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GOODS-Herschel: Ultra-deep XMM-Newton observations reveal AGN/star-formation connection

AuthorsRovilos, E.; Comastri, A.; Gilli, R.; Georgantopoulos, I.; Ranalli, P.; Vignali, C.; Lusso, E.; Cappelluti, N.; Zamorani, G.; Elbaz, D.; Dickinson, C.; Hwang, H. S.; Charmandaris, V.; Ivison, R. J.; Merloni, A.; Daddi, E.; Carrera, Francisco J. CSIC ORCID CVN ; Brandt, W. N.; Mullaney, J. R.; Scott, D.; Alexander, M.; Moro, A. del; Morrison, G.; Murphy, E. J.; Altieri, B.; Aussel, H.; Dannerbauer, H.; Kartaltepe, J.; Leiton, R.; Magdis, G. E.; Magnelli, B.; Popesso, P.; Valtchanov, Iván
Issue Date2012
PublisherEDP Sciences
CitationAstronomy and Astrophysics 546: A58 (2012)
AbstractModels of galaxy evolution assume some connection between the AGN and star formation activity in galaxies. We use the multi-wavelength information of the CDFS to assess this issue. We select the AGNs from the 3 Ms XMM-Newton survey and measure the star-formation rates of their hosts using data that probe rest-frame wavelengths longward of 20 μm, predominantly from deep 100 μm and 160 μm Herschel observations, but also from Spitzer-MIPS-70 μm. Star-formation rates are obtained from spectral energy distribution fits, identifying and subtracting an AGN component. Our sample consists of sources in the z ≈ 0.5-4 redshift range, with star-formation rates SFR ≈ 10 1-10 3 M ⊙ yr -1 and stellar masses M * ≈ 10 10-10 11.5 M ⊙. We divide the star-formation rates by the stellar masses of the hosts to derive specific star-formation rates (sSFR) and find evidence for a positive correlation between the AGN activity (proxied by the X-ray luminosity) and the sSFR for themost active systems with X-ray luminosities exceeding L x ≃ 10 43 erg s -1 and redshifts z ≥ 1. We do not find evidence for such a correlation for lower luminosity systems or those at lower redshifts, consistent with previous studies. We do not find any correlation between the SFR (or the sSFR) and the X-ray absorption derived from high-quality XMM-Newton spectra either, showing that the absorption is likely to be linked to the nuclear region rather than the host, while the star-formation is not nuclear. Comparing the sSFR of the hosts to the characteristic sSFR of star-forming galaxies at the same redshift (the so-called >main sequence>) we find that the AGNs reside mostly in main-sequence and starburst hosts, reflecting the AGN-sSFR connection; however the infrared selection might bias this result. Limiting our analysis to the highest X-ray luminosity AGNs (X-ray QSOs with L x > 10 44 erg s -1), we find that the highest-redshift QSOs (with z ≥ 2) reside predominantly in starburst hosts, with an average sSFR more than double that of the >main sequence>, and we find a few cases of QSOs at z ≈ 1.5 with specific star-formation rates compatible with the main-sequence, or even in the >quiescent> region. Finally, we test the reliability of the colour-magnitude diagram (plotting the rest-frame optical colours against the stellar mass) in assessing host properties, and find a significant correlation between rest-frame colour (without any correction for AGN contribution or dust extinction) and sSFR excess relative to the "main sequence" at a given redshift. This means that the most "starbursty" objects have the bluest rest-frame colours.
Publisher version (URL)http://dx.doi.org/10.1051/0004-6361/201218952
Identifiersdoi: 10.1051/0004-6361/201218952
issn: 0004-6361
e-issn: 1432-0746
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