Decomposing Star Formation and Active Galactic Nucleus with Spitzer Mid-Infrared Spectra: Luminosity Functions and Co-Evolution

Hai Fu; Lin Yan; Nick Scoville; Peter Capak; H. M Aussel; E. Le Floc'h; Olivier Ilbert; Mara Salvato; Jeyhan S Kartaltepe; D Frayer; David B Sanders; K Sheth; Y Taniguchi

doi:10.1088/0004-637X/722/1/653

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Decomposing Star Formation and Active Galactic Nucleus with Spitzer Mid-Infrared Spectra: Luminosity Functions and Co-Evolution

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Decomposing Star Formation and Active Galactic Nucleus with Spitzer Mid-Infrared Spectra: Luminosity Functions and Co-Evolution

Hai Fu, Lin Yan, Nick Scoville, Peter Capak, H. M Aussel, E. Le Floc'h, Olivier Ilbert, Mara Salvato, Jeyhan S Kartaltepe, D Frayer, …

The Astrophysical journal, Vol.722(1), pp.653-667

08/17/2010

DOI: 10.1088/0004-637X/722/1/653

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Abstract

We present Spitzer 7-38um spectra for a 24um flux limited sample of galaxies at z~0.7 in the COSMOS field. The detailed high-quality spectra allow us to cleanly separate star formation (SF) and active galactic nucleus (AGN) in individual galaxies. We first decompose mid-infrared Luminosity Functions (LFs). We find that the SF 8um and 15um LFs are well described by Schechter functions. AGNs dominate the space density at high luminosities, which leads to the shallow bright-end slope of the overall mid-infrared LFs. The total infrared (8-1000um) LF from 70um selected galaxies shows a shallower bright-end slope than the bolometrically corrected SF 15um LF, owing to the intrinsic dispersion in the mid-to-far-infrared spectral energy distributions. We then study the contemporary growth of galaxies and their supermassive black holes (BHs). Seven of the 31 Luminous Infrared Galaxies with Spitzer spectra host luminous AGNs, implying an AGN duty cycle of 23+/-9%. The time-averaged ratio of BH accretion rate and SF rate matches the local M_BH-M_bulge relation and the M_BH-M_host relation at z ~ 1. These results favor co-evolution scenarios in which BH growth and intense SF happen in the same event but the former spans a shorter lifetime than the latter. Finally, we compare our mid-infrared spectroscopic selection with other AGN identification methods and discuss candidate Compton-thick AGNs in the sample. While only half of the mid-infrared spectroscopically selected AGNs are detected in X-ray, ~90% of them can be identified with their near-infrared spectral indices.

Physics - Cosmology and Nongalactic Astrophysics

Details

Title: Subtitle: Decomposing Star Formation and Active Galactic Nucleus with Spitzer Mid-Infrared Spectra: Luminosity Functions and Co-Evolution
Creators: Hai Fu - California Institute of Technology
Lin Yan - California Institute of Technology
Nick Scoville - California Institute of Technology
Peter Capak - California Institute of Technology
H. M Aussel - Université Paris Diderot
E. Le Floc'h
Olivier Ilbert - Laboratoire d’Astrophysique de Marseille
Mara Salvato - Max Planck Society
Jeyhan S Kartaltepe - National Optical Astronomy Observatory
D Frayer - National Radio Astronomy Observatory
David B Sanders - University of Hawaii
K Sheth - University of Maryland, College Park
Y Taniguchi - Ehime University
Resource Type: Journal article
Publication Details: The Astrophysical journal, Vol.722(1), pp.653-667
DOI: 10.1088/0004-637X/722/1/653
ISSN: 0004-637X
eISSN: 1538-4357
Publisher: Institute of Physics (IOP)
Language: English
Date published: 08/17/2010
Academic Unit: Physics and Astronomy
Record Identifier: 9984199800002771

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