# The CatWISE2020 Catalog

Federico Marocco Jet Propulsion Laboratory, California Institute of
Technology, 4800 Oak Grove Drive, M/S 169-327, Pasadena, CA 91109, USA  IPAC,
Mail Code 100-22, California Institute of Technology, 1200 E. California
Blvd., Pasadena, CA 91125, USA  Peter R. M. Eisenhardt  Jet Propulsion
Laboratory, California Institute of Technology, 4800 Oak Grove Drive, M/S
169-327, Pasadena, CA 91109, USA  John W. Fowler 230 Pacific St., Apt. 205,
Santa Monica, CA 90405, USA  J. Davy Kirkpatrick IPAC, Mail Code 100-22,
California Institute of Technology, 1200 E. California Blvd., Pasadena, CA
91125, USA  Aaron M. Meisner NSF’s National Optical-Infrared Astronomy
Research Laboratory, 950 N Cherry Ave, Tucson, AZ 85719, USA  Edward F.
Schlafly Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley,
CA 94720, USA  S. Adam Stanford  Department of Physics, University of
California Davis, One Shields Avenue, Davis, CA 95616, USA  Nelson Garcia
IPAC, Mail Code 100-22, California Institute of Technology, 1200 E. California
Blvd., Pasadena, CA 91125, USA  Dan Caselden  Gigamon Applied Threat Research,
619 Western Avenue, Suite 200, Seattle, WA 98104, USA  Michael C. Cushing
Department of Physics and Astronomy, University of Toledo, 2801 West Bancroft
St., Toledo, OH 43606, USA  Roc M. Cutri  IPAC, Mail Code 100-22, California
Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
Jacqueline K. Faherty Department of Astrophysics, American Museum of Natural
History, Central Park West at 79th Street, NY 10024, USA  Christopher R.
Gelino  IPAC, Mail Code 100-22, California Institute of Technology, 1200 E.
California Blvd., Pasadena, CA 91125, USA  Anthony H. Gonzalez  Department of
Astronomy, University of Florida, 211 Bryant Space Center, Gainesville, FL
32611, USA  Thomas H. Jarrett Department of Astronomy, University of Cape
Town, Private Bag X3, Rondebosch, 7701, South Africa  Renata Koontz
University of California, Riverside, 900 University Ave, Riverside, CA 92521,
USA  Amanda Mainzer  Lunar and Planetary Laboratory, University of Arizona,
Tucson, AZ 85721, USA  Elijah J. Marchese  University of California,
Riverside, 900 University Ave, Riverside, CA 92521, USA  Bahram Mobasher
University of California, Riverside, 900 University Ave, Riverside, CA 92521
David J. Schlegel Lawrence Berkeley National Laboratory, Berkeley, CA, 94720,
USA  Daniel Stern  Jet Propulsion Laboratory, California Institute of
Technology, 4800 Oak Grove Drive, M/S 169-327, Pasadena, CA 91109, USA  Harry
I. Teplitz  IPAC, Mail Code 100-22, California Institute of Technology, 1200
E. California Blvd., Pasadena, CA 91125, USA  Edward L. Wright Department of
Physics and Astronomy, UCLA, 430 Portola Plaza, Box 951547, Los Angeles, CA
90095-1547, USA

###### Abstract

The CatWISE2020 Catalog consists of 1,890,715,640 sources over the entire sky
selected from WISE and NEOWISE survey data at 3.4 and 4.6 µm (W1 and W2)
collected from 2010 Jan. 7 to 2018 Dec. 13. This dataset adds two years to
that used for the CatWISE Preliminary Catalog (Eisenhardt et al., 2020),
bringing the total to six times as many exposures spanning over sixteen times
as large a time baseline as the AllWISE catalog. The other major change from
the CatWISE Preliminary Catalog is that the detection list for the CatWISE2020
Catalog was generated using crowdsource (Schlafly et al., 2019), while the
CatWISE Preliminary Catalog used the detection software used for AllWISE.
These two factors result in roughly twice as many sources in the CatWISE2020
Catalog. The scatter with respect to Spitzer photometry at faint magnitudes in
the COSMOS field, which is out of the Galactic plane and at low ecliptic
latitude (corresponding to lower WISE coverage depth) is similar to that for
the CatWISE Preliminary Catalog. The 90% completeness depth for the
CatWISE2020 Catalog is at W1=17.7 mag and W2=17.5 mag, 1.7 mag deeper than in
the CatWISE Preliminary Catalog. From comparison to Gaia, CatWISE2020 motions
are accurate at the 20 mas yr-1 level for W1$\sim$15 mag sources, and at the
$\sim 100$ mas yr-1 level for W1$\sim$17 mag sources. This level of precision
represents a 12$\times$ improvement over AllWISE. The CatWISE catalogs are
available in the WISE/NEOWISE Enhanced and Contributed Products area of the
NASA/IPAC Infrared Science Archive.

catalogs, infrared:stars, proper motions

##  1 Introduction

The CatWISE Preliminary Catalog (Eisenhardt et al., 2020), which was released
via the NASA/IPAC Infrared Science Archive in August 2019, consists of
900,849,014 sources over the entire sky selected from WISE (Wright et al.,
2010) and NEOWISE (Mainzer et al., 2014) survey data at 3.4 and 4.6 µm (W1 and
W2) collected from 2010 to 2016. This dataset includes four times as many
exposures and spans over ten times as large a time baseline as the AllWISE
catalog (Cutri et al., 2013). CatWISE adapts AllWISE software to measure the
sources in co-added images created by the unWISE team from six month subsets
of these data, each representing one coverage of the inertial sky, or epoch
(Meisner et al., 2018). The CatWISE Preliminary Catalog includes the measured
motion of sources in 8 epochs over the 6 year span of the data, which are ten
times more accurate than those from AllWISE. The CatWISE Preliminary Catalog
has been used to identify some of the coldest brown dwarfs known to date
(Marocco et al., 2019, 2020; Meisner et al., 2020).

Nevertheless, further significant improvements are possible. The most
important caveat for the CatWISE Preliminary Catalog is that the number of
sources per square degree has relatively small variation over the sky. This is
likely a consequence of the source detection methodology used for the
Preliminary Catalog (Eisenhardt et al., 2020), which, while optimal for
isolated point sources, results in significant incompleteness in high source
density regions such as the Galactic plane.

The CatWISE2020 Catalog addresses this issue by using an updated version of
the unWISE catalog (Schlafly et al., 2019) as the detection list. In addition,
the CatWISE2020 Catalog includes two more years of survey data from NEOWISE
than does the Preliminary Catalog, increasing the number of epochs to 12 and
the time span to over 8 years. As a result, the CatWISE2020 Catalog has more
than twice as many sources as the CatWISE Preliminary Catalog (five times as
many in the Galactic plane; see §2.2), and even better astrometric performance
for faint sources. Figure 1 shows a comparison of CatWISE2020 total proper
motions $\left({\rm i.e.}\ \mu_{\rm
tot}=\sqrt{\mu_{\alpha}^{*\,2}+\mu_{\delta}^{2}}\right)$111Throughout this
manuscript, we adopt the notation $\mu_{\alpha}^{*}=\mu_{\alpha}\cos\delta$
and $\Delta\alpha^{*}=\Delta\alpha\cos\delta$. for a sample of 224 ultra-cool
dwarfs within 20 pc from the Sun to values reported in the literature
(Kirkpatrick et al., 2020, and references therein). The agreement is excellent
across the whole motion range, and across a broad range of magnitudes, since
the sample includes objects as bright as W2$\sim$7.3 mag and as faint as
W2$\sim$16.7 mag. The CatWISE2020 Catalog is therefore an excellent resource
to identify ultra-cool dwarfs in the Solar neighborhood.

Eisenhardt et al. (2020) presents a detailed description of the CatWISE
Preliminary Catalog. Here we describe updates to the processing steps used for
the CatWISE2020 Catalog relative to the Preliminary Catalog (§2), assess the
astrometric and photometric performance of CatWISE2020 Catalog using
comparisons to Gaia and Spitzer data (§3), and provide information on
accessing the CatWISE2020 data products (§4). The Appendix summarizes known
issues in the CatWISE2020 Catalog.

