2004/04/30 by J. Christopher Howk, Arthur M. Wolfe, Jason X. Prochaska · 1 citation
Physics and Astronomy · #Absorption (acoustics) #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Excitation #Excitation temperature #Galaxies: Formation, Evolution, Phenomena #Kinetic energy #Limit (mathematics) #Lyman limit #Mean kinetic temperature #Quasar #Star formation #astro-ph
paper · pdf · doi:10.1086/429798
published as Astrophys.J. 433 (1994) 468 · Accepted to ApJ Letters; 13 pages, including figures and tables
arxiv created 2005/02/21 · openalex publication_date 2005/03/08 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
We discuss interstellar temperature determinations using the excitation equilibrium of the 2 P levels of Si II and C II. We show how observations of the 2 P 3/2 fine-structure levels of Si II and C II (which have significantly different excitation energies, corresponding to ~413 and 92 K, respectively) can be used to limit gas kinetic temperatures. We apply this method to the z = 4.224 damped Lyα system toward the quasar PSS 1443+27. The lack of significant absorption out of the Si II 2 P 3/2 level and the presence of very strong C II 2 P 3/2 provide an upper limit to the temperature of the C II*-bearing gas in this system. Assuming a solar Si/C ratio, the observations imply a 2 σ limit T < 954 K for this absorber; a supersolar Si/C ratio gives stricter limits, T < 524 K. The observations suggest the presence of a cold neutral medium; such cold gas may serve as the fuel for star formation in this young galaxy.