2006/08/29 by D. Weedman, D. W. Weedman, M. Polletta +11 · 2 citations
Physics and Astronomy · #Active galactic nucleus #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #Galaxy #Infrared #Luminosity #Luminous infrared galaxy #Physics #Redshift #Spectral line #Spectrograph #Spitzer Space Telescope #Stellar, planetary, and galactic studies #Telescope #astro-ph
paper · pdf · doi:10.1086/508647
published as Astrophys.J.653:101-111,2006 · 34 pages, 11 figures, ApJ accepted (Dec 2006)
arxiv created 2006/08/29 · openalex publication_date 2006/12/05 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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.