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X-rays across the galaxy population - III. The incidence of AGN as a function of star formation rate

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posted on 2019-05-22, 14:35 authored by J. Aird, A. L. Coil, A. Georgakakis
We map the co-eval growth of galaxies and their central supermassive black holes in detail by measuring the incidence of active galactic nuclei (AGNs) in galaxies as a function of star formation rate (SFR) and redshift (to z ∼ 4). We combine large galaxy samples with deep Chandra X-ray imaging to measure the probability distribution of specific black hole accretion rates (LX relative to stellar mass) and derive robust AGN fractions and average specific accretion rates. First, we consider galaxies along the main sequence of star formation. We find a linear correlation between the average SFR and both the AGN fraction and average specific accretion rate across a wide range in stellar mass (M∗ ∼ 108.5−11.5 M ) and to at least z ∼ 2.5, indicating that AGNs in main-sequence galaxies are driven by the stochastic accretion of cold gas. We also consider quiescent galaxies and find significantly higher AGN fractions than predicted, given their low SFRs, indicating that AGNs in quiescent galaxies are fuelled by additional mechanisms (e.g. stellar winds). Next, we bin galaxies according to their SFRs relative to the main sequence. We find that the AGN fraction is significantly elevated for galaxies that are still star forming but with SFRs below the main sequence, indicating further triggering mechanisms enhance AGN activity within these sub-main-sequence galaxies. We also find that the incidence of high accretion rate AGN is enhanced in starburst galaxies and evolves more mildly with redshift than within the rest of the galaxy population, suggesting mergers play a role in driving AGN activity in such high-SFR galaxies.


JA acknowledges support from an Science & Technology Facilities Council (STFC) Ernest Rutherford Fellowship, grant code: ST/P004172/1. AG acknowledges the THALES project 383549 that is jointly funded by the European Union and the Greek Government in the framework of the programme ‘Education and lifelong learning’. This work is based in part on observations taken by the CANDELS Multi-Cycle Treasury Program and the 3D-HST Treasury Program (GO 12177 and 12328) with the NASA/ESA HST, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Also based in part on the Ks-selected catalogue of the COSMOS/UltraVISTA field from Muzzin et al. (2013), which contains PSF-matched photometry in 30 photometric bands and includes the available GALEX (Martin et al. 2005), CFHT/Subaru (Capak et al. 2007), UltraVISTA (McCracken et al. 2012), S-COSMOS (Sanders et al. 2007), and zCOSMOS (Lilly et al. 2009) data sets. The scientific results reported in this article are based to a significant degree on observations made by the Chandra X-ray Observatory.



Monthly Notices of the Royal Astronomical Society, 2019, 484 (3), pp. 4360-4378

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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Monthly Notices of the Royal Astronomical Society


Oxford University Press (OUP), Royal Astronomical Society



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