0.62$ | $0.88$ | $45.9$ | Ring | DClust51 | 0.67 P
HAH $J105726.9+575944.0$ | $89$ | $164.36207$ | $57.99555$ | 1.47 | ACS | f814w | $22.1$ | $0.43$ | $0.43$ | $-157.7$ | Arc | DClust52 | 0.24 P
HAH $J111507.3+531955.8$ | $90$ | $168.78051$ | $53.33217$ | 1.12 | ACS | f606w | $21.2$ | $0.33$ | $0.62$ | $-136.6$ | Arc | DClust53 | 0.44 P
HAH $J111822.1+033802.1$ | $91$ | $169.59242$ | $3.63393$ | 1.33 | IR | f110w | $17.4$ | $1.10$ | $0.60$ | $-44.4$ | Ring | DClust54 | 0.42 S
HAH $J115940.8+011410.7$ | $92$ | $179.92011$ | $1.23632$ | 2.5 | ACS | f606w | $19.3$ | $2.94$ | $0.56$ | $-102.7$ | Arc |  | 0.44 S
HAH $J122944.7+112238.3$ | $93$ | $187.43610$ | $11.37730$ | 1.3 | ACS | f814w | $20.2$ | $0.26$ | $0.80$ | $84.3$ | Arc | DClust55 | 0.41 P
HAH $J123430.7+080444.4$ | $94$ | $188.62785$ | $8.07903$ | 2.1 | ACS | f814w | $20.3$ | $1.22$ | $0.85$ | $130.0$ | Arc |  | 0.5 S
HAH $J123618.8+260905.0$ | $95$ | $189.07830$ | $26.15140$ | 1.54 | ACS | f814w | $21.3$ | $0.66$ | $0.68$ | $-50.9$ | Arc | DClust56 |
HAH $J124756.2+134103.3$ | $96$ | $191.98435$ | $13.68426$ | 1.65 | ACS | f814w | $22.0$ | $1.34$ | $0.86$ | $105.2$ | Arc |  |
HAH $J125907.8-014439.0$ | $97$ | $194.78235$ | $-1.74418$ | 0.33 | ACS | f814w | $22.2$ | $0.68$ | $0.26$ | $-164.8$ | Double | DClust57 |
HAH $J130034.4+280022.4$ | $98$ | $195.14321$ | $28.00622$ | 0.7 | ACS | f814w | $20.7$ | $0.20$ | $0.61$ | $174.3$ | Arc |  | 0.49 P
HAH $J130152.7+275147.7$ | $99$ | $195.46939$ | $27.86325$ | 2.17 | ACS | f475w | $20.2$ | $1.15$ | $0.84$ | $157.9$ | Arc | DClust58 | 0.27 S
HAH $J132217.5+464630.4$ | $100$ | $200.57300$ | $46.77510$ | 3.19 | ACS | f814w | $18.4$ | $1.49$ | $0.66$ | $-60.9$ | Arc | DClust59 | 0.37 S
HAH $J132331.9+302155.8$ | $101$ | $200.88300$ | $30.36550$ | 2.5 | ACS | f814w | $21.1$ | $0.36$ | $0.87$ | $64.7$ | Arc | DClust60 | 0.46 S
|  |  |  | 2.5 | ACS | f814w | $19.3$ | $0.82$ | $0.73$ | $70.1$ | Arc |  | 0.46 S
HAH $J132529.1-474019.2$ | $102$ | $201.37147$ | $-47.67202$ | 0.71 | UVIS | f814w | $21.4$ | $0.40$ | $0.95$ | $-65.8$ | Ring |  |
HAH $J133240.6+503315.5$ | $103$ | $203.16900$ | $50.55430$ | 3.3 | ACS | f814w | $19.8$ | $0.46$ | $0.93$ | $-142.5$ | Arc | DClust61 | 0.33 P
HAH $J133252.7+503026.9$ | $104$ | $203.21991$ | $50.50747$ | 1.45 | ACS | f814w | $18.7$ | $2.39$ | $0.80$ | $-150.4$ | Arc | DClust62 | 0.29 P
HAH $J135953.3+623118.4$ | $105$ | $209.97199$ | $62.52180$ | 2.56 | ACS | f814w | $19.0$ | $1.03$ | $0.58$ | $-126.6$ | Arc | DClust63 | 0.35 P
HAH $J143236.3+344030.4$ | $106$ | $218.15140$ | $34.67510$ | 1.63 | ACS | f814w | $20.1$ | $0.77$ | $0.73$ | $30.6$ | Arc | DClust64 | 0.57 P
HAH $J145832.7-002349.9$ | $107$ | $224.63646$ | $-0.39719$ | 0.71 | UVIS | f475x | $23.1$ | $0.40$ | $1.00$ | $-34.0$ | Arc | DClust65 | 0.6 S
HAH $J151841.7+084549.2$ | $108$ | $229.67379$ | $8.76369$ | 2.01 | ACS | f814w | $19.7$ | $0.58$ | $0.95$ | $140.9$ | Arc | DClust66 | 0.49 P
HAH $J161311.2+565004.1$ | $109$ | $243.29650$ | $56.83446$ | 0.95 | IR | f140w | $19.8$ | $0.75$ | $0.79$ | $100.9$ | Arc | DClust67 | 0.4 P
HAH $J161420.9+323306.1$ | $110$ | $243.58700$ | $32.55170$ | 1.17 | ACS | f814w | $21.4$ | $0.41$ | $0.46$ | $4.5$ | Arc |  |
HAH $J162122.2+381006.5$ | $111$ | $245.34262$ | $38.16847$ | 0.91 | ACS | f814w | $21.7$ | $0.50$ | $1.00$ | $-70.2$ | Arc | DClust68 | 0.2 S
HAH $J173146.2+225237.6$ | $112$ | $262.94232$ | $22.87712$ | 1.14 | ACS | f814w | $18.8$ | $0.84$ | $0.75$ | $49.7$ | Arc | DClust69 | 0.44 P
HAH $J174109.0+690236.1$ | $113$ | $265.28755$ | $69.04336$ | 4.53 | ACS | f814w | $21.5$ | $0.31$ | $0.87$ | $-61.1$ | Arc |  |
HAH $J180652.4+292945.3$ | $114$ | $271.71867$ | $29.49593$ | 0.87 | ACS | f606w | $21.4$ | $0.23$ | $0.83$ | $8.8$ | Arc | DClust70 |
HAH $J191700.9-333207.0$ | $115$ | $289.25409$ | $-33.53530$ | 1.29 | ACS | f814w | $19.1$ | $1.14$ | $0.75$ | $-71.3$ | Arc | DClust71 |
HAH $J191709.5-333127.0$ | $116$ | $289.28972$ | $-33.52418$ | 0.67 | ACS | f814w | $22.5$ | $0.17$ | $0.56$ | $10.2$ | Arc | DClust72 |
HAH $J204548.7-243833.2$ | $117$ | $311.45298$ | $-24.64258$ | 1.52 | ACS | f814w | $19.6$ | $0.77$ | $0.94$ | $-167.5$ | Arc |  |
