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Preprint typeset using L ATEX style emulateapj v. 7/8/03 THE X-RAY SPECTRAL PROPERTIES OF SCUBA GALAXIES

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Abstract

Deep SCUBA surveys have uncovered a large population of massive submillimeter emitting galaxies (SMGs; f850µm> ∼ 4 mJy) at z> ∼ 1. Although it is generally believed that these galaxies host intense star-formation activity, there is growing evidence that a substantial fraction also harbor an Active Galactic Nucleus [AGN; i.e., an accreting super-massive black hole (SMBH)]. We present here possibly the strongest evidence for this viewpoint to date: the combination of ultra-deep X-ray observations (the 2 Ms Chandra Deep Field-North) and deep Keck spectroscopic data of SMGs with radio counterparts. We find that the majority ( ≈ 75%) of these radio-selected spectroscopically identified SMGs host AGN activity; the other ≈ 25 % have X-ray properties consistent with star formation (X-ray derived star-formation rates of ≈ 1300–2700 M⊙yr−1). The AGNs have properties generally consistent with those of nearby luminous AGNs (Γ ≈ 1.8±0.5, NH ≈ 1020 –1024 cm−2, and LX ≈ 1043 –1044.5 erg s−1) and the majority ( ≈ 80%) are heavily obscured (NH> ∼ 1023 cm−2). We construct composite rest-frame 2–20 keV spectra for three different obscuration classes (NH < 1023 cm−2, NH = 1– 5 ×1023 cm−2, and NH> 5 × 1023 cm−2) which reveal features not seen in the individual X-ray spectra. An ≈ 1 keV equivalent width Fe Kα emission line is seen in the composite X-ray spectrum of the most heavily obscured AGNs, suggesting Compton-thick or near Compton-thick absorption. Even taking into account th

Year: 2005
OAI identifier: oai:CiteSeerX.psu:10.1.1.316.6513
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