Figure 1: A comparison of CatWISE2020 total measured motion to values reported
in the literature, for 224 ultra-cool dwarfs within 20 pc of the Sun. All have
S/N $\geq$3 CatWISE2020 motion measurements. Vertical error bars are typically
smaller than the symbols.

##  2 CatWISE2020 Processing Updates

A full description of the processing steps for the CatWISE Preliminary Catalog
is given in Eisenhardt et al. (2020), and we only describe changes for
CatWISE2020 processing here. Coordinates in the CatWISE2020 Catalog are in the
ICRS system at epoch MJD=57170 (2015 May 28), while in the CatWISE Preliminary
Catalog they are in J2000 at epoch MJD=56700.

###  2.1 unWISE Coadds

The unWISE coadds follow the atlas tile footprint established by the WISE All-
Sky Release, dividing the sky into 18,240 overlapping square tiles, each
$\sim$1.56 deg on a side, aligned with right ascension and declination
coordinate grid. Each tile is identified by a coadd_id, in the form RRRRsDDD,
where RRRR is the tile center R.A. in deci-degrees, s is the tile center Dec
sign, with “p” for “+” and “m” for “–”, and DDD is the tile center Dec in
deci-degrees. For example, the tile containing the South Ecliptic Pole and
centered near R.A. = 89.0 deg and Dec = –66.7 deg is 0890m667. For further
detail, we refer the reader to section II.1.a in the Explanatory Supplement to
the AllWISE Data Release Products (Cutri et al., 2013).

The CatWISE2020 data products are based on the combination of W1 and W2
exposures in the two sky coverages used for the AllWISE data release (Cutri et
al., 2013) and in the ten additional sky coverages from the NEOWISE 2019 data
release222http://wise2.ipac.caltech.edu/docs/release/neowise/neowise_2019_release_intro.html,
while the CatWISE Preliminary data products use AllWISE and the six additional
sky coverages from the NEOWISE 2017 Data
Release333http://wise2.ipac.caltech.edu/docs/release/neowise/neowise_2017_release_intro.html.
The full-depth unWISE coadds from Meisner et al. (2018a) are used for both
source detection and aperture photometry in the CatWISE Preliminary Catalog.
The CatWISE2020 pipeline uses the full-depth unWISE coaddition of the AllWISE
and NEOWISE 2019 Data Release for aperture photometry, while source detection
is described in §2.2.

The CatWISE Preliminary pipeline used the 8 individual unWISE epoch coadds
from Meisner et al. (2018c) for point source photometry and astrometry, with
an adjustment to the world coordinate system (WCS) for the AllWISE epochs, as
described in Eisenhardt et al. (2020). The CatWISE2020 pipeline uses 12 unWISE
epoch coadds constructed using the methodology given in Meisner et al. (2019).
We assumed that the adjustment to the AllWISE epochs had been applied to this
set of 12 unWISE coadds, and did not discover the adjustment was not applied
until after the CatWISE2020 Catalog and Reject Table had been generated and
imported into the IRSA database. This results in small astrometric offsets for
sources in the CatWISE2020 Catalog, for which we provide a table of
corrections (see §3.3).

###  2.2 Detection

The histogram of the number of detected sources per square degree in the
CatWISE Preliminary Catalog is narrow (Figure 2). This means that the source
density is no higher in the Galactic plane than at the Galactic poles; in
fact, it is slightly lower in the Galactic plane, as the upper left panel of
Figure 3 shows. The unWISE Catalog (Schlafly et al., 2019) uses a crowded-
field point-source photometry code called crowdsource (Schlafly et al., 2018)
which detects far more sources in high density regions.

For the CatWISE2020 Catalog we therefore decided to replace the CatWISE
Preliminary Catalog detection step, which uses MDET, the Multiband Detection
software of Marsh & Jarrett (2012), with an updated version of the unWISE
Catalog (hereafter UUC)444The updated unWISE Catalog is available at
https://faun.rc.fas.harvard.edu/unwise/neo5/band-merged. The unWISE Catalog of
Schlafly et al. (2019) is based on the NEOWISE 2018 Data Release, while the
UUC used for the CatWISE2020 detection list is based on the NEOWISE 2019 Data
Release. The unWISE Catalog measures source fluxes and static positions in the
full-depth coadded image, with the measurements carried out independently in
W1 and W2, while the CatWISE2020 pipeline characterizes sources jointly in
both bands, measuring their fluxes, positions, and motions in epoch coadds.

CatWISE2020 processing begins with the band-merged UUC, where photometry for
W1 and W2 sources within 2$\farcs$4 is matched. Sources are measured in order
of decreasing signal-to-noise ratio (S/N) within each $\sim 1.56$ deg$\times
1.56$ deg tile on the sky. To generate a single S/N-ordered detection list
from the unWISE photometry in both bands, the CatWISE2020 pipeline determines
an average flux uncertainty $\sigma_{avg}$ for each band from the mean of the
flux uncertainty of sources in the tile whose flux $F$ is within $\pm 0.5\%$
of the median flux in the band. The S/N in each band is calculated from
$F/\sigma_{avg}$, and the W1 and W2 S/N values are root-sum-squared to
determine a combined S/N for each source in the tile.

Figure 2 shows the resultant histogram of source densities for the CatWISE2020
Catalog and Reject Table compared to the CatWISE Preliminary Catalog and
Reject Table, and Figure 3 compares the distribution of source density over
the sky. With more than twice as many sources overall, the CatWISE2020 Catalog
has a higher source density across the whole sky. The catalog source density
still drops in the central part of the Galactic plane and the Galactic center.
Source are successfully detected in these regions, but a significant fraction
of them fail one or more of the criteria for inclusion in the catalog, and
therefore go in the reject table. Further details on the selection criteria
and a more in-depth discussion of the resulting source density are presented
in §2.4.

One feature arising from the use of the UUC is the fact that some nearby,
resolved galaxies are split in multiple pieces, leading to spurious localized
overdensity of sources in the CatWISE2020 Catalog. A detailed discussion of
the crowdsource treatment of extended galaxies is given in Schlafly et al.
(2019, §4.4 and §6.8), and here we briefly summarize the most important
points. Splitting of extended galaxies only happens when the angular size of
the galaxy exceeds several arcseconds, due to the 6” FWHM of WISE. Large
galaxies listed in the HyperLEDA catalog (Makarov et al., 2014) received
special treatment in the unWISE catalog. Elliptical regions around these
galaxies are flagged in the unWISE bit masks (Meisner et al., 2019), and
crowdsource rejects candidate new sources in these regions if they
significantly overlap with a neighboring source. Galaxies in the HyperLEDA
catalog are therefore less likely to be split into multiple detections, but
heterogeneity in the catalog results in a somewhat sky position-dependent
effectiveness of this mitigation. Ultimately, this is a trade off between
completeness (specifically, the ability to successfully deblend real, blended
sources) and reliability (specifically, the need to minimize the fragmenting
of resolved sources). Completeness and reliability of the CatWISE2020 Catalog
are discussed in further detail in §3.1.

Figure 2: Number of tiles with a given source density, in bins of 1000 sources
per square degree, for the CatWISE2020 Catalog compared to the CatWISE
Preliminary Catalog. Deeper data, and a more effective detection of sources in
crowded fields, result in a broader distribution and a greater number of
sources per square degree in the CatWISE2020 Catalog. Figure 3: CatWISE
Preliminary and CatWISE2020 Catalog (top) and Reject Table (bottom) source
density, plotted in Galactic Coordinates. See §2.4 for details.

###  2.3 Source Measurement and Uncertainties

As for the CatWISE Preliminary Catalog, the CatWISE2020 pipeline used an
adapted version of the WPHOT software developed for the AllWISE pipeline to
carry out source photometry, astrometry, and motion estimation, processing
separately epochs taken with ascending vs. descending survey scan directions,
and then merging the results (Eisenhardt et al., 2020). For the CatWISE2020
pipeline however, we did not allow WPHOT to add new sources (“active
deblending”) to improve the $\chi^{2}$ of the fit to a source, as the
crowdsource algorithm (§2.2) already provides a much more complete set of
detected sources than does the MDET algorithm used for the CatWISE Preliminary
Catalog.

