Systematically Measuring Ultra-Diffuse Galaxies (SMUDGes). II. Expanded Survey Description and the Stripe 82 Catalog

TL;DR

This paper expands the catalog of ultra-diffuse galaxy candidates in SDSS Stripe 82 using improved detection methods, revealing no decline in their numbers with surface brightness and providing insights into their properties and evolution.

Contribution

The study introduces an enhanced procedure for detecting UDGs, increasing sensitivity and completeness, and provides the largest catalog to date in the Stripe 82 region.

Findings

No significant decline in UDG numbers with surface brightness.

Blue UDGs tend to have smaller Sersic n and will fade into the red sequence.

Red UDGs below the sensitivity limit are not descendants of blue UDGs.

Abstract

We present 226 large ultra-diffuse galaxy (UDG) candidates ($r_e > 5.3$\arcsec, $\mu_{0,g} > 24$ mag arcsec$^{-2}$) in the SDSS Stripe 82 region recovered using our improved procedure developed in anticipation of processing the entire Legacy Surveys footprint. The advancements include less constrained structural parameter fitting, expanded wavelet filtering criteria, consideration of Galactic dust, estimates of parameter uncertainties and completeness based on simulated sources, and refinements of our automated candidate classification. We have a sensitivity $\sim$1 mag fainter in $\mu_{0,g}$ than the largest published catalog of this region. Using our completeness-corrected sample, we find that (1) there is no significant decline in the number of UDG candidates as a function of $\mu_{0,g}$ to the limit of our survey ($\sim$ 26.5 mag arcsec$^{-2}$); (2) bluer candidates have smaller S\'ersic $n$; (3) most blue ($g-r < 0.45$ mag) candidates have $\mu_{0,g} \lesssim 25$ mag arcsec$^{-2}$ and will fade to populate the UDG red sequence we observe to $\sim 26.5$ mag arcsec$^{-2}$; (4) any red UDGs that exist significantly below our $\mu_{0,g}$ sensitivity limit are not descended from blue UDGs in our sample; and (5) candidates with lower $\mu_{0,g}$ tend to smaller $n$. We anticipate that the final SMUDGes sample will contain $\sim$ 30$\times$ as many candidates.