A VERY LARGE ARRAY RADIO SURVEY OF EARLY-TYPE GALAXIES IN THE VIRGO CLUSTER

We present the results of an 8.4 GHz Very Large Array radio survey of early-type galaxies extracted from the sample selected by Cote and collaborators for the Advanced Camera for Surveys Virgo Cluster Survey. The aim of this survey is to investigate the origin of radio emission in early-type galaxies and its link with the host properties in an unexplored territory toward the lowest levels of both radio and optical luminosities. Radio images, available for all 63 galaxies with B(T) < 14.4, show the presence of a compact radio source in 12 objects, with fluxes spanning from 0.13 mJy to 2700 mJy. The remaining 51 galaxies, undetected at a flux limit of similar to 0.1 mJy, have radio luminosities L less than or similar to 4 x 10(18) W Hz(-1). The fraction of radio-detected galaxies are a strong function of stellar mass, in agreement with previous results: none of the 30 galaxies with M(star) < 1.7 x 10(10) M(circle dot) is detected, while 8 of the 11 most massive galaxies have radio cores. There appears to be no simple relation between the presence of a stellar nucleus and radio emission. In fact, we find radio sources associated with two nucleated galaxies, but the majority of nucleated objects are not a radio emitter above our detection threshold. A multiwavelength analysis of the active galactic nucleus (AGN) emission, combining radio and X-ray data, confirms the link between optical surface brightness profile and radio loudness in the sense that the bright core galaxies are associated with radio-loud AGNs, while non-core galaxies host radio-quiet AGNs. Not all radio-detected galaxies have an X-ray nuclear counterpart (and vice versa). A complete census of AGNs (and supermassive black holes, SMBHs) thus requires observations, at least, in both bands. Nonetheless, there are massive galaxies in the sample, expected to host a large SMBH (M(BH) similar to 10(8) M(circle dot)), whose nuclear emission eludes detection despite their proximity and the depth and the spatial resolution of the available observations. Most likely this is due to an extremely low level of accretion onto the central SMBH.