In the CatWISE Preliminary Catalog, a minimum motion uncertainty of 10 mas
yr-1 was enforced, while for the CatWISE2020 Catalog, this floor was reduced
to 1 mas yr-1. This affects the $\chi^{2}$ values when comparing Gaia and
CatWISE2020 motions (see §3.3.2).

###  2.4 The CatWISE2020 Catalog

The final CatWISE2020 data products consist of a Catalog and a Reject Table.
Like the CatWISE Preliminary Catalog, CatWISE2020 Catalog sources are required
to:

1) be from the tile where that source is furthest from the tile edge (i.e.
flagged as “primary”)

and

2a) have W1 S/N $\geq 5$ with no identified artifacts (a value of 0 in the
left character of ab_flags)

or

2b) have W2 S/N $\geq 5$ with no identified artifacts (a value of 0 in the
right character of ab_flags).

There are 1,890,715,644 sources that meet these criteria. The 341,799,385
sources that fail to meet these criteria go into the Reject Table. Individual
tile reject tables typically contain 11,000 sources, although near the
Galactic center they can contain over 120,000 sources due to the large number
of artifacts. The larger number of artifacts in dense regions is illustrated
in Figure 3 (bottom-right panel), as well as in Figure 4, where we show the
fraction of non-primary sources (i.e. those that fail criteria 1), and the
fraction of primary sources with S/N$\geq$5 in at least one band but flagged
as artifacts in the same band (i.e. those that pass criteria 1 but fail
criteria 2a or 2b) in three 1 deg$\times 15$ deg strips. The three strips were
chosen to trace the border of the overdensity of reject sources around the
Galactic Center. They are:

1) $-0.5<l<0.5$ deg and $0<b<15$ deg;

2) $29.5<l<30.5$ deg and $0<b<15$ deg;

3) $-0.5<b<0.5$ deg and $35<l<50$ deg.

The fraction of sources rejected on account of being flagged as artifacts
grows rapidly as a function of Galactic latitude, spiking at $b<6$ deg. The
incidence of artifacts is also a function of Galactic longitude, with a clear
increase towards the Galactic Center. The increase in this case is not as
dramatic as the increase as a function of $b$. The fraction of non-primary
sources spikes whenever our chosen strips cross a tile boundary, which are
defined to be parallel to the equatorial grid, and, therefore, are slanted
when converted to galactic coordinates. There is no net trend for the fraction
of non-primary sources with either $l$ or $b$, as expected since the overlap
region between tiles does not vary significantly in this part of the sky.

Other noteworthy features of the source density map for the Reject Table
(Figure 3, bottom row), are the two very dense circles corresponding to the
celestial poles. This is purely a geometric effect, resulting from the
increasing overlap between adjacent tiles as a function of declination. While
tiles on the celestial equator overlap only by $\sim 7\%$, those near the
poles overlap by as much as $\sim 56\%$. The number of duplicate sources grows
accordingly, and since duplicates are removed from the catalog and placed in
the Reject Table, the resulting source density appears artificially high.

The source density in the CatWISE2020 Catalog increases around the ecliptic
poles ($l\sim 96$ deg, $b\sim 30$ deg, and $l\sim 276$ deg, $b\sim-30$ deg).
This is a consequence of the greater depth of the WISE data around the
ecliptic poles, which is in turn a result of the survey strategy of WISE
(Wright et al., 2010).

The individual CatWISE2020 Catalog and Reject files for the 18,240 tiles were
transferred to the NASA/IPAC Infrared Science
Archive555https://irsa.ipac.caltech.edu (IRSA), where they were merged into
the IRSA database. Information regarding access to the catalog is provided in
§4.

Figure 4: Fraction of non-primary sources (black), and sources with S/N$>$5 in
at least one band but rejected because are flagged as artifacts in the same
band (blue and red), in three $1\times 15$ deg strips.

###  2.5 CatWISE2020 Catalog Description

There are 187 formatted columns of information about each source in the
CatWISE2020 Catalog. The CatWISE2020 Reject Table adds a column to indicate
whether the source is primary in its tile (see §2.4). Descriptions of the
columns can be obtained from
IRSA666https://irsa.ipac.caltech.edu/data/WISE/CatWISE/gator_docs/catwise_colDescriptions.html.
Most of the columns have the same names as in the AllWISE Catalog, and are
described in §II.1.a of the AllWISE Explanatory Supplement (Cutri et al.,
2013). Table A1 of Eisenhardt et al. (2020) provides information about
selected columns in the CatWISE catalogs that augments the information
provided by IRSA.

The Galactic coordinates (glon and glat) for sources in the CatWISE
Preliminary Catalog were calculated incorrectly and were not included in the
IRSA release. In the CatWISE2020 Catalog, these columns are more accurate and
now are included in the IRSA release, but should not be used for astrometry.
Two columns (w1fitr and w2fitr) remain excluded from the IRSA release of
CatWISE2020 data products, for reasons explained in Table A1 of Eisenhardt et
al. (2020). Finally, the CatWISE2020 Catalog and Reject Table include a new
column (unwise_objid) which provides the updated unWISE Catalog (§2.2)
identification corresponding to the source. Note that these identifications
end in “r02” to avoid confusion with unrelated sources in the unWISE Catalog
of Schlafly et al. (2019).

CatWISE2020 source designations should have the prefix CWISE for objects in
the CatWISE2020 Catalog, and CWISER for objects in the CatWISE2020 Reject
Table. The designation for each source, based on its coordinates for the J2000
equinox following the IAU truncation convention and without the leading CWISE
or CWISER prefix, is given by the field source_name. For example, the quasar
3C 273 is CWISE J122906.70+020308.6.

##  3 Performance Characterization

The additional data, longer baseline, and different detection software lead to
an improvement on some key performance parameters for the CatWISE2020 Catalog
with respect to the CatWISE Preliminary Catalog. Following the performance
characterization strategy adopted in Eisenhardt et al. (2020), we focus on the
completeness and reliability of the CatWISE2020 Catalog at both the bright
(W1,W2 $<$ 8 mag, §3.1.1) and faint end (W1,W2 $>$ 12 mag, §3.1.2), the
photometric performance (§3.2), and the astrometric performance (§3.3).
Spitzer data were used as external truth for photometric comparison, while
Gaia DR2 was used for astrometric comparison.

###  3.1 Completeness and Reliability

####  3.1.1 Bright Sources

The CatWISE2020 Catalog completeness and reliability for sources with W1 or W2
$<$8 mag were assessed using an updated version of the WISE Bright Star List
(BSL) as a truth set. The list was generated by the WISE team for artifact
flagging (see §4.4.g.vi in the WISE All-Sky Release Explanatory Supplement;
Cutri et al., 2012), and updated for our performance assessment of the CatWISE
Preliminary Catalog (see Eisenhardt et al. 2020).

The CatWISE2020 Catalog completeness was determined as the percentage of BSL
sources that have astrometric matches in the CatWISE2020 Catalog as a function
of BSL magnitude. Differential CatWISE2020 Catalog reliability was determined
as the percentage of sources that have astrometric matches in the BSL as a
function of CatWISE2020 magnitude. A relatively large matching radius of
5$\farcs$5 (corresponding to two WISE pixels) was used, to account for the
poorer centroiding accuracy expected for highly saturated sources.

