# Composite Bulges – III. A Study of Nuclear Star Clusters in Nearby Spiral
Galaxies

Aishwarya Ashok Department of Physics and Astronomy, University of Utah, Salt
Lake City, UT 84112, USA  Anil Seth Department of Physics and Astronomy,
University of Utah, Salt Lake City, UT 84112, USA  Peter Erwin Max-Planck-
Insitut für extraterrestrische Physik, Giessenbachstrasse, D85748 Garching,
Germany  Universitäts-Sternwarte München, Scheinerstrasse 1, D-81679 München,
Germany  Victor P. Debattista  Jeremiah Horrocks Institute, University of
Central Lancashire, Preston, PR1 2HE, UK  Adriana de Lorenzo-Cáceres
Instituto de Astrofísica de Canarias, C/ Vía Láctea, S/N, E-38205 La Laguna,
Tenerife, Spain  Dmitri A. Gadotti  Centre for Extragalactic Astronomy,
Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
Jairo Méndez-Abreu  Instituto de Astrofísica de Canarias, C/ Vía Láctea, S/N,
E-38205 La Laguna, Tenerife, Spain  Departamento de Astrofísica, Universidad
de La Laguna, Avda. Astrofísico Fco. Sánchez s/n, 38200, La Laguna, Tenerife,
Spain  John E. Beckman  Instituto de Astrofísica de Canarias, C/ Vía Láctea,
S/N, E-38205 La Laguna, Tenerife, Spain  Departamento de Astrofísica,
Universidad de La Laguna, Avda. Astrofísico Fco. Sánchez s/n, 38200, La
Laguna, Tenerife, Spain  Consejo Superior de Investigaciones Científicas,
Spain  Ralf Bender  Max-Planck-Insitut für extraterrestrische Physik,
Giessenbachstrasse, D85748 Garching, Germany  Universitäts-Sternwarte München,
Scheinerstrasse 1, D-81679 München, Germany  Niv Drory  McDonald Observatory,
The University of Texas at Austin, 1 University Station, Austin, Texas 78712,
USA  Deanne Fisher  Center for Astrophysics and Supercomputing, Swinburne
University of Technology, Hawthorn, Australia  Ulrich Hopp  Max-Planck-Insitut
für extraterrestrische Physik, Giessenbachstrasse, D85748 Garching, Germany
Universitäts-Sternwarte München, Scheinerstrasse 1, D-81679 München, Germany
Matthias Kluge  Max-Planck-Insitut für extraterrestrische Physik,
Giessenbachstrasse, D85748 Garching, Germany  Universitäts-Sternwarte München,
Scheinerstrasse 1, D-81679 München, Germany  Tutku Kolcu  Astrophysics
Research Institute, Liverpool John Moores University, Twelve Quays House,
Egerton Wharf, Birkenhead CH41 1LD, UK  Witold Maciejewski  Astrophysics
Research Institute, Liverpool John Moores University, Twelve Quays House,
Egerton Wharf, Birkenhead CH41 1LD, UK  Kianusch Mehrgan  Max-Planck-Insitut
für extraterrestrische Physik, Giessenbachstrasse, D85748 Garching, Germany
Universitäts-Sternwarte München, Scheinerstrasse 1, D-81679 München, Germany
Taniya Parikh  Max-Planck-Insitut für extraterrestrische Physik,
Giessenbachstrasse, D85748 Garching, Germany  Universitäts-Sternwarte München,
Scheinerstrasse 1, D-81679 München, Germany  Roberto Saglia  Max-Planck-
Insitut für extraterrestrische Physik, Giessenbachstrasse, D85748 Garching,
Germany  Universitäts-Sternwarte München, Scheinerstrasse 1, D-81679 München,
Germany  Marja Seidel  IPAC, California Institute of Technology, 1200 East
California Boulevard, Pasadena, CA 91125, USA  Jens Thomas  Max-Planck-Insitut
für extraterrestrische Physik, Giessenbachstrasse, D85748 Garching, Germany
Universitäts-Sternwarte München, Scheinerstrasse 1, D-81679 München, Germany

###### Abstract

We present photometric and morphological analyses of nuclear star clusters
(NSCs) – very dense, massive star clusters present in the central regions of
most galaxies – in a sample of 33 massive disk galaxies within 20 Mpc, part of
the “Composite Bulges Survey.” We use data from the Hubble Space Telescope
including optical (F475W and F814W) and near-IR (F160W) images from the Wide
Field Camera 3. We fit the images in 2D to take into account the full
complexity of the inner regions of these galaxies (including the contributions
of nuclear disks and bars), isolating the nuclear star cluster and bulge
components. We derive NSC radii and magnitudes in all 3 bands, which we then
use to estimate NSC masses. Our sample significantly expands the sample of
massive late-type galaxies with measured NSC properties. We clearly identify
nuclear star clusters in nearly 80% of our galaxies, putting a lower limit on
the nucleation fraction in these galaxies that is higher than previous
estimates. We find that the NSCs in our massive disk galaxies are consistent
with previous NSC mass-NSC radius and Galaxy Mass-NSC Mass relations. However,
we also find a large spread in NSC masses, with a handful of galaxies hosting
very low-mass, compact clusters. Our NSCs are aligned in PA with their host
galaxy disks but are less flattened. They show no correlations with bar or
bulge properties. Finally, we find the ratio of NSC to BH mass in our massive
disk galaxy sample spans a factor of $\sim$300.

galaxies: structure – galaxies: nucleus – galaxies: spiral

††software: Astropy (Astropy Collaboration et al., 2013, 2018), DrizzlePac
(Hack et al., 2013), Imfit (Erwin, 2015, v1.8), grizli (Brammer, 2019)

##  1 Introduction

Most galaxies today have a central massive object that is indicative of
current or past extreme activity at their centers. These central massive
objects can be a supermassive black hole (SMBH), a nuclear star cluster (NSC),
or a combination of both. A review of NSC properties has recently been
compiled by Neumayer et al. (2020). NSCs are extremely luminous objects that
are present in the centers of a majority of all types of galaxies (e.g.,
Phillips et al., 1996; Carollo et al., 1998; Böker et al., 2002; Côté et al.,
2006; Georgiev et al., 2009). They are compact, massive star clusters with an
effective radius ranging from 3 – 20 pc (e.g., Böker et al., 2004; Côté et
al., 2006; Walcher et al., 2006; Georgiev & Böker, 2014; Georgiev et al.,
2016) and dynamical and stellar populaton based masses from $10^{5}$–$10^{8}$
$M_{\sun}$ (e.g., Walcher et al., 2005; Rossa et al., 2006; Erwin & Gadotti,
2012; Spengler et al., 2017; Nguyen et al., 2018). NSCs are known to be more
massive and denser than GCs (Walcher et al., 2005; Hopkins & Quataert, 2010).

NSCs are mostly frequently found in intermediate-mass galaxies ($>10^{8-10}$
$M_{\sun}$) with a nucleation fraction (the fraction of galaxies studied that
host an NSC) of $\sim 70$–90% in the early-type galaxies (Côté et al., 2006;
Turner et al., 2012; den Brok et al., 2014; Sánchez-Janssen et al., 2019;
Hoyer et al., 2021) and $>75$% in the late-types (Böker et al., 2002; Seth et
al., 2006; Georgiev & Böker, 2014; Neumayer et al., 2020; Hoyer et al., 2021)
in this same mass range. More recent studies of early-type galaxies have shown
a strong mass dependence and milder environmental dependence on the nucleation
fraction. Sánchez-Janssen et al. (2019), Zanatta et al. (2021), and Carlsten
et al. (2022) found the nucleation fraction to be as high as 90% for galaxy
stellar masses of $\sim$109 M⊙, decreasing towards both lower and higher mass
galaxies. Neumayer et al. (2020) and Hoyer et al. (2021) found a similar trend
for late-type galaxies at lower masses, but at higher masses ($>10^{10}$
$M_{\sun}$) a lack of data means we do not know if the nucleation fraction of
late-types decreases in the same way as early-types.

NSCs are located at the dynamical centers of their galaxies (Neumayer &
Walcher, 2012). NSCs and SMBHs are known to co-exist, including in the Milky
Way (e.g., Seth et al., 2008a; Graham & Spitler, 2009; Seth et al., 2010;
Georgiev et al., 2016; Nguyen et al., 2019; Neumayer et al., 2020). The
relative masses of NSCs and SMBHs appears to span a wide range, with NSCs
being more massive than SMBHs in many lower mass galaxies, while SMBHs are the
dominant component in higher mass galaxies (Graham & Spitler, 2009; Neumayer
et al., 2020). The relationship between NSCs and SMBHs is complicated and
unclear. NSCs may provide a seeding mechanism to create and/or grow massive
black holes at the centers of galaxies (e.g. Stone et al., 2017; Inayoshi et
al., 2020). A possible consequence of NSCs and SMBHs co-existing is the
presence of Tidal Disruption Events (TDEs). This occurs when tidal forces pull
apart a star as it approaches the SMBH. TDEs are observed mostly in low-mass
galaxies with some intermediate-mass galaxies (galaxy stellar masses between
109–1010; Wevers et al., 2019).

The formation history of NSCs can be directly probed through their stellar
populations. Spectroscopic analyses of NSCs show they have have multiple
stellar populations, extended star formation histories, and strong rotation
(e.g., Walcher et al., 2006; Rossa et al., 2006; Seth et al., 2006; Kacharov
et al., 2018; Pinna et al., 2021; Fahrion et al., 2021; Hannah et al., 2021;
Fahrion et al., 2022b). Another way of studying the formation mechanisms of
NSCs is through their correlation with the SMBHs at their centers and their
surrounding host galaxies. Mass measurements of NSCs and host galaxies have
shown that these quantities are strongly correlated; initially these were
thought to form a relation sismilar to SMBHs (e.g. Ferrarese et al., 2006;
Wehner & Harris, 2006; Balcells et al., 2007; Graham, 2012; Scott et al.,
2013); however, more recent work shows the NSC and SMBH scaling relations are
quite different (e.g. Erwin & Gadotti, 2012; Georgiev et al., 2016; Sánchez-
Janssen et al., 2019).

An in-depth analyses of NSC scaling relations in different galaxy environments
can help us understand what physical mechanisms play an important role in NSC
formation and how NSCs impact the overall evolution of the host galaxy.
Evidence from previous studies (e.g., Hartmann et al., 2011; Antonini et al.,
2012; Neumayer et al., 2020; Fahrion et al., 2021, 2022a) show that there are
two primary formation mechanisms that drive the growth of NSCs, (1) star
cluster mergers (Tremaine et al., 1975; Gnedin et al., 2014), or (2) in situ
formation (Bekki, 2007; Antonini et al., 2015). The relative importance of
these mechanisms seems to depend on the galaxy stellar mass. Specifically,
recent work (Neumayer et al., 2020; Fahrion et al., 2021, 2022a, 2022b) finds
that the NSCs of low mass galaxies primarily grow from cluster mergers, while
in higher mass galaxies the NSCs grow from in situ formation. A reflection of
this transition seems to be present in the scaling relations as well, with the
NSC masses scaling with the square root of their host galaxy masses at lower
masses but steepening to a more linear relationship in higher mass galaxies
(den Brok et al., 2014; Sánchez-Janssen et al., 2019).

The changing properties of NSCs as a function of galaxy morphology and the
resulting implications for their formation are not yet fully understood.
Overall, there have been more studies of early-type than late-type galaxies,
especially towards higher masses where dust and bulge contributions make
studying late-type NSCs more challenging. Therefore, most observations of NSCs
in late-type galaxies have focused on lower-mass galaxies; this includes both
HST imaging to quantify structure (Georgiev et al., 2009; Böker et al., 2002,
2004; Georgiev & Böker, 2014; Carson et al., 2015; Hoyer et al., 2023a), and
spectroscopic observations focused on kinematics and stellar populations
(Walcher et al., 2005; Kacharov et al., 2018; Pinna et al., 2021; Fahrion et
al., 2022b). These observations are broadly consistent with the NSC mass
trends discussed in the previous paragraph. However, some differences have
been suggested in NSCs in early vs. late-type galaxies. For instance, the
compilation of data by Georgiev et al. (2016) found that the sizes of NSCs in
massive early-type galaxy are $\sim$2$\times$ larger than those in late-type
galaxies, although Neumayer et al. (2020) suggested this difference may only
exist at the highest masses. Late-type galaxies also seem to show stronger
rotation on average than early-type galaxies (Pinna et al., 2021).

Some studies exist of higher-mass, more bulge-dominated late-type galaxies as
well, most notably the studies Carollo et al. (1998, 2002), which found that a
a majority of massive spiral galaxies do host NSCs. However, the information
available on these NSCs is quite heterogeneous (i.e. photometric bands, sizes)
making them challenging to interpret together. Stellar population measurements
of a subset of these galaxies by Rossa et al. (2006) found that these galaxies
clusters tended to be older than those in lower mass late-type galaxies. The
recent paper by Hoyer et al. (2023b) shows the promise of JWST for studying
NSCs in massive galaxies due to its high angular resolution, ability to
penetrate dust, and the broad spectral energy distribution measurements it can
obtain. Despite these studies, we still know little about the populations of
NSCs in massive late-type galaxies (like the Milky Way; MW hereafter), which
leads to a lack of knowledge about the NSCs in these galaxies and their co-
existence with the ubiquitous SMBHs in these galaxies. In this paper, we focus
on NSCs in high-mass ($\log(M_{\star}/M_{\sun})>10$) late-type galaxies,
presenting a study of NSCs in 33 galaxies with high resolution, uniform
imaging from the Composite Bulges Survey (CBS; Erwin et al. in prep).

Section 2 describes the galaxy sample selected from CBS, the high resolution
HST data, and the other data used in this work. In Section 3, we describe in
detail the morphological modelling process for the galaxies and NSCs,
including derivation of morphological NSC parameters. We also discuss the
quality of the fits and error estimates. In Section 4, we focus on the
properties of the NSCs, including the nucleation fraction of our sample, NSC
magnitudes and masses, and correlations between NSC internal properties. In
section 5, we present scaling relations of the NSCs with their host galaxies.
We also discuss briefly the presence of SMBHs in our galaxy sample. Section 6
summarizes our work in this paper.

##  2 Data sample

The work shown in this paper is part of the Composite Bulges Survey (CBS;
Erwin et al. in prep). This survey is aimed at a detailed analysis of the
stellar morphology and populations in the inner 1–2 kpc of massive disk
galaxies, using both HST optical and near-IR imaging and VLT-MUSE IFU data.

Figure 1: The stellar mass, distance, and Hubble type of the 33 NSC sample
galaxies (circles) selected from the 53 galaxy CBS survey (triangles). The MW-
like subsample of 20 galaxies are shown as squares.

CBS is based on a mass- and volume-limited sample of disk galaxies. These
galaxies were selected from the de Vaucouleurs et al. (1995, RC3) catalog,
restricted to galaxies with distances $\leq 20$ Mpc, stellar masses $\geq
10^{10}$ $M_{\sun}$, S0–Sbc morphologies, inclinations between 35∘ and 60∘,
declinations $\delta\leq+20^{\circ}$, and galactic latitudes $|b|>20^{\circ}$.
Based on these selections, a total of 53 galaxies were selected; these include
a large number of Virgo Cluster galaxies.

###  2.1 NSC and MW-like sample selection

For the work shown in this paper we present NSC fits for a sub-sample of 33
galaxies from the parent CBS sample (hereafter the “NSC sample”). This sub-
sample of the CBS survey was chosen to include a complete set of 20 galaxies
form a complete Milky-Way like sample (hereafter the “MW-like” subsample). Our
MW is a special galaxy which hosts the nearest NSC that can be studied in
unparalleled detail. Understanding how typical or atypical the NSC in the MW
is with the NSCs in similar galaxies is important. Hence we create this sample
of MW-like galaxies which represents all galaxies having spiral morphologies
($t\geq 1$) and stellar masses from $10^{10.4}$ to $10^{11.1}$ $M_{\sun}$ from
CBS. We present NSC fits for the complete sample of CBS galaxies that have fit
these criteria. In addition to these galaxies, we fit the NSCs of 13
additional galaxies – these galaxies are a random subsample of galaxies for
which we had available larger scale models; the full sample of CBS galaxies
morphological fits will be presented in Erwin et al. in prep. The circles in
Figure 1 show all the 33 of the NSC sample galaxies; of these the MW-like
subsample are shown as squares and the rest of the CBS sample as triangles. As
can be seen, a majority of the CBS galaxies that are not included in our NSC
sample are S0 type galaxies, while the NSC sample represents a nearly complete
set of the Sa-Sbc galaxies. The properties of the NSC sample galaxies are
summarized in Table 1.