HAH $J224324.6-093617.3$ | $118$ | $340.85260$ | $-9.60480$ | 2.06 | ACS | f606w | $21.1$ | $1.22$ | $0.37$ | $120.6$ | Arc | DClust73 | 0.44 P
HAH $J233220.8-535909.8$ | $119$ | $353.08657$ | $-53.98605$ | 1.26 | IR | f140w | $17.2$ | $0.72$ | $0.85$ | $-7.2$ | Arc | DClust74 |  0.4 $\star$
C grade Lenses |  |  |  |  |  |  |  |  |  |  |  |  |
HAH $J000146.0-544026.2$ | $120$ | $0.44161$ | $-54.67395$ | 1.15 | ACS | f606w | $20.9$ | $0.54$ | $0.92$ | $-118.0$ | Arc | DClust75 |
HAH $J002357.7-244154.3$ | $121$ | $5.99142$ | $-24.69858$ | 0.88 | ACS | f606w | $23.2$ | $0.85$ | $0.72$ | $-146.0$ | Arc | DClust76 |
HAH $J002616.0-110548.2$ | $122$ | $6.56680$ | $-11.09673$ | 2.9 | ACS | f814w | $20.9$ | $0.90$ | $0.67$ | $87.6$ | Arc |  | 0.35 P
HAH $J003501.7+023358.6$ | $123$ | $8.75690$ | $2.56628$ | 2.25 | ACS | f814w | $18.9$ | $0.78$ | $0.7$ | $-144.6$ | Arc | DClust77 | 0.38 P
HAH $J004802.0+402624.1$ | $124$ | $12.00867$ | $40.44004$ | 1.4 | ACS | f814w | $20.0$ | $0.67$ | $0.36$ | $133.2$ | Arc |  | 0.54 P
HAH $J013726.6-082747.9$ | $125$ | $24.36080$ | $-8.46330$ | 2.5 | ACS | f814w | $18.4$ | $1.60$ | $0.75$ | $-134.7$ | Double | DClust78 | 0.29 P
HAH $J014236.3+144114.3$ | $126$ | $25.65113$ | $14.68730$ | 1.5 | ACS | f775w | $19.3$ | $1.18$ | $0.96$ | $174.8$ | Arc |  | 0.5 S
HAH $J015246.7+360750.5$ | $127$ | $28.19450$ | $36.13070$ | 0.85 | ACS | f435w | $22.8$ | $1.23$ | $0.75$ | $-89.5$ | Ring x 2 | DClust79 |
HAH $J015317.2-135220.6$ | $128$ | $28.32207$ | $-13.87241$ | 0.65 | ACS | f814w | $21.4$ | $0.40$ | $0.69$ | $-137.8$ | Arc | DClust80 |
HAH $J022141.7-032038.9$ | $129$ | $35.42410$ | $-3.34414$ | 1.25 | ACS | f850lp | $20.4$ | $0.79$ | $0.67$ | $-101.9$ | Arc |  | 0.46 P
HAH $J022253.9+422616.4$ | $130$ | $35.72461$ | $42.43789$ | 2.04 | ACS | f814w | $20.6$ | $0.71$ | $0.66$ | $57.5$ | Arc |  |
HAH $J023726.4-262957.6$ | $131$ | $39.35982$ | $-26.49932$ | 2.76 | ACS | f606w | $19.3$ | $0.70$ | $0.76$ | $-165.5$ | Arc | DClust81 |
HAH $J024336.7-483319.4$ | $132$ | $40.90317$ | $-48.55540$ | 1.33 | UVIS | f200lp | $22.1$ | $0.45$ | $0.75$ | $-98.4$ | Ring | DClust82 |
HAH $J030901.7+264522.2$ | $133$ | $47.25701$ | $26.75616$ | 1.25 | ACS | f814w | $18.3$ | $2.26$ | $0.98$ | $-136.6$ | Arc | DClust83 |
HAH $J040411.1-554433.8$ | $134$ | $61.04657$ | $-55.74273$ | 1.64 | ACS | f606w | $17.6$ | $1.40$ | $0.64$ | $-158.2$ | Arc |  |
HAH $J041308.3-655338.7$ | $135$ | $63.28420$ | $-65.89428$ | 0.51 | ACS | f606w | $24.7$ | $0.28$ | $0.82$ | $-156.5$ | Ring |  |
HAH $J042905.4-101206.7$ | $136$ | $67.27276$ | $-10.20188$ | 1.84 | IR | f140w | $17.8$ | $0.73$ | $0.88$ | $-166.1$ | Arc | DClust84 |
HAH $J043916.2-460115.2$ | $137$ | $69.81779$ | $-46.02089$ | 0.97 | ACS | f606w | $21.8$ | $0.17$ | $0.91$ | $175.9$ | Arc | DClust85 |
HAH $J044632.8-591132.0$ | $138$ | $71.63668$ | $-59.19223$ | 1.5 | ACS | f814w | $19.9$ | $1.03$ | $0.78$ | $120.5$ | Arc |  |
HAH $J045159.3+000645.9$ | $139$ | $72.99696$ | $0.11276$ | 1.86 | ACS | f814w | $20.9$ | $0.01$ | $0.39$ | $-102.3$ | Cross | DClust86 |
HAH $J051537.3-432514.2$ | $140$ | $78.90505$ | $-43.42074$ | 2.87 | ACS | f814w | $18.1$ | $1.88$ | $0.70$ | $-170.3$ | Arc | DClust87 |  0.39 P$\star$
HAH $J051856.3-431439.1$ | $141$ | $79.73450$ | $-43.24420$ | 4.61 | ACS | f814w | $20.5$ | $0.39$ | $0.66$ | $72.0$ | Arc | DClust88 |
HAH $J051856.4-431444.4$ | $142$ | $79.73518$ | $-43.24569$ | 4.61 | ACS | f814w | $19.5$ | $1.90$ | $0.57$ | $13.4$ | Arc | DClust89 |
HAH $J052116.2-510409.5$ | $143$ | $80.31740$ | $-51.06930$ | 0.52 | ACS | f606w | $23.4$ | $0.45$ | $0.51$ | $-60.9$ | Triple | DClust90 |
HAH $J052214.2-362408.4$ | $144$ | $80.55929$ | $-36.40232$ | 1.09 | ACS | f814w | $21.0$ | $0.28$ | $0.87$ | $23.5$ | Arc | DClust91 |
HAH $J065327.1-574306.1$ | $145$ | $103.36301$ | $-57.71836$ | 1.21 | UVIS | f200lp | $20.3$ | $0.89$ | $0.41$ | $53.2$ | Ring | DClust92 |
HAH $J071718.8+374842.3$ | $146$ | $109.32870$ | $37.81175$ | 1.12 | ACS | f814w | $20.9$ | $0.02$ | $0.47$ | $113.9$ | Arc | DClust93 |
HAH $J071731.9+374449.9$ | $147$ | $109.38300$ | $37.74720$ | 1.04 | ACS | f814w | $19.3$ | $1.47$ | $0.42$ | $153.5$ | Arc | DClust94 |