Figure 5 shows the results for completeness. The CatWISE2020 Catalog appears
slightly less complete for bright sources than both the CatWISE Preliminary
and AllWISE Catalogs. While the CatWISE Preliminary Catalog achieves $\sim
99\%$ completeness in the BSL W1$\sim 5.5-8$ mag and BSL W2$\sim 5-8$ mag
ranges, the CatWISE2020 Catalog has slightly lower completeness, peaking at
98% in the 5.5$<$W1$<$6.25 mag range. The CatWISE2020 Catalog completeness
drops sharply for stars brighter than $\sim 4.5$ mag, in a similar fashion to
the CatWISE Preliminary Catalog, falling to $\sim 50\%$ by W1$\sim 4.3$ mag
and W2$\sim 3.6$ mag. Missing bright stars belong predominantly in two
categories: (1) bright variable stars (e.g. AGBs and Mira-type variables); (2)
blended stars in crowded, nebulous fields. Detailed assessment in two test
fields (2828p000 and 2657p288, which includes the Galactic Center) reveals
that the missing bright stars are either missed at the detection stage, or are
detected but then dropped by the PSF-fitting software because of the poor
quality of the PSF fit. There are 3742 bright stars within the footprint of
tile 2828p000 ($l=33.28;b=-0.54$), 65 of which are missing from the
CatWISE2020 Catalog and Reject Table, and 10504 bright stars in the Galactic
Center tile, 637 of which are missing. Of the 65 stars missing in the 2828p000
tile, 37 are missed at the detection stage, and the remaining 28 at the PSF-
fitting stage. In the Galactic Center tile, 616 stars are missed at the
detection stage, and 21 stars are missed at the PSF-fitting stage. Visual
inspection reveals that stars missed at the detection stage are almost
exclusively partly blended stars in fields with significant nebulosity due to
interstellar dust. We refer the reader to §4.4 in Schlafly et al. (2019) for a
more detailed discussion on the impact of nebulosity on crowdsource, and the
possible incompleteness in such regions. On the other hand, stars missed at
the PSF-fitting stage are predominantly very bright stars (W1$\lesssim 5$ mag
or W2$\lesssim 4$ mag), and we speculate that their large saturated cores
result in poor PSF fitting, leading to the sources being discarded by WPHOT.

As discussed in Eisenhardt et al. (2020), AllWISE completeness remains above
90% even for stars as bright as 0.25 mag, and should therefore be the catalog
of choice for bright star science that requires a complete sample.

The CatWISE2020 Catalog achieves comparable or better reliability than the
CatWISE Preliminary and AllWISE Catalogs for stars in the $2.8<$W1$<8.5$ mag
and $2<$W2$<8.5$ mag range, with reliability consistently above 97%, as can be
seen in Figure 6.

Figure 5: Differential completeness of the CatWISE2020 Catalog as a function
of the Bright Star List’s W1 (top) and W2 (bottom), compared to AllWISE and
the CatWISE Preliminary Catalog.

Figure 6: Differential reliability of the CatWISE2020 Catalog as a function of
CatWISE2020 W1 (top) and W2 (bottom), compared to AllWISE and the CatWISE
Preliminary Catalog.

####  3.1.2 Faint Sources

Completeness and reliability were assessed for faint sources in an area of
$\sim 94$ deg2 by comparison with the Spitzer South Pole Telescope Deep Field
survey (SSDF; Ashby et al., 2013).

The analysis followed the same method described in §3.1.1, except that a
smaller matching radius of 2$\farcs$5 was used. The results are shown in
Figures 7 and 8.

The CatWISE2020 Catalog consistently achieves greater completeness than the
CatWISE Preliminary Catalog with typical completeness of 99% across the
$12<$[3.6]$<17.1$ mag and $12<$[4.5]$<17$ mag range. Figure 7 shows that the
50% completeness limit for the CatWISE2020 Catalog is [3.6] = 18.3 mag, while
in [4.5] the completeness remains above 55% all the way down to [4.5] = 18.1
mag, the coverage depth of the SSDF (cf. 17.8 mag and 17.4 mag for the CatWISE
Preliminary Catalog).

The CatWISE2020 Catalog reliability is better than 99% for sources brighter
than 14.5 mag in both W1 and W2, similar to the CatWISE Preliminary Catalog.
For fainter sources, the CatWISE2020 Catalog reliability is slightly worse
than the CatWISE Preliminary Catalog, in particular in the 14.5–16 mag range
in both W1 and W2 (and down to 16.8 mag in W1), with reliability of $\sim$1%
below that achieved by the CatWISE Preliminary Catalog. At fainter magnitudes,
the CatWISE2020 Catalog remains a fraction of a percent less reliable than the
CatWISE Preliminary Catalog in W1, while it becomes a fraction of a percent
more reliable than the CatWISE Preliminary Catalog in W2.

Given that in the same brightness range the CatWISE Preliminary Catalog
completeness significantly deteriorates compared to the CatWISE2020 Catalog,
CatWISE2020 performance is overall superior to CatWISE Preliminary for faint
stars over the range assessed.

Figure 7: Completeness of the CatWISE2020 and Preliminary Catalog vs. Spitzer
$3.6\mu$m (top) and $4.5\mu$m (bottom) magnitude for sources in the SSDF.

Figure 8: Reliability of the CatWISE2020 and Preliminary Catalog as a function
of W1 (top) and W2 (bottom), for sources in the SSDF.

###  3.2 Photometric properties

The CatWISE2020 Catalog photometric depth was assessed using the SSDF and the
COSMOS field.

Figure 9 compares CatWISE Preliminary Catalog (left) and CatWISE2020 Catalog
(right) PSF-fitting photometry to 2$\farcs$9 radius aperture photometry from
the Spitzer S-COSMOS program (Sanders et al., 2007). These observations were
obtained using long integration times (20 minutes), so the S-COSMOS data are
much deeper than CatWISE. The closest CatWISE source within 2$\farcs$75 was
taken as the match to the S-COSMOS source. Because the CatWISE photometry is
measured via point source fitting, S-COSMOS sources were required to have
$<10\%$ flux increase between the 1$\farcs$9 and 2$\farcs$9 radius apertures.
In addition, because the W1 band is significantly bluer than the [3.6] band,
to minimize spurious color-related effects S-COSMOS sources at [3.6] were
required to have $-0.1\leq[3.6]-[4.5]\leq 0$. These are the same criteria used
in Eisenhardt et al. (2020) and Cutri et al. (2012). Figure 10 presents the
same comparison to photometry from the SSDF survey.

The comparison between the CatWISE Preliminary Catalog and CatWISE2020 Catalog
and Spitzer photometry is consistent in both bands, in both fields.
CatWISE2020 photometry becomes increasingly fainter than Spitzer beyond 16th
mag, up to $\sim 0.1$ mag fainter in W1 at 17.5 mag, and $\sim 0.06$ mag
fainter in W2 at 16.5 mag. This effect was also observed in CatWISE
Preliminary photometry. The measured scatter reaches 0.217 mag, equivalent to
a S/N of 5, at [3.6] = 17.41 mag and [4.5] = 16.50 mag. Adjusting for the mean
offsets in W1–[3.6] and W2–[4.5] at these magnitudes, and compensating for the
different depth of the three different surveys, the S/N=5 limits for the
CatWISE2020 Catalog are W1 = 17.43 mag and W2 = 16.47 mag (cf. W1 = 17.41 mag
and W2 = 16.33 mag for the CatWISE Preliminary Catalog).

Figure 9: Comparison of CatWISE Preliminary Catalog (left) and CatWISE2020
Catalog (right) photometry to Spitzer photometry for COSMOS. Top: Difference
between CatWISE W1 PSF and Spitzer S-COSMOS 2$\farcs$9 radius aperture
photometry at [3.6], for sources with $-0.1<[3.6]-[4.5]<0$ and $<10$% flux
increase from the 1$\farcs$9 to 2$\farcs$9 aperture. Median differences and
standard deviations in 0.5 mag bins are shown by the red points and error
bars. Bottom: Comparison for CatWISE W2 and Spitzer [4.5] photometry. No
restriction on Spitzer source color needs to be applied in this case (see
§3.2). Figure 10: Comparison of CatWISE photometry to Spitzer photometry for
the SSDF, using the same methodology as in Figure 9. The outer contour
represents a source density of 10 sources per $0.05\times 0.05$ mag bin, with
each additional contour showing a factor of two increase in source density.

###  3.3 Astrometric properties

####  3.3.1 Full-sky Astrometric Assessments

The astrometric performance of the CatWISE2020 Catalog over the entire sky was
assessed by comparing to Gaia DR2 (Gaia Collaboration et al., 2018; Lindegren
et al., 2018). Following the method described in Eisenhardt et al. (2020), in
each tile we selected the 10 brightest sources in each 0.5 mag bin over the
$10<$W1$<17.5$ mag range. This resulted in a sample of 150 sources per tile,
uniformly distributed on the sky. The full sample for astrometric comparison
consists of 2,735,892 sources. These sources were cross-matched with Gaia DR2
using a 5$\farcs$5 radius (corresponding to two WISE pixels), requiring the
Gaia counterpart to have measured proper motions. This returned 2,179,410
unique matches. The Gaia counterparts were propagated to the CatWISE2020 epoch
(MJD=57170) using Gaia astrometry, and then the median difference and standard
deviation between the CatWISE2020 motion-fit and Gaia position and motion
values were computed.

