Evidence for a Cool Neutral Medium in Damped Lyman-alpha Systems

Details Evidence for a Cool Neutral Medium in Damped Lyman-alpha Systems Evidence for a Cool Neutral Medium in Damped Lyman-alpha Systems

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003aas...203.9701h&link_type=abstract

American Astronomical Society Meeting 203, #97.01; Bulletin of the American Astronomical Society, Vol. 35, p.1365

Astronomy and Astrophysics

Astronomy

Scientific paper

I discuss the use of the relative populations of the fine-structure excited states of Si II and C II as temperature diagnostics in high-redshift damped Lyman-alpha systems (DLAs). The upper 2P3/2 states of these ions are populated through collisions with electrons and hydrogen as well as through direct pumping by CMB photons. The ratio of Si II* to C II* is dependent on the temperature of the gas, given the difference in the excitation energies for each ion; it depends only weakly on the density (so long as the densities in the absorber are not near the critical density of either ion). I demonstrate the application of this diagnostic, showing that the ISM in high-redshift DLAs must contain a cold neutral phase, implying they may be capable of forming stars.
This work is presented in Howk, Wolfe, and Prochaska (2004).

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