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Keck spectroscopy of z = 1-3 ULIRGs from the Spitzer SWIRE survey

Berta, S. and Lonsdale, C. J. and Siana, B. and Farrah, D. and Smith, H. E. and Polletta, M. and Franceschini, A. and Fritz, J. and Pérez-Fournon, I. and Rowan-Robinson, M. and Shupe, D. and Surace, J. (2007) Keck spectroscopy of z = 1-3 ULIRGs from the Spitzer SWIRE survey. Astronomy and Astrophysics, 467 (2). pp. 565-584. ISSN 0004-6361. doi:10.1051/0004-6361:20066795.

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Context. High-redshift ultra luminous infrared galaxies contribute the bulk of the cosmic IR background and are the best candidates for very massive galaxies in formation at z > 1.5. Aims. It is necessary to identify the energy source for their huge luminosities, starburst or AGN activity, in order to correctly interpret the role of ULIRGs in galaxy evolution, and compute reliable estimates of their star formation rates, stellar masses, and accretion luminosities. Methods. We present Keck/LRIS optical spectroscopy of 35 z ≥ 1.4 luminous IR galaxies in the Spitzer Wide-area Infra-Red Extragalactic survey (SWIRE) northern fields (Lockman Hole, ELAIS-N1, ELAIS-N2). The primary targets belong to the “IR-peak” class of galaxies, having the 1.6 μm (restframe) stellar feature detected in the IRAC Spitzer channels. The spectral energy distributions of the main targets are thoroughly analyzed, by means of spectro-photometric synthesis and multi-component fits (stars + starburst dust + AGN torus). Results. The IR-peak selection technique is confirmed to successfully select objects above z = 1.4, though some of the observed sources lie at lower redshift than expected. Among the 16 galaxies with spectroscopic redshift, 62% host an AGN component, two thirds being type-1 and one third type-2 objects. The selection, limited to r' < 24.5, is likely biased to optically-bright AGNs. All IR-peakers without emission lines have a non negligible continuum detection, and are likely to be very powerful starbursts, heavily extinguished by dust (A_V ≥ 5 mag). The SEDs of non-AGN IR-peakers resemble those of starbursts (SFR = 20–500 M_⊙/yr) hosted in massive (M > 10^(11) M_⊙) galaxies. The presence of an AGN component provides a plausible explanation for the spectroscopic/photometric redshift discrepancies, as the torus produces an apparent shift of the peak to longer wavelengths. These sources are analyzed in IRAC and optical-IR color spaces. In addition to the IR-peak galaxies, we present redshifts and spectral properties for 150 objects, out of a total of 301 sources on slits.

Item Type:Article
Related URLs:
URLURL TypeDescription
Berta, S.0000-0002-0320-1532
Lonsdale, C. J.0000-0003-0898-406X
Siana, B.0000-0002-4935-9511
Farrah, D.0000-0003-1748-2010
Polletta, M.0000-0001-7411-5386
Shupe, D.0000-0003-4401-0430
Surace, J.0000-0001-7291-0087
Additional Information:© ESO 2007. Received 22 November 2006. Accepted 8 March 2007 We wish to thank the Keck night staff for their availability in producing calibration frames at the science targets ALT,AZ positions. We are grateful to M. Meneghetti for tests on a supposed gravitational lens (which turned out not to be). We thank A. Bressan and C. Chiosi for useful discussions on UV and near-IR spectral features, S. Ciroi for suggestions on optical spectral classification, F. Di Mille and S. Siviero for elucidation on spectrographs and optical paths. The Spitzer Space Telescope is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. SWIRE was supported by NASA through the SIRTF Legacy Program under contract 1407 with the Jet Propulsion Laboratory.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:galaxies : distance and redshifts; galaxies : active; galaxies : starburst; galaxies : high redshift; galaxies : fundamental parameters; infrared : galaxies
Issue or Number:2
Record Number:CaltechAUTHORS:20091016-135838249
Persistent URL:
Official Citation:Keck spectroscopy of z = 1–3 ULIRGs from the Spitzer SWIRE survey S. Berta, C. J. Lonsdale, B. Siana, D. Farrah, H. E. Smith, M. C. Polletta, A. Franceschini, J. Fritz, I. Perez-Fournon, M. Rowan-Robinson, D. Shupe and J. Surace A&A 467 (2) 565-584 (2007) DOI: 10.1051/0004-6361:20066795
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:16370
Deposited By: Tony Diaz
Deposited On:26 Oct 2009 17:44
Last Modified:08 Nov 2021 23:26

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