As mentioned in §2.1, CatWISE2020 processing did not apply the WCS adjustments
to the unWISE coadds for the AllWISE epochs. This results in small systematic
offsets between the CatWISE2020 Catalog and Gaia DR2 in both position and
motions. The R.A. and Dec offset with respect to the Gaia DR2 counterpart
(i.e. R.A.${}_{\textit{Gaia}}$–R.A.${}_{\rm CatWISE2020}\times\cos{\rm
Dec_{CatWISE2020}}$ and Dec${}_{\textit{Gaia}}$–DecCatWISE2020), as well as
the proper motion difference, was computed for all 2,179,410 sources in the
comparison sample. Figure 11 shows the offset distribution, revealing a
roughly Gaussian distributions in R.A. and Dec (top panel), with a 1-sigma
dispersion of 46 mas and 32 mas respectively. The proper motion offsets
(bottom panel) show a more complex distribution, since they are the result of
the projected Solar motion through the Galaxy.

Figure 11: The distribution of median offsets between CatWISE2020 positions
(top) and proper motions (bottom) and Gaia DR2 in the 18,240 tiles.

Figure 12 maps the systematic offsets between the CatWISE2020 Catalog and Gaia
DR2, in Galactic coordinates. The systematic offset is not dependent on source
density, i.e. there is no obvious degradation in high density regions. In the
very center of the Milky Way the maps appear more noisy, but that is a
spurious result of the low number of matches between the CatWISE2020 Catalog
and Gaia DR2, rather than a real astrometric effect. All maps show patterns
that are consistent with the projection of the Solar motion through the
Galaxy. The offsets are typically in the $\pm$150 mas range in position, and
in the $\pm$40 mas yr-1 range in proper motion. The median position and proper
motion offsets in each tile are provided in a machine-readable table, and a
sample is shown in Table 1. For any application that requires the study of the
kinematics of a large sample of objects, we recommend using these median
values to correct motion and positions on a tile-by-tile basis. The tile in
which a source is measured is encoded in the first 8 characters of the
source_id, given in the first column of the CatWISE2020 Catalog and Reject
Table. For example, source 0000p000_b0-013835 was measured in tile 0000p000.

Figure 12: Systematic offset between the CatWISE2020 Catalog and Gaia DR2 positions (top row) and proper motion (bottom row).  Table 1: Systematic offsets between the CatWISE2020 Catalog and Gaia DR2 (full table available on-line in machine readable format)  |  Gaia DR2 – CatWISE2020 Catalog
---|---
Tile | $\Delta\alpha^{*}$ | $\Delta\alpha$ | $\Delta\delta$ | $\Delta\mu_{\alpha}^{*}$ | $\Delta\mu_{\delta}$
| deg | deg | deg | arcsec yr-1 | arcsec yr-1
0000m016 | 7.038531$\times 10^{-7}$ | 7.041276$\times 10^{-7}$ | 2.211593$\times 10^{-6}$ |  $-$0.01956579 | 0.018327646
0000m031 | 9.905521$\times 10^{-6}$ | 9.920038$\times 10^{-6}$ | 6.129016$\times 10^{-6}$ |  $-$0.017017405 | 0.0168396
0000m046 | 1.5195505$\times 10^{-5}$ | 1.5244609$\times 10^{-5}$ |  $-$1.5518368$\times 10^{-5}$ |  $-$0.013825462 | 0.016300509
0000m061 | 2.3382128$\times 10^{-5}$ | 2.3515273$\times 10^{-5}$ |  $-$8.676556$\times 10^{-6}$ |  $-$0.014948687 | 0.012481616
0000m076 | 4.49237$\times 10^{-5}$ | 4.532183$\times 10^{-5}$ |  $-$1.4328044$\times 10^{-5}$ |  $-$0.015264964 | 0.016823826
… | … | … | … | … |

We applied the systematic offsets presented in Table 1 to the 2,179,410
sources in the comparison sample, and computed standard deviation between the
CatWISE2020 motion-fit and Gaia position and motion values. The results are
summarized in Figure 13.

The positional accuracy floor for bright sources approaches $\sim 35$ mas, a
factor $\sim 1.4$ better than the performance achieved by the CatWISE
Preliminary Catalog (Figure 13, top left panel). At fainter magnitudes, the
CatWISE2020 Catalog also shows improved astrometric precision. The dispersion
in the 15.0–15.5 mag bin is $\sim$165 mas in the CatWISE2020 Catalog, while it
is $\sim$220 mas in the CatWISE Preliminary Catalog. In the faintest magnitude
bin the dispersion in the CatWISE2020 Catalog is $\sim 700$ mas.

The motion accuracy floor for bright stars is just over 6 to 7 mas yr-1, as
illustrated in the top right panel of Figure 13. At the faint end, the
CatWISE2020 Catalog also shows improved performance with respect to the
CatWISE Preliminary Catalog. In the 15.0–15.5 mag bin the one-sigma dispersion
is $\sim$20 mas yr-1, compared to $\sim$26 mas yr-1 in the CatWISE Preliminary
Catalog. In the faintest magnitude bin the dispersion in the CatWISE2020
Catalog is $\sim 100$ mas yr-1.

The $\chi^{2}$ panels show different performance for positions and motions.
The bottom left panel of Figure 13 shows improved $\chi^{2}$ values for bright
stars in the CatWISE2020 catalog with respect to the CatWISE Preliminary
Catalog, with the $\chi^{2}$ values rising in fainter sources to the same
level observed in the CatWISE Preliminary catalog. The motion $\chi^{2}$
(bottom right panel) for bright sources on the other hand are worse in the
CatWISE2020 Catalog than in the CatWISE Preliminary Catalog, gradually
improving towards fainter magnitudes and reaching the same level as the
CatWISE Preliminry Catalog at W1,W2$\sim$15 mag. The position $\chi^{2}$ are
significantly improved most likely as a result of the better deblending, while
motion $\chi^{2}$ are worse because of the smaller floor on the motion
uncertainty imposed by the CatWISE2020 pipeline (§2.3).

Figure 13: CatWISE Preliminary and CatWISE2020 astrometric performance with
respect to Gaia DR2. CatWISE2020 positions and proper motions have been
corrected for the systematic offsets, as discussed in §3.3.1. Top: the
1-$\sigma$ dispersion between CatWISE and Gaia R.A. (specifically,
$\Delta\alpha^{*}$) and Dec. (left), and proper motion (right), for a
subsample of $\sim$2.1 million sources in the $10<$W1$<17.5$ mag range,
uniformly distributed over the entire sky. Bottom: the median $\chi^{2}$
computed taking into account CatWISE catalog uncertainties, Gaia catalog
uncertainties, and the uncertainty introduced by the translation of Gaia’s
positions to the CatWISE epoch.