HAH $J074704.6+693824.0$ | $148$ | $116.76942$ | $69.64002$ | 1.43 | ACS | f606w | $20.5$ | $0.98$ | $0.87$ | $37.8$ | Arc | DClust95 |
HAH $J080911.4+064341.9$ | $149$ | $122.29730$ | $6.72820$ | 2.41 | ACS | f606w | $18.2$ | $1.84$ | $0.68$ | $174.8$ | Arc | DClust96 | 0.36 P
HAH $J083637.2+005332.6$ | $150$ | $129.15500$ | $0.89240$ | 3.5 | ACS | f850lp | $17.7$ | $1.53$ | $0.53$ | $128.2$ | Arc |  | 0.22 P
HAH $J084349.0+411635.4$ | $151$ | $130.95433$ | $41.27651$ | 0.68 | ACS | f814w | $21.2$ | $0.50$ | $0.90$ | $-110.8$ | Ring | DClust97 | 0.44 P
HAH $J084959.8+360340.6$ | $152$ | $132.49950$ | $36.06130$ | 0.82 | ACS | f814w | $21.7$ | $0.85$ | $0.65$ | $-16.1$ | Arc | DClust98 | 0.32 P
HAH $J091023.7+021049.2$ | $153$ | $137.59885$ | $2.18035$ | 0.9 | UVIS | f606w | $22.1$ | $0.82$ | $0.92$ | $-42.7$ | Ring | DClust99 | 0.69 P
HAH $J091044.5+424945.8$ | $154$ | $137.68550$ | $42.82940$ | 1.78 | ACS | f814w | $20.2$ | $0.34$ | $0.69$ | $15.2$ | Arc | DClust100 | 0.62 P
HAH $J092141.2-062241.6$ | $155$ | $140.42165$ | $-6.37810$ | 0.79 | ACS | f606w | $22.7$ | $0.49$ | $0.85$ | $-84.0$ | Arc | DClust101 |
HAH $J094058.7+074541.1$ | $156$ | $145.24482$ | $7.76142$ | 0.87 | ACS | f814w | $20.9$ | $0.96$ | $0.50$ | $-40.5$ | Arc | DClust102 | 0.49 P
HAH $J095557.2-095159.0$ | $157$ | $148.98830$ | $-9.86640$ | 1.19 | ACS | f606w | $21.0$ | $0.31$ | $0.81$ | $67.5$ | Arc |  |
HAH $J100050.2+013251.5$ | $158$ | $150.20939$ | $1.54765$ | 0.9 | IR | f140w | $19.2$ | $0.85$ | $0.75$ | $152.7$ | Arc | DClust103 | 0.69 P
HAH $J100142.8+015448.1$ | $159$ | $150.42840$ | $1.91330$ | 1.48 | ACS | f814w | $18.6$ | $0.51$ | $0.92$ | $-65.9$ | Arc | DClust104 | 0.32 P
HAH $J100222.3+023220.0$ | $160$ | $150.59303$ | $2.53890$ | 1.1 | ACS | f814w | $21.5$ | $1.32$ | $0.98$ | $-164.3$ | Arc |  |  1.23 P$\star$
HAH $J103943.7-001516.3$ | $161$ | $159.93217$ | $-0.25453$ | 1.2 | ACS | f814w | $20.7$ | $1.26$ | $0.91$ | $-30.4$ | Arc |  |
HAH $J111554.8+013015.5$ | $162$ | $168.97830$ | $1.50430$ | 1.09 | ACS | f606w | $20.6$ | $0.56$ | $0.68$ | $-151.8$ | Arc | DClust105 | 0.39 P
HAH $J112001.3-120351.1$ | $163$ | $170.00540$ | $-12.06420$ | 1.02 | ACS | f606w | $22.5$ | $0.29$ | $0.73$ | $84.0$ | Arc |  | 0.51 P
HAH $J113305.2+500840.9$ | $164$ | $173.27207$ | $50.14471$ | 1.81 | ACS | f814w | $20.2$ | $0.37$ | $0.42$ | $-56.3$ | Double | DClust106 | 0.4 P
HAH $J114923.6+222926.7$ | $165$ | $177.34814$ | $22.49076$ | 2.61 | ACS | f814w | $16.1$ | $4.58$ | $0.75$ | $50.6$ | Arc |  | 0.21 S
HAH $J115054.9-280548.7$ | $166$ | $177.72889$ | $-28.09686$ | 0.95 | ACS | f814w | $20.1$ | $0.64$ | $0.39$ | $111.6$ | Arc | DClust107 |
HAH $J115855.4-185941.2$ | $167$ | $179.73093$ | $-18.99480$ | 1.55 | ACS | f606w | $19.3$ | $1.22$ | $0.29$ | $50.2$ | Arc |  |
HAH $J122027.5+752124.6$ | $168$ | $185.11459$ | $75.35685$ | 1.82 | ACS | f850lp | $19.1$ | $0.91$ | $0.85$ | $77.7$ | Arc |  |
HAH $J122809.5+221743.3$ | $169$ | $187.03964$ | $22.29538$ | 1.59 | ACS | f814w | $19.5$ | $0.83$ | $0.77$ | $158.4$ | Arc |  | 0.37 S
HAH $J123227.1-125100.0$ | $170$ | $188.11304$ | $-12.85002$ | 1.13 | ACS | f814w | $20.2$ | $0.45$ | $0.93$ | $-22.7$ | Arc |  |
HAH $J123904.4+121231.4$ | $171$ | $189.76824$ | $12.20872$ | 1.73 | ACS | f814w | $21.4$ | $0.39$ | $0.81$ | $118.2$ | Double |  | 0.48 P
HAH $J124355.9+320341.0$ | $172$ | $190.98280$ | $32.06140$ | 1.9 | ACS | f814w | $20.5$ | $0.37$ | $0.80$ | $162.6$ | Arc |  | 0.73 P
HAH $J125801.0-431814.1$ | $173$ | $194.50418$ | $-43.30393$ | 0.85 | ACS | f606w | $20.4$ | $0.50$ | $0.57$ | $-56.1$ | Arc |  |
HAH $J130154.4+275347.0$ | $174$ | $195.47657$ | $27.89638$ | 1.24 | ACS | f475w | $22.8$ | $0.64$ | $0.73$ | $43.8$ | Arc | DClust108 | 0.57 S
HAH $J130236.3+141055.0$ | $175$ | $195.65149$ | $14.18195$ | 1.02 | UVIS | f350lp | $21.9$ | $0.20$ | $0.75$ | $76.2$ | Arc | DClust109 |
HAH $J133422.4+503133.0$ | $176$ | $203.59323$ | $50.52586$ | 1.76 | ACS | f775w | $20.1$ | $0.34$ | $0.69$ | $9.2$ | Arc | DClust110 | 0.63 S
HAH $J134711.8-114157.8$ | $177$ | $206.79914$ | $-11.69944$ | 2.38 | ACS | f850lp | $18.5$ | $0.92$ | $0.37$ | $-53.0$ | Arc | DClust111 |
