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2010ApJ...714...25G - Astrophys. J., 714, 25-36 (2010/May-1)

AMUSE-virgo. II. Down-sizing in black hole accretion.

GALLO E., TREU T., MARSHALL P.J., WOO J.-H., LEIPSKI C. and ANTONUCCI R.

Abstract (from CDS):

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 3.7x1038 erg/s 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 supermassive 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 (XLF), we conclude that between 24% and 34% of the galaxies in our sample host an X-ray active SMBH (at the 95% confidence level). This sets a firm lower limit to the black hole (BH) occupation fraction in nearby bulges within a cluster environment. The differential logarithmic XLF of active SMBHs scales with the X-ray luminosity as LX–0.4±0.1 up to 1042 erg/s. 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 BH mass as MBH{{–0.62{+0.13}_{-0.12}}}, with an intrinsic scatter of 0.46+0.08–0.06dex. This finding can be interpreted as observational evidence for "down-sizing" of BH accretion in local early types, that is, low-mass BHs 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 BH mass.

Journal keyword(s): black hole physics - galaxies: clusters: individual: Virgo

VizieR on-line data: <Available at CDS (J/ApJ/714/25): table1.dat>