To assess the possible role of increasing Gaia errors, Figure 14 shows the
astrometric performance of the CatWISE2020 Catalog as a function of Gaia G
magnitude (top row) and distance (bottom row). The top row plots show a
behaviour similar to the one illustrated in Figure 13, with accuracy floors of
30 mas and 6 mas yr-1 in positions and proper motions respectively, and
accuracies of 600 mas and 60 mas yr-1 at the faint end. The bottom row plots
of Figure 14 on the other hand show a less intuitive trend. The very nearest
distance bins are dominated by very bright, highly saturated sources. As a
result, the measured performances with respect to Gaia are $\sim$200 mas in
position and 40 mas yr-1 in proper motion. The astrometric performance
improves very quickly as a function of distance, with minimum dispersion in
the 60–80 pc bin. Beyond 80 pc the astrometry deteriorates again, as one might
expect since in more distant bins the stars appear, on average, fainter. At
$\sim$2.1 kpc, however, the trend briefly reverses, reaching a local minimum
at $\sim$2.6 kpc. Beyond $\sim$2.6 kpc the astrometric performance resumes
very gradually deteriorating as a function of distance for positions, while
for motions it slightly improves with distance. This pattern is a result of
the change of the brightness distribution of stars in the CatWISE2020 Catalog
as a function of distance. The top panel of Figure 15 illustrates this point.
The nearest bin is dominated by bright sources, and as such the astrometric
performance is comparable to the astrometric performance in the brightest bins
in Figure 13. The brightness distribution of more distant bins peaks at
fainter magnitudes, and as such the astrometric performance degrades, once
again following the well-demonstrated trend with brightness. Somewhat
counterintuitively, however, beyond $\sim$2.1 kpc the brightness distribution
becomes bimodal, with a growing peak at bright magnitudes. This bright peak is
most likely due to red giant stars. This can be seen as well in the bottom
panel of Figure 15, where the distance distribution of $10<{\rm W1}\leq 10.5$
mag stars shows a secondary peak at d$\sim$2.6 kpc. RGB stars have $-5\lesssim
M_{W1}\lesssim-2$ mag (Conroy et al., 2018), roughly corresponding to the
observed W1 = 10 mag at this distance. Moving beyond $\sim$2.6 kpc, the top
panel of Figure 15 shows that the bright peak moves towards fainter magnitudes
and, therefore, the accuracy of position measurements resumes degrading. While
sources in a given distance bin become on average fainter with distance, their
proper motion becomes on average smaller, counteracting the brightness-
dependent astrometric degradation and resulting in a slow improvement of the
proper motion performance as a function of distance.

Figure 14: CatWISE2020 astrometric performance with respect to Gaia DR2. Top:
the 1-$\sigma$ dispersion between CatWISE2020 and Gaia R.A. and Dec. (left)
and proper motion (right), as a function of Gaia G magnitude. Bottom: same as
the top row, but as a function of Gaia measured distance, in bins of 20 pc.

Figure 15: Top: the W1 magnitude distribution for CatWISE2020 Catalog sources
with Gaia counterparts in four distance bins. The three nearest distance bins
shown are chosen to be the three inflection points in the bottom row plots of
Figure 14. The fourth distance bin is chosen to represent the brightness
distribution for sources with d $\gtrsim 2.6$ kpc. Bottom: the distance
distribution of sources in four magnitude bins. The distribution in the two
brightest magnitude intervals show clear secondary peaks at d$>2$ kpc, which
are due to bright, distant RGBs.

The overall astrometric performance is, as one might expect, not uniform over
the sky. Figures 16–19 show the 1-$\sigma$ dispersion in each tile with
respect to Gaia positions and motion components for the full magnitude range
considered (Figures 16 and 18), and in three smaller magnitude intervals
(Figures 17 and 19). The maps for the full magnitude range are smooth overall,
indicating a fairly constant astrometric performance for the CatWISE2020
Catalog over the majority of the sky. The main features can be easily
identified – the Galactic plane (and in particular the bulge), and the Small
and Large Magellanic Clouds (SMC and LMC). In those denser regions, the
astrometric accuracy for the bright stars deteriorates to $\sim 500$ mas for
positions and $\sim 30$ mas yr-1 for motions, and to $\sim 1,000$ mas and
$\sim 200$ mas yr-1 (or worse) for the faint stars.

Figure 16: 1-$\sigma$ dispersion of the CatWISE2020 Catalog $\alpha$ (left)
and $\delta$ (right) with respect to Gaia DR2, for sources in the
$10<$W1$<17.5$ mag range.

Figure 17: Same as Figure 16, but for three W1 magnitude ranges. Gray tiles
are those where there were no sources in the CatWISE2020 Catalog in the given
magnitude bin.

Figure 18: Same as Figure 16, but for the proper motion components.

Figure 19: Same as Figure 18, but for three W1 magnitude ranges. Gray tiles
are those where there were no sources in the CatWISE2020 Catalog in the given
magnitude bin.

The motion accuracy maps of Figure 18 and 19 show additional features, already
noted in the CatWISE Preliminary Catalog, that appear to be related to the
WISE survey strategy, and to the transition between the cryogenic and post-
cryogenic phases of the mission.

The maps for the faintest magnitude interval (bottom row of Figure 17 and 19)
are more noisy, partly because of the low number of sources with a Gaia
counterpart in each tile, and partly because the CatWISE2020 pipeline detects
only brighter sources in high density regions because of confusion noise. The
astrometric performance of the CatWISE2020 Catalog remains fairly homogeneous
over the sky even for the faintest sources, but the performance starts
degrading at higher $b$ as one considers fainter and fainter sources. This is
most likely due to the fact that the astrometry for faint sources is more
susceptible to degradation due to blending.

To further assess the astrometric performance of the CatWISE2020 pipeline on
faint, red sources that are not seen by Gaia, we compared the CatWISE2020
positions and motions to those measured in the Extended Gaia-PS1-SDSS Proper
Motion Catalog (GPS1+; Tian et al., 2020). The GPS1+ catalog provides
positions and proper motions for $\sim 400$ million sources with $19.0\lesssim
r\lesssim 22.5$ mag over 3/4 of the sky, measured using the combination of
Gaia, PS1, SDSS, and 2MASS data.

We cross-matched our astrometric comparison sample of 2,735,892 stars with
GPS1+ with a matching radius of 5$\farcs$5, the same radius used in the
comparison against Gaia DR2. We then computed the one-sigma dispersion between
the CatWISE2020 Catalog and GPS1+ positions and proper motions following the
same procedure adopted for our comparison against Gaia DR2. Since GPS1+ omits
sources with r $\lesssim$ 19 mag, the correct matching source is often missing
for CatWISE2020 sources of W1 $<$ 14.5 mag. Therefore, for the rest of the
analysis we only consider sources with W1 $\geq$ 14.5 mag.

Figure 20 shows the results of the comparison. The one-sigma dispersion,
presented in the top row, increase as a function of brightness, from $\sim
200$ mas for positions and $\sim 20$ mas yr-1 for proper motions for the
brightest sources, to $\sim 650$ mas for positions and $\sim 90$ mas yr-1 for
proper motions for the faintest sources. The performance at the faint end
agrees well with the full-sky performance derived in the comparison against
Gaia DR2. At the bright end the omitted GPS1+ sources and resulting mismatches
degrade the performance relative to the Gaia DR2 comparison shown in Figures
13. The bottom row of Figure 20 shows that the median $\chi^{2}$ increase as a
function of brightness, with a clearer trend for positions. Once again, this
can be partly explained by the omission of bright GPS1+ sources and resulting
mismatches in the brightest bins.

Figure 20: CatWISE2020 astrometric performance with respect to GPS1+. Top: the
1-$\sigma$ dispersion between CatWISE2020 and GPS1+ R.A. and Dec. (left), and
proper motion (right). Bottom: the median $\chi^{2}$ computed taking into
account CatWISE2020 Catalog uncertainties, GPS1+ catalog uncertainties, and
the uncertainty introduced by the translation of GPS1+ positions to the
CatWISE2020 epoch.

####  3.3.2 Astrometric Assessments in Selected Tiles

We assessed the astrometric performance of the CatWISE2020 Catalog in four
representative tiles. These are the same four tiles we chose for the
astrometric assessment of the CatWISE Preliminary Catalog (Eisenhardt et al.,
2020), and are the following:

  * •

the COSMOS tile (tile 1497p015), representative of most of the sky, i.e. a
field with average WISE coverage and average source density;

  * •

the North Ecliptic Pole tile (NEP, tile 2709p666), a field with maximal WISE
coverage and average source density;

  * •

the South Ecliptic Pole tile (SEP, tile 0890m667) a field with maximal WISE
coverage and high source density (the SEP tile contains part of the LMC); and

  * •

the Galactic Center tile (GC, tile 2657m288) a field with average WISE
coverage and maximal source density.

The astrometric performance of the CatWISE2020 Catalog was assessed following
the same method described in §3.3.1. The results are shown in Figures 21 to
24. We quantitatively characterized the performance of the CatWISE2020 Catalog
using the same ten metrics used in Eisenhardt et al. (2020):

  * •

$\sigma_{\rm min}$ and $\sigma_{\mu,\,\rm min}$ are the accuracy floor for
positions and motions, respectively, determined as the median dispersion with
respect to Gaia DR2 in the $8<$W1,W2$<10$ mag interval. In the GC we restrict
to $8<$W1,W2$<9$ mag since the astrometric accuracy starts deteriorating
significantly beyond W1,W2$\sim$9 mag (see Figure 24).