HAH $J135343.4+050952.1$ | $178$ | $208.43113$ | $5.16448$ | 1.7 | ACS | f606w | $20.7$ | $0.53$ | $0.80$ | $159.6$ | Arc |  | 0.4 P
HAH $J141809.5+524058.8$ | $179$ | $214.53970$ | $52.68300$ | 1.89 | ACS | f606w | $18.9$ | $0.99$ | $0.76$ | $-61.9$ | Arc |  | 0.23 P
HAH $J142018.4+530157.3$ | $180$ | $215.07651$ | $53.03259$ | 2.07 | ACS | f606w | $20.0$ | $0.88$ | $0.77$ | $130.3$ | Arc |  | 0.37 P
HAH $J142952.3+554752.8$ | $181$ | $217.46790$ | $55.79800$ | 0.93 | UVIS | f600lp | $20.9$ | $0.38$ | $0.67$ | $119.7$ | Arc | DClust112 | 0.6 P
HAH $J143808.8+341940.3$ | $182$ | $219.53684$ | $34.32787$ | 3.22 | ACS | f814w | $19.9$ | $0.43$ | $0.72$ | $75.7$ | Arc | DClust113 | 0.54 S
HAH $J144727.3+083001.9$ | $183$ | $221.86388$ | $8.50054$ | 0.68 | ACS | f606w | $21.7$ | $0.29$ | $0.48$ | $35.3$ | Arc | DClust114 | 0.51 P
HAH $J151832.6-813031.8$ | $184$ | $229.63600$ | $-81.50883$ | 0.75 | ACS | f814w | $20.8$ | $0.60$ | $0.37$ | $-59.2$ | Arc | DClust115 |
HAH $J160613.2-000039.5$ | $185$ | $241.55523$ | $-0.01097$ | 0.91 | ACS | f606w | $22.8$ | $0.51$ | $0.87$ | $96.3$ | Ring |  | 0.28 P
HAH $J161543.8-060959.7$ | $186$ | $243.93268$ | $-6.16660$ | 3.09 | ACS | f814w | $17.5$ | $1.57$ | $0.92$ | $34.9$ | Arc | DClust116 |  0.2 $\star$
HAH $J162308.1+072141.5$ | $187$ | $245.78380$ | $7.36153$ | 1.74 | ACS | f850lp | $19.5$ | $0.43$ | $0.82$ | $-55.5$ | Arc |  | 0.42 P
HAH $J171721.7+593126.0$ | $188$ | $259.34068$ | $59.52392$ | 1.67 | ACS | f814w | $19.1$ | $0.89$ | $0.95$ | $-150.2$ | Arc |  | 0.38 P
HAH $J173142.8+225101.0$ | $189$ | $262.92838$ | $22.85027$ | 1.4 | ACS | f814w | $20.3$ | $0.49$ | $0.48$ | $75.0$ | Arc | DClust117 | 0.36 P
HAH $J173647.0+461847.1$ | $190$ | $264.19645$ | $46.31250$ | 2.31 | IR | f110w | $16.2$ | $1.58$ | $0.91$ | $29.1$ | Arc | DClust118 |
HAH $J175151.7+443859.0$ | $191$ | $267.96554$ | $44.64972$ | 2.9 | ACS | f814w | $20.4$ | $0.47$ | $0.94$ | $46.9$ | Arc | DClust119 | 0.38 P
HAH $J221450.1-140049.7$ | $192$ | $333.70891$ | $-14.01380$ | 2.08 | ACS | f555w | $18.9$ | $1.29$ | $0.76$ | $-35.5$ | Arc | DClust120 |
HAH $J224154.3+173336.5$ | $193$ | $340.47639$ | $17.56015$ | 0.81 | ACS | f814w | $19.2$ | $0.54$ | $0.31$ | $87.0$ | Arc | DClust121 | 0.31 P
HAH $J224901.9-443103.9$ | $194$ | $342.25819$ | $-44.51777$ | 1.58 | ACS | f814w | $21.9$ | $0.96$ | $0.14$ | $-80.8$ | Arc | DClust122 |
HAH $J230104.7+300726.4$ | $195$ | $345.26983$ | $30.12401$ | 1.8 | ACS | f850lp | $17.6$ | $1.91$ | $0.81$ | $26.2$ | Arc | DClust123 |
HAH $J233813.3+270418.0$ | $196$ | $354.55585$ | $27.07173$ | 0.58 | UVIS | f814w | $22.8$ | $1.83$ | $0.18$ | $7.2$ | Double |  |
HAH $J234232.8-541329.7$ | $197$ | $355.63659$ | $-54.22491$ | 1.04 | ACS | f606w | $22.2$ | $0.26$ | $0.79$ | $-130.6$ | Arc | DClust124 |
HAH $J235747.7+414740.8$ | $198$ | $359.44843$ | $41.79490$ | 4.5 | ACS | f814w | $18.3$ | $2.64$ | $0.63$ | $39.9$ | Arc |  |
Table 2: continued.

Notes. This table summarises a list of characteristics related to each newly
discovered lens. The lens objects are named using the standard IAU name, where
the acronym HAH stands for Hubble Asteroid Hunter. They are grouped by grades
(A, B, C) which were assigned by the authors of this paper as a qualitative
assessment of the candidates. RA and Dec: right ascension and declination
given in degrees of celestial coordinates J2000.0. $r_{\rm arc}$: the arc
radius (in arcsec) corresponding to the angular separation between the lens
and the surrounding images. Instru. and filter: the HST instrument (ACS/WFC,
WFC3/UVIS or WFC3/IR) and the filter with which the HST image was taken.
$Mag$, $r_{\rm e}$, $q$, and $PA$: the apparent magnitude, the effective
radius (in arcsec), the axis ratio and the position angle of the foreground
lens galaxy (measured from North through East, same orientation as in Figures
2-4) ; these parameters were retrieved with Galfit. class: the morphological
class of the source images (Arc, Quad, Ring, Double). clust.: a flag
indicating the presence of a foreground or background nearby cluster, details
are available in table LABEL:tab:clusters. $z$: the photometric (P) or
spectroscopic (S) redshift, retrieved from SDSS (no mark) or NED (marked
$\star$).

