ONGOING AND CO-EVOLVING STAR FORMATION IN zCOSMOS GALAXIES HOSTING ACTIVE GALACTIC NUCLEI
- Institute of Astronomy, ETH Zuerich, CH-8093, Zuerich (Switzerland)
- Laboratoire d'Astrophysique de Toulouse-Tarbes, Universite de Toulouse, CNRS, 14 avenue Edouard Belin, F-31400 Toulouse (France)
- European Southern Observatory, Karl-Schwarzschild-Strasse 2, Garching, D-85748 (Germany)
- Max-Planck-Institut fuer extraterrestrische Physik, D-84571 Garching (Germany)
- INAF Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127, Bologna (Italy)
- INAF - IASF Milano, Milan (Italy)
- Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)
- Laboratoire d'Astrophysique de Marseille, Marseille (France)
We present a study of the host galaxies of active galactic nucleus (AGN) selected from the zCOSMOS survey to establish if accretion onto supermassive black holes (SMBHs) and star formation are explicitly linked up to z {approx} 1. We identify 152 galaxies that harbor AGN, based on their X-ray emission (L {sub 0.5-10keV}>10{sup 42} erg s{sup -1}) detected by XMM-Newton observations of 7543 galaxies (i {sub acs} < 22.5). Star formation rates (SFRs), including those weighted by stellar mass, of a subsample are determined using the [O II]{lambda}3727 emission-line luminosity, corrected for an AGN contribution based on the observed [O III]{lambda}5007 strength or that inferred by their hard (2-10 keV) X-ray luminosity. We find that an overwhelming majority of AGN host galaxies have significant levels of star formation with a distribution spanning {approx}1-100 M {sub sun} yr{sup -1}; their average SFR is higher than that of galaxies with equivalent stellar mass (M {sub *}>4 x 10{sup 10} M {sub sun}). The close association between AGN activity and star formation is further substantiated by an increase in the fraction of galaxies hosting AGN with the youthfulness of their stars as indicated by the rest-frame color (U-V) and spectral index D{sub n} (4000); we demonstrate that a mass-selected sample is required to alleviate an artificial peak in the AGN fraction falling in the transition region due to the fact that many 'blue cloud' galaxies have low mass-to-light ratios in luminosity-limited samples. We also find that the SFRs of AGN hosts evolve with cosmic time in a manner that closely mirrors the overall galaxy population and naturally explains the low SFRs in AGNs (z < 0.3) from the SDSS. We conclude that the conditions most conducive for AGN activity are a massive host galaxy and a large reservoir of gas. Furthermore, a direct correlation between mass-accretion rate onto SMBHs and SFR is shown to be weak although the average ratio ({approx}10{sup -2}) is constant with redshift, effectively shifting the evidence for a co-evolution scenario in a statistical manner to smaller physical scales (i.e., within the same galaxies). The order-of-magnitude increase in this ratio compared to the locally measured value of M {sub BH}/M {sub bulge} is consistent with an AGN lifetime substantially shorter than that of star formation. Our findings illustrate an intermittent scenario with underlying complexities regarding fueling over vastly different physical (and temporal) scales yet to be firmly determined.
- OSTI ID:
- 21296202
- Journal Information:
- Astrophysical Journal, Vol. 696, Issue 1; Other Information: DOI: 10.1088/0004-637X/696/1/396; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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