1201.4394 (P. Santini et al.)

Enhanced star formation rates in AGN hosts with respect to inactive galaxies from PEP-Herschel observations    [PDF]

P. Santini, D. Rosario, L. Shao, D. Lutz, R. Maiolino, D. M. Alexander, B. Altieri, P. Andreani, H. Aussel, F. E. Bauer, S. Berta, A. Bongiovanni, W. N. Brandt, M. Brusa, J. Cepa, A. Cimatti, E. Daddi, D. Elbaz, A. Fontana, N. M. Forster Schreiber, R. Genzel, A. Grazian, E. Le Floc'h, B. Magnelli, V. Mainieri, R. Nordon, A. M. Perez Garcia, A. Poglitsch, P. Popesso, F. Pozzi, L. Riguccini, G. Rodighiero, M. Salvato, M. Sanchez-Portal, E. Sturm, L. J. Tacconi, I. Valtchanov, S. Wuyts

We compare the average star formation (SF) activity in X-ray selected AGN hosts with mass-matched control inactive galaxies,including star forming and quiescent sources, at 0.510sigma) for bright AGNs. However, when comparing to star forming galaxies only, AGN hosts are broadly consistent with the locus of their `main sequence'. We investigate the relative far-IR luminosity distributions of active and inactive galaxies, and find a higher fraction of PACS detected, hence normal and highly star forming systems among AGN hosts. Although different interpretations are possible, we explain our findings as a consequence of a twofold AGN growth path: faint AGNs evolve through secular processes, with instantaneous AGN accretion not tightly linked to the current total SF in the host, while luminous AGNs co-evolve with their hosts through periods of enhanced AGN activity and SF, possibly through major mergers. While an increased SF with respect to non-AGNs of similar mass is expected in the latter, we interpret the modest SF offsets measured in low-Lx AGN hosts as either a) generated by non-synchronous accretion and SF histories in a merger scenario or b) due to possible connections between instantaneous SF and accretion that can be induced by smaller scale (non-major merger) mechanisms. Far-IR luminosity distributions favour the latter scenario.

View original: http://arxiv.org/abs/1201.4394