Table 3: Rediscovered lenses identified in this study. IAU Name | ID | RA | Dec | $r_{\rm arc}\,(\arcsec)$ | instru. | filter | $mag$ | $r_{\rm e}\,(\arcsec)$ | $q$ | PA | class | clust. | $z$ | reference
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---
A grade Lenses |  |  |  |  |  |  |  |  |  |  |  |  |  |
HAH $J001426.3-302255.3$ | $199$ | $3.60962$ | $-30.38202$ | 1 | ACS | f814w | $18.9$ | $0.55$ | $0.72$ | $-137.7$ | Arc | RClust125 |  0.24 $\star$ | Pawase et al. (2014)
HAH $J015242.4-135618.2$ | $200$ | $28.17683$ | $-13.93838$ | 0.97 | ACS | f775w | $21.4$ | $0.30$ | $0.92$ | $-96.3$ | Arc | RClust126 |  | Grillo et al. (2008)
HAH $J032940.8-021318.5$ | $201$ | $52.42010$ | $-2.22180$ | 0.82 | ACS | f435w | $22.2$ | $0.67$ | $0.94$ | $-148.2$ | Arc | RClust127 |  | Desprez et al. (2018)
HAH $J033238.2-275653.3$ | $202$ | $53.15930$ | $-27.94810$ | 1.67 | ACS | f606w | $21.0$ | $1.08$ | $0.53$ | $-124.5$ | Arc |  |  | More et al. (2011)
HAH $J033304.4-065144.3$ | $203$ | $53.26850$ | $-6.86230$ | 0.83 | IR | f160w | $19.7$ | $0.69$ | $0.75$ | $104.2$ | Arc | RClust128 | 0.57 P | Sharon et al. (2020)
HAH $J041604.1-240522.2$ | $204$ | $64.01720$ | $-24.08950$ | 1.2 | ACS | f814w | $20.0$ | $0.57$ | $0.32$ | $28.6$ | Arc | RClust129 |  0.4 P$\star$ | Diego et al. (2015)
HAH $J045400.6-030833.8$ | $205$ | $73.50260$ | $-3.14280$ | 1.88 | ACS | f814w | $17.0$ | $3.45$ | $0.69$ | $-8.6$ | Arc | RClust130 |  | Schirmer et al. (2010)
HAH $J045413.1+025733.8$ | $206$ | $73.55475$ | $2.95939$ | 2.6 | ACS | f814w | $16.5$ | $2.55$ | $0.96$ | $-3.0$ | Ring | RClust131 |  | Clowe et al. (2012)
HAH $J074450.9+392736.0$ | $207$ | $116.21211$ | $39.45986$ | unfit | ACS | f606w | $22.5$ | $1.43$ | $0.39$ | $21.7$ | Arc | RClust132 |  0.62 P$\star$ | Horesh et al. (2010)
HAH $J091617.5-002405.9$ | $208$ | 139.07306 | -0.40164 | 0.74 | ACS | f814w |  |  |  |  | Arc | RClust133 |  | Clowe et al. (2012)
HAH $J095921.8+020638.5$ | $209$ | $149.84068$ | $2.11064$ | 0.71 | ACS | f814w | $20.5$ | $0.34$ | $0.78$ | $49.4$ | Quad |  | 0.58 P | Faure et al. (2008)
HAH $J095930.9+023427.8$ | $210$ | $149.87890$ | $2.57440$ | 0.92 | ACS | f814w | $21.9$ | $0.38$ | $0.61$ | $-69.8$ | Arc |  |  0.89 $\star$ | Lagattuta et al. (2010)
HAH $J095956.0+021901.8$ | $211$ | $149.98330$ | $2.31719$ | 2.36 | ACS | f814w | $22.9$ | $4.65$ | $0.21$ | $10.7$ | Arc |  |  0.93 $\star$ | More et al. (2012)
|  |  |  | 2.36 | ACS | f814w | $21.3$ | $0.74$ | $0.88$ | $-64.5$ | Arc |  |  0.93 $\star$ |
HAH $J100012.6+022015.8$ | $212$ | $150.05258$ | $2.33772$ | 0.73 | ACS | f814w | $19.3$ | $0.49$ | $0.81$ | $5.9$ | Arc | RClust134 | 0.37 P | Cabanac et al. (2007)
HAH $J100018.5+023845.6$ | $213$ | $150.07700$ | $2.64600$ | 1.51 | ACS | f814w | $23.6$ | $0.12$ | $0.71$ | $10.8$ | Arc | RClust135 |  0.42 P$\star$ | Cabanac et al. (2007)
HAH $J100108.4+024029.9$ | $214$ | $150.28495$ | $2.67496$ | 1.41 | ACS | f814w | $19.3$ | $0.34$ | $0.86$ | $1.8$ | Arc |  |  0.32 P$\star$ | Pourrahmani et al. (2018)
HAH $J100133.7+022135.3$ | $215$ | $150.39058$ | $2.35982$ | 2.54 | ACS | f814w | $20.3$ | $0.54$ | $0.44$ | $-29.4$ | Arc | RClust136 | 0.36 P | More et al. (2012)
HAH $J100211.2+021139.5$ | $216$ | $150.54675$ | $2.19429$ | 3.45 | ACS | f814w | $20.5$ | $1.77$ | $0.46$ | $13.7$ | Arc |  | 0.7 P | Faure et al. (2008)
HAH $J114936.7+222612.0$ | $217$ | $177.40280$ | $22.43667$ | 0.859 | ACS | f814w | $19.8$ | $0.48$ | $0.80$ | $60.8$ | Cross |  | 0.5 P | Desprez et al. (2018)
HAH $J133235.0+503237.3$ | $218$ | $203.14564$ | $50.54369$ | 4.2 | ACS | f606w | $18.9$ | $1.66$ | $0.72$ | $-156.6$ | Arc |  | 0.28 S | Ragozzine et al. (2012)
HAH $J133241.0+503346.3$ | $219$ | $203.17064$ | $50.56286$ | 2.52 | ACS | f606w | $18.2$ | $1.89$ | $0.90$ | $149.3$ | Ring | RClust137 | 0.28 S | Ragozzine et al. (2012)
HAH $J135409.1+771557.2$ | $220$ | $208.53795$ | $77.26590$ | 1.79 | ACS | f814w | $21.0$ | $0.60$ | $0.75$ | $-179.5$ | Arc | RClust138 |  | Repp & Ebeling (2018)
HAH $J135409.2+771549.9$ | $221$ | $208.53816$ | $77.26385$ | 2.26 | ACS | f814w | $20.5$ | $0.91$ | $0.65$ | $-90.1$ | Arc | RClust139 |  | Repp & Ebeling (2018)
HAH $J140237.0+542716.3$ | $222$ | $210.65450$ | $54.45455$ | 1.8 | ACS | f814w | $18.1$ | $1.14$ | $0.74$ | $-114.1$ | Arc |  |  | Pawase et al. (2014)
HAH $J141735.7+522646.3$ | $223$ | $214.39891$ | $52.44621$ | 1.6 | ACS | f814w | $20.2$ | $0.98$ | $0.62$ | $-142.5$ | Cross |  | 0.59 P | Ratnatunga et al. (1995)
HAH $J141820.8+523611.1$ | $224$ | $214.58664$ | $52.60309$ | 0.81 | ACS | f814w | $21.2$ | $0.62$ | $0.76$ | $-91.0$ | Arc |  | 0.58 S | Moustakas et al. (2007)
HAH $J143703.3+350153.3$ | $225$ | $219.26352$ | $35.03145$ | 0.65 | ACS | f814w | $22.5$ | $0.36$ | $0.76$ | $-78.8$ | Ring |  | 0.56 P | Pawase et al. (2014)
HAH $J145250.0+580135.3$ | $226$ | $223.20849$ | $58.02649$ | 3.22 | ACS | f814w | $18.3$ | $1.17$ | $0.67$ | $42.3$ | Arc | RClust140 | 0.33 S | Repp & Ebeling (2018)