###  2.2 HST data from CBS

For modeling the central morphology of each galaxy, we use a consistent set of
high resolution HST data obtained using the Wide Field Camera 3 (WFC3) in the
UVIS and IR modes (Cycle 25, Proposal ID 15133). We use the full-field WFC3/IR
image in the F160W filter with a total integration time of 600s. The optical
images were restricted to the C1K1C aperture for efficient readout and data
transmission. This aperture is a 1024 X 1024-pixel subarray of the full-field
WFC3/UVIS images centered on the galaxy nuclei. We use the F814W filter with a
total integration time of 500s and the F475W filter with a total integration
time of 700s. All of our images are divided into four dithered exposures to
provide sub-pixel sampling. We note that the galaxies more than fill both
detectors in many cases.

All the individual exposures from each band are combined using the Python-
based DrizzlePac code. We set the output image scale for the UVIS images to
0.03″/pixel and for the IR images to 0.06″/pixel with a pixfrac = 0.7 in all
cases. The sky subtraction during the processing of these images is turned
off; we estimate the sky background using larger-scale ground-based or Spitzer
IRAC1 images as explained in detail in Section 3.1.

###  2.3 Other data used in this work

For the large scale galaxy fitting and to determine the F160W image sky
levels, we use Spitzer IRAC1 (3.6µm) images. The images for the galaxies come
from either the S4G survey with a final mosaic pixel size of 0.75″/pixel
(Sheth et al., 2010) or archive-generated mosaic images (Watkins et al., 2022)
for galaxies not in S4G, with a default archive mosaic pixel of 0.6″/pixel.
The program IDs for the IRAC1 images are listed in Table 1.

For determining the background sky levels in the UVIS images (Section 3.1), we
use either SDSS $g$ and $i$ images or (for galaxies without SDSS images) $B$,
$V$, and $I$ images from the Carnegie-Irvine Galaxy Survey (Ho et al., 2011),
kindly provided by Luis Ho.

Table 1: Properties of galaxies in the NSC sample

Galaxy | Hubble type | RC3 type | Sample | log( M⋆/ M⊙) | Distance | Source | Spitzer program ID | AF814W | PAGal | $\epsilon_{\rm Gal}$ | log(M${}_{BH})$
---|---|---|---|---|---|---|---|---|---|---|---
|  |  |  |  | (Mpc) |  |  |  | degrees |  | M⊙
(1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | (9) | (10) | (11) | (12)
IC 2051 | 4 | SBbc | MW-like | 10.69 | 19.9 | 1 | 61060 | 0.18 | 70 | 0.42 | –
NGC 289 | 4 | SBbc | MW-like | 10.44 | 20.2 | 1 | 61064 | 0.03 | 130 | 0.29 | –
NGC 613 | 4 | SBbc | MW-like | 10.62 | 18.1 | 1 | 61064 | 0.03 | 115 | 0.19 | –
NGC 1097 | 3 | SBb | MW-like | 10.85 | 14.8 | 1 | 159 | 0.04 | 134 | 0.29 | –
NGC 1300 | 4 | SBbc | MW-like | 10.51 | 19.6 | 1 | 61065 | 0.05 | 87 | 0.17 | 7.91
NGC 1440 | -2 | SB0 | NSC | 10.72 | 19.9 | 1 | 10043 | 0.16 | 25 | 0.20 | –
NGC 1566 | 4 | SABbc | MW-like | 10.61 | 17.0 | 1 | 159 | 0.01 | 34 | 0.14 | –
NGC 2775 | 2 | SAab | MW-like | 10.98 | 18.7 | 1 | 69 | 0.07 | 165 | 0.21 | –
NGC 3351 | 3 | SBb | MW-like | 10.56 | 10.0 | 3 | 159 | 0.04 | 10 | 0.29 | –
NGC 3368 | 2 | SABab | MW-like | 11.01 | 10.5 | 3 | 69 | 0.04 | 172 | 0.37 | 6.88
NGC 3412 | -2 | SB0 | NSC | 10.53 | 11.0 | 2 | 10043 | 0.04 | 152 | 0.45 | 6.85
NGC 4237 | 4 | SAbc | NSC | 10.31 | 18.9 | 5 | 50128 | 0.05 | 106 | 0.38 | –
NGC 4321 | 4 | SABbc | MW-like | 10.83 | 15.2 | 4 | 159 | 0.04 | 152 | 0.14 | –
NGC 4377 | -3 | SAB0 | NSC | 10.13 | 17.7 | 5 | 10043 | 0.06 | 5 | 0.20 | –
NGC 4380 | 3 | SAb | MW-like | 10.46 | 15.9 | 5 | 30496 | 0.04 | 157 | 0.46 | –
NGC 4450 | 2 | SABab | MW-like | 10.78 | 16.7 | 6 | 159 | 0.04 | 170 | 0.31 | –
NGC 4501 | 3 | SAb | MW-like | 10.86 | 16.5 | 6 | 30945 | 0.06 | 141 | 0.49 | 7.30
NGC 4531 | -1 | SA0 | NSC | 10.30 | 15.2 | 5 | 61060 | 0.07 | 154 | 0.33 | –
NGC 4548 | 3 | SBb | MW-like | 10.72 | 16.2 | 3 | 3674 | 0.06 | 149 | 0.23 | –
NGC 4578 | -2 | SA0 | NSC | 10.20 | 16.4 | 5 | 10043 | 0.03 | 31 | 0.30 | –
NGC 4579 | 3 | SABb | MW-like | 10.92 | 20.1 | 5 | 159 | 0.06 | 95 | 0.22 | –
NGC 4608 | -2 | SB0 | NSC | 10.69 | 17.3 | 5 | 10043 | 0.03 | 105 | 0.18 | –
NGC 4612 | -2 | SAB0 | NSC | 10.51 | 17.3 | 5 | 10043 | 0.04 | 143 | 0.27 | –
NGC 4643 | 0 | SB0/a | NSC | 10.92 | 19.1 | 1 | 61063 | 0.05 | 53 | 0.20 | –
NGC 4689 | 4 | SAbc | NSC | 10.12 | 17.5 | 5 | 69 | 0.04 | 163 | 0.20 | –
NGC 4698 | 2 | SAab | MW-like | 10.69 | 16.5 | 7 | 30496 | 0.04 | 170 | 0.50 | –
NGC 4699 | 3 | SABb | NSC | 11.29 | 19.3 | 1 | 61064 | 0.05 | 35 | 0.19 | 8.24
NGC 5121 | 1 | SAa | MW-like | 10.55 | 18.6 | 1 | N/A | 0.11 | 28 | 0.22 | –
NGC 5248 | 4 | SABbc | MW-like | 10.46 | 17.3 | 1 | 69 | 0.04 | 114 | 0.28 | –
NGC 5364 | 4 | SAbc | NSC | 10.37 | 18.4 | 1 | 61065 | 0.04 | 37 | 0.28 | –
NGC 6744 | 4 | SABbc | MW-like | 11.07 | 9.2 | 4 | 10136 | 0.07 | 14 | 0.37 | –
NGC 7177 | 3 | SABb | MW-like | 10.44 | 17.5 | 1 | 30496 | 0.11 | 83 | 0.31 | –
NGC 7513 | 3 | SBb | NSC | 10.14 | 19.8 | 1 | 61065 | 0.06 | 105 | 0.29 | –

Note. — (1) Galaxy name, (2) morphological Hubble classification type, (3)
Galaxy classification from the RC3 catalog (de Vaucouleurs et al., 1995), (4)
NSC sample or MW-like sample defined in this work, (5) logarithmic galaxy
stellar mass derived using the HyperLEDA $B$ band absolute magnitude, ($B-V$)
color and M/L ratio from Bell et al. (2003), (6) Distance in Mpc, (7) Source
for distances: 1 = Virgocentric-corrected redshift from HyperLEDA + H0 = 72; 2
= Surface Brightness Fluctuation (SBF; Jensen+2021); 3 = Surface Brightness
Fluctuation (SBF; Tonry+2001, with correction from Mei+2005); 4 = Cepheids
(metallicity-corrected values, Freedman+2001); 5 = TRGB (Anand+2021); 6 = SBF
(Cantiello+2018); 7 = Default Virgo Cluster distance, (8) Spitzer ID program,
(9) F814W galactic extinction obtained from Ned IPAC. For the F475W image and
F160W images, we scale the extinction by 0.49 and 2.87 respectively, (10)
Galaxy Position Angle (PA), (11) Galaxy Ellipticity, (12) Black Hole mass from
Saglia et al. (2016) used in Section 5.3.

##  3 Dissecting the Galaxies’ Stellar Components

In this section we explain in detail the process of modeling each of the
galaxy components for the NSC sample galaxies. We describe how we identify and
create accurate models for the inner regions of the galaxy, especially the NSC
component. The fits for each of the galaxies is done as a three-step process.
First, we use the sky-subtracted IRAC1 images to fit the large-scale
components (mainly the bar and disc related components) as explained in
section 3.2. Using this fit, we then use the HST images (first the wider
field-of-view (FOV) F160W images and then the UVIS images) to fit for the
inner components (e.g., bulge, nuclear disc). Once we have a good model for
the overall structure of the galaxy, we then identify, refine and constrain
the NSC component using mostly the HST UVIS images as explained in section
3.3.

We fit our galaxies using the fast, multi-component image fitting program
imfit111https://github.com/perwin/imfit version 1.8 (Erwin, 2015). This code
creates 2-D models for each galaxy component using user-defined input
parameters, adds them together, and then convolves the summed image with a
user-supplied PSF image. These are fitted to the images with the default
$\chi^{2}$ minimization using a Levenberg-Marquardt (L-M) minimization
algorithm. In some cases where we run into local minima issues while modeling
the images, we also use the Nelder-Mead (N-M) minimization algorithm to
explore a wider range of solutions. The per-pixel uncertainties are estimated
from the data values using the Gaussian approximation to Poisson statistics.
When fitting models to the IRAC1 images, we convert the pixel values in the
latter to ADUs with an assumed A/D gain of 3.7; the units of the HST images
are in electrons and require no scaling.

Figure 2: 2D image modeling of an example galaxy, NGC 4689, using imfit. Each
row describes fits on a different scale; the top row shows the largest scale
fits to the Spitzer IRAC1 image, the middle row, the HST/WFC3-IR F160W image,
while the bottom row shows the smallest scale and highest resolution fits to
the HST/WFC3-UVIS F814W image. The left column shows the data, the next column
rigth shows the best-fit model, and the right most columns show the residuals.
In the bottom row, three residual images are shown, the left one is from a fit
with no NSC, the middle with a point source NSC component, and the right with
the best-fit model image shown; the stretch of all three of these residual
images is identical and clearly shows the need for a resolved NSC component in
this galaxy. Figure 3: Top panel: An example 1-D surface brightness profile of
NGC 4689 from our F814W imaging and modeling. Note this is the same galaxy
shown in Fig. 2. The data is shown as green crosses, the best-fit model is
shown as the blue solid line, and the best-fit NSC component is shown as the
purple solid line. Lower panel: The residuals (model – data) in magnitudes.
Three different residuals are shown corresponding to the right three panels in
Fig. 2. The best-fit model with a resolved NSC, point source NSC model, and no
NSC model are shown as blue, orange, and red lines respectively.

We use a wide range of 2-D functions to accurately fit our galaxies disk,
bulge and bar components as well as their NSCs. The most commonly used
components are listed in detail in Appendix B.

###  3.1 Sky subtraction

While the primary goal of this paper is the nuclear morphology of galaxies,
our modeling still requires accurate sky background estimates so that we can
correctly model the large scale components of the glaaxies. The galaxies in
our sample are massive and nearby, and thus they are almost always larger in
angular size than the FOV of our HST images. (This is nearly always true for
the $160\times 160\arcsec$ FOV of WFC3-IR, and always true for our $41\times
41\arcsec$ WFC3-UVIS C1K1C images.) It is thus not possible to accurately
estimate the sky background from the HST images themselves. To determine
reasonable estimates for the sky backgrounds, we match surface-brightness
profiles from ellipse-fitting of the HST images to those from ground- or
spaced-based images at similar wavelengths with larger FOV (i.e., large enough
to determine the overall background outside the galaxy). The surface
brightnesses were measured with the iraf ellipse task using ellipses with
position angles and ellipticities matching the galaxy main-disk orientation;
on the non-HST images, we used masks reproducing the orientation and FOV of
the HST images. The resulting HST profile was then scaled to match the
corresponding larger-FOV profile, using measurements outside the region
strongly affected by differences in the PSFs, including an additive component
representing the unknown HST background.

For the UVIS F475W and F814W images, the reference images are SDSS $g$ and
$i$-band images, respectively, where we apply a mask mimicking the orientation
and FOV of the HST images. In the case of galaxies lacking SDSS images, we
make use of images from the Carnegie-Irvine Galaxy Survey (Ho et al., 2011),
matching their $I$-band images to the F814W images and averaging the results
from matching the $B$\- and $V$-band images to the F475W images. For a small
number of galaxies where the matching with ground-based profiles failed we use
the average sky values obtained from the rest of the galaxies in the NSC
sample: 9.14 electrons for F814W images and 13.56 electrons for the F475W
images. For the HST F160W images we generally used Spitzer IRAC1 images as the
reference images. (Exceptions were NGC 3351, where we used an $H$-band image
from the 2MASS Large Galaxy Atlas (Jarrett et al., 2003), and NGC 1300 and NGC
4321, where we made use of $H$-band images from Grosbøl & Dottori (2012).)
Just as with the optical images, we match the surface brightness profiles
within the larger HST F160W FOV to that of the IRAC1 images. (See Erwin et
al., in prep, for more details.)

The sky background is incorporated into our imfit modeling using a constant
(fixed value) FlatSky function.

###  3.2 Large scale fitting

We initially use the large scale IRAC1 images to fit the larger, outer
components of the galaxy. For all of our galaxies, we started with the
combination of a single Sérsic component and a single Exponential component,
and then added components to best fit the galaxy. These models were fit using
an appropriate PSF; we have used the official in-flight Pixel-Response-
Function (PRF)
images222https://irsa.ipac.caltech.edu/data/SPITZER/docs/irac/calibrationfiles/psfprf/
that are down-sampled to the appropriate pixel scale from the original scale
of 0.24″/pixel at column, row = 129,129; the approximate central location of
most of our galaxies. We also generate a bad-pixel mask to remove bright
foreground stars and background galaxies; we do this by running SExtractor
(Bertin & Arnouts, 1996) on the image, and then scaling detected objects using
circles (for stars) or ellipses (for background galaxies). Notable image
defects are masked by hand.

After running our initial fit, we then refine the fit by adding components
based on (1) visible patterns in the residual images, (2) surface brightness
profiles, and (3) changes in the ellipticity and position angle of the galaxy
isophotes. For some galaxies, we find significantly better fits if we replace
the initial Exponential with a BrokenExponential component. (Figures 5 and 8
in Erwin et al. (2021) show examples of this for the galaxies NGC 4608 and NGC
4643.) We also incorporate information from the galaxy morphology (e.g. known
rings or bars) from previous studies. We continue to add additional components
to the model until the galaxy is well represented; specifically, when there
are no clearly visible systematic residual patterns that could be fit with an
additional component. Typically, this includes an exponential or broken
exponential disk component, a bar component, and at least one bulge component.
Occasionally, we also fit ring and spiral arm components, especially when this
is critical for understanding the bar and bulge structures. These components
are always an addition to the initial Sérsic + Exponential model, except for
cases where we have replaced the initial Exponential with a BrokenExponential.

