Coma Cluster Ultra-Diffuse Galaxies Are Not Standard Radio Galaxies

Abstract

Matching members in the Coma cluster catalogue of ultra-diffuse galaxies (UDGs, Yagi et al. 2016) from SUBARU imaging with a very deep radio continuum survey source catalogue of the cluster (Miller et al. 2009) using the Karl G. Jansky Very Large Array (VLA) within a rectangular region of ~ 1.19 square degrees centred on the cluster core reveals matches consistent with random. An overlapping set of 470 UDGs and 696 VLA radio sources in this rectangular area finds 33 matches within a separation of 25 arcsec; dividing the sample into bins with separations bounded by 5 arcsec, 10 arcsec, 20 arcsec and 25 arcsec finds 1, 4, 17 and 11 matches. An analytical model estimate, based on the Poisson probability distribution, of the number of randomly expected matches within these same separation bounds is 1.7, 4.9, 19.4 and 14.2, each respectively consistent with the 95 percent Poisson confidence intervals of the observed values. Dividing the data into five clustercentric annuli of 0.1 degree, and into the four separation bins, finds the same result. This random match of UDGs with VLA sources implies that UDGs are not radio galaxies by the standard definition. Those VLA sources having integrated flux > 1 mJy at 1.4 GHz in Miller et al. (2009) without SDSS galaxy matches are consistent with the known surface density of background radio sources. We briefly explore the possibility that some unresolved VLA sources near UDGs could be young, compact, bright, supernova remnants of type Ia events, possibly in the intracluster volume.