Journal Article

The AGN content in luminous infrared galaxies at <i>z</i>∼ 2 from a global SED analysis including <i>Herschel</i> data

F. Pozzi, C. Vignali, C. Gruppioni, A. Feltre, J. Fritz, D. Fadda, P. Andreani, S. Berta, A. Cimatti, I. Delvecchio, D. Lutz, B. Magnelli, R. Maiolino, R. Nordon, P. Popesso, G. Rodighiero, D. Rosario, P. Santini and M. Vaccari

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 423, issue 2, pages 1909-1920
Published in print June 2012 | ISSN: 0035-8711
Published online June 2012 | e-ISSN: 1365-2966 | DOI:
The AGN content in luminous infrared galaxies at z∼ 2 from a global SED analysis including Herschel data

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We use Herschel-PACS far-infrared (IR) data, combined with previous multiband information and mid-IR spectra, to properly account for the presence of an active nucleus and constrain its energetic contribution in luminous IR sources at z∼ 2. The sample is composed of 24 sources in the GOODS-South field, with typical IR luminosity of 1012 L. Data from the 4 Ms Chandra X-ray imaging in this field are also used to identify and characterize active galactic nucleus (AGN) emission.

We reproduce the observed spectral energy distribution (SED), decomposed into a host-galaxy and an AGN component. A smooth-torus model for circumnuclear dust is used to account for the direct and reprocessed contribution from the AGN.

We confirm that galaxies with typical at z∼ 2 are powered predominantly by star formation. An AGN component is present in nine objects (∼35 per cent of the sample) at the 3σ confidence level, but its contribution to the 8–1000 m emission accounts for only ∼5 per cent of the energy budget. The AGN contribution rises to ∼23 per cent over the 5–30 m range (in agreement with Spitzer IRS results) and to ∼60 per cent over the narrow 2–6 m range. The presence of an AGN is confirmed by X-ray data for three (out of nine) sources, with X-ray spectral analysis indicating the presence of significant absorption, i.e. NH∼ 1023–1024 cm−2. An additional source shows indications of obscured AGN emission from X-ray data. The comparison between the mid-IR-derived X-ray luminosities and those obtained from X-ray data suggests that obscuration is likely present also in the remaining six sources that harbour an AGN according to the SED-fitting analysis.

Keywords: galaxies: active; galaxies: nuclei; infrared: galaxies

Journal Article.  7652 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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