Journal Article

Spectroscopic follow-up of 70-<i>μ</i>m sources in <i>Spitzer</i> Wide-area Infrared Extragalactic Legacy Survey

H. Patel, D. L. Clements, M. Rowan-Robinson and M. Vaccari

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 415, issue 2, pages 1738-1750
Published in print August 2011 | ISSN: 0035-8711
Published online July 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.18828.x
Spectroscopic follow-up of 70-μm sources in Spitzer Wide-area Infrared Extragalactic Legacy Survey

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We present spectroscopic follow-up observations of 70-μm selected galaxies from the Spitzer Wide-area InfraRed Extragalactic Survey XMM-LSS and Lockman Hole fields. We have measured spectroscopic redshifts for 293 new sources down to a 70 μm flux limit of 9 mJy and r < 22 mag. The redshift distribution peaks at z ∼ 0.3 and has a high redshift tail out to z = 3.5. We perform emission line diagnostics for 91 sources where [O iii], Hβ, [N ii], Hα and [S ii] emission lines are available to determine their power source. We find in our sample 13 quasi-stellar objects, one type 2 Seyfert galaxy, 33 star-forming galaxies, 30 composite galaxies, five LINERs and 21 ambiguous galaxies. We fit single temperature dust spectral energy distributions (SEDs) to 81 70-μm sources with 160-μm photometry to estimate dust temperatures and masses. Assuming the dust emissivity factor (β) as 1.5, we determine dust temperatures in the range ∼20–60 K and dust masses with a range of 106–109 M. Plotting these objects in the luminosity–temperature diagram suggests that these objects have lower dust temperatures than local IR luminous galaxies. The Herschel Space Observatory will be crucial in understanding the nature of these sources and to accurately determine the shape of the Rayleigh–Jeans tail of the dust SED. We then model SEDs from optical to far-IR (FIR) for each source using a set of galaxy and quasar templates in the optical and near-IR and with a set of dust emission templates [cirrus, M82 starburst, Arp 220 starburst and active galactic nucleus (AGN) dust torus] in the mid-IR to FIR. The numbers of objects fitted with each dust template are 57 Arp 220, 127 M82, nine cirrus, one AGN dust torus, 70 M82 and cirrus, 26 M82 and AGN dust torus, and three Arp 220 and AGN dust torus. We determine the total IR luminosity (LIR) in range 108–1015 L by integrating the SED models from 8 to 1000 μm.

Keywords: galaxies: active; galaxies: general; galaxies: photometry; galaxies: starburst; infrared: galaxies

Journal Article.  8601 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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