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Active Galactic Nucleus and Starburst Classification from Spitzer Mid-Infrared Spectra for High-Redshift SWIRE Sources

Weedman, D. and Polletta, M. and Lonsdale, C. J. and Wilkes, B. J. and Siana, B. and Houck, J. R. and Surace, J. and Shupe, D. and Farrah, D. and Smith, H. E. (2006) Active Galactic Nucleus and Starburst Classification from Spitzer Mid-Infrared Spectra for High-Redshift SWIRE Sources. Astrophysical Journal, 653 (1). pp. 101-111. ISSN 0004-637X. doi:10.1086/508647.

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Spectra have been obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope for 20 sources in the Lockman Hole field of the SWIRE survey. The sample is divided between sources with indicators of an obscured AGN, based primarily on X-ray detections of optically faint sources, and sources with indicators of a starburst, based on optical and near-infrared spectral energy distributions (SEDs), which show a luminosity peak from stellar photospheric emission. Ten of the 11 AGN sources have IRS spectra that show silicate absorption or are power laws; only one AGN source shows PAH emission features. All nine of the sources showing starburst SEDs in the near-infrared show PAH emission features in the IRS spectra. Redshifts are determined from the IRS spectra for all nine starbursts (1.0 < z < 1.9) and 8 of the 11 AGNs (0.6 < z < 2.5). Classification as AGN because of an X-ray detection, the classification as AGN or starburst derived from the photometric SED, and the IRS spectroscopic classification as AGN (silicate absorption) or starburst (PAH emission) are all consistent in 18 of 20 sources. The surface density for starbursts that are most luminous in the mid-infrared is less than that for the most luminous AGNs within the redshift interval 1.7 ≾ z ≾ 1.9. This result implies that mid-infrared source counts at high redshift are dominated by AGNs for f_ν(24 μm) ≳ 1.0 mJy.

Item Type:Article
Related URLs:
URLURL TypeDescription
Polletta, M.0000-0001-7411-5386
Lonsdale, C. J.0000-0003-0898-406X
Wilkes, B. J.0000-0003-1809-2364
Siana, B.0000-0002-4935-9511
Surace, J.0000-0001-7291-0087
Shupe, D.0000-0003-4401-0430
Farrah, D.0000-0003-1748-2010
Additional Information:© 2006 The American Astronomical Society. Received 2006 May 9; accepted 2006 August 24. We thank D. Devost, G. Sloan, and P. Hall for help in improving our IRS spectral analysis, and S. Higdon and J. Higdon for their effort in developing the SMART analysis package. We thank B. Schulz for providing ISO spectra of quasars. M. P. and B.W. acknowledge financial support for Chandra observations through NASA grant G04-5158A. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. The SWIRE project is part of the Spitzer Legacy Science Program. Support for this work by the IRS GTO team at Cornell University was provided by NASA through contract 1257184, issued by JPL/Caltech.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:dust, extinction; galaxies: active; galaxies: high-redshift; galaxies: starburst; infrared: galaxies; X-rays: galaxies
Issue or Number:1
Record Number:CaltechAUTHORS:20110616-141006266
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Official Citation:Active Galactic Nucleus and Starburst Classification from Spitzer Mid-Infrared Spectra for High-Redshift SWIRE Sources D. Weedman, M. Polletta, C. J. Lonsdale, B. J. Wilkes, B. Siana, J. R. Houck, J. Surace, D. Shupe, D. Farrah, and H. E. Smith doi: 10.1086/508647
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:24037
Deposited By: Ruth Sustaita
Deposited On:16 Jun 2011 21:43
Last Modified:09 Nov 2021 16:20

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