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Detections of CO Molecular Gas in 24 μm Bright ULIRGs at z ~ 2 in the Spitzer First Look Survey

Yan, Lin and Tacconi, L. J. and Fiolet, N. and Sajina, A. and Omont, A. and Lutz, D. and Zamojski, M. and Neri, R. and Cox, P. and Dasyra, K. M. (2010) Detections of CO Molecular Gas in 24 μm Bright ULIRGs at z ~ 2 in the Spitzer First Look Survey. Astrophysical Journal, 714 (1). pp. 100-114. ISSN 0004-637X.

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We present CO observations of nine ultra-luminous infrared galaxies (ULIRGs) at z ~ 2 with f_(ν)(24 μm) ≳ 1 mJy, previously confirmed with the mid-IR spectra in the Spitzer First Look Survey. All targets are required to have accurate redshifts from Keck/GEMINI near-IR spectra. Using the Plateau de Bure millimeter-wave Interferometer at the Institute for Radioastronomy at Millimeter Wavelengths, we detect CO J(3-2) (seven objects) or J(2-1) (one object) line emission from eight sources with integrated intensities I_c ~ 5σ-9σ. The CO-detected sources have a variety of mid-IR spectra, including strong polycyclic aromatic hydrocarbon, deep silicate absorption, and power-law continuum, implying that these molecular gas-rich objects at z ~ 2 could be either starbursts or dust-obscured active galactic nuclei (AGNs). The measured line luminosity L'_(CO) is (1.28-3.77) × 10^(10) K km/s pc^2. The averaged molecular gas mass is 1.7 × 10^(10) M_☉, assuming CO-to-H_2 conversion factor of 0.8 M (K km/s pc^2)^(–1). Three sources (33%)—MIPS506, MIPS16144, and MIPS8342—have double peak velocity profiles. The CO double peaks in MIPS506 and MIPS16144 show spatial separations of 45 kpc and 10.9 kpc, allowing the estimates of the dynamical masses of 3.2 × 10^(11) sin^(–2)(i) M_☉ and 5.4 × 10^(11) sin^(–2)(i) M, respectively. The implied gas fraction, M_(gas)/M_(dyn), is 3% and 4%, assuming an average inclination angle. Finally, the analysis of the Hubble Space Telescope/NIC2 images, mid-IR spectra, and IR spectral energy distribution revealed that most of our sources are mergers, containing dust-obscured AGNs dominating the luminosities at (3-6) μm. Together, these results provide some evidence suggesting submillimeter galaxies, bright 24 μm, z ~ 2 ULIRGs, and QSOs could represent three different stages of a single evolutionary sequence, however, a complete physical model would require much more data, especially high spatial resolution spectroscopy.

Item Type:Article
Related URLs:
URLURL TypeDescription
Yan, Lin0000-0003-1710-9339
Tacconi, L. J.0000-0002-1485-9401
Sajina, A.0000-0002-1917-1200
Omont, A.0000-0002-4721-3922
Lutz, D.0000-0003-0291-9582
Neri, R.0000-0002-7176-4046
Cox, P.0000-0003-2027-8221
Additional Information:© 2010 American Astronomical Society. Received 2009 November 4; accepted 2010 March 9; published 2010 April 7. Sylvain Veilleux is thanked for providing the electronic version of the mid-IR spectra for local IRAS 1 Jy sample. D. Riechers is gratefully acknowledged for very helpful discussions and for providing us a compiled list of high-z QSOs with high-resolution CO observations. This work is based on observations with 30 m telescope of the Institute for Radioastronomy at MillimeterWavelengths (IRAM; which is funded by the German Max Planck Society, the French CNRS, and the Spanish National Geographical Institute.We thank the staff of the IRAM Observatory for their support of this program. Also based on observations taken with Spitzer Space Telescope, which is funded by NASA and operated by JPL/Caltech. H-band imaging data are from observations made with the NASA/ESA Hubble Space Telescope and obtained at Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. We thank helpful discussions with Nick Scoville and Arjun Dey.
Group:Infrared Processing and Analysis Center (IPAC)
Subject Keywords:galaxies: evolution; galaxies: high-redshift; galaxies: ISM; galaxies: starburst
Issue or Number:1
Classification Code:PACS: 95.80.+p; 98.58.Ca; 98.58.Bz; 98.62.Qz; 98.54.Cm; 98.62.Ai
Record Number:CaltechAUTHORS:20100519-114331336
Persistent URL:
Official Citation:Lin Yan et al 2010 ApJ 714 100 doi: 10.1088/0004-637X/714/1/100
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:18353
Deposited By: Jason Perez
Deposited On:20 May 2010 19:59
Last Modified:04 Nov 2019 02:15

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