An example of this fitting procedure can be seen in the upper panel of Figure
2 which shows the IRAC1 image, best-fitting model and the residual ratio image
for NGC 4689.

###  3.3 HST image fitting

Once we have the best-fit IRAC1 model, we then model the galaxy’s inner
components in more detail using the HST images, beginning with the F160W
image. This includes components such as a boxy-peanut bulge, classical bulge,
star forming disk, etc..

PSFs – For each model we fit to the HST data (in all three band images), we
provide an appropriate PSF image for convolution. For the HST images, we
generated the PSF images using the grizli
software333https://github.com/gbrammer/grizli. An “empirical PSF” image from
Anderson (2016)444http://www.stsci.edu/~jayander/STDPSFs/WFC3IR/ is inserted
into the each of the four individual exposures at the location of the galaxy
center; these are then run through the same drizzling process used to prepare
the final HST image (as explained in section 2.2). The final PSF image is then
extracted from the combined, drizzled image.

Masks – Foreground objects and dust can prevent us from getting an accurate
model fit to the data. We initially identify the foreground stars, background
galaxies and other image defects using SExtractor (Bertin & Arnouts, 1996). We
then create a mask to flag all those pixels in the image. We also mask other
regions of the galaxies that are not well fit by our models, these include
spiral arms in many cases, as well as other non-axisymmetric features that are
challenging to model.

Dust extinction near the centers of our galaxies can also significantly impact
the best-fit nuclear models. To mask dust features, we use UVIS F475W-F814W
color maps to find reddened pixels. We mask pixels using the distribution of
pixel values in unreddened regions, choosing a slightly different color
threshold for each galaxy. We then translate this mask to the F160W image as
well. In addition to masking reddened regions, we also mask star-forming
regions in some cases using a blue color threshold.

Fitting the F160W images – We start the modeling of the F160W image by using
the best-fitting IRAC1 model as an initial guess (this involves translating
size and angular parameters to account for differences in the pixel scales and
image orientation, and estimating the difference in intensity values for
intensity parameters).

Since some galaxy components (i.e. the disk) from the IRAC1 model can extend
well outside the F160W FOV, we model these components by holding the
translated best-fit shape, orientation and size parameters fixed, and fit only
for the intensity of these largest components. For components that are mostly
or entirely within the F160W [or WFC3-IR] FOV, we use the IRAC1 values as
initial guesses, but leave all parameters free. We then iterate by running
imfit to determine the best-fit parameters, followed by inspection of the
residuals, adding additional components to the model if needed and re-running
the fit.

In addition to examining the residuals, we also apply a more quantitative
approach to adding components. Specifically, we add components when (1) we see
residuals in the radial profile that are $>10$% of the data value and when (2)
the addition of a component improves (i.e., reduces) the Akaike Information
Criterion ($\Delta$AIC; Akaike, 1974) of the fit by 1000 or more relative to
the original fit (as in Erwin et al., 2021). Often at this stage we include an
initial NSC component that fits for the central excess light; we describe our
final NSC determinations below.

An example of this fitting procedure can be seen in the middle panel of figure
2 which shows the F160W image, best-fitting F160W model image and the residual
ratio image for NGC 4689. We obtain a decent F160W model for this galaxy with
a preliminary NSC component that fits for the central excess light.

Translation to the F814W images – The F814W images are read out in a sub-
array, and thus they span a smaller region (the inner $41\arcsec\times
41\arcsec$) of the galaxy than the F160W images. They are also higher
resolution than the F160W images, with an original pixel scale of
0.04$\arcsec$ and a final processed image scale of 0.03$\arcsec$ pixels
(critically sampling the $\sim$0$\farcs$07 FWHM PSF) and thus provide better
constraints on the nuclear structure than the F160W images as long as the
galaxies are not too dusty. We translate the best-fit F160W model to create
the initial guess for the F814W model by (1) scaling the intensity parameters
by the ratio of fluxes in a fixed angular area in the two images, and (2)
scaling the sizes of components to the higher resolution pixel scale. For
components that extend well beyond the edge of our chip, we hold their shape
parameters fixed and fit just for their intensity parameters. As with the
F160W images, we add components as necessary in the higher resolution F814W
images; again this often includes an initial NSC fit to the central light
excess.

Final NSC fitting – Once we have a good fit to the model that accurately
represents the whole F814W band image, we focus on modeling the NSC component.
We choose to use a Sérsic function to describe the NSC component, following
previous work by several authors (e.g. Graham & Spitler, 2009; Carson et al.,
2015; Nguyen et al., 2017).

As a first step, we check for the presence of a nuclear excess in the galaxy.
For this, we exclude any NSC component from the F814W model and use the
remaining components as initial conditions for a new fit – this allows us to
check whether any nuclear light can be fit through adjusting the parameters of
the larger components. We inspect the residuals of these fits and the surface
brightness profiles in the central 10-15 pixels for the presence of the excess
light. In all galaxies we find there is central excess light; in many cases
this is due to an NSC. However, we expect central light excess can also be due
to an AGN component, in which case we expect the light to be unresolved.
Therefore, as a next step, we add a PointSource component to the model in an
attempt to fit the nuclear excess.

Table 2: NSC modeling properties.

Galaxy | Sample | Primary Band | ${\\#}$ |  $\Delta$ AIC | Quality | Notes
---|---|---|---|---|---|---
(1) | (2) | (3) | (4) | (5) | (6) | (7)
IC 2051 | MW-like | F160W | 6 | 3.04x105 | 2 | Dust in UVIS affecting NSC fits
NGC 289 | MW-like | – | – | – | 0 | Very dusty, bad fit NSC
NGC 613 | MW-like | F160W | 6 | 1.01x102 | 1 | Unresolved NSC, weak AGN emissions
NGC 1097 | MW-like | F160W | 7 | 3.52x104 | 2 | Dust in UVIS affecting NSC fits
NGC 1300 | MW-like | F814W | 6 | 5.03x102 | 1 | Unresolved NSC, weak AGN emissions
NGC 1440 | NSC | F814W | 6 | 2.41x102 | 1 | Unresolved NSC
NGC 1566 | MW-like | – | – | – | 0 | Center saturated with strong AGN emission
NGC 2775 | MW-like | F814W | 5 | 1.11x103 | 1 | Unresolved NSC
NGC 3351 | MW-like | F814W | 7 | 3.48x104 | 4 |
NGC 3368 | MW-like | F814W | 8 | 3.61x105 | 4 |
NGC 3412 | NSC | F814W | 7 | 4.18x104 | 5 |
NGC 4237 | NSC | F814W | 3 | 4.65x105 | 4 |
NGC 4321 | MW-like | F160W | 10 | 1.22x105 | 2 | Dust in UVIS affecting NSC fits
NGC 4377 | NSC | F814W | 6 | 1.24x104 | 5 |
NGC 4380 | MW-like | F160W | 6 | 1.75x104 | 2 |
NGC 4450 | MW-like | F814W | 9 | 1.08x104 | 4 |
NGC 4501 | MW-like | F160W | 3 | 4.71x105 | 2 | Dust in UVIS affecting NSC fits
NGC 4531 | NSC | F814W | 5 | 1.42x105 | 4 |
NGC 4548 | MW-like | F160W | 7 | 1.64x104 | 2 | Dust in UVIS affecting NSC fits
NGC 4578 | NSC | F814W | 5 | 5.19x104 | 5 |
NGC 4579 | MW-like | F814W | 5 | 4.92x104 | 2 | Dust in UVIS affecting NSC fits
NGC 4608 | NSC | F814W | 6 | 4.12x105 | 5 |
NGC 4612 | NSC | F814W | 7 | 5.81x103 | 3 |
NGC 4643 | NSC | F814W | 6 | 4.74x105 | 4 |
NGC 4689 | NSC | F814W | 5 | 4.32x103 | 4 |
NGC 4698 | MW-like | F814W | 7 | 7.28x103 | 5 |
NGC 4699 | NSC | F814W | 9 | 1.24x105 | 4 |
NGC 5121 | MW-like | F814W | 7 | 2.17x103 | 4 |
NGC 5248 | MW-like | F814W | 7 | 2.29x104 | 5 |
NGC 5364 | NSC | F814W | 6 | 3.21x103 | 4 |
NGC 6744 | MW-like | F160W | 5 | 4.05x104 | 2 | Dust in UVIS affecting NSC fits
NGC 7177 | MW-like | – | – | – | 0 | Very dusty, bad fit NSC
NGC 7513 | NSC | F814W | 5 | 4.76x105 | 4 |

Note. — (1) Galaxy name, (2) NSC sample or MW-like subsample, (3) primary band
used for modelling the different components in the galaxy, (4) total number of
components we fit for in the galaxy (including the NSC component), (5) NSC
component PointSource vs. Sérsic $\Delta$AIC values (explained in detail in
section 3.3), (6) quality of the NSC fits, see Section 3.4, (7) brief notes on
the NSC fits.

We inspect the residuals of the centers for any visible pattern that is not
being modeled. If the central light excess appears to be resolved, we then
replace the PointSource function with a Sérsic function. We consider this
central component to be unresolved if the (i) $\Delta$AIC between the
PointSource and Sérsic function is $<$ 3000 and (ii) the difference in the
surface brightness profile residuals between the PointSource and Sérsic
function fits is $<$ 5$\%$. We consider resolved sources to be NSCs. Table 2
indicates sources that are unresolved as well as the PointSource vs. Sérsic
$\Delta$AIC values. For some galaxies with known strong AGN, we use an
additional PointSource component along with the NSC Sérsic component. The
evidence for AGN and details on the fits are given in Appendix C. Out of the
33 galaxies we fit, we find four of them to have unresolved nuclear components
(using the $\Delta$AIC $<3000$ constraint discussed above). We discuss these
four sources in more detail in Section 4.1 below.

An example of this fitting procedure can be seen in the lower panel of Figure
2, which shows the HST F814W image, the best-fitting F814W model image and the
residual ratio images for three models: the first with no central (NSC)
component, the second with a central PointSource component and the the third
with the best-fitting NSC Sersıc component. From these three residual ratio
images, we can visually judge the presence of a NSC component. The superiority
of the third model, with the absence of any residual nuclear excess is
evident. The AIC values for each of the 3 models are given below their
respective residual ratio images; the NSC-Sérsic model has AIC $\sim-32,000$.

In most cases, we use the F814W image as the primary filter for modeling the
NSCs. Once we have a good fitting model in the F814W filter, we then translate
all the components to the F475W image as well as the F160W image – we fit only
for the intensity of these components, and keep the shape parameters fixed to
scaled best-fit F814W values. This ensures that we measure accurate colors for
the NSCs (and other components). Allowing the NSC shape parameters to be fit
independently in each filter can result in unphysical colors when e.g. the NSC
component is much larger in one filter than another.

For galaxies that are very dusty in their centers (10 out of the 33), we
instead use the F160W image as the primary band to fit our NSCs, and perform
the methods outlined above on the F160W image directly, without translating to
F814W. The lower extinction in F160W helps us better fit the nuclear structure
despite the lower spatial resolution. In these cases, we still fit the F475W
and F814W images with shape parameters fixed to the best-fit F160W values in
order to derive colors for the NSCs in all three filters. Once we have the
best-fitting model in all three filters, we then calculate the magnitudes for
all of the components – explained in detail in section 4.2. Table 2 includes
the primary filter used for modelling the NSCs.

The top panel in figure 3 shows an example of the 1-D surface brightness
profiles we create to inspect the quality of the fit. These profiles were
derived using circular aperture photometry with python’s photutils library. We
ignore masked pixels in deriving the surface brightness of both the original
image (green points) as well as the best-fitting model (blue solid line). The
NSC Sérsic component (purple solid line) can be identified as the visible bump
seen at the smallest radii. The bottom panel shows the residuals (model –
data) in magnitudes; radii where the data is brighter than the model have
positive values in this panel. We also show the residuals for models with no
central component (shown in red) and a central PointSource component (shown in
orange). Here, we can observe changes in the residuals due to improving the
NSC model fits. The residual based on the best-fitting model has residual
below 0.05 magnitudes all the way out to 10″.

###  3.4 Fit Quality, AGN, and Exceptions

Here we discuss the process of evaluating the goodness of the fits to the
galaxy data. As mentioned in section 3.2 and section 3.3, our quality check
and criteria for adding new components for the each fit to the galaxy are
based on (1) improvements in the residuals and (2) improvements in the AIC.

Some of the galaxies in our NSC sample (especially in the MW-like subsample)
have literature data that indicates they have an AGN. Detailed descriptions of
these AGN components and associated X-ray sources are provided in Appendix A).
For galaxies with a known AGN, we test whether an additional point source
component needs to be included in the model as well, but find no cases where
both a point-source and resolved NSC component provide a significantly
improved fit. In one case, NGC 1566, the AGN is bright enough (and in fact
saturation artifacts affect the $r\lesssim 0.3\arcsec$ central region in the
optical images) that no clear NSC component is visible. Accordingly, we do not
present NGC 1566 in our NSC parameters table.

Dust can also prevent us from obtaining good fits to the NSCs. In two galaxies
(NGC 289 and NGC 7177) we are unable to determine accurate NSC morphologies
due to dust obscuring the centers of all three bands.

We rate the overall quality of our fits using a single number. The quality
values are as follows:
Quality 0: These galaxies are those for which we do not obtain good fits for
the NSCs – this includes the galaxies discussed above, NGC 289, NGC 1566 and
NGC 7177. No fits to these galaxies are shown in Table 3.
Quality 1: Unresolved NSC components in four galaxies. When comparing a point
source component to a Sérsic component fit the $\Delta$AIC between these fits
is $\lesssim$ 1000, giving minimal evidence that the nuclear component is
resolved. The nature of these sources is discussed in Section 4.1.
Quality 2: dusty galaxies where dust absorption is evident all the way to the
center. However, we are able to estimate NSC properties using the F160W images
in these galaxies.
Quality 3: galaxies with complex central regions with poorly modeled
structures (e.g., spiral arms) that result in large radial surface-brightness
profile residuals ($>$0.1 mag).
Quality 4: galaxies with some dust in the nuclear regions (but not crossing
the center). Fits have surface brightness profile residuals $<$0.1 magnitudes.
Quality 5: galaxies with no dust within the central 2$\arcsec$. Fits have
surface brightness profile residuals $<$0.1 magnitudes.

There are 27 galaxies with quality $\geq$2\. For the plots in the paper, we
exclude all NSCs with Quality $<$ 2, while Quality 2 fits are shown with open
symbols.

Figure 4: Top panel: CMD with the NSC UVIS color VS F814W band absolute
magnitude. The circles denote the NSCs in our sample. The MW-like subsample is
denoted by the squares. The open circles represent the dusty galaxies with a
NSC quality fit = 2. Bottom panel: NSC color–color plot (UVIS vs. IR). Colored
pluses and squares show PARSEC 1.2S SSP models (Bressan et al., 2012) at two
metallicities (-1.0 and +0.3) and with ages from 1–13 Gyr (indicated by the
color). An extinction vector of corresponding to $A_{V}=1$ is also shown. All
plotted magnitudes in both panels are foreground extinction corrected. Figure
5: The mass-size relation of our NSCs compared to previous literature
measurements. The circles denote our NSC sample galaxies, with surrounding
squares indicating the MW-like subsample. Open circles indicate uncertain
measurements due to dust (i.e., quality flag = 2 in Table 3). The points are
colored red or blue based on their Hubble type (early- and late- type
respectively). The literature sample of NSCs from early- (red stars) and late-
(blue stars) type galaxies are obtained from Côté et al. (2006); Spengler et
al. (2017); Georgiev & Böker (2014); Sánchez-Janssen et al. (2019); Erwin &
Gadotti (2012); Eigenthaler et al. (2018); Pechetti et al. (2020).

