We present Hubble Space Telescope imaging of 14 gas-rich, low-surface-brightness galaxies in the field at distances of 25–36 Mpc, with mean effective radii and
We present our photometric search for potential nuclear star clusters (NSCs) in ultra-diffuse galaxies (UDGs) as an extension of the SMUDGes catalog. We identify 325 SMUDGes galaxies with NSCs and, from the 144 with existing distance estimates, identify 33 NSC hosts as UDGs (
- NSF-PAR ID:
- 10485941
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astronomical Journal
- Volume:
- 167
- Issue:
- 2
- ISSN:
- 0004-6256
- Format(s):
- Medium: X Size: Article No. 61
- Size(s):
- ["Article No. 61"]
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract g -band central surface brightnesses of 1.9 kpc and 24.2 mag arcsec−2. Nine meet the standard criteria to be considered ultra-diffuse galaxies (UDGs). An inspection of point-like sources brighter than the turnover magnitude of the globular cluster luminosity function and within twice the half-light radii of each galaxy reveals that, unlike those in denser environments, gas-rich, field UDGs host very few old globular clusters (GCs). Most of the targets (nine) have zero candidate GCs, with the remainder having one or two candidates each. These findings are broadly consistent with expectations for normal dwarf galaxies of similar stellar mass. This rules out gas-rich, field UDGs as potential progenitors of the GC-rich UDGs that are typically found in galaxy clusters. However, some in galaxy groups may be directly accreted from the field. In line with other recent results, this strongly suggests that there must be at least two distinct formation pathways for UDGs, and that this subpopulation is simply an extreme low surface brightness extension of the underlying dwarf galaxy population. The root cause of their diffuse stellar distributions remains unclear, but the formation mechanism appears to only impact the distribution of stars (and potentially dark matter), without strongly impacting the distribution of neutral gas, the overall stellar mass, or the number of GCs. -
more » « less
Abstract We present a catalog of 5598 ultra-diffuse galaxy (UDG) candidates with effective radius
r e > 5.″3 distributed throughout the southern portion of the DESI Legacy Imaging Survey covering ∼15,000 deg2. The catalog is most complete for physically large (r e > 2.5 kpc) UDGs lying in the redshift range 1800 ≲cz /km s−1≲ 7000, where the lower bound is defined by where incompleteness becomes significant for large objects on the sky and the upper bound by our minimum angular size selection criterion. Because physical size is integral to the definition of a UDG, we develop a method of distance estimation using existing redshift surveys. With three different galaxy samples, two of which contain UDGs with spectroscopic redshifts, we estimate that the method has a redshift accuracy of ∼75% when the method converges, although larger, more representative spectroscopic UDG samples are needed in order to fully understand the behavior of the method. We are able to estimate distances for 1079 of our UDG candidates (19%). Finally, to illustrate some uses of the catalog, we present both distance-independent and distance-dependent results. In the latter category, we establish that the red sequence of UDGs lies on the extrapolation of the red sequence relation for bright ellipticals and that the environment–color relation is at least qualitatively similar to that of high surface brightness galaxies. Both of these results challenge some of the models proposed for UDG evolution. -
ABSTRACT We use high-resolution Hubble Space Telescope imaging data of dwarf galaxies in the Local Volume ($\lesssim {11}\, \mathrm{Mpc}$) to parameterize 19 newly discovered nuclear star clusters (NSCs). Most of the clusters have stellar masses of $M_{\star }^{\mathrm{nsc}} \lesssim 10^{6}{\, {\rm M}_{\odot }}$ and compare to Galactic globular clusters in terms of ellipticity, effective radius, stellar mass, and surface density. The clusters are modelled with a Sérsic profile and their surface brightness evaluated at the effective radius reveals a tight positive correlation to the host galaxy stellar mass. Our data also indicate an increase