We study the relationship between the structure and star formation rate (SFR) of X-ray selected low and moderate luminosity active galactic nuclei (AGNs) in the two Chandra Deep Fields, using Hubble Space Telescope imaging from the Cosmic Assembly Near Infrared Extragalactic Legacy Survey (CANDELS) and deep far-infrared maps from the PEP+GOODS-Herschel survey. We derive detailed distributions of structural parameters and FIR luminosities from carefully constructed control samples of galaxies, which we then compare to those of the AGNs. At z ~ 1, AGNs show slightly diskier light profiles than massive inactive (non-AGN) galaxies, as well as modestly higher levels of gross galaxy disturbance (as measured by visual signatures of interactions and clumpy structure). In contrast, at z ~ 2, AGNs show similar levels of galaxy disturbance as inactive galaxies, but display a red central light enhancement, which may arise from a more pronounced bulge in AGN hosts or extinguished nuclear light. We undertake a number of tests of both these alternatives, but our results do not strongly favor one interpretation over the other. The mean SFR and its distribution among AGNs and inactive galaxies are similar at z > 1.5. At z < 1, however, clear and significant enhancements are seen in the SFRs of AGNs with bulge-dominated light profiles. These trends suggest an evolution in the relation between nuclear activity and host properties with redshift, towards a minor role for mergers and interactions at z > 1.5.
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This work is based on observations taken by the CANDELS Multi-Cycle Treasury Program with the NASA/ESA HST, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. PACS has been developed by a consortium of institutes led by MPE (Germany) and including UVIE (Austria); KUL, CSL, IMEC (Belgium); CEA, OAMP (France); MPIA (Germany); IFSI, OAP/AOT, OAA/CAISMI, LENS, SISSA (Italy); IAC (Spain). This development has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI (Italy), and CICYT/MCYT (Spain). F.E.B. acknowledges support from Basal-CATA PFB-06/2007, CONICYT-Chile (through FONDECYT 1101024, Gemini-CONICYT 32120003, “EMBIGGEN” Anillo ACT1101), and Project IC120009 “Millennium Institute of Astrophysics (MAS)”, funded by the Iniciativa Cientifica Milenio del Ministerio de Economia, Fomento y Turismo. D.M.A. acknowledges support from the Science and Technology Facilities Council (STFC) grant ST/I001573/1 and the Leverhulme Trust.
Kocevski, Dale D.; Rosario, D. J.; McIntosh, D. H.; van der Wel, A.; Kartaltepe, J.; Lang, P.; Santini, P.; Wuyts, S.; Lutz, D.; Rafelski, M.; and Villforth, C., "The Host Galaxies of X-Ray Selected Active Galactic Nuclei to z = 2.5: Structure, Star Formation, and Their Relationships from CANDELS and Herschel/PACS" (2015). Physics and Astronomy Faculty Publications. 340.