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

By R. Srianand, P. Noterdaeme, C. Ledoux, P. Petitjean. 2008

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We present the first detection of carbon monoxide (CO) in a damped Lyman-α 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 ,H 2 ,a nd 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 ,i s 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 K, while 9.315 ± 0.007 K 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.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/0e5f0f8b561ee938fcba804cac5ca414cd6a3d96

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Citations in the corpus

The evolution of the cosmic microwave background temperature Measurements of TCMB at high redshift from carbon monoxide excitation (2010, methodology): “The use of CO in this kind of experiments was prevented by the fact that CO has been detected in absorption only very recently at high-z (Srianand et al., 2008; Noterdaeme et al., 2009, 2010).”
THE FIRST POSITIVE DETECTION OF MOLECULAR GAS IN A GRB HOST GALAXY (2009, background): “Previous detections of intervening CO absorption toward quasars have only shown trace quantities of molecular gas (Srianand et al. 2008).”