###  3.5 Error Estimation

We estimate the errors on our imfit models using bootstrap resampling. This
method allows us to capture asymmetric errors and the covariance of NSC
parameters with the other fitted components. It also provides more accurate
errors than those estimated from the Leavenberg-Marquardt algorithm. We
performed 200 iterations of bootstrapping for each galaxy model. For the NSC
models, the effective radii have median errors of $\sim$9%, while the median
error on Sérsic indices are $\sim$14%. For ellipticities above 0.05, the
errors on the ellipticity are just $\sim$7%.

##  4 NSC properties and results

###  4.1 Nucleation Fraction

Of the 33 galaxies in our sample, we find unambiguous, resolved NSCs with
radii $<$50 pc in 26. Previously measured NSCs have typical effective radii of
$\sim$3 pc with a small tail towards larger sizes and a cutoff suggested at
$\sim$50 pc by Neumayer et al. (2020). In three galaxies, the presence of a
nuclear cluster can’t be constrained due to dust opaque enough to obscure the
nucleus even in F160W (NGC 289 and NGC 7177), or the presence of a very bright
AGN (NGC 1566) as discussed in Section 3.4. In another four galaxies, the
potential NSC components are unresolved: NGC 613 and NGC 1300 have a low
luminosity AGN, and thus may not be NSCs. On the other hand in NGC 2775 and
NGC 1440 the nuclear light appears to be stellar; specifically, the nuclear
sources in both have very similar colors to the surrounding galaxy light, and
the nuclear spectra (Ho et al., 1995) shows very little emission. Therefore it
is likely these two galaxies host compact NSCs that we just cannot resolve
with HST. The best-fit Sérsic $r_{e}$ are used here as upper limits; for NGC
2775 and NGC 1440 these are 3.87 pc and 4.65 pc or 0$\farcs$042 and
0$\farcs$048\. Our ability to resolve NSCs in our CBS galaxies is complicated
due to varying galaxy backgrounds, however, it does extend to more compact
sources than these in some galaxies – the most compact clearly resolved NSC is
in NGC 4377 with an $r_{e}$ of 1.91 pc or 0$\farcs$22; this is similar to the
limit on resolving NSCs found for galaxies at similar distances by Côté et al.
(2006).

Using only the unambiguous resolved NSCs, we get a nucleation fraction of
78.8${}_{-7.9}^{+6.2}$% (26/33) for the full sample, with errors calculated
using the Wilson interval. The nucleation fraction is 68.4${}_{-11.4}^{+9.5}$%
(13/19) for the MW-like subsample. On the other hand, we cannot exclude the
presence of NSCs in any of our galaxies, thus the nucleation fraction in both
samples could be as high as 100%. We note that our galaxy sample are all high
mass ($\log M_{\star})>10.1$) and mostly late-type galaxies; if we take all
late-types in our sample, we get 76.0${}_{-9.4}^{+7.4}$% (19/25) with NSCs.

Two previous measurements exist for the nucleation fraction of massive late-
type galaxies. We took the data from Neumayer et al. (2020) and Hoyer et al.
(2021) to find a comparable nucleation fraction for galaxies with ($\log
M_{\star})>10.1$); from the Neumayer et al. (2020) compilation, 10/21
(47.6${}_{-10.5}^{+10.7}$%) galaxies in this mass range are nucleated, while
in the Hoyer et al. (2021) Local Volume sample, 10/15
(66.7${}_{-13.8}^{+10.7}$%) galaxies with nucleation measurements are
nucleated. Thus we find a higher nucleation fraction than either study, with
our results being consistent with the measurement in Hoyer et al. (2021). Our
values are much higher than the nucleation fraction of $\sim$30% seen in
early-type galaxies with similar mass (Neumayer et al., 2020; Hoyer et al.,
2021).

###  4.2 Magnitude and color

For all the NSCs, we estimate the magnitude using the imfit makeimage program,
which can calculate fluxes and magnitudes for each component in the model. To
determine the magnitudes of the NSC in the 3 HST bands, we divide the total
counts by the total exposure time; 600s for F160W band, 500s for F814W band
and 700s for F475W band. We then use the following zeropoints: 24.6949 in
F160W, 24.684 in F814W, and 25.801 in F475W
555https://www.stsci.edu/hst/instrumentation/wfc3/data-analysis/photometric-
calibration/uvis-photometric-calibration. These are Vega based zeropoints, and
thus all magnitudes listed here are in the Vega system. We correct for
foreground extinction using the $A_{F814W}$ values and conversions to the
other two bands in Table 1 and the notes to that table. The extinction
corrected NSC magnitudes in each filter band are presented in Table 3.

Figure 4 shows the color-magnitude and color-color (UVIS-IR) diagrams of the
NSCs. Padova PARSEC 1.2S single-stellar population models (Bressan et al.,
2012) with ages from 1-13 Gyr and at two metallicities are overploted. A
majority of the galaxies are consistent with these models with modest
extinction up to ($A_{V}\lesssim 2$). Of these, only two require populations
younger than $\sim$10 Gyr – due to the age-extinction degeneracy it is not
possible to separately constrain the ages and extinctions using our colors.
Almost half of the galaxies fall redwards of these SSP models in the
F814W$-$F160W color in a way that is inconsistent with the reddening vector
(which assume $R_{V}=3.1$), in some cases by $>$1 magnitude. This offset in
F814W$-$F160W color could be due to (1) a mismatch between the data and SSP
models, or (2) issues with calculating the NSC magnitudes. To investigate this
last issue, we measured aperture photometry within the center 0$\farcs$5, and
compared these aperture colors to the model NSC colors. For clusters with
bright, prominent NSCs, the aperture and integrated NSC values agreed.
However, for fainter NSCs that make up a smaller light fraction of the galaxy,
we see a blueward offset of up to 0.5 mags for the aperture magnitudes
relative to the NSC model magnitudes. This blueward offset can be explained by
a combination of the lower encircled energy in F160W and bluer surrounding
bulge components. Overall, this test suggests we are accurately measuring the
NSC colors with our model magnitudes. While some NSCs have clear evidence for
significant dust absorption (i.e. the open circles), others appear dust-free,
suggesting that the PARSEC models may under-predict the F814W$-$F160W colors
of NSCs.

###  4.3 Mass

We determine the NSC masses using the F814W magnitude and color-$M/L$
relations from Roediger & Courteau (2015). Specifically, we first convert our
F814W magnitude to the Sloan $i$ band and then convert our HST F475W$-$F814W
color to $g-i$ using relations derived from PARSEC 1.2S stellar population
models (Bressan et al., 2012):

$\displaystyle i-\mathrm{F814W}$ $\displaystyle=$ $\displaystyle
0.099\times({\mathrm{F475W}-\mathrm{F814W})+0.404}$ $\displaystyle g-i$
$\displaystyle=$ $\displaystyle
0.92304\times({\mathrm{F475W}-\mathrm{F814W}})-0.48565$

We then use the $g-i$ color vs $i$ band magnitude relation of Table 2 in
(Roediger & Courteau, 2015) to determine the $i$-band $M/L$ ratio. The
resulting NSC masses are presented in Table 3. For our NSCs the
$\log(M_{\mathrm{NSC}}/M_{\sun})$ values range from 5.7 to 8.74 with a median
of 7.16 for all our NSCs and 7.26 for the NSCs in the MW-like subsample. We
determine the errors for the derived NSC mass using the bootstrap sampling
(see Section 3.5), recalculating the luminosities, colors, and derived $M/L$s
for each sample.

###  4.4 NSC size, mass relations

We use the derived color and mass to understand our NSCs and compare them with
the available literature from both early- and late-type galaxies. In Figure 5
we plot the radius of the NSCs (in pc) versus their derived masses. The solid
circles denote our NSC sample galaxies, with surrounding squares indicating
the MW-like subsample. All galaxies are color coded into early- (red) and
late- (blue) type. The dashed line show the relationships for early- and late-
type galaxies from Georgiev et al. (2016). As has been found in many previous
studies (e.g. Hopkins & Quataert, 2010; Norris et al., 2014; Georgiev et al.,
2016; Neumayer et al., 2020), the NSC radii correlate with their masses, i.e.,
massive NSCs have a larger radii. Our NSC sample improves the available
literature, especially for the massive late-type galaxies
($>10^{10}M_{\sun}$). Overall, the masses and radii of these clusters agree
well with the overall trend seen in previously published data (shown as small
stars in Fig. 5). Georgiev et al. (2016) fit mass-radii relations and find
that the NSCs in the late-type galaxies (blue-dashed line) are roughly two
times smaller than the NSCs in early-type galaxies (red dashed line). Our data
does not seem to support this difference; in particular most of the late-type
galaxies in our sample fall above the blue dashed line, while all of the
early-type galaxies fall below the red-dashed line. This weakens the previous
literature findings that there is a difference in the mass-radius relationship
in early and late-type galaxies.

Figure 6: Top panel: NSC mass vs. NSC Sérsic index. Bottom panel: NSC mass vs.
NSC ellipticity. The solid circles denote our NSC sample galaxies, with
squares indicating the MW-like subsample. All dusty galaxies (i.e., quality
flag = 2) are denoted by open circles. The points are colored red or blue
based on their Hubble type (Early- and Late- type respectively).

The biggest NSCs ($>25$ pc) in our sample are found in IC 2051, NGC 4380, NGC
4501, NGC 4699, NGC 5248 and NGC 7513. These largest objects may be ambiguous
in their classification as NSCs, however, the continuity of the mass–radius
relationship suggests these are related components. For NGC 7513, Carollo et
al. (2002) found the NSC to be a very compact source unlike in our model. The
difference in the NSC model is discussed in detail in section 4.6.

Four objects (NGC 613, NGC 1300, NGC 1440 and NGC 2775) are unresolved in our
sample but nonetheless appear to be NSCs; these are shown as upper limits on
the mass radius diagram. These galaxies fall on the compact side of the locus
of previous NSC measurements and thus are significantly denser than typical
NSCs.

Table 3: NSC Sérsic Parameters and derived properties.