  * •

W1min, W2min, W1${}_{\mu,\,\rm min}$, and W2${}_{\mu,\,\rm min}$ are the W1
and W2 mag at which $\sigma_{\rm min}$ and $\sigma_{\mu,\,\rm min}$ are
exceeded by no more than 20 mas and 5 mas yr-1, respectively.

  * •

W1500 and W2500 are the W1 and W2 mag at which the accuracy on positions
reaches 500 mas.

  * •

W1μ, 100 and W2μ, 100 are the W1 and W2 mag at which the accuracy on motion
reaches 100 mas yr-1.

The results for the four representative tiles are summarized and compared to
the corresponding CatWISE Preliminary Catalog values in Table 2.

Table 2: CatWISE Astrometric Performance Evaluation Fields

| 0890m667 | 1497p015 | 2657m288 | 2709p666
---|---|---|---|---
| SEP, LMC | COSMOS | GC | NEP
$l$ (deg) | 276.5 | 237.3 | 359.8 | 96.4
$b$ (deg) | $-30.2$ | 41.4 | 0.6 | 29.5
$\beta$ (deg) | $-89.6$ | $-10.2$ | $-5.4$ | 89.6
| Prelim. | 2020 | Prelim. | 2020 | Prelim. | 2020 | Prelim. | 2020
Exp. | 7154 | 9230 | 90 | 140 | 86 | 133 | 7839 | 10000
$\\#$ | 71462 | 209518 | 58961 | 75639 | 63368 | 231239 | 61702 | 142975
$\sigma_{\rm min}$ (mas) | 52.9 | 40.5 | 27.3 | 42.8 | 526.4 | 391.2 | 37.7 | 25.8
W1min (mag) | 11.0 | 11.5 | 12.5 | 14.5 | 8.0 | 8.5 | 12.0 | 12.0
W1500 (mag) | 15.1 | 16.0 | 17.0 | 17.5 | 8.4 | 9.0 | 18.5 | 18.0
W2min (mag) | 11.0 | 12.0 | 12.5 | 14.5 | 8.0 | 8.5 | 12.0 | 12.5
W2500 (mag) | 15.0 | 16.0 | 16.8 | 17.5 | 8.3 | 9.0 | 19.0 | 20.5
$\sigma_{\mu,\rm min}$ (mas yr-1) | 7.4 | 8.6 | 8.5 | 8.0 | 22.2 | 20.0 | 7.3 | 7.0
W1μ,min (mag) | 14.5 | 13.5 | 13.5 | 14.5 | 9.0 | 9.0 | 15.5 | 14.5
W1μ,100 (mag) | 18.2 | 18.5 | 16.8 | 17.5 | $>11.0$ | 11.5 | $>19.0$ | 21.0
W2μ,min (mag) | 14.5 | 13.5 | 13.5 | 14.5 | 9.0 | 9.0 | 15.5 | 14.0
W2μ,100 (mag) |  $>$20.5 | 19.0 | 16.7 | 17.5 |  $>$11.5 | 11.5 |  $>$20.0 | 20.5

Note. — $l$, $b$, and $\beta$ are the Galactic longitude, Galactic latitude,
and ecliptic latitude for the center of the tile, in degrees. Exp. indicates
the number of exposures for the tile, $\\#$ the number of sources (combining
catalog and reject entries). The subsequent metrics are described in detail in
§3.3.

In the COSMOS tile (Figure 21), the CatWISE2020 Catalog shows improved
astrometric performance with respect to the CatWISE Preliminary Catalog in all
metrics except the position precision floor. Table 2 shows that $\sigma_{\rm
min}$ deteriorated from 27.3 to 42.8 mas. Inspection of the top left panel of
Figure 21 suggests that the asymptotic performance is actually comparable for
the CatWISE2020 and Preliminary Catalog, with a precision floor of $\sim$40
mas yr-1. The CatWISE Preliminary Catalog however shows a dip in the measured
motion sigma at W1,W2$\sim$9 mag, which drives the $\sigma_{\rm min}$ to low
values. Because the number of sources in this brightness regime is much lower
compared to the fainter brightness regime (32 objects with W1,W2 $\leq$9.5
mag), we suspect that that our metric may be affected by small number
statistic fluctuations. The motion precision floor is not affected by the
already mentioned systematic offsets, since in an individual tile the
systematic offset is roughly constant over the entire tile area, and therefore
does not impact the measured dispersion with respect to Gaia.

In the Galactic Center (Figure 24), the major gain of the CatWISE2020 Catalog
with respect to the CatWISE Preliminary Catalog is the increased depth to
which sources are recovered, with the CatWISE2020 Catalog now reaching down to
16th magnitude in W1 and W2. Most metrics also show improved or consistent
performance, with the position precision floor ($\sigma_{\rm min}$) having
improved significantly as a result of the more effective deblending. W1min and
W2min, as well as W1500 and W2500, are 0.5–0.7 mag deeper in the CatWISE2020
Catalog. The motion metrics show comparable or slightly improved performance.
The position $\chi^{2}$ are significantly improved as a result of the better
deblending, while motion $\chi^{2}$ are worse because of the smaller floor on
the motion uncertainty (§2.3).

The NEP and SEP (Figure 22 and 23) show improved performance for positions,
but somewhat worse performance for motions. All position metrics either
improved or remained constant in the CatWISE2020 Catalog, with the exception
of W1500 in the NEP, which is 0.5 mag shallower. This metric, however, is
close to the S/N 5 depth, and small number statistics noise is to be expected,
because of the small number of CatWISE2020 sources that have a counterpart in
Gaia DR2 at such brightness. The motion metrics, on the other hand, are
somewhat degraded. While the precision floor is at the same level achieved by
the CatWISE Preliminary Catalog, the top right panel of Figures 22 and 23
shows that the CatWISE2020 motion dispersion is higher than in the CatWISE
Preliminary Catalog across the entire magnitude range considered. Position
$\chi^{2}$ are better at both poles, while motion $\chi^{2}$ are worse, once
again because of the smaller uncertainty floor.

Overall, for faint sources all metrics in the CatWISE2020 Catalog retain the
clear dependence on source density and coverage that was already noted by
Eisenhardt et al. (2020) in the CatWISE Preliminary Catalog. The NEP (high
coverage, average density) shows better W1500, W2500, W1μ, 100 and W2μ, 100
than the SEP (high coverage, high density) and COSMOS (average coverage,
average density), which are in turn better than the GC (average coverage, high
density).

Figure 21: CatWISE Preliminary Catalog (blue) and CatWISE2020 Catalog (red)
astrometric performance with respect to Gaia DR2 in the COSMOS tile
(1497p015). The top row shows the 1-$\sigma$ dispersion between CatWISE and
Gaia R.A. (specifically, $\Delta\alpha\ \textrm{cos}(\delta)$) and Dec.
(left), and proper motion (right). The bottom row shows the median $\chi^{2}$
computed taking into account CatWISE catalog uncertainties, Gaia catalog
uncertainties, and the uncertainty introduced by the translation of Gaia’s
positions to the CatWISE epoch.)  Figure 22: Same as Figure 21 but for the
North Ecliptic Pole tile (2709p666)  Figure 23: Same as Figure 21 but for the
South Ecliptic Pole tile (0890m667).  Figure 24: Same as Figure 21 but for the
Galactic Center tile (2657m288)

####  3.3.3 Fast Movers

In Eisenhardt et al. (2020) we discussed the performance of the CatWISE
Preliminary Catalog on a sample of cold, fast moving brown dwarfs in the Solar
neighborhood. Re-assessment of the CatWISE2020 Catalog performance on the same
sample of brown dwarfs reveals that the motion accuracy is comparable in the
two versions of the catalog. Moreover, thanks to a more effective deblending
of partly blended sources, the CatWISE2020 pipeline successfully measures WISE
J163940.83–684738.6 and WISEPC J205628.90+145953.3, the only two objects in
our sample of 19 test objects that were missing from the CatWISE Preliminary
Catalog.

