Photometric Identification and Characterization of Ultra Diffuse Galaxies in Hyper Suprime-Cam Ultradeep Data

Abstract

Ultra Diffuse Galaxies (UDGs) are extremely faint and extended galaxies, with surface brightness (SB) <= mag/arcsec2 and effective radius >= 3 arcsec. The study of these objects helps us understand the distribution of dark matter and the evolution of galaxies. Motivated by the recent discovery of approximately 1,000 UDGs in the Coma Cluster by Koda et al. (2015) and van Dokkum et al. (2015a,b), we report on our photometric identification routine for UDGs using the Hyper Suprime-Cam Ultradeep (HSC-UD) data in the COSMOS field. By combining a set of surface brightness (SB) constraints and angular size constraints, we select 1396 UDG candidates in the HSC-UD data and present a preliminary discussion of the photometric and clustering properties of our UDG candidates. We also propose a more robust and complete UDG identification routine that places a central SB constraint without utilizing any angular size constraint in this paper. Using this new routine, we identify approximately 359,000 low surface brightness galaxies (LSBs). We calculate the clustering redshift of these LSBs and show that they are high redshift z ~ 2 diffuse star burst galaxies. Eventually, by applying our pipeline to the wider HSC database, we expect to find many more UDGs and LSBs in the near future, increasing the current sample size of UDGs by an order of magnitude.