First detection of CO in a high-redshift damped Lyman-α system

Details First detection of CO in a high-redshift damped Lyman-α system First detection of CO in a high-redshift damped Lyman-α system

May 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008a%26a...482l..39s&link_type=abstract

Astronomy and Astrophysics, Volume 482, Issue 3, 2008, pp.L39-L42

Astronomy and Astrophysics

Astrophysics

39

Galaxies: Abundances, Galaxies: Quasars: Absorption Lines

Scientific paper

We present the first detection of carbon monoxide (CO) in a damped Lyman-α system (DLA) at z_abs = 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 T_CMBR = 9.15±0.72 K, while 9.315±0.007 K is expected from the hot big-bang theory. This is the most precise high-redshift measurement of T_CMBR and the first confirmation of the theory using molecular transitions at high redshift.
Based on observations carried out at the European Southern Observatory (ESO), under programme 278.A-5062 with the UVES echelle spectrograph installed at the ESO Very Large Telescope (VLT), unit Kueyen, on Mount Paranal in Chile.

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