Nuclear Accretion in Galaxies of the Local Universe: Clues fromChandraObservations

In order to find an explanation for the radiative quiescence of supermassiveblack holes in the local Universe, for a sample of nearby galaxies the mostaccurate estimates are collected for the mass of a central black hole M_BH, thenuclear X-ray luminosity L_X,nuc and the circumnuclear hot gas density andtemperature, by using Chandra data. L_X,nuc varies by \sim 3 orders ofmagnitude and does not show a relationship with M_BH or with the Bondi massaccretion rate \dotM_B. L_X,nuc is always much lower than expected if \dotM_Bends in a standard accretion disc with high radiative efficiency (this insteadcan be the case of the active nucleus of Cen A). Radiatively inefficientaccretion as in the standard ADAF modeling may explain the low luminosities ofa few cases; for others, the predicted luminosity is still too high and, interms of Eddington-scaled quantities, it is increasingly higher than observed,for increasing \dotM_B. Variants of the simple radiatively inefficient scenarioincluding outflow and convection may reproduce the low emission levelsobserved, since the amount of matter actually accreted is reduced considerably.However, the most promising scenario includes feedback from accretion on thesurrounding gas: this has the important advantages of naturally explaining theobserved lack of relationship between L_X,nuc, M_BH and \dotM_B, and of evadingthe problem of the fate of the material accumulating in the central galacticregions over cosmological times.Comment: 19 pages, 3 figures; accepted for publication in The Astrophysical Journa