HAH $J152745.2+065220.8$ | $227$ | $231.93830$ | $6.87247$ | 1.78 | UVIS | f606w | $22.0$ | $0.30$ | $0.33$ | $39.7$ | Arc | RClust141 | 0.32 P | Koester et al. (2010)
HAH $J213512.7-010143.9$ | $228$ | $323.80296$ | $-1.02886$ | 0.98 | ACS | f814w | $20.7$ | $0.64$ | $0.65$ | $98.8$ | Arc | RClust142 | 0.3 P | Smail et al. (2007)
HAH $J221142.0-035052.4$ | $229$ | $332.92486$ | $-3.84790$ | 1.15 | ACS | f814w | $21.7$ | $0.19$ | $0.77$ | $-67.4$ | Cross | RClust143 | 0.42 P | Bettoni et al. (2019)
HAH $J224851.7-443105.1$ | $230$ | $342.21568$ | $-44.51858$ | 3.17 | ACS | f814w | $20.9$ | $0.11$ | $0.82$ | $33.3$ | Arc | RClust144 |  0.33 $\star$ | Guzzo et al. (2009)
|  |  |  | 3.17 | ACS | f814w | $17.7$ | $2.40$ | $0.82$ | $-103.8$ | Arc |  |  0.33 $\star$ |
|  |  |  | 3.17 | ACS | f814w | $19.0$ | $3.39$ | $0.86$ | $-10.8$ | Arc |  |  0.33 $\star$ |
|  |  |  | 3.17 | ACS | f814w | $20.1$ | $0.27$ | $0.69$ | $-32.1$ | Arc |  |  0.33 $\star$ |
HAH $J235130.6-261500.7$ | $231$ | $357.87744$ | $-26.25008$ | 3.32 | ACS | f814w | $16.3$ | $4.47$ | $0.74$ | $-124.2$ | Arc |  |  0.27 $\star$ | Pawase et al. (2014)
B grade Lenses |  |  |  |  |  |  |  |  |  |  |  |  |  |
HAH $J001423.0-302109.7$ | $232$ | $3.59578$ | $-30.35270$ | 1.7 | ACS | f814w | $19.8$ | $0.83$ | $0.85$ | $22.5$ | Arc | RClust145 |  0.25 $\star$ | Pawase et al. (2014)
HAH $J033153.2-274619.3$ | $233$ | $52.97181$ | $-27.77194$ | 1.05 | ACS | f840w | $20.7$ | $0.66$ | $0.76$ | $-62.5$ | Arc |  |  0.73 $\star$ | More et al. (2011)
HAH $J095939.1+023044.1$ | $234$ | $149.91311$ | $2.51224$ | 1.7 | ACS | f814w | $20.0$ | $0.76$ | $0.69$ | $62.6$ | Arc | RClust146 | 0.72 P | Faure et al. (2008)
HAH $J100013.9+022249.8$ | $235$ | $150.05800$ | $2.38050$ | 1.65 | ACS | f606w | $19.3$ | $1.90$ | $0.79$ | $-110.8$ | Arc | RClust147 | 0.35 S | Faure et al. (2008)
HAH $J100047.7+015023.3$ | $236$ | $150.19854$ | $1.83981$ | 1.71 | ACS | f814w | $20.6$ | $0.75$ | $0.72$ | $2.2$ | Arc | RClust148 |  0.89 $\star$ | Faure et al. (2008)
HAH $J100055.7+013821.1$ | $237$ | $150.23214$ | $1.63919$ | 1.06 | ACS | f814w | $20.9$ | $0.35$ | $0.95$ | $92.4$ | Arc | RClust149 | 0.55 P | Faure et al. (2008)
HAH $J100056.8+021225.8$ | $238$ | $150.23661$ | $2.20719$ | 1.67 | ACS | f814w | $18.8$ | $1.01$ | $0.66$ | $64.1$ | Arc |  | 0.36 S | Faure et al. (2008)
HAH $J103751.4-124326.3$ | $239$ | $159.46400$ | $-12.72398$ | 1.12 | ACS | f814w | $19.5$ | $1.39$ | $0.70$ | $-49.2$ | Arc |  |  0.58 $\star$ | Pawase et al. (2014)
|  |  |  | 1.12 | ACS | f814w | $19.8$ | $0.66$ | $0.86$ | $-53.7$ | Arc |  |  0.58 $\star$ |
HAH $J121228.4-121723.1$ | $240$ | $183.11829$ | $-12.29002$ | 2.84 | ACS | f814w | $21.9$ | $0.18$ | $0.79$ | $-105.5$ | Arc |  |  | Ebeling et al. (2019)
|  |  |  | 2.84 | ACS | f814w | $20.1$ | $1.03$ | $0.84$ | $-175.4$ | Arc |  |  |
HAH $J123729.9+621300.7$ | $241$ | $189.37456$ | $62.21685$ | 2.12 | ACS | f814w | $19.9$ | $0.81$ | $0.91$ | $48.9$ | Arc |  | 0.49 P | Fassnacht et al. (2004)
HAH $J130042.7+280523.6$ | $242$ | $195.17804$ | $28.08989$ | 1.08 | ACS | f814w | $18.2$ | $1.70$ | $0.61$ | $-118.2$ | Arc | RClust150 | 0.37 S | Pawase et al. (2014)
HAH $J131829.4-010421.6$ | $243$ | $199.62246$ | $-1.07267$ | 0.67 | ACS | f814w | $19.9$ | $0.67$ | $0.84$ | $-85.0$ | Arc |  | 0.66 S | Brownstein et al. (2012)
HAH $J141833.1+524352.5$ | $244$ | $214.63790$ | $52.73126$ | 0.69 | ACS | f814w | $20.5$ | $1.32$ | $0.68$ | $97.2$ | Arc |  | 0.47 P | Marshall et al. (2009)
HAH $J214014.8-233904.3$ | $245$ | $325.06171$ | $-23.65125$ | 2.58 | ACS | f606w | $20.0$ | $0.58$ | $0.94$ | $133.2$ | Arc |  |  | Fort et al. (1992)
HAH $J230824.7-021213.3$ | $246$ | $347.10300$ | $-2.20370$ | 3.24 | ACS | f606w | $18.2$ | $2.76$ | $0.53$ | $-88.3$ | Arc | RClust151 | 0.27 P | Jacobs et al. (2019)
C grade Lenses |  |  |  |  |  |  |  |  |  |  |  |  |  |
HAH $J013152.3-133658.3$ | $247$ | $22.96793$ | $-13.61621$ | 1.9 | ACS | f475w | $19.0$ | $1.58$ | $0.86$ | $-170.7$ | Arc | RClust152 |  | Zitrin et al. (2015)
HAH $J071815.0+374200.3$ | $248$ | $109.56253$ | $37.70009$ | 1.91 | ACS | f814w | $20.6$ | $0.44$ | $0.96$ | $61.4$ | Arc | RClust153 | 0.34 P | Ebeling et al. (2014)
HAH $J095810.1+022942.0$ | $249$ | $149.54211$ | $2.49500$ | 2.21 | ACS | f814w | $18.9$ | $1.05$ | $0.75$ | $-57.8$ | Arc |  | 0.4 P | Jackson (2008)
HAH $J114934.3+222440.5$ | $250$ | $177.39310$ | $22.41127$ | 0.61 | ACS | f606w | $23.1$ | $0.67$ | $0.93$ | $7.0$ | Arc | RClust154 | 0.47 P | Morishita et al. (2017)
HAH $J173217.5+193250.3$ | $251$ | $263.07333$ | $19.54731$ | 1.2 | ACS | f814w | $19.8$ | $0.61$ | $0.93$ | $44.6$ | Arc | RClust155 |  | Ebeling et al. (2018)
HAH $J203146.3-403705.4$ | $252$ | $307.94293$ | $-40.61818$ | 1.02 | ACS | f814w | $22.4$ | $0.30$ | $0.76$ | $0.2$ | Arc | RClust156 |  | Richard et al. (2015)
Table 3: (continued.)

