Hidden in Plain Sight: Illuminating Low Surface Brightness Galaxies with the Hyper Suprime-Cam

Abstract

Low surface brightness (LSB) galaxies are a common outcome of galaxy formation. Yet, our census of this population is severely incomplete because of the challenges of detecting and studying such diffuse systems. In this thesis, I explore the detection and characterization of these elusive galaxies in the era of deep, wide, and high-resolution optical surveys. I develop software and image-processing algorithms to carry out an automated search for LSB galaxies with the ongoing Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Using the first ~15% of HSC-SSP's survey area, I uncover a diverse sample of ~800 LSB galaxies, ranging from dwarf ellipticals in nearby groups to isolated blue ultra-diffuse galaxies to giant LSB spirals.

I constrain the redshift distribution of these galaxies using a combination of follow-up spectroscopy and a statistical method that exploits the clustering of galaxies. Their typical distances range from ~30-100 Mpc, with an implied effective radius range of ~0.5-10 kpc. I identify very isolated ultra-diffuse dwarfs, with rotation curve measurements for one such object that suggest it occupies a typical dwarf-like dark matter halo. Using image simulations, I measure the completeness of our survey as a function of galaxy properties, which I combine with the statistical redshift distribution to make a tentative measurement of the mean space density of LSB galaxies with surface brightnesses ~1 mag/arcsec^2 fainter than all previous measurements.

The work presented in this thesis will lay the foundation for a more comprehensive search for LSB galaxies with the HSC-SSP, as well as with future wide-field surveys such as the Large Synoptic Survey Telescope. Pushing the surface-brightness limits of these surveys will be necessary to form a more complete census of the galaxy population, which will ultimately provide one of the strongest tests of our standard cosmological framework.