Galaxy | PAnsc | $\epsilon_{\rm nsc}$ | nnsc | re | mF475W | mF814W | mF160W | log(MNSC) | B/Tpm | Lbar
---|---|---|---|---|---|---|---|---|---|---
|  |  |  | pc | mag | mag | mag | M⊙ |  | L⊙
(1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | (9) | (10) | (11)
IC 2051 | 64.44${}_{0.77}^{0.97}$ | 0.17${}_{0.01}^{0.01}$ | 2.65${}_{0.08}^{0.06}$ | 37.26${}_{0.46}^{0.87}$ | 16.71${}_{0.02}^{0.06}$ | 15.02${}_{0.02}^{0.02}$ | 13.63${}_{0.06}^{0.14}$ | 8.23${}_{0.03}^{0.03}$ | 0.46 | 9.67
NGC 289 | – | – | – | – | – | – | – | – | – | –
NGC 613 | 143.72${}_{0.00}^{0.00}$ | 0.00${}_{0.00}^{0.00}$ | 0.50${}_{0.00}^{0.02}$ | 2.86${}_{0.21}^{0.26}$ | 21.02${}_{0.04}^{0.02}$ | 19.52${}_{0.05}^{0.03}$ | 16.56${}_{0.08}^{0.11}$ | 6.18${}_{0.08}^{0.06}$ | 0.17 | 10.89
NGC 1097 | 59.14${}_{1.24}^{3.08}$ | 0.16${}_{0.01}^{0.01}$ | 3.23${}_{2.35}^{2.20}$ | 14.77${}_{0.37}^{0.17}$ | 17.60${}_{0.07}^{0.07}$ | 16.12${}_{0.02}^{0.04}$ | 13.53${}_{0.03}^{0.27}$ | 7.34${}_{0.11}^{0.09}$ | 0.16 | 10.94
NGC 1300 | 73.04${}_{4.46}^{4.85}$ | 0.15${}_{0.02}^{0.02}$ | 1.53${}_{0.23}^{0.23}$ | 8.32${}_{0.77}^{0.80}$ | 18.93${}_{0.03}^{0.03}$ | 17.01${}_{0.09}^{0.12}$ | 14.95${}_{0.05}^{0.13}$ | 7.62${}_{0.14}^{0.12}$ | – | 10.80
NGC 1440 | 93.67${}_{0.00}^{0.00}$ | 0.00${}_{0.00}^{0.00}$ | 3.48${}_{0.61}^{0.01}$ | 4.65${}_{0.55}^{0.12}$ | 20.29${}_{0.11}^{0.04}$ | 18.44${}_{0.01}^{0.29}$ | 15.69${}_{0.01}^{0.29}$ | 7.00${}_{0.36}^{0.02}$ | 0.67 | 10.17
NGC 1566 | – | – | – | – | – | – | – | – | – | –
NGC 2775 | 131.77${}_{0.00}^{0.00}$ | 0.00${}_{0.00}^{0.00}$ | 0.52${}_{0.01}^{0.01}$ | 3.87${}_{0.24}^{0.38}$ | 20.98${}_{0.62}^{0.77}$ | 18.89${}_{0.10}^{0.12}$ | 16.62${}_{0.07}^{0.06}$ | 6.98${}_{0.57}^{0.76}$ | 0.40 | –
NGC 3351 | 150.00${}_{0.00}^{0.00}$ | 0.00${}_{0.00}^{0.00}$ | 0.79${}_{0.02}^{0.07}$ | 4.35${}_{0.32}^{0.29}$ | 19.60${}_{0.03}^{0.03}$ | 18.16${}_{0.04}^{0.05}$ | 16.71${}_{0.03}^{0.03}$ | 6.16${}_{0.07}^{0.07}$ | 0.70 | 10.14
NGC 3368 | 60.68${}_{1.24}^{0.98}$ | 0.16${}_{0.04}^{0.00}$ | 2.21${}_{0.71}^{1.05}$ | 10.41${}_{1.51}^{1.00}$ | 16.42${}_{0.10}^{0.66}$ | 14.81${}_{0.05}^{0.07}$ | 12.87${}_{0.56}^{0.06}$ | 7.69${}_{0.25}^{0.21}$ | 0.75 | 10.67
NGC 3412 | 152.98${}_{1.07}^{1.05}$ | 0.31${}_{0.02}^{0.02}$ | 1.78${}_{0.49}^{0.59}$ | 6.34${}_{1.04}^{1.86}$ | 17.07${}_{0.01}^{0.01}$ | 15.39${}_{0.17}^{0.12}$ | 13.64${}_{0.01}^{0.02}$ | 7.56${}_{0.16}^{0.22}$ | 0.36 | 9.59
NGC 4237 | 116.78${}_{2.21}^{4.07}$ | 0.03${}_{0.01}^{0.02}$ | 4.63${}_{0.33}^{0.03}$ | 7.36${}_{0.05}^{0.63}$ | 19.70${}_{0.17}^{0.01}$ | 18.37${}_{0.05}^{0.16}$ | 17.39${}_{0.09}^{0.04}$ | 6.53${}_{0.14}^{0.08}$ | 0.05 | –
NGC 4321 | 55.85${}_{3.23}^{4.45}$ | 0.13${}_{0.05}^{0.15}$ | 2.34${}_{0.21}^{0.32}$ | 17.92${}_{1.57}^{1.24}$ | 17.53${}_{0.03}^{0.02}$ | 15.71${}_{0.07}^{0.05}$ | 13.47${}_{0.06}^{0.06}$ | 7.83${}_{0.07}^{0.07}$ | 0.14 | 10.63
NGC 4377 | 158.94${}_{0.01}^{0.01}$ | 0.21${}_{0.01}^{0.00}$ | 5.73${}_{0.60}^{1.50}$ | 1.91${}_{0.00}^{0.10}$ | 20.28${}_{0.09}^{0.09}$ | 18.49${}_{0.17}^{0.01}$ | 16.65${}_{0.04}^{0.03}$ | 6.82${}_{0.09}^{0.16}$ | 0.42 | 9.75
NGC 4380 | 149.79${}_{1.46}^{1.06}$ | 0.18${}_{0.02}^{0.01}$ | 6.95${}_{0.13}^{0.16}$ | 27.04${}_{1.57}^{2.87}$ | 19.88${}_{0.01}^{0.02}$ | 17.47${}_{0.04}^{0.04}$ | 15.39${}_{0.04}^{0.06}$ | 7.67${}_{0.05}^{0.04}$ | 0.17 | 9.12
NGC 4450 | 2.69${}_{0.00}^{0.00}$ | 0.00${}_{0.00}^{0.00}$ | 4.95${}_{0.11}^{0.09}$ | 15.70${}_{0.32}^{1.27}$ | 17.36${}_{0.06}^{0.01}$ | 15.75${}_{0.04}^{0.02}$ | 13.60${}_{0.07}^{0.03}$ | 7.72${}_{0.08}^{0.08}$ | 0.49 | 10.55
NGC 4501 | 143.74${}_{1.74}^{1.54}$ | 0.22${}_{0.01}^{0.01}$ | 1.58${}_{0.06}^{0.07}$ | 29.99${}_{0.34}^{0.34}$ | 17.63${}_{0.01}^{0.05}$ | 15.13${}_{0.06}^{0.04}$ | 12.79${}_{0.07}^{0.07}$ | 8.72${}_{0.03}^{0.07}$ | 0.14 | –
NGC 4531 | 6.89${}_{5.47}^{4.79}$ | 0.05${}_{0.01}^{0.01}$ | 4.36${}_{0.34}^{0.29}$ | 10.86${}_{1.50}^{0.80}$ | 19.07${}_{0.03}^{0.01}$ | 17.30${}_{0.05}^{0.02}$ | 15.69${}_{0.17}^{0.09}$ | 7.15${}_{0.03}^{0.02}$ | 0.22 | –
NGC 4548 | 147.12${}_{0.00}^{0.00}$ | 0.20${}_{0.03}^{0.04}$ | 2.47${}_{0.38}^{0.44}$ | 19.89${}_{2.78}^{2.83}$ | 20.49${}_{0.12}^{0.17}$ | 17.58${}_{0.02}^{0.03}$ | 14.80${}_{0.04}^{0.03}$ | 8.07${}_{0.11}^{0.14}$ | 0.36 | 10.31
NGC 4578 | 10.96${}_{1.31}^{1.24}$ | 0.14${}_{0.01}^{0.00}$ | 2.76${}_{0.13}^{0.15}$ | 12.09${}_{0.50}^{0.72}$ | 17.87${}_{0.01}^{0.01}$ | 15.91${}_{0.05}^{0.04}$ | 13.97${}_{0.01}^{0.01}$ | 7.94${}_{0.06}^{0.06}$ | 0.62 | –
NGC 4579 | 64.28${}_{1.63}^{1.94}$ | 0.30${}_{0.11}^{0.12}$ | 1.54${}_{0.45}^{0.23}$ | 7.09${}_{1.34}^{1.17}$ | 17.57${}_{0.08}^{0.10}$ | 15.99${}_{0.06}^{0.06}$ | 13.67${}_{0.03}^{0.03}$ | 7.75${}_{0.11}^{0.10}$ | 0.30 | 10.48
NGC 4608 | 145.63${}_{1.12}^{1.80}$ | 0.13${}_{0.04}^{0.04}$ | 1.19${}_{0.07}^{0.09}$ | 2.90${}_{0.10}^{0.10}$ | 20.42${}_{0.04}^{0.04}$ | 18.45${}_{0.01}^{0.01}$ | 16.40${}_{0.06}^{0.05}$ | 6.97${}_{0.03}^{0.04}$ | 0.72 | 10.27
NGC 4612 | 117.04${}_{0.00}^{2.73}$ | 0.02${}_{0.02}^{0.02}$ | 3.14${}_{0.08}^{0.21}$ | 11.74${}_{0.43}^{0.60}$ | 17.58${}_{0.04}^{0.04}$ | 15.63${}_{0.07}^{0.07}$ | 13.14${}_{0.07}^{0.11}$ | 8.08${}_{0.09}^{0.10}$ | – | –
NGC 4643 | 114.16${}_{0.00}^{0.00}$ | 0.00${}_{0.00}^{0.00}$ | 0.75${}_{0.34}^{2.70}$ | 4.11${}_{0.53}^{3.86}$ | 20.53${}_{0.03}^{0.04}$ | 18.52${}_{2.00}^{0.11}$ | 16.45${}_{0.02}^{0.02}$ | 7.08${}_{0.15}^{1.25}$ | 0.37 | 10.61
NGC 4689 | 160.36${}_{0.00}^{0.00}$ | 0.00${}_{0.00}^{0.00}$ | 2.85${}_{0.15}^{0.19}$ | 5.03${}_{0.15}^{0.13}$ | 20.03${}_{0.03}^{0.06}$ | 18.21${}_{0.08}^{0.06}$ | 16.73${}_{0.07}^{0.11}$ | 6.95${}_{0.04}^{0.08}$ | 0.06 | 9.28
NGC 4698 | 66.76${}_{1.23}^{1.46}$ | 0.48${}_{0.04}^{0.01}$ | 1.39${}_{0.24}^{0.65}$ | 7.64${}_{1.46}^{0.29}$ | 20.62${}_{0.19}^{0.20}$ | 18.53${}_{0.05}^{0.05}$ | 16.76${}_{0.08}^{0.14}$ | 7.01${}_{0.16}^{0.17}$ | 0.44 | –
NGC 4699 | 152.00${}_{0.00}^{0.00}$ | 0.00${}_{0.00}^{0.00}$ | 1.87${}_{0.28}^{0.44}$ | 25.75${}_{3.42}^{2.27}$ | 16.46${}_{0.07}^{0.03}$ | 14.37${}_{0.06}^{0.07}$ | 12.41${}_{0.01}^{0.12}$ | 8.80${}_{0.03}^{0.09}$ | 0.14 | 10.19
NGC 5121 | 5.41${}_{0.59}^{1.63}$ | 0.14${}_{0.03}^{0.04}$ | 1.26${}_{0.14}^{0.14}$ | 6.56${}_{0.35}^{0.35}$ | 18.51${}_{0.03}^{0.03}$ | 16.78${}_{0.09}^{0.08}$ | 15.19${}_{0.02}^{0.03}$ | 7.50${}_{0.11}^{0.11}$ | 0.34 | 9.67
NGC 5248 | 107.37${}_{0.97}^{0.91}$ | 0.27${}_{0.01}^{0.01}$ | 0.97${}_{0.04}^{0.03}$ | 33.99${}_{0.20}^{0.28}$ | 17.16${}_{0.03}^{0.02}$ | 15.18${}_{0.01}^{0.05}$ | 13.50${}_{0.04}^{0.03}$ | 8.29${}_{0.03}^{0.04}$ | – | –
NGC 5364 | 159.09${}_{0.00}^{0.00}$ | 0.16${}_{0.02}^{0.02}$ | 3.53${}_{0.39}^{0.22}$ | 18.29${}_{4.74}^{0.58}$ | 19.18${}_{0.01}^{0.02}$ | 17.63${}_{0.03}^{0.15}$ | 16.30${}_{0.02}^{0.02}$ | 7.00${}_{0.18}^{0.04}$ | 0.26 | –
NGC 6744 | 14.44${}_{1.64}^{2.00}$ | 0.38${}_{0.02}^{0.02}$ | 2.28${}_{0.20}^{0.29}$ | 11.33${}_{0.83}^{1.18}$ | 18.75${}_{0.01}^{0.06}$ | 16.85${}_{0.05}^{0.07}$ | 14.50${}_{0.04}^{0.09}$ | 7.01${}_{0.04}^{0.05}$ | 0.15 | 9.99
NGC 7177 | – | – | – | – | – | – | – | – | – | –
NGC 7513 | 74.66${}_{0.00}^{0.00}$ | 0.00${}_{0.00}^{0.00}$ | 5.92${}_{0.20}^{0.13}$ | 43.54${}_{1.35}^{2.42}$ | 19.42${}_{0.03}^{0.01}$ | 17.35${}_{0.16}^{0.02}$ | 15.66${}_{0.08}^{0.05}$ | 7.60${}_{0.19}^{0.08}$ | 0.12 | 9.94

Note. — (1) Galaxy name, (2) NSC position angle (PA), (3) ellipticity, (4)
Sérsic index, (5) effective radius, (6) F475W magnitude, (7) F814W magnitude,
(8) F160W magnitude, (9) logarithmic stellar mass estimated using the $M/L$
ratio (see Section 4.3, (10) Photometric bulge to total ratio of the galaxy
(see Section 5.2.1), (11) bar luminosity determined using the bar component
magnitudes. All magnitudes are corrected for Galactic extinction.

###  4.5 NSC mass vs. ellipticity and Sérsic index

In Figure 6, we compare the NSC mass with the NSC Sérsic index (top panel) and
ellipticity (bottom panel).

We see no correlation between NSC masses and Sérsic indices, indicating that
the NSCs have a wide range of concentrations (see also Hoyer et al., 2023a).
One of the possible reasons for a high Sérsic index ($>5$) is the presence of
multiple components within the NSC, as seen in previous studies of very nearby
NSCs where these components can be resolved (e.g., Seth et al., 2006, 2010;
Nguyen et al., 2018). The Sérsic indexes of our NSCs range from 0.1–5.9 with a
median value of 2.7. The median value of the Sérsic indices of the MW-like
subsample is 2.2. We have no evidence for multiple component NSCs in our
sample except for in NGC 4612, in which we obtain a two component fit. We only
plot the average ellipticity obtained from the two component NSC in Figure 6
and do not plot the Sérsic index of this NSC. More information about the NSC
fit for this galaxy is provided in the Appendix C.

A trend of higher ellipticities in higher mass NSCs was seen in early-type
galaxies by Spengler et al. (2017), however, we find no correlation between
the NSC mass and ellipticity (bottom panel in figure 6). The ellipticities of
all our NSCs range from 0–0.5 with a median value of 0.14 (0.16 for the MW-
like subsample).

Figure 7: Left panel: Galaxy ellipticity vs NSC ellipticity. The population of
NSCs is typically rounder than their host galaxy disks, suggesting a less
flattened distribution. Circles denote the NSC sample with squares showing the
MW-like subsample. The galaxies are colored red and blue based on their Hubble
type (early and late type respectively). The NSCs with quality flag = 2, i.e.,
dusty centers are denoted by open circles. Right panel: Difference between NSC
and Galaxy position angles ($\delta$PA). We plot the difference for all those
NSCs whose $\epsilon$ $>0.05$. There is a clear preference for near-alignment
between NSCs and their host galaxies’ disks.

###  4.6 NSC literature comparison

The NSCs of five of the galaxies from our sample – NGC 289, NGC 1566, NGC
4237, NGC 4612 and NGC 7513 – have been studied previously in the literature.
Two of these galaxies (NGC 289 and NGC 1566) have NSCs presented in Carollo et
al. (2002); due to the bright AGN component (in NGC 1566) and dust (in NGC
289), we are unable to obtain reliable, unambiguous NSC fits for them, and so
we focus on the other three objects, below.

NGC 4237 – This unbarred Virgo Cluster spiral galaxy has been previously
studied in Georgiev & Böker (2014). They determine the effective radius of the
NSC to be 0$\farcs$07 with an F814W magnitude of 17.74. They model the NSC
using multiple images from HST including F606W and F814W band. From our work,
the NSC in this galaxy has an effective radius of $0\farcs 08$, with an F814W
magnitude of 18.37. So while the effective radii are similar, our fit to the
NSC is considerably fainter than Georgiev & Böker (2014). This is likely due
to our more careful modeling of the galaxy background. We note we also are
fitting higher resolution images than the wide field chip WFPC2 images fitted
in Georgiev & Böker (2014).

NGC 4612 – This barred S0 Virgo Cluster galaxy was previously studied in Côté
et al. (2006) and Spengler et al. (2017) as part of the ACS Virgo Cluster
Survey. They determine the NSC in this galaxy to be unresolved with an
effective radius of $0\farcs 024$. In our model, we find that the NSC is best
fit by a two component model, a compact Sérsic surrounded by a larger
exponential with a combined effective radius of $0.14\arcsec$. This model is
preferred to a point source model with a $\Delta$ AIC of 5810. We can directly
compare the F475W magnitudes of the sources; they find 17.73 (after conversion
to Vega magnitudes), while our combined NSC has a magnitude of 17.66, thus
these agree quite well. We note that our approaches differ significantly; Côté
et al. (2006) fit 1-D profiles with a single Sérsic background galaxy models,
while we fit a more sophisticated galaxy model and fit in 2D.
NGC 7513 –This barred galaxy was previously studied in Carollo et al. (2002).
They modeled the NSC using NICMOS2 data in the F110W and F160W filters and
determine the NSC in this galaxy to have an F160W magnitude of 18.3 and an
effective radsius of 0$\farcs$06 (0.97 pc), slightly smaller than the
0$\farcs$075 pixels. We find a much bigger and brighter NSC component in this
galaxy, with an effective radius of $0.45\arcsec$ (43.54 pc) and an F160W
magnitude of 15.66; an unresolved point source or compact component provides a
much worse fit to the nuclear regions. The Carollo et al. (2002) fits did not
model the galaxy background at all, and we suspect that this methodological
difference may be responsible for this discrepancy.

##  5 NSC-Galaxy relations

In this section, we discuss in detail the relation of the NSCs to the
properties of their host galaxies. We also briefly discuss the relations
between the NSC mass and supermassive black hole mass from Saglia et al.
(2016) for 4 galaxies in our sample in Section 5.3.

Figure 8: The NSC mass is plotted against the host galaxy mass. The markings
are the same as in Figure 5. The literature sample contains both early- and
late- type galaxies from Côté et al. (2006); Turner et al. (2012); Georgiev et
al. (2016); Sánchez-Janssen et al. (2019).

###  5.1 Structural Parameters

In Figure 7 we compare the ellipticity ($\varepsilon=b/a$) and position angle
(PA) of our NSCs relative to their host galaxies. For the host galaxies, we
use the PA and $\varepsilon$ from Table 1. It is important to note that the
CBS selection criteria selects galaxies with inclinations between 35∘ and 60∘.
In the left panel of the figure, we see the NSCs have ellipticies equal to or
smaller than the ellipticites of their host galaxies, suggesting that NSCs are
typically rounder than their host galaxy disks.

The right panel of the figure shows the difference in PA between the NSCs and
the galaxies. Here we plot the difference for all NSCs with ellipticities
$>0.05$ where we can robustly estimate the NSC PA. We see that the
distribution does not appear to be uniform as would be expected if there was
no correlation between the galaxy disks and NSCs, but instead most of the NSCs
have PAs within 25∘ of their host galaxies. Using Kolmogorov-Smirnov and
Anderson-Darling tests, we can reject the relative PAs being drawn from a
uniform distribution at high significance ($p$-values of 0.0072 and 0.00075).
This result is similar to what is seen in our Milky Way and in edge-on
galaxies, where the NSC and galaxy PAs are typically aligned (Seth et al.,
2006, 2008b; Feldmeier et al., 2014). However, this correlation of PAs is not
seen by Georgiev & Böker (2014). Their sample included a much wider range of
inclinations, and less correlation between NSC and galaxy PAs would be
expected to be visible in more face-on galaxies.

The correlation of NSC and galaxy PAs suggests that NSCs are flattened and
aligned with their large-scale galaxy disks. This favors NSC formation from
material in the disk – either from gas accretion followed by in situ star
formation, or by formation and inspiral of young star clusters (e.g. Seth et
al., 2006; Agarwal & Milosavljević, 2011; Tsatsi et al., 2017), and is
consistent with strong rotation seen in many NSCs (Pinna et al., 2021). It
disfavors NSC formation from inspiral of a more spherical distribution of
globular clusters (e.g. Tremaine et al., 1975; Hartmann et al., 2011). This
result is in agreement with previous work that suggests NSC formation is
dominated by in situ star formation in more massive galaxies
(log($M_{\star}/M_{\odot}$)$\gtrsim$9) like those in the CBS sample (Neumayer
et al., 2020; Fahrion et al., 2021, 2022a).

