First detection of CO in a high-redshift damped Lyman-αsystem

Srianand, R. ; Noterdaeme, P. ; Ledoux, C. ; Petitjean, P. (2008) First detection of CO in a high-redshift damped Lyman-αsystem Astronomy and Astrophysics, 482 (3). L39-L42. ISSN 0004-6361

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Official URL: http://www.aanda.org/articles/aa/abs/2008/18/aa097...

Related URL: http://dx.doi.org/10.1051/0004-6361:200809727

Abstract

We present the first detection of carbon monoxide (CO) in a damped Lyman- system (DLA) at zabs = 2.41837 toward SDSS J143912.04+111740.5. We also detected H2 and HD molecules. The measured total column densities (in log units) of H I, H2, and CO are 20.10±0.10, 19.38±0.10, and 13.89±0.02, respectively. The molecular fraction, f = 2N(H2)/(N(H I)+2N(H2)) = 0.27 +0.10-0.08, is the highest among all known DLAs. The abundances relative to solar of S, Zn, Si, and Fe are -0.03±0.12, +0.16±0.11, -0.86±0.11, and -1.32±0.11, respectively, indicating a high metal enrichment and a depletion pattern onto dust-grains similar to the cold ISM of our Galaxy. The measured N(CO)/N(H2) = 3 ×10-6 is much less than the conventional CO/H2 ratio used to convert the CO emission into gaseous mass but is consistent with what is measured along translucent sightlines in the Galaxy. The CO rotational excitation temperatures are higher than those measured in our Galactic ISM for similar kinetic temperature and density. Using the C I fine structure absorption lines, we show that this is a consequence of the excitation being dominated by radiative pumping by the cosmic microwave background radiation (CMBR). From the CO excitation temperatures, we derive TCMBR = 9.15±0.72 Κ, while 9.315±0.007 Κ is expected from the hot big-bang theory. This is the most precise high-redshift measurement of TCMBR and the first confirmation of the theory using molecular transitions at high redshift.

Item Type:Article
Source:Copyright of this article belongs to EDP Sciences.
Keywords:Galaxies: Abundances; Galaxies: Quasars: Absorption Lines
ID Code:55225
Deposited On:18 Aug 2011 08:14
Last Modified:18 May 2016 07:34

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