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The z = 1.6748 C I Absorber toward PKS 1756+237

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Published 5 March 1999 • © 1999. The American Astronomical Society. All rights reserved. Printed in U.S.A.
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Article information
Author e-mails

kroth@pha.jhu.edu

Author affiliations

1 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96825

2 Hubble Fellow

3 Visiting Astronomer, W. M. Keck Observatory, operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. W. M. Keck Observatory was made possible by the generous financial support of the W. M. Keck Foundation

4 Current address: Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218

Dates

Received 1 December 1998
Accepted 18 February 1999
Published

Citation

Katherine C. Roth and James M. Bauer 1999 ApJ 515 L57

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DOI

https://doi.org/10.1086/311974

Keywords

cosmic microwave background; dust, extinction; ISM: abundances; quasars: absorption lines; quasars: individual (PKS 1756+237)

Journal RSS feed

1538-4357/515/2/L57

Abstract

We report the detection of the λ1560 and λ1657 ground-state C I absorption features in the zabs=1.6748 system toward the QSO PKS 1756+237. We find no associated C I* lines with a resulting 3 σ excitation temperature upper limit of Tex≤8.54(+0.65−0.56) K, which is consistent with the predicted cosmic microwave background radiation (CMBR) temperature of TCMBR=7.291 K. Because the redshifted CMBR populates the J=1 level and leaves little room for additional local excitation through either collisions or UV pumping, our data place 2-3 times more stringent limits on particle densities and UV fields than existing Copernicus observations of similar column density sight lines in the Milky Way. We also detect several Ni II lines and the weak Fe II λ1611 line. From the Ni/Fe column density ratio, we find evidence for dust at a dust-to-metals ratio similar to that seen toward warm Galactic disk clouds. Based on these findings and supported by our Lyα spectrum, we propose to reclassify this system as a damped Lyα absorber.

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