Figure 9: The NSC mass plotted against the photometric bulge to total ratio
(top panel) and the bar luminosity (bottom panel). The markings are the same
as in figure 4. Figure 10: The ratio of black hole mass to NSC mass is plotted
against the host galaxy mass (left panel) and against the NSC mass (right
panel) based on plots from Neumayer et al. (2020) but adding in data with new
NSC masses from our sample. The circles denote our NSC sample galaxies, with
surrounding squares indicating the MW-like subsample. Open circles indicate
uncertain measurements due to dust (i.e., quality flag = 2 in Table 3). The
points are colored red or blue based on their Hubble type (Early- and Late-
type respectively). Literature sample from Early- (red stars) and Late- (Blue
stars) type galaxies are obtained from Seth et al. (2008a); Graham & Spitler
(2009); Neumayer & Walcher (2012); Georgiev et al. (2016); Nguyen et al.
(2018). Literature results with upper and lower limits for the BH and NSC
masses are represented by the arrows. The solid horizontal line indicates
equal NSC and BH masses in the galaxies.

###  5.2 Correlations of NSC Mass with Host Galaxy Properties

Previous studies have found scaling relations between the mass of the NSC and
its host galaxy properties. This includes scaling relations with bulge
luminosity, velocity dispersion, and total stellar mass (e.g., Ferrarese et
al., 2006; Wehner & Harris, 2006; Rossa et al., 2006). Initially, the NSC
scaling relations were found to be similar to the BH scaling relations, but
recent studies with more data over wider ranges of host galaxy properties have
shown that, unlike BH scaling relations, the NSC mass correlates better with
galaxy mass than bulge mass or stellar velocity dispersionf, and does not
follow the same scaling relations (e.g., Erwin & Gadotti, 2012; Georgiev et
al., 2016; Sánchez-Janssen et al., 2019).

In Figure 8, we plot the NSCs mass against their host galaxy stellar mass. We
observe that the bulk of our galaxies fall among the highest NSC masses as
expected given their high galaxy stellar mass. All the NSCs in our sample have
masses $>10^{6}M_{\sun}$, with a median mass of $4.2\times 10^{7}M_{\sun}$.
The typical masses fall along the relation for late-type galaxies from
Georgiev et al. (2016), with a tight cluster of points around the median
sample mass. However there is also a very large, $>$2 order of magnitude
spread in the NSC mass, with several significant low outliers including NGC
3351 ($\log M_{\star}=10.56$ and $\log M_{\mathrm{NSC}}=6.16$) and NGC 6744
($\log M_{\star}=11.07$ and $\log M_{\mathrm{NSC}}=7.01$) and the very compact
NSC in NGC 2775 ($\log M_{\star}=10.98$ and $\log M_{\mathrm{NSC}}=6.98$).
This broad range of masses suggests a wide range of formation and evolutionary
processes in the NSCs in these massive (mostly late-type) galaxies. As noted
in Section 4.1, the nucleation fraction in our NSC sample is much higher than
the nucleation fraction of early-type galaxies with similar mass (Côté et al.,
2006; Neumayer et al., 2020), where binary BH mergers might have destroyed
NSCs (e.g. Milosavljević & Merritt, 2001). With the ongoing formation of NSCs
in late-type galaxies (e.g. Walcher et al., 2006; Rossa et al., 2006), the
absence of an NSC after a binary BH merger would likely be short-lived and the
existence of low mass outliers may trace galaxies where NSCs have been
destroyed in the relatively recent past. The compact radii ($<5$ pc) of two of
these clusters may be due to the reformation resulting in more compact NSCs;
recent star formation is seen to be centrally concentrated in nearby NSCs
including the Milky Way (Feldmeier-Krause et al., 2015), M31 (Lauer et al.,
2012), and other nearby late-type NSCs (Carson et al., 2015).

####  5.2.1 Bulge and Bar Relations

Given that NSCs are located in the centers of galaxies, it is interesting to
understand how they relate with the bulge and bar components in their hosts.
Understanding this relationship might provide insights into their formation
mechanism. In this section, we discuss in detail the correlations of the NSC
mass with the fraction of light in the photometric bulge and the luminosity of
the bar components hosted by our sample of galaxies. In Figure 9, we plot the
NSC mass against the photometric bulge to total ($B/T$) light ratio (top
panel) and the bar luminosities (bottom panel). We define the photometric
bulge to consist of all the components (including the NSCs) except the bar and
the disk. We determine the luminosity of the bar components in the galaxy,
integrating the flux of the bar and the boxy-peanut bulge components (we note
that 8/26 of the galaxies with NSCs lack bar components and are not included).
Also, since we do not model the disk in NGC 1300 and NGC 5248, we exclude
these galaxies from the top panel in the figure.

We find no correlation between the NSC mass and the photometric $B/T$ ratio in
our sample. This indicates that the bulges in galaxies appear to be
uncorrelated with the formation of the NSCs. Similarly, we do not see any
correlation between the NSC mass and the bar luminosities.

###  5.3 NSC-Black Hole relations

NSCs and BH are found to co-exist in many massive galaxies ($>$
10${}^{9}M_{\sun}$, e.g. Seth et al., 2008a; González Delgado et al., 2008).
Early studies of scaling relations and the relative masses of these quantities
suggested there may be a transition between NSCs dominating the nuclear mass
in low mass galaxies and BHs dominating in higher mass galaxies (Ferrarese et
al., 2006; Wehner & Harris, 2006; Graham & Spitler, 2009). The recent
compilation of co-existing BH and NSC mass measurements in Neumayer et al.
(2020) shows a clear trend where NSCs are typically more massive than BHs in
lower-mass galaxies, while the opposite is true in higher mass galaxies. NSCs
become less common in massive early-type galaxies ($>10^{10}M_{\sun}$). This
could be due to the dynamical impact of binary BH mergers (e.g. Milosavljević
& Merritt, 2001; Antonini et al., 2015). However, the trend in NSC/BH mass is
not a simple one – This large scatter can be seen in the very different
relative masses of the BHs and NSCs in the Milky Way (where the NSC is
$\sim$10$\times$ the BH mass) and M31 (where the opposite is true).
Unfortunately, a lack of NSC mass measurements in massive spiral galaxies has
limited our ability to make this comparison more widely for MW-like galaxies.

From our galaxies with good NSC measurements, 4 galaxies have black hole mass
measurements available in the Saglia et al. (2016) compilation (NGC 3368, NGC
3412, NGC 4501, and NGC 4699). In Figure 10 we show the ratio of BH and NSC
mass of these galaxies against their host galaxy stellar mass (left panel) and
the NSC mass (right panel) added to the data from Neumayer et al. (2020). The
solid line in the figure represents equal NSC and BH mass. The objects above
this line (including our measurement for the very massive late-type galaxy NGC
4699) have a more massive BH than NSC. Our measurement confirm that there are
a wide range of BH to NSC mass ratios in massive galaxies.

##  6 Conclusions

In this paper, we have presented the photometric and morphological analyses of
nuclear star clusters in 33 nearby galaxies from the Composite Bulges Survey.
This includes a subsample of 20 MW-like galaxies with spiral morphologies (T =
1–4) and stellar mass from $10^{10.4}M_{\sun}$ to $10^{11.1}M_{\sun}$. This
MW-like subsample is a complete volume-limited sample of galaxies similar to
the Milky Way that also meet the distance ($<20$ Mpc), inclination (35 to
60∘), and Galactic latitude ($|b|>20^{\circ}$) criteria of the complete CBS
sample.

Using imfit, we obtain accurate models for the nuclear regions of the
galaxies. We model the NSCs using Sérsic profiles in three HST filters and
derive their sizes, colors, and masses. We present the Sérsic profile fit
parameters of the NSCs in Table 2 and their derived properties in Table 3.

Our main results are:

  * •

We clearly identify NSCs in 78.8${}_{-7.9}^{+6.2}$% of our 33 galaxies, and
68.4${}_{-11.4}^{+9.5}$% for the MW-like subsample. NSCs may be present in
other galaxies, but are missed due to dust or AGN, thus these nucleation
fractions are lower limits. This work significantly expands the number of
nucleated galaxies known in higher mass, late-type galaxies. The nucleation
fractions are higher than, but consistent within the errors of the
determination in Neumayer et al. (2020).

  * •

We calculated the mass of our NSCs using color-$M/L$ relations, and find a
median mass of NSCs in our galaxies of $\log(M_{\mathrm{NSC}}/M_{\sun})=7.16$.

  * •

Our NSCs are consistent with the mass-radius relationship of literature NSCs
(Figure. 5). They also follow the galaxy stellar mass-NSC mass relation for
late-type galaxies from Georgiev et al. (2016), significantly expanding the
sample of NSCs at the high mass end (Figure. 8).

  * •

We find a large scatter in NSC mass over a small range of galaxy mass, with
two prominent low-mass outliers. These outliers also have small radii,
suggesting a possible difference in NSC formation mechanism or evolution.

  * •

Our NSCs are preferentially aligned with but are less flattened than their
host galaxy disks. This alignment suggests these NSCs are forming either from
gas accretion or star clusters inspiraling from the disk due to dynamical
friction.

  * •

Our NSCs do not show any correlation with the bar luminosity or photometric
$B/T$ ratios.

  * •

We add four more galaxies to the small number of galaxies with known NSC and
BH masses. One has a BH $\sim 10$ times the mass of the NSC, while the others
have NSCs that greatly exceed their BH masses. This confirms that massive
galaxies have a wide range of NSC-to-BH mass ratios.

ACKNOWLEDGEMENTS
We would like to thank David Ohlson for sharing his galaxy catalog with us
pre-publication. We would also like to thank Luis Ho for providing us with
optical images from the Carnegie-Irvine Galaxy Survey and Preben Grosbøl for
providing us with near-IR images from Grosbøl & Dottori (2012).

This research is based on observations made with the NASA/ESA Hubble Space
Telescope obtained from the Space Telescope Science Institute, which is
operated by the Association of Universities for Research in Astronomy, Inc.,
under NASA contract NAS 5–26555. These observations are associated with
program HST-GO-15133. Support for this work was provided from that program.
J.M.A. acknowledges the support of the Viera y Clavijo Senior program funded
by ACIISI and ULL. This work is based in part on observations made with the
Spitzer Space Telescope, which was operated by the Jet Propulsion Laboratory,
California Institute of Technology under a contract with NASA. It has also
made use of the NASA/IPAC Extragalactic Database (NED), which is operated by
the Jet Propulsion Laboratory, California Institute of Technology, under
contract with the National Aeronautics and Space Administration. We also made
use of data from the Sloan Digital Sky Survey.

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##  Appendix A AGN detections in the NSC sample of galaxies

Table 4: Nuclear Classification & AGN Table

Name | Nuclear Class | AGN Source | log($L_{X}$ [ergs/s]) | Notes
---|---|---|---|---
NGC0289 |  |  |  |
NGC0613 | S? | 2 |  |
NGC1097 | L/S1 | 2 | 40.96 | (a)
NGC1300 | T | 2 | 40.12 |
NGC1440 |  |  |  |
IC2051 |  |  |  |
NGC1566 | S1.2 | 3 | 41.1-42.5 | (b)
NGC2775 |  |  |  |
NGC3351 (M95) | H | 1 |  |
NGC3368 (M96) | L2 | 1 |  |
NGC3412 | A | 1 |  |
NGC4643 | T2 | 1 |  |
NGC4699 |  |  |  |
NGC5121 |  |  |  |
NGC5248 | H | 1 | 38.32 |
NGC5364 | H | 1 |  |
NGC6744 |  |  |  |
NGC7513 |  |  |  |
NGC4237 |  |  |  |
NGC4321 (M100) | T2 | 1 |  |
NGC4377 |  |  |  |
NGC4380 | H | 1 |  |
NGC4450 | L1.9 | 1 | 40.55 |
NGC4501 (M88) | S2 | 1 | 40.16 |
NGC4528 |  |  |  |
NGC4531 |  |  |  |
NGC4548 (M91) | L2 | 1 | 39.93 |
NGC4578 | A | 2 |  |
NGC4579 (M58) | S1.9/L1.9 | 1 | 41.61 |
NGC4608 |  |  |  |
NGC4612 | A | 1 |  |
NGC4689 | H | 1 |  |
NGC4698 | S2 | 1 | 38.93 |

Note. — Nuclear class gives nuclear classifications based on optical spectra:
L=LINER, S=Seyfert A=Absorption, H=HII, and T=Transition spectrum, and number
indicates Type 1 (broad line) or Type 2 (narrow line). AGN Source provides the
reference of the AGN nuclear classification: (1) Ho et al. (1997), (2)
compiled by Bi et al. (2020), (3) Alloin et al. (1985). The log($L_{X}$
[ergs/s]) give 2-10 keV X-ray luminosities; all are from Bi et al. (2020)
rescaled to the distances for each galaxy used in this paper except where
noted. Notes: (a) changing look AGN including change from LINER to Seyfert
Storchi-Bergmann et al. (1993), classified as L1 in Bi et al. (2020), (b)
X-ray fluxes varying values from (Liu et al., 2022), changing look AGN (e.g.
da Silva et al., 2017).

##  Appendix B Common Components Used in Our imfit Modeling

Below we list the most frequently used components used in our imfit fits.

  * •

FlatSky – a uniform sky background (as discussed in section 3.1).

  * •

Exponential – an elliptical 2D exponential function. We use this primarily for
fitting the disk and other highly elliptical components.

  * •

BrokenExponential – two exponential zones having different scale lengths
joined by a transition region of variable sharpness. We use this for fitting
the outer disk component in some galaxies.

  * •

GaussianRing – an elliptical ring with a radial profile consisting of a
Gaussian function. We use this to ring or pseudoring features, such as nuclear
rings.

  * •

FlatBar – this is meant to represent the outer parts of bars, with a major-
axis broken-exponential profile and a single-exponential minor-axis profile;
it is described further in Erwin et al. (2021).

  * •

Sersic_GenEllipse – an elliptical 2D Sérsic function using generalized
ellipses (“boxy” to “disky” shapes). We use this to fit boxy-shaped bulge
features.

  * •

Sersic – an elliptical 2D Sérsic function. We use this to fit NSC and the
(non-boxy) bulge features.

  * •

PointSource – a scaled representation of the image PSF, used primarily to
model unresolved AGN emission.

We provide detailed notes on each galaxy in the next section, including a
handful of additional components other than these listed here.

##  Appendix C Detailed notes on individual galaxy decomposition from the NSC
sample

In this section, we describe the components of the best-fitting models for
each galaxy in the NSC sample. The models are obtained in the primary band
filter provided in Table 2 (column 3). For each component, we provide our best
interpretation of what kind of structure it is, the imfit image function used
(in brackets), and then the best-fit parameter values. The ordering generally
reflects an inside-out description. Note that bar “spurs” refers to the outer,
more elongated part of a bar, outside of the B/P-bulge part of the bar (see,
e.g. Erwin & Debattista, 2013; Erwin et al., 2021).
IC 2051

  * •

NSC [Sersíc] (PA=17.0, $\epsilon$=0.18, n=2.65, $\mu_{e}$=14.60,
$r_{e}$=0.39″)

  * •

Nuclear disk(?) [Sersíc] (PA=22.3, $\epsilon$=0.40, n=0.98, $\mu_{e}$=15.95,
$r_{e}$=2.98″)

  * •

B/P bulge [Sersíc$\\_$GenEllipse] (PA=27.4, $\epsilon$=0.40, n=1.44,
$\mu_{e}$=18.22, $r_{e}$=7.06″)

  * •

Bar spurs [FlatBar] (PA=144.7, $\epsilon$=0.63, $\mu_{0}$=17.11, Rbrk=19.6″)

  * •

Inner ring [GaussianRingAZ] (PA=12.0, $\epsilon$=0.29, Amaj=19.15, Amin-
rel=27.34, $R_{ring}$=28.10″, $\sigma_{r}$=6.44″)

  * •

Outer disk [BrokenExponential] (PA=23.3, $\epsilon$=0.45, $\mu_{0}$=19.15,
Rbrk=60.17″)

NGC 289
We do not trust the NSC measurements for this galaxy due to strong dust lanes
obscuring the NSC, as mentioned in Section 3.4. Hence, we do not provide the
best-fit models for this galaxy.

