Issue |
A&A
Volume 482, Number 3, May II 2008
|
|
---|---|---|
Page(s) | L39 - L42 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:200809727 | |
Published online | 26 March 2008 |
Letter to the Editor
First detection of CO in a high-redshift damped Lyman-α system*
1
IUCAA, Post Bag 4, Ganeshkhind, Pune 411 007, India e-mail: anand@iucaa.ernet.in
2
European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago 19, Chile
3
UPMC Paris 06, Institut d'Astrophysique de Paris, UMR7095 CNRS, 98bis Boulevard Arago, 75014 Paris, France
Received:
6
March
2008
Accepted:
20
March
2008
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, H2, and CO are 20.10±0.10, 19.38±0.10, and
13.89±0.02, respectively. The molecular fraction, f = (H2)/(N(H i)+2
H2)) =
, 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 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.
Key words: galaxies: abundances / galaxies: quasars: absorption lines
© ESO, 2008
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