1999/11/09 by W. M. Lane, F. H. Briggs, F. Briggs +1 · 6 citations
Chemistry · Physics and Astronomy · #Absorption (acoustics) #Absorption spectroscopy #Analytical Chemistry (journal) #Astronomy #Astrophysics #Astrophysics and Cosmic Phenomena #Astrophysics and Star Formation Studies #Atomic physics #Chemistry #Context (archaeology) #Full width at half maximum #Galaxies: Formation, Evolution, Phenomena #Line (geometry) #Mean kinetic temperature #Optics #Phase (matter) #Physics #Quasar #Redshift #Spectral line #Thermal #Thermodynamics #Voigt profile #astro-ph
paper · pdf · doi:10.1086/308578
15 pages, incl. 4 figures, accepted for publication in ApJ
arxiv created 1999/11/09 · openalex publication_date 2000/03/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present a detailed study of the H I 21 cm absorption system at z = 0.0912 toward the radio quasar B0738+313. The uncommonly narrow main absorption line and weak secondary line are resolved for the first time and have FWHM velocities of Δ v 1 = 3.7 and Δ v 2 = 2.2 km s -1 (main and secondary components, respectively). In addition, we find it necessary to add a third, broader shallow component to obtain a good fit to the spectrum. Although the harmonic mean spin temperature calculated by comparison of the 21 cm lines to the damped Lyα line is = 775 ± 100 K, the thermal kinetic temperatures of the two narrow components, calculated from their widths, are much lower: T k ≤ 297 ± 3 and ≤103 ± 10 K, respectively. This is the first case of a redshifted absorption system for which T k is measured to be less than . We discuss this result in the context of a two-phase gas model, in which the damped Lyα gas is sensitive to a significant neutral column density of warm-phase gas as well as the cold-phase gas of the narrow 21 cm lines. The third component is interpreted as representing the warm-phase gas with T k ≤ 5050 ± 950 K. The combined column density of the three 21 cm components is approximately equal to that derived from fits to the damped Lyα line.