NGC 613
The NSC in this galaxy is unresolved (see section 4.1). For the purpose of
determining the NSC properties, we provide a Sersíc component fit. Note that
the FlatBar component is offset by $\sim 1\arcsec$ from the other components.

  * •

NSC [Sersíc] (PA=0, $\epsilon$=0.0, n=0.5, $\mu_{e}$=11.53, $r_{e}$=0.03″)

  * •

Classical bulge(?) [Sersíc] (PA=144.3, $\epsilon$=0.11, n=0.79,
$\mu_{e}$=14.88, $r_{e}$=0.71″)

  * •

Nuclear disk [Exponential] (PA=151, $\epsilon$=0.32, $\mu_{0}$=13.94, h=3.23″)

  * •

B/P bulge [Sersíc$\\_$GenEllipse] (PA=160, $\epsilon$=0.32, n=0.2,
$\mu_{e}$=18.90, $r_{e}$=16.4″)

  * •

Bar spurs [FlatBar] (PA=162, $\epsilon$=0.92, $\mu_{0}$=17.70, Rbrk=51.64″)

  * •

Outer disk [Exponential] (PA=154, $\epsilon$=0.41, $\mu_{0}$=17.93, h=47.06″)

NGC 1097

  * •

NSC [Sersíc] (PA=117.1, $\epsilon$=0.16, n=3.23, $\mu_{e}$=13.20,
$r_{e}$=0.21″)

  * •

Inner-bar B/P bulge [Sersíc] (PA=178.1, $\epsilon$=0.05, n=1.09,
$\mu_{e}$=15.32, $r_{e}$=3.08″)

  * •

Inner-bar spurs [FlatBar] (PA=86.3, $\epsilon$=0.62, $\mu_{0}$=15.00,
Rbrk=6.39″

  * •

Nuclear ring [GaussianRing] (PA=29.7, $\epsilon$=0.18, A=15.91,
$R_{ring}$=10.19″, $\sigma_{r}$=0.89″)

  * •

Nuclear disk [BrokenExponential] (PA=10.4, $\epsilon$=0.20, $\mu_{0}$=16.61,
Rbrk=12.93″)

  * •

Outer-bar B/P bulge [Sersíc] (PA=11.1, $\epsilon$=0.29, n=0.38,
$\mu_{e}$=18.21, $r_{e}$=27.72″)

  * •

Outer-bar spurs [FlatBar] (PA=26.3, $\epsilon$=0.92, $\mu_{0}$=17.75,
Rbrk=73.74″)

NGC 1300

  * •

NSC [Sersíc] (PA=59.9, $\epsilon$=0.15, n=1.53, $\mu_{e}$=14.49,
$r_{e}$=0.09″)

  * •

Classical bulge(?) [Sersíc] (PA=90.3, $\epsilon$=0.11, n=0.49,
$\mu_{e}$=16.37, $r_{e}$=0.40″)

  * •

Nuclear disk [Exponential] (PA=83.7, $\epsilon$=0.12, $\mu_{e}$=15.65,
h=1.56″)

  * •

Nuclear Ring [GaussianRing2Side] (PA=86.7, $\epsilon$=0.16, Amin=19.35,
Amaj=13.60, $R_{ring}$=3.86″, $\sigma_{r-in}$=0.27″, $\sigma_{r-out}$=1.64″)

  * •

B/P Bulge [Sersíc$\\_$GenEllipse] (PA=86.7, $\epsilon$=0.42, n=0.78,
$\mu_{e}$=20.19, $r_{e}$=25.13″)

  * •

Bar spurs [FlatBar] (PA=90.9, $\epsilon$=0.91, $\mu_{0}$=23.82, Rbrk=80.43″)

NGC 1440
The NSC in this galaxy is unresolved (see section 4.1). For the purpose of
determining the NSC properties, we provide a Sersíc component fit.

  * •

NSC [Sersíc] (PA=0, $\epsilon$=0.0, n=3.48, $\mu_{e}$=15.34, $r_{e}$=0.05″)

  * •

Classical bulge(?) [Sersíc] (PA=112.2, $\epsilon$=0.13, n=2.13,
$\mu_{e}$=17.28, $r_{e}$=1.73″)

  * •

Nuclear disk [Sersíc] (PA=106.9, $\epsilon$=0.19, n=64, $\mu_{e}$=18.02,
$r_{e}$=1.96″)

  * •

B/P bulge [Sersíc] (PA=120.0, $\epsilon$=0.16, n=41, $\mu_{e}$=18.51,
$r_{e}$=6.34″)

  * •

Bar spurs [FlatBar] (PA=140.9, $\epsilon$=0.77, $\mu_{0}$=18.60, Rbrk=18.245″)

  * •

Main disk [BrokenExponential] (PA=108.1, $\epsilon$=0.23, $\mu_{0}$=19.93,
Rbrk=36.85″)

NGC 1566
Due to significant nuclear saturation in all bands, we do not provide fits for
this galaxy (see section 3.4).

NGC 2775

  * •

NSC [Sersíc] (PA=0, $\epsilon$=0.0, n=0.52, $\mu_{e}$=14.51, $r_{e}$=0.04″)

  * •

Classical bulge(?) [Sersíc] (PA=23.8, $\epsilon$=0.12, n=2.81,
$\mu_{e}$=18.20, $r_{e}$=6.05″)

  * •

Outer bulge [Sersíc] (PA=26.5, $\epsilon$=0.12, n=1.06, $\mu_{e}$=19.34,
$r_{e}$=17.12″)

  * •

Ring [GaussianRing] (PA=24.0, $\epsilon$=0.21, A=22.03, $R_{ring}$=31.51″,
$\sigma_{r}$=17.81″)

  * •

Main disk [Exponential] (PA=31.7, $\epsilon$=0.22, $\mu_{0}$=19.14, h=42.59″)

NGC 3351

  * •

NSC [Sersíc] (PA=0, $\epsilon$=0.0, n=0.8, $\mu_{e}$=15.56, $r_{e}$=0.09″)

  * •

Classical bulge(?) [Sersíc] (PA=58.1, $\epsilon$=0.32, n=0.42,
$\mu_{e}$=16.85, $r_{e}$=0.75″)

  * •

Nuclear disk + ring [BrokenExponential] (PA=33.3, $\epsilon$=0.12,
$\mu_{0}$=16.88, Rbrk=6″)

  * •

B/P bulge [Sersíc$\\_$GenEllipse] (PA=46.1, $\epsilon$=0.28, n=0.89,
$\mu_{e}$=18.89, $r_{e}$=14.58″)

  * •

Bar spurs [FlatBar] (PA=142.8, $\epsilon$=0.74, $\mu_{0}$=19.02, Rbrk=41.18″)

  * •

Inner ring [GaussianRing] (PA=20.4, $\epsilon$=0.14, A=20.03,
$R_{ring}$=59.92″, $\sigma_{r}$=15.70″)

  * •

Main disk [BrokenExponential] (PA=41, $\epsilon$=0.27, $\mu_{0}$=21.25,
Rbrk=141.6″)

NGC 3368

  * •

NSC [Sersíc] (PA=81.7, $\epsilon$=0.16, n=2.21, $\mu_{e}$=14.29,
$r_{e}$=0.204″)

  * •

Classical bulge(?) or inner-bar B/P bulge [Sersíc] (PA=27.6, $\epsilon$=0.33,
n=0.21, $\mu_{e}$=15.86, $r_{e}$=0.93″)

  * •

Inner-bar spurs [Sersíc$\\_$GenEllipse] (PA=141, $\epsilon$=0.61, n=0.31,
$\mu_{e}$=16.69, $r_{e}$=3.41″)

  * •

Nuclear disk [Sersíc] (PA=2.8, $\epsilon$=0.22, n=0.33, $\mu_{e}$=17.13,
$r_{e}$=5.42″)

  * •

B/P bulge [Sersíc$\\_$GenEllipse] (PA=-1.8, $\epsilon$=0.28, n=1.73,
$\mu_{e}$=18.98, $r_{e}$=30.52″)

  * •

SE outer-bar spur [Sersíc] (PA=9.7, $\epsilon$=0.54, n=0.70, $\mu_{e}$=21.39,
$r_{e}$=37.56″)

  * •

NW outer-bar spur [Sersíc] (PA=5.6, $\epsilon$=0.48, n=0.73, $\mu_{e}$=22.69,
$r_{e}$=32.76″)

  * •

Disk [BrokenExponential] (PA=13.9, $\epsilon$=0.36, $\mu_{0}$=20.48,
Rbrk=178.65″)

NGC 3412

  * •

NSC [Sersíc] (PA=149.0, $\epsilon$=0.31, n=1.78, $\mu_{e}$=13.38,
$r_{e}$=0.12″)

  * •

Classical bulge(?) [Sersíc] (PA=151.0, $\epsilon$=0.36, n=1.05,
$\mu_{e}$=15.37, $r_{e}$=0.95″)

  * •

Inner elliptical (counter-rotating) component [Sersíc$\\_$GenEllipse]
(PA=148.9, $\epsilon$=0.29, n=0.87, $\mu_{e}$=16.35, $r_{e}$=2.68″)

  * •

B/P bulge [Sersíc$\\_$GenEllipse] (PA=137.2, $\epsilon$=0.22, n=0.56,
$\mu_{e}$=18.75, $r_{e}$=5.46″)

  * •

Bar spurs [Sersíc$\\_$GenEllipse] (PA=106.6, $\epsilon$=0.30, n=0.51,
$\mu_{e}$=18.63, $r_{e}$=10.79″)

  * •

Disk [BrokenExponential] (PA=150.2, $\epsilon$=0.50, $\mu_{0}$=19.81,
Rbrk=69.41″)

  * •

Halo [Sersíc] (PA=144.6, $\epsilon$=0.34, n=0.64, $\mu_{e}$=22.28,
$r_{e}$=57.78″)

NGC 4237

  * •

NSC [Sersíc] (PA=132.7, $\epsilon$=0.12, n=4.42, $\mu_{e}$=17.56,
$r_{e}$=0.21″)

  * •

Bulge [Sersíc] (PA=121.0, $\epsilon$=0.27, n=0.75, $\mu_{e}$=18.46,
$r_{e}$=1.92″)

  * •

Disk [Exponential] (PA=121.3, $\epsilon$=0.40, $\mu_{0}$=17.95, h=14.81″)

NGC 4377

  * •

NSC [Sersíc] (PA=10.2, $\epsilon$=0.21, n=5.73, $\mu_{e}$=13.60,
$r_{e}$=0.02″)

  * •

Classical bulge [Sersíc] (PA=47.4, $\epsilon$=0.13, n=1.62, $\mu_{e}$=16.10,
$r_{e}$=0.74″)

  * •

B/P Bulge [Sersíc$\\_$GenEllipse] (PA=13.1, $\epsilon$=0.16, n=1.27,
$\mu_{e}$=16.78, $r_{e}$=2.61″)

  * •

Bar spurs [FlatBar] (PA=1.4, $\epsilon$=0.81, $\mu_{0}$=18.80, Rbrk=6.91″)

  * •

Outer ring [GaussianRing] (PA=39.8, $\epsilon$=0.14, A =23.12,
$R_{ring}$=20.12″, $\sigma_{r}$=5.70″)

  * •

Disk [Exponential] (PA=30.8, $\epsilon$=0.19, $\mu_{0}$=18.20, h=10.89″)

NGC 4380

  * •

NSC [Sersíc] (PA=166.7, $\epsilon$=0.18, n=7.0, $\mu_{e}$=16.59,
$r_{e}$=0.35″)

  * •

Classical bulge(?) [Sersíc] (PA=177.1, $\epsilon$=0.21, n=1.73,
$\mu_{e}$=17.55, $r_{e}$=2.46″)

  * •

Inner ring [GaussianRing] (PA=173.9, $\epsilon$=0.46, A =19.05,
$R_{ring}$=12.15″, $\sigma_{r}$=6.47″)

  * •

Inner disk(?) [Sersíc] (PA=174.2, $\epsilon$=0.42, n=0.5, $\mu_{e}$=17.63,
$r_{e}$=5.50″)

  * •

Outer ring [GaussianRing] (PA=169.2, $\epsilon$=0.43, A =20.56,
$R_{ring}$=27.42″, $\sigma_{r}$=3.87″)

  * •

Main disk [BrokenExponential] (PA=173.3, $\epsilon$=0.47, $\mu_{0}$=18.60,
Rbrk=71.48″)

NGC 4450

  * •

NSC [Sersíc] (PA=0, $\epsilon$=0.0, n=4.95, $\mu_{e}$=15.73, $r_{e}$=0.19″)

  * •

Classical bulge(?) or inner-bar B/P bulge [Sersíc] (PA=86.7, $\epsilon$=0.21,
n=1.21, $\mu_{e}$=16.06, $r_{e}$=0.64″)

  * •

Inner bar (spurs?) [Sersíc] (PA=46.5, $\epsilon$=0.12, n=0.89,
$\mu_{e}$=17.07, $r_{e}$=1.62″)

  * •

Nuclear ring [GaussianRing] (PA=168.6, $\epsilon$=0.43, A =18.99,
$R_{ring}$=3.54″, $\sigma_{r}$=1.01″)

  * •

Nuclear disk [Exponential] (PA=81.8, $\epsilon$=0.22, $\mu_{0}$=16.34,
h=3.24″)

  * •

Outer-bar B/P bulge [Sersíc$\\_$GenEllipse] (PA=87.1, $\epsilon$=0.35, n=1.0,
$\mu_{e}$=19.53, $r_{e}$=28.30″)

  * •

N outer-bar spur [Sersíc$\\_$GenEllipse] (PA=49.4, $\epsilon$=0.37, n=0.85,
$\mu_{e}$=22.71, $r_{e}$=22.34″)

  * •

S outer-bar spur [Sersíc$\\_$GenEllipse] (PA=51.7, $\epsilon$=0.38, n=1.0,
$\mu_{e}$=22.43, $r_{e}$=31.0″)

  * •

Disk [BrokenExponential] (PA=166.0, $\epsilon$=0.33, $\mu_{0}$=21.11,
Rbrk=108.27″)

NGC 4501

  * •

NSC [Sersíc] (PA=144.2, $\epsilon$=0.22, n=1.58, $\mu_{e}$=13.33,
$r_{e}$=0.38″)

  * •

Bulge [Sersíc] (PA=135.9, $\epsilon$=0.33, n=3.02, $\mu_{e}$=16.93,
$r_{e}$=10.67″)

  * •

Disk [Exponential] (PA=140.4, $\epsilon$=0.51, $\mu_{0}$=16.24, h=41.17″)

NGC 4531

  * •

NSC [Sersíc] (PA=39.5, $\epsilon$=0.05, n=4.36, $\mu_{e}$=16.59,
$r_{e}$=0.15″)

  * •

Unclear [Exponential] (PA=71.1, $\epsilon$=0.73, $\mu_{0}$=21.29, h=10.18″)

  * •

Inner disk/pseudobulge(?) [Sersíc] (PA=152.1, $\epsilon$=0.23, n=1.24,
$\mu_{e}$=21.06, $r_{e}$=15.06″)

  * •

Ring [GaussianRing] (PA=24.3, $\epsilon$=0.22, A =21.92, $R_{ring}$=17.98″,
$\sigma_{r}$=2.83″)

  * •

Disk [Exponential] (PA=14.8, $\epsilon$=0.46, $\mu_{0}$=19.27, h=29.62″)

NGC 4548

  * •

NSC [Sersíc] (PA=0, $\epsilon$=0.20, n=2.47, $\mu_{e}$=14.35, $r_{e}$=0.25″)

  * •

Inner-bar B/P bulge(?) [Sersíc] (PA=157.1, $\epsilon$=0.03, n=0.60,
$\mu_{e}$=15.86, $r_{e}$=0.62″)

  * •

Inner bar [Sersíc] (PA=132.7, $\epsilon$=0.30, n=0.50, $\mu_{e}$=17.60,
$r_{e}$=2.01″)

  * •

Nuclear disk [Sersíc] (PA=158.2, $\epsilon$=0.12, n=1.0, $\mu_{e}$=18.19,
$r_{e}$=5.66″)

