Active Galactic Nucleus and Starburst Classification fromSpitzerMid‐Infrared Spectra for High‐Redshift SWIRE Sources
Author(s) -
D. W. Weedman,
M. Polletta,
Carol J. Lonsdale,
B. J. Wilkes,
Brian Siana,
J. R. Houck,
J. Surace,
D. L. Shupe,
D. Farrah,
H. E. Smith
Publication year - 2006
Publication title -
the astrophysical journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.376
H-Index - 489
eISSN - 1538-4357
pISSN - 0004-637X
DOI - 10.1086/508647
Subject(s) - physics , astrophysics , redshift , active galactic nucleus , spitzer space telescope , infrared , luminosity , astronomy , luminous infrared galaxy , spectral line , spectrograph , telescope , galaxy
Spectra have been obtained with the Infrared Spectrograph (IRS) on theSpitzer Space Telescope for 20 sources in the Lockman Hole field of the SWIREsurvey. The sample is divided between sources with indicators of an obscuredAGN, based primarily on X-ray detections of optically-faint sources, andsources with indicators of a starburst, based on optical and near-infraredspectral energy distributions (SEDs) which show a luminosity peak from stellarphotospheric emission. Ten of the 11 AGN sources have IRS spectra which showsilicate absorption or are power laws; only one AGN source shows PAH emissionfeatures. All 9 of the sources showing starburst SEDs in the near-infrared showPAH emission features in the IRS spectra. Redshifts are determined from the IRSspectra for all 9 starbursts (1.0 < z < 1.9) and 8 of the 11 AGN (0.6 < z <2.5). Classification as AGN because of an X-ray detection, the classificationas AGN or starburst derived from the photometric SED, and the IRS spectroscopicclassification as AGN (silicate absorption) or starburst (PAH emission) are allconsistent in 18 of 20 sources. The surface density for starbursts which aremost luminous in the mid-infrared is less than that for the most luminous AGNwithin the redshift interval 1.7 < z < 1.9. This result implies thatmid-infrared source counts at high redshift are dominated by AGN forf(24micron) > 1.0 mJy.Comment: 34 pages, 11 figures, ApJ accepted (Dec 2006
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