Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aj....109.1522c&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 109, no. 4, p. 1522-1530
Astronomy and Astrophysics
Astronomy
258
Galactic Structure, Lyman Alpha Radiation, Metallicity, Molecular Clouds, Velocity Distribution, High Dispersion Spectrographs, High Resolution, Lyman Spectra, Spectral Resolution, Telescopes
Scientific paper
Using very high signal-to-noise (S/N), high spectral resolution data obtained with the HIRES spectrograph on the Keck 10 m telescope, we show that roughly half of Lyman-alpha forest clouds with NHI greater than or equal 3 X 1014/sq cm have measurable C IV lines with NC IV greater than 10 12/sq cm. We find the ratio of the median column density of C IV to the median NHI to be 2 X 10-3 roughly corresponding to a metallicity of 10-2 solar. This is shown to be comparable to that of a sample of Lyman-limit system clouds with NHI approximately 3 X 1017/sq cm and to the mean value in lower column density samples. The kinematic structure of the C IV lines shows that the Ly-alpha clouds are blended complexes of cloudlets individually having T approximately equal 35,000-70,000 K and velocity dispersions of approximately 18 km/s; these complexes require a gravitational confinement mechanism.
Cowie Lennox L.
Hu Esther M.
Kim Tae-Sun
Songaila Antoinette
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