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Spectroscopic follow-up of 70μm sources in Spitzer Wide-area Infrared Extragalactic Legacy Survey

We present spectroscopic follow-up observations of 70μm selected galaxies from the SWIRE XMMLSS and Lockman Hole fields. We have measured spectroscopic redshifts for 293 new sources down to a 70μm flux limit of 9mJy and R < 22. 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 [OIII], Hβ, [NII], Hα and [SII] emission lines are available to determine their power source. We find in our sample 13 QSOs, 1 Seyfert II galaxy, 33 star forming galaxies, 30 composite galaxies, 5 LINERs and 21 ambiguous galaxies. We fit single temperature dust spectral energy distributions (SEDs) to 81 70μm sources with 160μm photometry to estimate dust temperatures and masses. Assuming the dust emissivity factor (β) as 1.5, we determine temperatures in the range ~ 20-60K and dust masses with a range of 10{^6}-10{^9} M{_\odot}. 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 determining the shape of the Rayleigh-Jeans tail of the dust SED. We then model SEDs from optical to far-IR for each source using a set of galaxy and quasar templates in the optical and near-IR (NIR) and with a set of dust emission templates (cirrus, M82 starburst, Arp 220 starburst and AGN dust torus) in the mid-IR (MIR) to far-IR (FIR). The number of objects fit with each dust template are: 57 Arp 220, 127 M82, 9 cirrus, 1 AGN dust torus, 70 M82 and cirrus, 26 M82 and AGN dust torus and 3 Arp 220 and AGN dust torus. We determine the total IR luminosity (LIR) in range 10{^8}-10{^{15}} L{_\odot} by integrating the SED models from 8 to 1000μm.