On the Properties of Spectroscopically-Confirmed Ultra-Diffuse Galaxies
  Across Environment
  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 at 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 ($r_e\geq1.5$ kpc and $\mu_g(0)\geq24$ 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 non-cluster
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 cluster-centric
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 ($r_e \geq 3.5$ 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 GALEX NUV flux in nearly half of the UDGs in
sparse environments, suggest that field UDGs are a population of slowly
evolving galaxies.