in slope of the density profiles with increasing mass, perhaps indicating an increasing role for in situ star formation in more massive hosts. We evaluate the scaling relation between the clusters and their host galaxy stellar mass to find an environmental dependence: for NSCs in field galaxies, the slope of the relation is $\alpha = 0.82^{+0.08}_{-0.08}$ whereas $\alpha = 0.55^{+0.06}_{-0.05}$ for dwarfs in the core of the Virgo cluster. Restricting the fit for the cluster to $M_{\star }^{\mathrm{gal}} \ge 10^{6.5}{\, {\rm M}_{\odot }}$ yields $\alpha = 0.70^{+0.08}_{-0.07}$, in agreement with the field environment within the 1σ interval. The environmental dependence is due to the lowest-mass nucleated galaxies and we speculate that this is either due to an increased number of progenitor globular clusters merging to become an NSC, or due to the formation of more massive globular clusters in dense environments, depending on the initial globular cluster mass function. Our results clearly corroborate recent results in that there exists a tight connection between NSCs and globular clusters in dwarf galaxies.more » « less
-
more » « less
Abstract To better understand the formation of large, low-surface-brightness galaxies, we measure the correlation function between ultradiffuse galaxy (UDG) candidates and Milky Way analogs (MWAs). We find that: (1) the projected radial distribution of UDG satellites (projected surface density ∝
r −0.84±0.06) is consistent with that of normal satellite galaxies; (2) the number of UDG satellites per MWA (S UDG) is ∼0.5 ± 0.1 over projected radii from 20 to 250 kpc and −17 <M r < −13.5; (3)S UDGis consistent with a linear extrapolation of the relationship between the number of UDGs per halo versus halo mass obtained over galaxy group and cluster scales; (4) red UDG satellites dominate the population of UDG satellites (∼80%); (5) over the range of satellite magnitudes studied, UDG satellites comprise ∼10% of the satellite galaxy population of MWAs; and (6) a significant fraction of these (∼13%) have estimated total masses >1010.9M ⊙or, equivalently, at least half the halo mass of the LMC, and populate a large fraction (∼18%) of the expected subhalos down to these masses. All of these results suggest a close association between the overall low-mass galaxy population and UDGs, which we interpret as favoring models where UDG formation principally occurs within the general context of low-mass galaxy formation over models invoking more exotic physical processes specifically invoked to form UDGs. -
more » « less
ABSTRACT We study the formation of ultradiffuse galaxies (UDGs) using the cosmological hydrodynamical simulation TNG50 of the Illustris-TNG suite. We define UDGs as dwarf galaxies in the stellar mass range $\rm {7.5 \le log (M_{\star } / {\rm M}_{\odot }) \le 9 }$ that are in the 5 per cent most extended tail of the simulated mass–size relation. This results in a sample of UDGs with half-mass radii $\rm {r_{h \star } \gtrsim 2 \ kpc}$ and surface brightness between $\rm {24.5}$ and $\rm {28 \ mag \ arcsec^{-2}}$, similar to definitions of UDGs in observations. The large cosmological volume in TNG50 allows for a comparison of UDGs properties in different environments, from the field to galaxy clusters with virial mass $\rm {M_{200} \sim 2 \times 10^{14} ~ {\rm M}_{\odot }}$. All UDGs in our sample have dwarf-mass haloes ($\rm {M_{200}\sim 10^{11} ~ {\rm M}_{\odot } }$) and show the same environmental trends as normal dwarfs: field UDGs are star-forming and blue while satellite UDGs are typically quiescent and red. The TNG50 simulation predicts UDGs that populate preferentially higher spin haloes and more massive haloes at fixed $\rm {M_{\star }}$ compared to non-UDG dwarfs. This applies also to most satellite UDGs, which are actually ‘born’ UDGs in the field and infall into groups and clusters without significant changes to their size. We find, however, a small subset of satellite UDGs ($\lesssim 10~{{\ \rm per\ cent}}$) with present-day stellar size a factor ≥1.5 larger than at infall, confirming that tidal effects, particularly in the lower mass dwarfs, are also a viable formation mechanism for some of these dwarfs, although sub-dominant in this simulation.
