Illuminating Low-Surface-Brightness Galaxies with the Hyper Suprime-Cam
  Survey
  We present a catalog of extended low-surface-brightness galaxies (LSBGs)
identified in the Wide layer of the Hyper Suprime-Cam Subaru Strategic Program
(HSC-SSP). Using the first ${\sim}$200 deg$^2$ of the survey, we have uncovered
781 LSBGs, spanning red ($g-i\geq0.64$) and blue ($g-i<0.64$) colors and a wide
range of morphologies. Since we focus on extended galaxies
($r_\mathrm{eff}=2.5$-$14^{\prime\prime}$), our sample is likely dominated by
low-redshift objects. We define LSBGs to have mean surface brightnesses
$\bar{\mu}_\mathrm{eff}(g)>24.3$ mag arcsec$^{-2}$, which allows nucleated
galaxies into our sample. As a result, the central surface brightness
distribution spans a wide range of $\mu_0(g)=18$-$27.4$ mag arcsec$^{-2}$, with
50% and 95% of galaxies fainter than 24.3 and 22 mag arcsec$^{-2}$,
respectively. Furthermore, the surface brightness distribution is a strong
function of color, with the red distribution being much broader and generally
fainter than that of the blue LSBGs, and this trend shows a clear correlation
with galaxy morphology. Red LSBGs typically have smooth light profiles that are
well-characterized by single-component S\'{e}rsic functions. In contrast, blue
LSBGs tend to have irregular morphologies and show evidence for ongoing star
formation. We crossmatch our sample with existing optical, HI, and ultraviolet
catalogs to gain insight into the physical nature of the LSBGs. We find that
our sample is diverse, ranging from dwarf spheroidals and ultra-diffuse
galaxies in nearby groups to gas-rich irregulars to giant LSB spirals,
demonstrating the potential of the HSC-SSP to provide a truly unprecedented
view of the LSBG population.
