We present a pilot study of the atomic neutral hydrogen gas (H i) content of ultra-diffuse galaxy (UDG) candidates. In this paper, we use the pre-pilot Eridanus field data from the Widefield ASKAP L-band Legacy All-sky Blind Survey to search for H i in UDG candidates found in the Systematically Measuring Ultra-diffuse Galaxies survey (SMUDGes). We narrow down to 78 SMUDGes UDG candidates within the maximum radial extents of the Eridanus subgroups for this study. Most SMUDGes UDGs candidates in this study have effective radii smaller than 1.5 kpc and thus fail to meet the defining size threshold. We only find one H i detection, which we classify as a low-surface-brightness dwarf. Six putative UDGs are H i-free. We show the overall distribution of SMUDGes UDG candidates on the size–luminosity relation and compare them with low-mass dwarfs on the atomic gas fraction versus stellar mass scaling relation. There is no correlation between gas-richness and colour indicating that colour is not the sole parameter determining their H i content. The evolutionary paths that drive galaxy morphological changes and UDG formation channels are likely the additional factors to affect the H i content of putative UDGs. The actual numbers of UDGs for the Eridanus and NGC 1332 subgroups are consistent with the predicted abundance of UDGs and the halo virial mass relation, except for the NGC 1407 subgroup, which has a smaller number of UDGs than the predicted number. Different group environments suggest that these putative UDGs are likely formed via the satellite accretion scenario.
We explore the environment of 252 H i-bearing ultra-diffuse galaxies (HUDs) from the 100 per cent ALFALFA survey catalogue in an attempt to constrain their formation mechanism. We select sources from ALFALFA with surface brightnesses, magnitudes, and radii consistent with other samples of ultra-diffuse galaxies (UDGs) without restrictions on their isolation or environment, more than doubling the previously reported ALFALFA sample. We quantify the galactic environment of HUDs using several metrics, including nth nearest neighbour, tidal influence, membership in a group/cluster, and distance from nearest group/cluster or filament. We find that HUDs inhabit the same environments as other samples of H i-selected galaxies and that they show no environmental preference in any metric. We suggest that these results are consistent with a picture of the extreme properties of HUDs being driven by internal mechanisms and that they are largely unperturbed by environmental impacts. While environmental effects may be necessary to convert HUDs into gas-poor cluster UDGs, these effects are not required for diffuse galaxies to exist in the first place.
more » « less- NSF-PAR ID:
- 10120780
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 490
- Issue:
- 1
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- p. 566-577
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract We present new redshift measurements for 19 candidate ultra-diffuse galaxies (UDGs) from the Systematically Measuring Ultra-Diffuse Galaxies (SMUDGes) survey after conducting a long-slit spectroscopic follow-up campaign on 23 candidates with the Large Binocular Telescope. We combine these results with redshift measurements from other sources for 29 SMUDGes and 20 non-SMUDGes candidate UDGs. Together, this sample yields 44 spectroscopically confirmed UDGs ( r e ≥ 1.5 kpc and μ g (0) ≥ 24 mag arcsec −2 within uncertainties) and spans cluster and field environments, with all but one projected on the Coma cluster and environs. We find no statistically significant differences in the structural parameters of cluster and noncluster confirmed UDGs, although there are hints of differences among the axis ratio distributions. Similarly, we find no significant structural differences among those in locally dense or sparse environments. However, we observe a significant difference in color with respect to projected clustercentric radius, confirming trends observed previously in statistical UDG samples. This trend strengthens further when considering whether UDGs reside in either cluster or locally dense environments, suggesting starkly different star formation histories for UDGs residing in high- and low-density environments. Of the 16 large ( r e ≥ 3.5 kpc) UDGs in our sample, only one is a field galaxy that falls near the early-type galaxy red sequence. No other field UDGs found in low-density environments fall near the red sequence. This finding, in combination with our detection of Galaxy Evolution Explorer NUV flux in nearly half of the UDGs in sparse environments, suggests that field UDGs are a population of slowly evolving galaxies.more » « less
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