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GOODS-Herschel : impact of active galactic nuclei and star formation activity on infrared spectral energy distributions at high redshift.

Kirkpatrick, A. and Pope, A. and Alexander, D.M. and Charmandaris, V. and Daddi, E. and Dickinson, M. and Elbaz, D. and Gabor, J. and Hwang, H.S. and Ivison, R. and Mullaney, J. and Pannella, M. and Scott, D. and Altieri, B. and Aussel, H. and Bournaud, F. and Buat, V. and Coia, D. and Dannerbauer, H. and Dasyra, K. and Kartaltepe, J. and Leiton, R. and Lin, L. and Magdis, G. and Magnelli, B. and Morrison, G. and Popesso, P. and Valtchanov, I. (2012) 'GOODS-Herschel : impact of active galactic nuclei and star formation activity on infrared spectral energy distributions at high redshift.', Astrophysical journal., 759 (2). p. 139.


We explore the effects of active galactic nuclei (AGNs) and star formation activity on the infrared (0.3-1000 μm) spectral energy distributions (SEDs) of luminous infrared galaxies from z = 0.5 to 4.0. We have compiled a large sample of 151 galaxies selected at 24 μm (S 24 >~ 100 μJy) in the GOODS-N and ECDFS fields for which we have deep Spitzer IRS spectroscopy, allowing us to decompose the mid-IR spectrum into contributions from star formation and AGN activity. A significant portion (~25%) of our sample is dominated by an AGN (>50% of the mid-IR luminosity) in the mid-IR. Based on the mid-IR classification, we divide our full sample into four sub-samples: z ~ 1 star-forming (SF) sources, z ~ 2 SF sources, AGNs with clear 9.7 μm silicate absorption, and AGNs with featureless mid-IR spectra. From our large spectroscopic sample and wealth of multi-wavelength data, including deep Herschel imaging at 100, 160, 250, 350, and 500 μm, we use 95 galaxies with complete spectral coverage to create a composite SED for each sub-sample. We then fit a two-temperature component modified blackbody to the SEDs. We find that the IR SEDs have similar cold dust temperatures, regardless of the mid-IR power source, but display a marked difference in the warmer dust temperatures. We calculate the average effective temperature of the dust in each sub-sample and find a significant (~20 K) difference between the SF and AGN systems. We compare our composite SEDs to local templates and find that local templates do not accurately reproduce the mid-IR features and dust temperatures of our high-redshift systems. High-redshift IR luminous galaxies contain significantly more cool dust than their local counterparts. We find that a full suite of photometry spanning the IR peak is necessary to accurately account for the dominant dust temperature components in high-redshift IR luminous galaxies. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Item Type:Article
Keywords:Dust, Extinction, Active, Galaxies, Evolution, Star formation, Infrared.
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Publisher statement:© 2012. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
Date accepted:No date available
Date deposited:23 December 2013
Date of first online publication:November 2012
Date first made open access:No date available

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