  * •

Outer-bar B/P bulge [Sersíc] (PA=113.5, $\epsilon$=0.15, n=0.37,
$\mu_{e}$=19.76, $r_{e}$=16.90″)

  * •

Outer-bar spurs [FlatBar] (PA=97.7, $\epsilon$=0.80, $\mu_{0}$=20.42,
Rbrk=41.16″)

  * •

W spiral arm [LogSpiralBrokenExp] (PA=0, $\epsilon$=0, $R_{i}$=124.38″,
$\sigma_{az}$=17.81″, $\mu_{max}$=19.78, $r_{b}$=108.97″, $R_{max}$=70.13″,
$\sigma_{trunc}$=56.99″)

  * •

E spiral arm [LogSpiralBrokenExp] (PA=163.0, $\epsilon$=0.14, $R_{i}$=115.95″,
$\sigma_{az}$=29.31″, $\mu_{max}$=19.67, $r_{b}$=134.24″, $R_{max}$=70.13″,
$\sigma_{trunc}$=14.32″)

  * •

Disk [BrokenExponential] (PA=173.0, $\epsilon$=0.21, $\mu_{0}$=20.33,
Rbrk=116.09″)

NGC 4578

  * •

NSC [Sersíc] (PA=42.0, $\epsilon$=0.14, n=2.76, $\mu_{e}$=14.89,
$r_{e}$=0.15″)

  * •

Classical bulge [Sersíc] (PA=64.8, $\epsilon$=0.23, n=2.47, $\mu_{e}$=18.39,
$r_{e}$=4.96″)

  * •

Nuclear ring [GaussianRing] (PA=62.3, $\epsilon$=0.27, A =18.50,
$R_{ring}$=0.75″, $\sigma_{r}$=3.74″)

  * •

Outer ring [GaussianRing] (PA=64.9, $\epsilon$=0.31, A =21.88,
$R_{ring}$=44.99″, $\sigma_{r}$=27.51″)

  * •

Disk [Exponential] (PA=62.5, $\epsilon$=0.32, $\mu_{0}$=18.46, h=12.92″)

NGC 4579

  * •

NSC [Sersíc] (PA=95.0, $\epsilon$=0.30, n=1.54, $\mu_{e}$=10.52,
$r_{e}$=0.07″)

  * •

Classical bulge or nuclear disk [Sersíc] (PA=118.2, $\epsilon$=0.19, n=2.49,
$\mu_{e}$=15.53, $r_{e}$=5.18″)

  * •

B/P Bulge [Sersíc] (PA=93.7, $\epsilon$=0.36, n=0.78, $\mu_{e}$=18.53,
$r_{e}$=20.78″)

  * •

Bar spurs [FlatBar] (PA=86.3, $\epsilon$=0.90, $\mu_{0}$=17.33, Rbrk=30.13″)

  * •

Disk [Exponential] (PA=125.0, $\epsilon$=0.20, $\mu_{0}$=17.42, h=47.82″)

NGC 4608

  * •

NSC [Sersíc] (PA=164.0, $\epsilon$=0.13, n=1.19, $\mu_{e}$=13.80,
$r_{e}$=0.03″)

  * •

Classical bulge [Sersíc] (PA=105.7, $\epsilon$=0.05, n=2.75, $\mu_{e}$=18.96,
$r_{e}$=8.01″)

  * •

B/P bulge [Sersíc$\\_$GenEllipse] (PA=46.7, $\epsilon$=0.18, n=1.07,
$\mu_{e}$=19.42, $r_{e}$=11.40258″)

  * •

Bar spurs [FlatBar] (PA=44.9, $\epsilon$=0.87, $\mu_{0}$=19.40, Rbrk=40.71″)

  * •

Inner ring [GaussianRingAz] (PA=124.5, $\epsilon$=0.09, Amaj =20.46, Amin-
rel=22.07, $R_{ring}$=48.03″, $\sigma_{r}$=6.44″)

  * •

Disk [BrokenExponential] (PA=124.9, $\epsilon$=0.13, $\mu_{0}$=23.82,
Rbrk=69.78″)

NGC 4612
The NSC in this galaxy is fitted using a two-component model. The properties
of this NSC provided in Table 3 are integrated over the two NSC components
below.

  * •

Inner NSC [Sersíc] (PA=0, $\epsilon$=0.0, n=3.14, $\mu_{e}$=12.39,
$r_{e}$=0.03″)

  * •

Outer NSC [Exponential] (PA=23.25, $\epsilon$=0.22, $\mu_{0}$=14.05, h=0.14″)

  * •

Nuclear disk [Exponential] (PA=26.9, $\epsilon$=0.22, $\mu_{0}$=14.84,
h=1.16″)

  * •

B/P bulge [Exponential$\\_$GenEllipse] (PA=33.3, $\epsilon$=0.30,
$\mu_{0}$=17.90, h=5.01″)

  * •

Bar spurs [FlatBar] (PA=156.7, $\epsilon$=0.35, $\mu_{0}$=18.37, Rbrk=16.23″)

  * •

Inner ring [GaussianRing] (PA=21.9, $\epsilon$=0.40, A =21.69,
$R_{ring}$=28.02″, $\sigma_{r}$=8.13″)

  * •

Disk [BrokenExponential] (PA=15.7, $\epsilon$=0.27, $\mu_{0}$=20.02,
Rbrk=48.51″)

NGC 4643

  * •

NSC [Sersíc] (PA=0, $\epsilon$=0.0, n=0.76, $\mu_{e}$=14.37, $r_{e}$=0.04″)

  * •

Classical bulge(?) [Sersíc] (PA=96.6, $\epsilon$=0.11, n=0.69,
$\mu_{e}$=15.79, $r_{e}$=0.32″)

  * •

Nuclear disk [BrokenExponential] (PA=118.3, $\epsilon$=0.13, $\mu_{0}$=15.19,
Rbrk=2.99″)

  * •

B/P bulge [Sersíc] (PA=8.4, $\epsilon$=0.13, n=0.62, $\mu_{e}$=18.44,
$r_{e}$=12.92″)

  * •

Bar spurs [FlatBar] (PA=18.9, $\epsilon$=0.90, $\mu_{0}$=19.08, Rbrk=44.49″)

  * •

Disk [Exponential] (PA=124.6, $\epsilon$=0.18, $\mu_{0}$=20.55, h=81.27″)

NGC 4689
The precise structural/morphological nature of the 2nd–4th components in our
model is currently unclear, so we only refer to them as “inner components”.

  * •

NSC [Sersíc] (PA=0, $\epsilon$=0.0, n=2.85, $\mu_{e}$=15.33, $r_{e}$=0.06″)

  * •

Inner component 1 [Sersíc] (PA=13.4, $\epsilon$=0.22, n=0.70, $\mu_{e}$=19.91,
$r_{e}$=0.91″)

  * •

Inner component 2 [Sersíc] (PA=2.8, $\epsilon$=0.14, n=1.47, $\mu_{e}$=20.63,
$r_{e}$=6.74″)

  * •

Inner component 3 [Sersíc] (PA=79.6, $\epsilon$=0.13, n=0.88, $\mu_{e}$=20.63,
$r_{e}$=7.19″)

  * •

Ring [GaussianRing] (PA=66.5, $\epsilon$=0.30, A =21.81, $R_{ring}$=16.92″,
$\sigma_{r}$=2.97″)

  * •

Disk [Exponential] (PA=87.7, $\epsilon$=0.26, $\mu_{0}$=19.75, h=43.68″)

NGC 4698

  * •

NSC [Sersíc] (PA=76.6, $\epsilon$=0.48, n=1.39, $\mu_{e}$=15.61,
$r_{e}$=0.10″)

  * •

Orthogonal bulge [Sersíc] (PA=80.2, $\epsilon$=0.53, n=1.96, $\mu_{e}$=17.64,
$r_{e}$=2.36″)

  * •

Classical bulge(?) [Sersíc] (PA=171.3, $\epsilon$=0.08, n=3.10,
$\mu_{e}$=19.78, $r_{e}$=20.01″)

  * •

Inner ring [GaussianRing2Side] (PA=176.9, $\epsilon$=0.67, A=21.13,
$R_{ring}$=40.39″, $\sigma_{r-in}$=8.62″, $\sigma_{r-out}$=15.29″)

  * •

Outer ring [GaussianRing] (PA=178.9, $\epsilon$=0.67, A =22.86,
$R_{ring}$=64.25″, $\sigma_{r}$=3.41″)

  * •

Disk [BrokenExponential] (PA=176.5, $\epsilon$=0.63, $\mu_{0}$=22.10,
Rbrk=67.91″)

  * •

Halo [Sersíc] (PA=179.3, $\epsilon$=0.32, n=1.21, $\mu_{e}$=21.99,
$r_{e}$=54.79″)

NGC 4699

  * •

NSC [Sersíc] (PA=0, $\epsilon$=0.0, n=1.87, $\mu_{e}$=14.62, $r_{e}$=0.28″)

  * •

Classical bulge(?) [Sersíc] (PA=73.3, $\epsilon$=0.21, n=1.13,
$\mu_{e}$=14.79, $r_{e}$=1.52″)

  * •

B/P bulge [Sersíc$\\_$GenEllipse] (PA=73.2, $\epsilon$=0.39, n=0.43,
$\mu_{e}$=16.48, $r_{e}$=3.21″)

  * •

Bar spurs [Sersíc$\\_$GenEllipse] (PA=78.4, $\epsilon$=0.56, n=0.26,
$\mu_{e}$=17.49, $r_{e}$=7.93″)

  * •

NE bar ansa [Sersíc] (PA=8.1, $\epsilon$=0.38, n=0.88, $\mu_{e}$=19.13,
$r_{e}$=3.60″)

  * •

SW bar ansa [Sersíc] (PA=87.7, $\epsilon$=0.35, n=0.96, $\mu_{e}$=19.40,
$r_{e}$4.18″)

  * •

Inner disk [Exponential] (PA=67.5, $\epsilon$=0.26, $\mu_{0}$=16.29, h=12.58″)

  * •

Ring [GaussianRing2Side] (PA=67.7, $\epsilon$=0.38, A=21.17,
$R_{ring}$=49.39″, $\sigma_{r-in}$=2.38″, $\sigma_{r-out}$=18.04″)

  * •

Main disk [Exponential] (PA=57.8, $\epsilon$=0.14, $\mu_{0}$=20.14, h=67.34″)

NGC 5121

  * •

NSC [Sersíc] (PA=35.2, $\epsilon$=0.14, n=1.26, $\mu_{e}$=13.84,
$r_{e}$=0.07″)

  * •

Classical bulge(?) or nuclear-bar B/P bulge [Sersíc] (PA=111.1,
$\epsilon$=0.17, n=0.57, $\mu_{e}$=15.32, $r_{e}$=0.28″)

  * •

Nuclear bar [FlatBar] (PA=45.5, $\epsilon$=0.74, $\mu_{0}$=15.57, Rbrk=1.13″)

  * •

Nuclear disk [Exponential] (PA=57.1, $\epsilon$=0.12, $\mu_{0}$=14.27,
h=0.87″)

  * •

Outer-bar B/P bulge(?) [Sersíc$\\_$GenEllipse] (PA=84.2, $\epsilon$=0.03,
n=0.44, $\mu_{e}$=18.18, $r_{e}$=3.90″)

  * •

Outer-bar spurs(?) [Sersíc] (PA=51.3, $\epsilon$=0.25, n=0.21,
$\mu_{e}$=19.69, $r_{e}$=8.98″)

  * •

Disk [BrokenExponential] (PA=57.0, $\epsilon$=0.21, $\mu_{0}$=18.45,
Rbrk=36.23″)

NGC 5248

  * •

NSC [Sersíc] (PA=128.3, $\epsilon$=0.27, n=0.97, $\mu_{e}$=15.60,
$r_{e}$=0.41″)

  * •

Classical bulge(?) [Sersíc] (PA=156.2, $\epsilon$=0.30, n=0.38,
$\mu_{e}$=17.71, $r_{e}$=1.02″)

  * •

Nuclear disk [Exponential] (PA=125.5, $\epsilon$=0.32, $\mu_{0}$=16.34,
h=4.34″)

  * •

Boxy zone [Sersíc$\\_$GenEllipse] (PA=123.0, $\epsilon$=0.44, n=0.21,
$\mu_{e}$=20.20, $r_{e}$=18.75″)

  * •

N inner spiral [LogSpiralArc] (PA=0, $\epsilon$=0, r${}_{s}cale$=64.17,
$\mu_{max}$=20.39, $\sigma_{r}$=10.60″, $\sigma_{\theta_{c}cw}$=0.45″,
$\sigma_{\theta_{c}w}$=9.0″)

  * •

S inner spiral [LogSpiralArc] (PA=0 $\epsilon$=0, r${}_{s}cale$=52.55,
$\mu_{max}$=20.62, $\sigma_{r}$=11.23″, $\sigma_{\theta_{c}cw}$=1.96″,
$\sigma_{\theta_{c}w}$=3.19″)

  * •

Bar [Sersíc] (PA=157.4, $\epsilon$=0.36, n=1.0, $\mu_{e}$=21.44,
$r_{e}$=66.78″)

NGC 5364

  * •

NSC [Sersíc] (PA=0, $\epsilon$=0.16, n=3.52, $\mu_{e}$=17.36, $r_{e}$=0.21″)

  * •

Classical bulge(?) [Sersíc] (PA=55.4, $\epsilon$=0.26, n=0.65,
$\mu_{e}$=18.66, $r_{e}$=0.69″)

  * •

Pseudobulge(?) [Sersíc] (PA=28.3, $\epsilon$=0.17, n=1.0, $\mu_{e}$=19.90,
$r_{e}$=6.26″)

  * •

Ring [GaussianRing] (PA=70.1, $\epsilon$=0.49, A=21.84, $R_{ring}$=31.04″,
$\sigma_{r}$=9.39″)

  * •

Inner disk [Exponential] (PA=67.8, $\epsilon$=0.46, $\mu_{0}$=19.56, h=25.80″)

  * •

Outer disk [Exponential] (PA=28.6, $\epsilon$=0.32, $\mu_{0}$=20.49, h=59.47″)

NGC 6744

  * •

NSC [Sersíc] (PA=41.7, $\epsilon$=0.38, n=2.28, $\mu_{e}$=14.12,
$r_{e}$=0.25″)

  * •

Classical bulge [Sersíc] (PA=38.4, $\epsilon$=0.15, n=3.05, $\mu_{e}$=17.35,
$r_{e}$=7.18″)

  * •

B/P bulge [Sersíc$\\_$GenEllipse] (PA=31.6, $\epsilon$=0.38, n=0.89,
$\mu_{e}$=17.41, $r_{e}$=15.52″)

  * •

Bar spurs [Sersíc] (PA=25.6, $\epsilon$=0.74, n=0.64, $\mu_{e}$=19.33,
$r_{e}$=71.10″)

  * •

Disk [BrokenExponential] (PA=39.5, $\epsilon$=0.31, $\mu_{0}$=19.02,
Rbrk=99.73″)

NGC 7177
We do not trust the NSC measurements for this galaxy due to strong dust lanes
obscuring the NSC, as mentioned in Section 3.4. Hence, we do not provide the
best-fit models for this galaxy.

NGC 7513

  * •

NSC [Sersíc] (PA=150.0, $\epsilon$=0.0, n=5.92, $\mu_{e}$=19.29,
$r_{e}$=0.45″)

  * •

Classical bulge(?) [Sersíc] (PA=133.3, $\epsilon$=0.18, n=0.66,
$\mu_{e}$=19.98, $r_{e}$=1.97″)

  * •

B/P bulge [Sersíc$\\_$GenEllipse] (PA=151.4, $\epsilon$=0.26, n=0.96,
$\mu_{e}$=20.01, $r_{e}$=8.58″)

  * •

Bar spurs [FlatBar] (PA=145.5, $\epsilon$=0.92, $\mu_{0}$=19.39, Rbrk=30.31″)

  * •

Disk [BrokenExponential] (PA=3.4, $\epsilon$=0.33, $\mu_{0}$=21.08,
Rbrk=62.04″)