A Caltech Library Service

Ultra-deep Mid-infrared Spectroscopy of Luminous Infrared Galaxies at z ~ 1 and z ~ 2

Fadda, Dario and Yan, Lin and Lagache, Guilaine and Sajina, Anna and Lutz, Dieter and Wuyts, Stijn and Frayer, David T. and Marcillac, Delphine and Le Floc'h, Emeric and Caputi, Karina and Spoon, Henrik W. W. and Veilleux, Sylvain and Blain, Andrew and Helou, George (2010) Ultra-deep Mid-infrared Spectroscopy of Luminous Infrared Galaxies at z ~ 1 and z ~ 2. Astrophysical Journal, 719 (1). pp. 425-450. ISSN 0004-637X.

PDF - Published Version
See Usage Policy.

[img] PDF - Submitted Version
See Usage Policy.


Use this Persistent URL to link to this item:


We present ultra-deep mid-infrared spectra of 48 infrared-luminous galaxies in the GOODS-south field obtained with the Infrared Spectrograph on the Spitzer Space Telescope. These galaxies are selected among faint infrared sources (0.14-0.5 mJy at 24 μm) in two redshift bins (0.76-1.05 and 1.75-2.4) to sample the major contributors to the cosmic infrared background at the most active epochs. We estimate redshifts for 92% of the sample using polycyclic aromatic (PAH) and Si absorption features obtaining, in particular, eight new redshifts difficult to measure from ground-based observations. Only a few of these galaxies (5% at z ~ 1 and 12% at z ~ 2) have their total infrared luminosity dominated by emission from active galactic nuclei (AGNs). The averaged mid-IR spectrum of the z ~ 1 luminous infrared galaxies (LIRGs) is a very good match to the averaged spectrum of local starbursts. The averaged spectrum of the z ~ 2 ultra-luminous infrared galaxies (ULIRGs), because of a deeper Si absorption, is better fitted by the averaged spectrum of H II-like local ULIRGs. Combining this sample with other published data, we find that 6.2 μm PAH equivalent widths (EW) reach a plateau of ~ 1 μm for L 24 μm ≾ 10^(11) L_⊙. At higher luminosities, EW_(6.2 μm) anti-correlates with L _(24 μm). Intriguingly, high-z ULIRGs and sub-millimeter galaxies (SMGs) lie above the local EW_(6.2 μm)-L_(24 μm) relationship suggesting that, at a given luminosity, high-z ULIRGs have AGN contributions to their dust emission lower than those of local counterparts. A quantitative analysis of their morphology shows that most of the luminous IR galaxies have morphologies similar to those of IR-quiet galaxies at the same redshift. All z ~ 2 ULIRGs of our sample are IR-excess BzK galaxies and most of them have L_(FIR)/L_(1600 Å) ratios higher than those of starburst galaxies at a given UV slope. The "IR excess" is mostly due to strong 7.7 μm PAH emission and underestimation of UV dust extinction. On the basis of the AGN-powered L_(6 μm) continuum measured directly from the mid-IR spectra, we estimate an average intrinsic X-ray AGN luminosity of L_(2–10 keV) = (0.1± 0.6)× 10^(43) erg s^(–1), a value substantially lower than the prediction by Daddi et al.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Fadda, Dario0000-0002-3698-7076
Yan, Lin0000-0003-1710-9339
Lagache, Guilaine0000-0003-1492-2519
Sajina, Anna0000-0002-1917-1200
Lutz, Dieter0000-0003-0291-9582
Frayer, David T.0000-0003-1924-1122
Caputi, Karina0000-0001-8183-1460
Spoon, Henrik W. W.0000-0002-8712-369X
Veilleux, Sylvain0000-0002-3158-6820
Blain, Andrew0000-0001-7489-5167
Helou, George0000-0003-3367-3415
Additional Information:© 2010 The American Astronomical Society. Received 2009 December 21; accepted 2010 June 14; published 2010 July 20. This research made use of Tiny Tim/Spitzer, developed by John Krist for the Spitzer Science Center. The Center is managed by the California Institute of Technology under a contract with NASA. We are grateful to Haojing Yan for providing us the reduced NICMOS H-band stamp images for some of our sources. We thank P. Capak for helpful discussions. We are grateful to the anonymous referee for the detailed reading of the paper and for many ideas and suggestions to improve the quality of the paper. Support for this work was provided by NASA through an award issued by JPL/Caltech. S. Wuyts acknowledges support from the W. M. Keck Foundation.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:galaxies: evolution; galaxies: high-redshift; galaxies: starburst; infrared: galaxies
Issue or Number:1
Classification Code:PACS: 98.54.Ep; 98.62.Py; 98.62.Ai; 95.30.Ky; 98.70.Vc; 98.58.Bz
Record Number:CaltechAUTHORS:20100823-143138995
Persistent URL:
Official Citation:Dario Fadda et al 2010 ApJ 719 425 doi: 10.1088/0004-637X/719/1/425
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:19602
Deposited By: Tony Diaz
Deposited On:23 Aug 2010 22:10
Last Modified:04 Nov 2019 02:14

Repository Staff Only: item control page