There is considerable interest in understanding the demographics of galaxies within the local universe (defined, for our purposes, as the volume within a radius of 200 Mpc or z<0.05). In this pilot paper we investigate the redshift completeness of catalogs of such nearby galaxies. Our sample consists of host galaxies of nearby, z_SN < 0.05, supernovae (SNe) discovered by the flux-limited ASAS-SN survey. Thanks to their brilliance SNe are easy to find and with some care can be used to study galaxy populations. In particular, type Ia SNe arise in both old and young stellar populations and thus can be used to study the general demographics of galaxies. We define the redshift completeness fraction (RCF) as the number of SN host galaxies with known redshift prior to SN discovery, determined, in this case, via the NASA Extragalactic Database (NED), divided by the total number of newly discovered SNe. By raw numbers, we find RCF ~ 0.8 for z < 0.03. We examine the distribution of hosts with and without cataloged redshifts as a function of absolute magnitude and redshift, and, unsurprisingly, find that higher-$z$ and fainter hosts are less likely to have a known redshift prior to the detection of the SN. We conclude with thoughts on the future improvement of RCF measurements, which will benefit greatly from upcoming surveys.
S. Kulkarni, D. Perley and A. Miller
Fri, 13 Oct 17