paper

Towards a Complete Census of AGNs in Nearby Galaxies: The Incidence of Growing Black Holes

arXiv:1003.3015 · doi:10.1111/j.1365-2966.2010.16700.x

Abstract

We investigate the local supermassive black hole (SMBH) density function and relative mass accretion rates of all active galactic nuclei (AGNs) identified in a volume-limited sample of infrared (IR) bright galaxies (L_IR > 3 x 10^9 L_sun) to D<15 Mpc (Goulding & Alexander 2009). A database of accurate SMBH mass (M_BH) estimates is compiled from literature sources using physically motivated AGN modeling techniques (reverberation mapping, maser mapping and gas kinematics) and well-established indirect M_BH estimation methods (the M-sigma and M_BH-L_(K,bul) relations). For the three sources without previously published M_BH estimates, we use 2MASS K-band imaging and GALFIT to constrain the bulge luminosities, and hence SMBH masses. In general, we find the AGNs in the sample host SMBHs which are spread over a wide mass range (M_BH ~ (0.1-30) x 10^7 M_sun), but with the majority in the poorly studied M_BH ~ 10^6-10^7 M_sun region. Using sensitive hard X-ray (2-10 keV) and mid-IR constraints we calculate the bolometric luminosities of the AGNs (L_(Bol,AGN)) and use them to estimate relative mass accretion rates. We use these data to calculate the volume-average SMBH growth rate of galaxies in the local Universe and find that the AGNs hosting SMBHs in the mass range M_BH ~ 10^6-10^7 M_sun are dominated by optically unidentified AGNs. These relatively small SMBHs are acquiring a significant proportion of their mass in the present-day, and are amongst the most rapidly growing in the local Universe (SMBH mass doubling times of ~6 Gyrs). Additionally, we find tentative evidence for an increasing volume-weighted AGN fraction with decreasing SMBH mass in the M_BH ~ 10^6-10^8 M_sun range. Overall, we conclude that significant mass accretion onto small SMBHs may be missed in even the most sensitive optical surveys due to absent or weak optical AGN signatures.

17 pages, 5 figures. Accepted for publication in MNRAS

References in corpus (23)

Cited by in corpus (60)