The VLA-COSMOS 3 GHz Large Project: AGN and host-galaxy properties out to z less than or similar to 6

Delvecchio, I. and Smolčić, Vernesa and Zamorani, G. and Lagos, C. Del P. and Berta, S. and Delhaize, J. and Baran, N. and Alexander, D. M. and Rosario, D. J. and Gonzalez-Perez, V. and Ilbert, O. and Lacey, C. G. and Le Fevre, O. and Miettinen, Oscari and Aravena, M. and Bondi, M. and Carilli, C. and Ciliegi, P. and Mooley, K. and Novak, Mario and Schinnerer, E. and Capak, P. and Civano, F. and Fanidakis, N. and Ruiz, N. Herrera and Karim, A. and Laigle, C. and Marchesi, S. and McCracken, H. J. and Middleberg, E. and Salvato, M. and Tasca, L. (2017) The VLA-COSMOS 3 GHz Large Project: AGN and host-galaxy properties out to z less than or similar to 6. Astronomy and Astrophysics, 602. Art. No. A3-22. ISSN 0004-6361

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We explore the multiwavelength properties of AGN host galaxies for different classes of radio-selected AGN out to z ≲ 6 via a multiwavelength analysis of about 7700 radio sources in the COSMOS field. The sources were selected with the Very Large Array (VLA) at 3 GHz (10 cm) within the VLA–COSMOS 3 GHz Large Project, and cross-matched with multiwavelength ancillary data. This is the largest sample of high-redshift (z ≲ 6) radio sources with exquisite photometric coverage and redshift measurements available. We constructed a sample of moderate-to-high radiative luminosity AGN (HLAGN) via spectral energy distribution decomposition combined with standard X-ray and mid-infrared diagnostics. Within the remainder of the sample we further identified low-to-moderate radiative luminosity AGN (MLAGN) via excess in radio emission relative to the star formation rates in their host galaxies. We show that at each redshift our HLAGN havesystematically higher radiative luminosities than MLAGN and that their AGN power occurs predominantly in radiative form, while MLAGN display a substantial mechanical AGN luminosity component. We found significant differences in the host properties of the two AGN classes, as a function of redshift. At z< 1.5, MLAGN appear to reside in significantly more massive and less star-forming galaxies compared to HLAGN. At z> 1.5, we observed a reversal in the behaviour of the stellar mass distributions with the HLAGN populating the higher stellar mass tail. We interpret this finding as a possible hint of the downsizing of galaxies hosting HLAGN, with the most massive galaxies triggering AGN activity earlier than less massive galaxies, and then fading to MLAGN at lower redshifts. Our conclusion is that HLAGN and MLAGN samples trace two distinct galaxy and AGN populations in a wide range of redshifts, possibly resembling the radio AGN types often referred to as radiative- and jet-mode (or high- and low-excitation), respectively, whose properties might depend on the different availability of cold gas supplies.

Item Type: Article
Keywords: radio continuum: galaxies, galaxies: nuclei, galaxies: active, galaxies: evolution
Date: 13 June 2017
Subjects: NATURAL SCIENCES > Physics > Astronomy and Astrophysics
Additional Information: © 2017 ESO. Received 21 July 2016. Accepted 21 October 2016. Published online 13 June 2017. The authors are grateful to the anonymous referee for his/her careful reading and useful comments, which improved the content of this manuscript. I.D., V.S., J.D., M.N., and O.M. acknowledge the European Union’s Seventh Framework programme under grant agreement 337595 (ERC Starting Grant, “CoSMass”). N.B. acknowledges the European Union’s Seventh Framework programme under grant agreement 333654 (CIG, “AGN feedback”). C.L. is funded by a Discovery Early Career Researcher Award (DE150100618). Parts of this research were conducted by the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020. M.B. and P.C. acknowledge supports from the PRIN-INAF 2014. M.A. acknowledges partial support from FONDECYT through grant 1140099. A.K. acknowledges support by the Collaborative Research Council 956, subproject A1, funded by the Deutsche Forschungsgemeinschaft (DFG). This work was partially supported by NASA Chandra grant number GO3-14150C and GO3-14150B (FC, S.M.). I.D. is grateful to B. Magnelli for useful suggestions and to Takamitsu Miyaji for his help with CSTACK.
Divisions: Faculty of Science > Department of Physics
Publisher: EDP Sciences
Depositing User: Vernesa Smolčić
Date Deposited: 20 Nov 2017 10:06
Last Modified: 20 Nov 2017 10:06

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