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Published April 10, 2018 | Published + Submitted
Journal Article Open

The Spitzer-IRAC/MIPS Extragalactic Survey (SIMES). II. Enhanced Nuclear Accretion Rate in Galaxy Groups at z ∼ 0.2


For a sample of star-forming galaxies in the redshift interval 0.15 < z < 0.3, we study how both the relative strength of the active galactic nucleus (AGN) infrared emission, compared to that due to the star formation (SF), and the numerical fraction of AGNs change as a function of the total stellar mass of the hosting galaxy group (M*_(group)) between 10^(10.25) and 10^(11.9) M ⊙. Using a multicomponent spectral energy distribution SED fitting analysis, we separate the contribution of stars, AGN torus, and star formation to the total emission at different wavelengths. This technique is applied to a new multiwavelength data set in the SIMES field (23 not-redundant photometric bands), spanning the wavelength range from the UV (GALEX) to the far-IR (Herschel) and including crucial AKARI and WISE mid-IR observations (4.5 μm < λ < 24 μm), where the black hole thermal emission is stronger. This new photometric catalog, which includes our best photo-z estimates, is released through the NASA/IPAC Infrared Science Archive (IRSA). Groups are identified through a friends-of-friends algorithm (~62% purity, ~51% completeness). We identified a total of 45 galaxies requiring an AGN emission component, 35 of which are in groups and 10 in the field. We find the black hole accretion rate (BHAR) ∝ (M*_(group))^(1.21±0.27) and (BHAR/SFR) ∝ ((M*_(group))^(1.04±0.24), while, in the same range of M*_(group), we do not observe any sensible change in the numerical fraction of AGNs. Our results indicate that the nuclear activity (i.e., the BHAR and the BHAR/SFR ratio) is enhanced when galaxies are located in more massive and richer groups.

Additional Information

© 2018 The American Astronomical Society. Received 2017 October 2; revised 2018 February 26; accepted 2018 March 15; published 2018 April 16. This work is based on observations obtained with AKARI, a JAXA project with the participation of ESA; data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration; data from the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA; data from Herschel, an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA; and observations made with the NASA Galaxy Evolution Explorer, operated for NASA by the California Institute of Technology under NASA contract NAS5-98034. Further fundamental observations were obtained with the ESO VST and VISTA and the CTIO observatories. We gratefully acknowledge Simon Lilly and Alvio Renzini for supplying us with the extended sample of spectroscopic redshifts measured in the COSMOS field. M.V. acknowledges support from the European Commission Research Executive Agency (FP7-SPACE-2013-1 GA 607254), the South African Department of Science and Technology (DST/CON 0134/2014), and the Italian Ministry for Foreign Affairs and International Cooperation (PGR GA ZA14GR02). R.C. acknowledges financial support from CONICYT Doctorado Nacional No. 21161487. I.B. thanks Stefano Rubele for the useful discussions concerning the technical details of the optical data reduction, Lee Armus for his comments on the AGN fraction reliability, and Gabriele Rodeghiero and Maurizio Pajola for their helpful comments about data representation.

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Published - Baronchelli_2018_ApJ_857_64.pdf

Submitted - 1803.06356.pdf


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