2007/03/26 by Jason Tumlinson, Jason X. Prochaska, Hsiao-Wen Chen +4 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Galaxy #Gamma-ray burst #Gamma-ray bursts and supernovae #Hydrogen molecule #Interstellar medium #Metallicity #Molecular cloud #RADIUS #Star formation #Stars #astro-ph
paper · pdf · doi:10.1086/521294
7 pg, 3 color figures. Submitted to ApJ
arxiv created 2007/03/26 · openalex publication_date 2007/10/19 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We examine the abundance of molecular hydrogen (H 2 ) in the spectra of gamma ray burst afterglows (GRBs). In nearby galaxies, H 2 traces the cold neutral medium (CNM) and dense molecular star-forming interstellar gas. Although H 2 is detected in at least half of all sight lines toward hot stars in the Magellanic Clouds and in ≈25% of damped Lyα systems toward quasars, it is not detected in any of the five GRB environments with a similar range of neutral hydrogen column density and metallicity. We detect no vibrationally excited H 2 that would imply that the GRB itself has photodissociated its parent molecular cloud, so such models are ruled out unless the parent cloud was ≲4 pc in radius and was fully dissociated prior to the spectroscopic observations, or the star escaped its parent cloud during its main-sequence lifetime. The low molecular fractions for the GRBs are mysterious in light of their large column densities of neutral H and expectations based on local analogs, i.e., 30 Doradus in the LMC. This surprising lack of H 2 in GRB damped Lyα absorbers indicates that the destruction processes that suppress molecule formation in the LMC and SMC are more effective in the GRB hosts, most probably due to a combination of low metallicity and an FUV radiation field 10-100 times the Galactic mean field. These inferred conditions place strong constraints on the star-forming regions in these early galaxies.