Astron. Astrophys. 330, 443-446 (1998)

5. Concluding remarks

We have searched for redshifted [C II ] towards a damped Ly absorption system that has a large neutral hydrogen column density and which was controversially reported to be a source of CO emission, indicative of rapid star formation. We find no sign of [C II ] emission and have placed an upper limit of K km s^-1 on the integrated line intensity.

This places a useful constraint on the [C II ]/CO(1-0) line-intensity ratio (, based on the line intensity reported by Frayer et al. 1994) which is consistent with ratios measured in normal-metallicity systems in the present-day Universe, but is significantly lower than the ratio found in systems with low metallicities such as we might expect to find in high-redshift damped Lyman absorption systems. We interpret this as evidence against the reality of the CO line detections towards this system, as long as the system is not significantly larger than present-day disk galaxies such as the Milky Way (which would compromise our measured ratios on the basis of disparate beam sizes).

We have also demonstated the dangers inherent in knitting together overlapping bands to increase velocity coverage. Clearly, wide-band receivers and backends are urgently required if we are to generate a trustworthy database of CO, [C II ], etc., spectra of high-redshift systems.

© European Southern Observatory (ESO) 1998

Online publication: January 16, 1998
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