Bibcode
Santini, P.; Rosario, D. J.; Shao, L.; Lutz, D.; Maiolino, R.; Alexander, D. M.; Altieri, B.; Andreani, P.; Aussel, H.; Bauer, F. E.; Berta, S.; Bongiovanni, A.; Brandt, W. N.; Brusa, M.; Cepa, J.; Cimatti, A.; Daddi, E.; Elbaz, D.; Fontana, A.; Förster Schreiber, N. M.; Genzel, R.; Grazian, A.; Le Floc'h, E.; Magnelli, B.; Mainieri, V.; Nordon, R.; Pérez-Garcia, A. M.; Poglitsch, A.; Popesso, P.; Pozzi, F.; Riguccini, L.; Rodighiero, G.; Salvato, M.; Sanchez-Portal, M.; Sturm, E.; Tacconi, L. J.; Valtchanov, I.; Wuyts, S.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 540, id.A109
Fecha de publicación:
4
2012
Revista
Número de citas
189
Número de citas referidas
182
Descripción
We compare the average star formation (SF) activity in X-ray selected
AGN hosts with a mass-matched control sample of inactive galaxies,
including both star forming and quiescent sources, in the 0.5 < z
< 2.5 redshift range. Recent observations carried out by PACS, the
60-210 μm photometric camera on board the Herschel Space Observatory,
in GOODS-S, GOODS-N and COSMOS allow us to obtain an unbiased estimate
of the far-IR luminosity, and hence of the SF properties, of the two
samples. Accurate AGN host stellar mass estimates are obtained by
decomposing their total emission into the stellar and the nuclear
components. We report evidence of a higher average SF activity in AGN
hosts with respect to the control sample of inactive galaxies. The level
of SF enhancement is modest (~0.26 dex at ~3σ confidence level) at
low X-ray luminosities (LX ≲ 1043.5 erg
s-1) and more pronounced (0.56 dex at > 10σ
confidence level) in the hosts of luminous AGNs. However, when comparing
to star forming galaxies only, AGN hosts are found 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 AGNaccretion not tightly linked to the current total SF in
the host galaxy, while the luminous AGNs co-evolve with their hosts
through periods of enhanced AGN activity and star formation, possibly
through major mergers. While an increased SF activity with respect to
inactive galaxies 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.
Herschel is an ESA space observatory with science instruments provided
by European-led Principal Investigator consortia and with important
participation from NASA.Throughout the paper, the wording
"inactive"/"active" refers to galaxies lacking/showing nuclear activity
(non-AGNs/AGNs), regardless of their star formation rate.
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