Notes. This table summarises a list of characteristics related to each
rediscovered lens. The lens objects are named using the standard IAU name,
where the acronym HAH stands for Hubble Asteroid Hunter. The lenses are
grouped by grades (A,B,C) which were assigned by the authors of this paper as
a qualitative assessment of the candidates. RA and Dec: right ascension and
declination given in degrees of celestial coordinates J2000.0. $r_{\rm arc}$:
the arc radius (in arcsec) corresponding to the angular separation between the
lens and the surrounding images. Instru. and filter: the HST instrument
(ACS/WFC, WFC3/UVIS or WFC3/IR) and the filter with which the HST image was
taken. $Mag$, $r_{\rm e}$, $q$, and $PA$: the apparent magnitude, the
effective radius (in arcsec), the axis ratio and the position angle of the
foreground lens galaxy (measured from North through East, same orientation as
in Figures 2-4); these parameters were retrieved with Galfit. class: the
morphological class of the source images (Arc, Quad, Ring, Double). clust.: a
flag indicating the presence of a foreground or background nearby cluster,
details are available in table LABEL:tab:clusters. $z$: the photometric (P) or
spectroscopic (S) redshift, retrieved from SDSS (no mark) or NED (marked
$\star$). The reference columns shows the paper where the the strong lensing
system is mentioned, as listed by the ESASky portal. Because of the complexity
of lens ID 207, we did not manage to measure its arc radius. Finally, We did
not manage to obtain a good model for the lens ID 208 and, therefore, left the
GALFIT parameters blank.

Table 4: Candidate cluster flags.

Flag |  |  | HST Observation Target |  | DESI Catalog |  | redMaPPer SDSS Catalog
---|---|---|---|---|---|---|---
| IAU name |  | Targeted Cluster ID |  | Candidate Cluster ID | Distance (″) |  | Candidate Cluster ID | Distance (″)
Discovery group |  |  |  |  |  |  |  |  |
DClust1 |  HAH $J002348.6-244149.6$ |  |  |  | $3469200139$ | $84$ |  |  |
DClust2 |  HAH $J002753.2-753730.0$ |  |  SMACS $J0028.2-7537$ |  |  |  |  |  |
DClust3 |  HAH $J004924.3-205729.8$ |  |  ESO $540-31$ |  | $3316000106$ | $93$ |  |  |
DClust4 |  HAH $J015949.3-084906.0$ |  |  MACS $J0159.8-0849$ |  | $2830900043$ | $64$ |  |  RM $J015949.3-084958.9$ | $53$
DClust5 |  HAH $J024329.8-593102.7$ |  |  SPT-CL $J0243-5930$ |  |  |  |  |  |
DClust6 |  HAH $J024533.6-530203.5$ |  |  ACO S$295$ |  | $4427400112$ | $36$ |  |  |
DClust7 |  HAH $J025241.6-150025.5$ |  |  |  | $3087900009$ | $30$ |  |  |
DClust8 |  HAH $J025659.9-163059.5$ |  |  |  | $3164700123$ | $32$ |  |  |
DClust9 |  HAH $J034445.2-642133.8$ |  |  SPT-CL $J0345-6419$ |  |  |  |  |  |
DClust10 |  HAH $J054707.0-390516.3$ |  |  MACS $J0547.0-3904$ |  | $3986900096$ | $67$ |  |  |
DClust11 |  HAH $J061345.7-562750.4$ |  |  SPT-CL $J0613-5627$ |  | $4505800076$ | $0$ |  |  |
DClust12 |  HAH $J072221.9+072326.7$ |  |  PSZ2 $G209.79+10.23$ |  |  |  |  |  |
DClust13 |  HAH $J083420.3+452506.9$ |  |  |  | $692800146$ | $70$ |  |  RM $J083416.3+452420.0$ | $63$
DClust14 |  HAH $J102914.8+262207.0$ |  |  |  | $1355200029$ | $92$ |  |  |
DClust15 |  HAH $J105722.7+580046.5$ |  |  |  | $369000033$ | $92$ |  |  |
DClust16 |  HAH $J111337.4+221249.2$ |  |  A$1300$ |  |  |  |  |  |
DClust17 |  HAH $J114938.4+222107.7$ |  |  |  | $1510200105$ | $161$ |  |  RM $J114935.7+222354.6$ | $172$
DClust18 |  HAH $J131953.6+700420.8$ |  |  MACS $J1319.9+7003$ |  | $157400151$ | $75$ |  |  |
DClust19 |  HAH $J133525.9+405952.4$ |  |  ACO $1763$ |  | $846500034$ | $14$ |  |  RM $J133520.1+410004.1$ | $67$
DClust20 |  HAH $J141139.2+565200.9$ |  |  |  | $406600086$ | $80$ |  |  |
DClust21 |  HAH $J214817.6-484350.5$ |  |  SPT-CL $J2148-4843$ |  |  |  |  |  |
DClust22 |  HAH $J234106.5-000007.5$ |  |  |  | $2470000044$ | $141$ |  |  |
DClust23 |  HAH $J001419.9-302600.7$ |  |  Abell $2744$ |  |  |  |  |  |
DClust24 |  HAH $J002706.3+170313.5$ |  |  |  | $1728400102$ | $48$ |  |  |
DClust25 |  HAH $J003350.8-074959.9$ |  |  MACS $J0033.8-0751$ |  | $2778200022$ | $75$ |  |  RM $J003353.1-075210.4$ | $135$
DClust26 |  HAH $J004426.2-403941.4$ |  |  SPT-CL $J0044-4037$ |  | $4058400124$ | $140$ |  |  |
DClust27 |  HAH $J005141.6+272001.5$ |  |  MACS $J0051.6+2720$ |  | $1319300120$ | $49$ |  |  RM $J005138.6+271959.9$ | $40$
DClust28 |  HAH $J011138.3-454015.1$ |  |  |  | $4208300009$ | $70$ |  |  |
DClust29 |  HAH $J013723.7-082852.2$ |  |  WHL $J013719.8-082841$ |  | $2804900125$ | $78$ |  |  RM $J013725.0-082722.7$ | $92$
DClust30 |  HAH $J023951.1-013205.9$ |  |  |  | $2498800056$ | $177$ |  |  RM $J023952.7-013418.9$ | $135$
DClust31 |  HAH $J024535.7-530125.5$ |  |  ACO S$295$ |  | $4427400112$ | $36$ |  |  |
