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Published September 21, 2013 | Submitted + Published
Journal Article Open

The roles of star formation and AGN activity of IRS sources in the HerMES fields


In this work, we explore the impact of the presence of an active galactic nucleus (AGN) on the mid- and far-infrared (IR) properties of galaxies as well as the effects of simultaneous AGN and starburst activity in the same galaxies. To do this, we apply a multicomponent, multiband spectral synthesis technique to a sample of 250 μm selected galaxies of the Herschel Multi-tiered Extragalactic Survey (HerMES), with Infrared Spectrograph (IRS) spectra available for all galaxies. Our results confirm that the inclusion of the IRS spectra plays a crucial role in the spectral analysis of galaxies with an AGN component improving the selection of the best-fitting hot dust (torus) model. We find a correlation between the obscured star formation rate, SFR_IR, derived from the IR luminosity of the starburst component, and SFRPAH, derived from the luminosity of the PAH features, L_PAH, with SFR_FIR taking higher values than SFR_PAH. The correlation is different for AGN- and starburst-dominated objects. The ratio of L_PAH to that of the starburst component, L_PAH/L_SB, is almost constant for AGN-dominated objects but decreases with increasing L_SB for starburst-dominated objects. SFR_FIR increases with the accretion luminosity, L_acc, with the increase less prominent for the very brightest, unobscured AGN-dominated sources. We find no correlation between the masses of the hot (AGN-heated) and cold (starburst-heated) dust components. We interpret this as a non-constant fraction of gas driven by the gravitational effects to the AGN while the starburst is ongoing. We also find no evidence of the AGN affecting the temperature of the cold dust component, though this conclusion is mostly based on objects with a non-dominant AGN component. We conclude that our findings do not provide evidence that the presence of AGN affects the star formation process in the host galaxy, but rather that the two phenomena occur simultaneously over a wide range of luminosities.

Additional Information

© 2013 The Royal Astronomical Society. Accepted 2013 June 25; Received 2013 June 25; In original form 2013 April 3. SPIRE has been developed by a consortium of institutes led by Cardiff Univ. (UK), including Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); and Caltech, JPL, NHSC, Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy);MCINN (Spain); SNSB (Sweden); STFC, UKSA (UK); and NASA (USA). The SPIRE data presented in this paper are available through the HerMES Database in Marseille (HeDaM; http://hedam.oamp.fr/HerMES). The Cornell Atlas of Spitzer/IRS Sources (CASSIS) is a product of the Infrared Science Center at Cornell University, supported by NASA and JPL. Funding for the creation and distribution of the SDSS Archive has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the US Department of Energy, the Japanese Monbukagakusho and the Max Planck Society. The SDSS website is http://www.sdss.org/. Much of the analysis presented in this work was done with TOPCAT (http://www.star.bris.ac.uk/∼mbt/topcat/), developed by M. Taylor.

Attached Files

Published - MNRAS-2013-Feltre-2426-37.pdf

Submitted - 1306.5946v1.pdf


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