Preprint typeset using LATEX style emulateapj v. 11/10/09 AMUSE-VIRGO. II: DOWN-SIZING IN BLACK HOLE ACCRETION

We complete the census of nuclear X-ray activity in 100 early type Virgo galaxies observed by the Chandra X-ray Telescope as part of the AMUSE-Virgo survey, down to a (3σ) limiting luminosity of 3.7×1038 erg s−1 over 0.5-7 keV. The stellar mass distribution of the targeted sample, which is mostly composed of formally ‘inactive ’ galaxies, peaks below 1010 M, a regime where the very existence of nuclear super-massive black holes (SMBHs) is debated. Out of 100 objects, 32 show a nuclear X-ray source, including 6 hybrid nuclei which also host a massive nuclear cluster as visible from archival Hubble Space Telescope images. After carefully accounting for contamination from nuclear low-mass X-ray binaries based on the shape and normalization of their X-ray luminosity function, we conclude that between 24−34 % of the galaxies in our sample host a X-ray active SMBH (at the 95 % C.L.). This sets a firm lower limit to the black hole occupation fraction in nearby bulges within a cluster environment. The differential logarithmic X-ray luminosity function of active SMBHs scales with the X-ray luminosity as LX−0.4±0.1 up to 1042 erg s−1. At face value, the active fraction –down to our luminosity limit – is found to increase with host stellar mass. However, taking into account selection effects, we find that the average Eddington-scaled X-ray luminosity scales with black hole mass as MBH−0.62 +0.13 −0.12, with an intrinsic scatter of 0.46+0.08−0.06 dex. This finding can be interpreted as observational evidence for ‘down-sizing ’ of black hole accretion in local early types, that is, low mass black holes shine relatively closer to their Eddington limit than higher mass objects. As a consequence, the fraction of active galaxies, defined as those above a fixed X-ray Eddington ratio, decreases with increasing black hole mass