One feature common to all of the fast moving brown dwarfs considered in this
analysis is that their fast motion leads to multiple (spurious) detections,
since they are essentially “smeared” in the full-depth unWISE coadds used for
source detection. These multiple apparitions (up to seven for the fastest
objects) are then passed through our photometry- and motion-measuring
software. The first detection processed by WPHOT gets accurate motion and
magnitude measurements, while the subsequent detections get progressively
worse measurements. Those with the lowest S/N are typically discarded in the
Reject Table, but the higher S/N ones remain in the catalog. For example the
fastest moving brown dwarf, WISE J085510.83–071442.5, appears five times in
the CatWISE2020 Catalog, with three of those five apparitions having motion
measurements consistent with the literature values.

As briefly discussed in §1, the performance of the CatWISE2020 Catalog on fast
moving sources was further assessed by comparing the CatWISE2020 offset-
corrected total measured motion for a sample of ultra-cool dwarfs within 20 pc
from the Sun to values reported in the literature (Kirkpatrick et al., 2020,
and references therein). The full sample consists of 224 objects, all of them
with a counterpart in the CatWISE2020 Catalog, and with good quality proper
motion measurements (i.e. $\mu_{\rm tot}/\sigma\mu_{\rm tot}\geq 3$). Figure 1
shows a comparison of the CatWISE2020 measurements for these 224 objects to
values reported in the literature. The agreement is excellent, and does not
show strong dependence on total proper motion nor brightness, since the sample
includes objects as bright as W2$\sim$7.3 mag and as faint as W2$\sim$16.7
mag. The one-sigma dispersion is $\sim$29 mas yr-1, while the median offset is
$\sim$12 mas yr-1. Many of the 224 objects in this sample are too faint at
optical wavelengths to be seen by Gaia. Therefore, the CatWISE2020 Catalog
crucially complements the ESA mission for late type stars and brown dwarfs.

##  4 Data Access

The merged files for the 18,240 tiles for the CatWISE2020 Catalog and Reject
Table are available from IRSA777https://irsa.ipac.caltech.edu/cgi-
bin/Gator/nph-scan?mission=irsa&submit=Select&projshort=WISE in the
WISE/NEOWISE Enhanced and Contributed Products area. IRSA’s catalog search
tools allow for complex search queries. IRSA also hosts the AllWISE
Explanatory Supplement (Cutri et al., 2013), which provides full details on
the AllWISE processing algorithms, and includes descriptions of the AllWISE
Catalog columns, many of which are applicable to the CatWISE data products.
§2.5 provides additional information about CatWISE2020 columns.

The individual tile files have also been transferred to a data repository at
the National Energy Research Scientific Computing
Center888https://portal.nersc.gov/project/cosmo/data/CatWISE/2020 (NERSC), and
are available in 18,240 pairs of gzipped ASCII files (one catalog and one
reject file per tile) in IPAC table format, organized into 359 directories,
one for each decimal degree of right ascension from 0° to 358° (there are no
tiles whose ID begins with 359). Text files providing the format and a brief
description of the columns in the catalog and reject files are also provided
there. As for the CatWISE Preliminary Catalog, the catalog and reject files
for tiles near the ecliptic poles (listed in Table 1 in Eisenhardt et al.,
2020), where a single PSF per band was used for processing, include the string
“opt0” in their names. Files for tiles where different PSFs were used for
ascending and descending scans include the string “opt1” in their names.

Current information about CatWISE data products and links to the data on IRSA
and NERSC are provided at the CatWISE website https://catwise.github.io.

We thank the anonymous referee for their careful review and thoughtful
suggestions. CatWISE uses data products from WISE, which is a joint project of
the University of California, Los Angeles, and the Jet Propulsion Laboratory
(JPL)/California Institute of Technology (Caltech), funded by the National
Aeronautics and Space Administration (NASA), and from NEOWISE, which is a
JPL/Caltech project funded by NASA. Characterization of CatWISE performance
uses data from Gaia and from Spitzer. CatWISE is led by JPL/Caltech, with
funding from NASA’s Astrophysics Data Analysis Program (ADAP), and is also
supported in part by ADAP grant NNH17AE75I at Lawrence Berkeley Laboratory. FM
acknowledges support from the NASA Postdoctoral Program at the Jet Propulsion
Laboratory, administered by Universities Space Research Association under a
contract with NASA. FM also acknowledges support from grant 80NSSC20K0452
under the NASA Astrophysics Data Analysis Program. FM would like to thank
Dongwei Fan for help with accessing the GPS1+ data via che China-VO.

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##  Appendix A Caveats

The CatWISE2020 Catalog contains a number of features that users should be
aware of. Among these are:

  * •

The CatWISE2020 Catalog represents a dramatic improvement over the CatWISE
Preliminary Catalog in terms of depth and completeness in the Galactic plane.
However, the CatWISE2020 Catalog astrometric performance degrades as source
density increases. Figures 16–19 illustrate this.

  * •

The completeness for bright sources is low (Figure 5). Users interested in
complete samples brighter than 4.5 mag in WISE bands should use AllWISE.
However, the CatWISE2020 Catalog has much better reliability for bright
sources than does the CatWISE Preliminary Catalog (Figure 6).

  * •

Small systematic offsets are present in CatWISE2020 astrometry with respect to
Gaia DR2 (see §2.1, §3.3, and Figure 12). Because adjustments were made to the
WCS for the AllWISE epochs for the CatWISE Preliminary Catalog but not for the
CatWISE2020 Catalog, these systematic offsets are different between the two
catalogs. Table 1 provides the corresponding systematic corrections to the
CatWISE2020 Catalog position and motion for each tile.

  * •

Because of coordinate singularities, CatWISE tile Point Spread Functions (see
§3.2 of Eisenhardt et al., 2020) within a few degrees of the equatorial poles
used an unnecessarily large range of rotation angles, resulting in smearing of
these PSFs.

  * •

Magnitude and position uncertainties occasionally round to 0.

  * •

The aperture magnitudes are the result of averaging fluxes in the CatWISE2020
Catalog, while in the CatWISE Preliminary Catalog, the aperture magnitudes
from the ascending and descending epochs were averaged.

  * •

In the NERSC version of the CatWISE2020 data products, the standard aperture
magnitude uncertainties, w1sigm and w2sigm, are often 0.0 or 1.0 because of an
error in the CatWISE2020 pipeline when averaging fluxes. The corresponding
magnitudes, w1mag and w2mag, are correct, as are the individual aperture
magnitude uncertainties. Users who are interested in standard aperture
magnitudes should use the w1sigm_2 and w2sigm_2 for the uncertainties, as
those are identical to what the w1sigm and w2sigm should have been. In the
IRSA version, this error was corrected on 2020 Aug. 25, and w1sigm and w2sigm
values retrieved after this date are correct.

  * •

A floor of 1 mas yr-1 was imposed on the tabulated motion uncertainties for
the CatWISE2020 data products, while for the CatWISE Preliminary data products
the floor was 10 mas yr-1. The lower CatWISE2020 uncertainty floor is now
significantly smaller than the minimum measured scatter with respect to Gaia
motion, as illustrated in the right column of Figures 21 to 24.

  * •

CatWISE2020 source designations (source_name) include a lower case letter
suffix to distinguish sources that would otherwise have the same designation.
In the CatWISE Preliminary Catalog, the first such source (usually the
brightest) did not receive a suffix while subsequent such sources did,
beginning with “b”. In the CatWISE2020 data products, the first such source
receives an “a” suffix.

  * •

Sources in the updated unWISE catalog detection list may be omitted from the
CatWISE2020 Reject Table if they are too near tile edges, probably due to the
fitting region used by WPHOT being truncated. This does not affect the CatWISE
Preliminary Reject Table because the MDET software does not find sources this
close to tile edges.

  * •

As discussed in §2.2, resolved galaxies result in multiple detections by
crowdsource and hence multiple entries in the CatWISE2020 Catalog. Users
interested in local overdensities in the galaxy distribution (such as for
clustering analyses or detection of galaxy clusters) should be aware of this
feature and take precautions to avoid misinterpretation.