H2, C I, Metallicity, and Dust Depletion in the Z = 2.34 Damped Lyα Absorption System toward QSO 1232+0815

Details H2, C I, Metallicity, and Dust Depletion in the Z = 2.34 Damped Lyα Absorption System toward QSO 1232+0815 H2, C I, Metallicity, and Dust Depletion in the Z = 2.34 Damped Lyα Absorption System toward QSO 1232+0815

Jan 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001apj...547l...1g&link_type=abstract

The Astrophysical Journal, Volume 547, Issue 1, pp. L1-L5.

Astronomy and Astrophysics

Astronomy

38

Cosmology: Cosmic Microwave Background, Ism: Dust, Extinction, Cosmology: Early Universe, Galaxies: Abundances, Ism: Molecules, Galaxies: Quasars: Absorption Lines, Quasars: Individual (Qso 1232+0815)

Scientific paper

We report the detection of strong molecular hydrogen (H2) absorption lines in the z=2.34 damped Lyα absorber (DLA) toward QSO 1232+0815. This is the second detection in our survey for high-redshift molecules. The new ultraviolet spectrum of the QSO 1232+0815 at 0.9 Å resolution, taken with the Multiple Mirror Telescope Blue Channel Spectrograph, shows the υ=0-0 up to 10-0 Lyman bands and also the Werner υ=0-0 band of H2 associated with the z=2.34 DLA. We have estimated the total H2 column density in this system. It ranges from ~3×1019 cm-2 to ~3×1017 cm-2 depending on the Doppler parameters, b=6 or 10 km s-1. Based on the best fit with b=6 km s-1, the estimated kinetic temperature is TK~80 K. The measurements of the abundance of zinc and iron in the same DLA show that the metallicity measured by the relatively undepleted element zinc is [Zn/H]=-0.86, while the relative abundance ratio [Fe/Zn] is -1.04, indicating dust depletion. Combining our work with previous results on H2 and relative heavy-element depletion, we find that there is a correlation between them, which suggests that the formation of H2 on dust grains is perhaps the dominant formation process in high-redshift DLAs. Detections of strong absorption from the ground and excited states of neutral carbon (C I) in the z=2.34 DLA are also presented. The excitation temperature between the two fine-structure levels of C I is 15.7+/-3.5 K, an upper limit for the cosmic microwave background radiation temperature at z=2.34. This value is consistent with the prediction by the standard big bang cosmology. Observations here were obtained with the Multiple Mirror Telescope, a joint facility of the University of Arizona and the Smithsonian Institution.

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