DClust32 |  HAH $J025735.5-220928.5$ |  |  |  | $3369500071$ | $55$ |  |  |
DClust33 |  HAH $J025740.9-221027.3$ |  |  |  | $3369500071$ | $55$ |  |  |
DClust34 |  HAH $J032030.9+003242.8$ |  |  |  | $2422800030$ | $88$ |  |  |
DClust35 |  HAH $J033530.7-540734.7$ |  |  |  | $4447600038$ | $41$ |  |  |
DClust36 |  HAH $J033645.9-535536.7$ |  |  |  | $4428100085$ | $63$ |  |  |
DClust37 |  HAH $J035851.7-295418.7$ |  |  MACS $J0358.8-2955$ |  | $3677800030$ | $79$ |  |  |
DClust38 |  HAH $J041631.5-240512.5$ |  |  MACS $J0416.1-2403$ |  |  |  |  |  |
DClust39 |  HAH $J044208.3-281503.7$ |  |  RCS $J044207-2815.0$ |  | $3601800082$ | $150$ |  |  |
DClust40 |  HAH $J045430.7-030133.2$ |  |  |  | $2578000137$ | $128$ |  |  |
DClust41 |  HAH $J045441.7-030319.9$ |  |  |  | $2578000137$ | $142$ |  |  |
DClust42 |  HAH $J051850.3-431442.0$ |  |  |  | $4114300083$ | $60$ |  |  |
DClust43 |  HAH $J055326.6-334254.0$ |  |  MACS $J0553.4-3342$ |  | $3807900148$ | $98$ |  |  |
DClust44 |  HAH $J072218.2+072314.8$ |  |  PSZ2 $G209.79+10.23$ |  |  |  |  |  |
DClust45 |  HAH $J072333.8-732550.9$ |  |  SMACS $J0723.3-7327$ |  |  |  |  |  |
DClust46 |  HAH $J084712.7+344910.9$ |  |  |  | $1046200011$ | $65$ |  |  |
DClust47 |  HAH $J094949.9+170614.4$ |  |  RXC $J0949.8+1707$ |  | $1738400144$ | $51$ |  |  RM $J094951.8+170710.6$ | $62$
DClust48 |  HAH $J095803.9+653409.1$ |  |  |  | $216600094$ | $17$ |  |  |
DClust49 |  HAH $J100030.1+023716.7$ |  |  |  | $2353000132$ | $98$ |  |  |
DClust50 |  HAH $J100124.2+555407.2$ |  |  |  | $421600140$ | $67$ |  |  |
DClust51 |  HAH $J104132.0+000125.0$ |  |  |  | $2456200026$ | $114$ |  |  |
DClust52 |  HAH $J105726.9+575944.0$ |  |  |  | $369000033$ | $92$ |  |  |
DClust53 |  HAH $J111507.3+531955.8$ |  |  MACS $J1115.2+5320$ |  | $499300020$ | $79$ |  |  RM $J111514.8+531954.6$ | $67$
DClust54 |  HAH $J111822.1+033802.1$ |  |  |  |  |  |  |  RM $J111814.9+033931.6$ | $141$
DClust55 |  HAH $J122944.7+112238.3$ |  |  |  | $1971700080$ | $99$ |  |  |
DClust56 |  HAH $J123618.8+260905.0$ |  |  |  | $1383000036$ | $68$ |  |  |
DClust57 |  HAH $J125907.8-014439.0$ |  |  Abell $1650-9-13-0$ |  |  |  |  |  |
DClust58 |  HAH $J130152.7+275147.7$ |  |  |  | $1306700027$ | $151$ |  |  |
DClust59 |  HAH $J132217.5+464630.4$ |  |  |  | $674100042$ | $62$ |  |  RM $J132226.8+464630.2$ | $95$
DClust60 |  HAH $J132331.9+302155.8$ |  |  |  | $1204700022$ | $63$ |  |  RM $J132334.1+302249.2$ | $60$
DClust61 |  HAH $J133240.6+503315.5$ |  |  Abell $1758N-P2$ |  | $563100075$ | $67$ |  |  RM $J133238.4+503336.0$ | $29$
DClust62 |  HAH $J133252.7+503026.9$ |  |  Abell $1758N-P1$ |  | $563100075$ | $142$ |  |  |
DClust63 |  HAH $J135953.3+623118.4$ |  |  |  | $275000026$ | $34$ |  |  RM $J135950.6+623105.5$ | $23$
DClust64 |  HAH $J143236.3+344030.4$ |  |  |  | $1052300092$ | $59$ |  |  |
DClust65 |  HAH $J145832.7-002349.9$ |  |  |  | $2486400029$ | $55$ |  |  |
DClust66 |  HAH $J151841.7+084549.2$ |  |  |  | $2102700082$ | $55$ |  |  RM $J151846.8+084550.5$ | $75$
DClust67 |  HAH $J161311.2+565004.1$ |  |  |  | $408100043$ | $44$ |  |  |
DClust68 |  HAH $J162122.2+381006.5$ |  |  MACS $J1621.3+3810$ |  | $926200081$ | $35$ |  |  RM $J162124.8+381008.9$ | $30$
DClust69 |  HAH $J173146.2+225237.6$ |  |  |  | $1516300115$ | $87$ |  |  |
DClust70 |  HAH $J180652.4+292945.3$ |  |  |  | $1260900074$ | $29$ |  |  |
DClust71 |  HAH $J191700.9-333207.0$ |  |  PLCK ESZ $G004.5-19.5$ ACS |  |  |  |  |  |
DClust72 |  HAH $J191709.5-333127.0$ |  |  PLCK ESZ $G004.5-19.5$ IR |  |  |  |  |  |
DClust73 |  HAH $J224324.6-093617.3$ |  |  MACS $J0717+3745$ ACS |  | $2878600004$ | $43$ |  |  RM $J224319.8-093530.9$ | $85$
DClust74 |  HAH $J233220.8-535909.8$ |  |  SMACS $J2332.4-5358$ |  | $4463600107$ | $84$ |  |  |
DClust75 |  HAH $J000146.0-544026.2$ |  |  SPT-CL $J0001-5440$ |  | $4444800055$ | $89$ |  |  |
DClust76 |  HAH $J002357.7-244154.3$ |  |  |  | $3469200139$ | $84$ |  |  |
DClust77 |  HAH $J003501.7+023358.6$ |  |  MACS $J0034.9+0234$ |  | $2343000008$ | $64$ |  |  RM $J003457.8+023331.8$ | $64$
DClust78 |  HAH $J013726.6-082747.9$ |  |  WHL $J013719.8-082841$ |  | $2804900125$ | $78$ |  |  RM $J013725.0-082722.7$ | $35$
DClust79 |  HAH $J015246.7+360750.5$ |  |  NGC $708$ |  |  |  |  |  |
DClust80 |  HAH $J015317.2-135220.6$ |  |  |  | $3035600139$ | $99$ |  |  |
DClust81 |  HAH $J023726.4-262957.6$ |  |  RXC $J0237.4-2630$ |  | $3548400119$ | $30$ |  |  |
DClust82 |  HAH $J024336.7-483319.4$ |  |  SPT-CL $J0243-4833$ |  | $4279300045$ | $50$ |  |  |
DClust83 |  HAH $J030901.7+264522.2$ |  |  MACS $J0308.9+2645$ |  |  |  |  |  |
DClust84 |  HAH $J042905.4-101206.7$ |  |  |  | $2884800097$ | $71$ |  |  |
DClust85 |  HAH $J043916.2-460115.2$ |  |  SMACS $J0439.2-4600$ |  | $4211700086$ | $25$ |  |  |