C I Fine-Structure Excitation by the CMBR at z=1.973

Details C I Fine-Structure Excitation by the CMBR at z=1.973 C I Fine-Structure Excitation by the CMBR at z=1.973

Jan 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aas...18912217r&link_type=abstract

American Astronomical Society, 189th AAS Meeting, late abstracts, #122.17; Bulletin of the American Astronomical, Vol. 29, p. 73

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Scientific paper

We present high-resolution (6.5 km s(-1) ) spectra of C I absorption in the z=1.9731 damped Lyalpha system toward the QSO 0013--004. The C I data, including both the lambda 1560 and lambda 1657 multiplets, were obtained in Nov/Dec 1996 with HIRES on the Keck 10m telescope. This system was identified by Ge, Bechtold & Black (1996) as a potential C I candidate due to the large H I column density and relatively high metal abundance and dust content compared to other damped absorbers. The C I fine-structure lines provide a sensitive probe of the Cosmic Microwave Background Radiation (CMBR) at high redshift. Since the temperature of the CMBR is predicted to have been higher in the past [T(z)=T_deg(1+z)], CMBR photons will be more efficient at populating the excited-state levels and can compete with local collisional and UV pumping excitation mechanisms that dominate in the Milky Way interstellar medium. The observed C I excitation temperature is a strict upper limit to the CMBR temperature, providing a direct test of standard Friedman cosmology. The high spectral resolution of our data solves the problem of blending between the various fine-structure multiplet members. This is particularly important given the complex velocity structure seen in other tracers of the neutral absorbing gas. We clearly detect both ground-state C I lines as well as first excited-state absorption consistent with excitation by the redshifted CMBR [T(z=1.9731)=8.105 K].

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