Open AccessMolecular hydrogen in damped Ly α systems: spatial distribution
Author(s) -
Hirashita H.,
Ferrara A.,
Wada K.,
Richter P.
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2003.06648.x
Subject(s) - physics , astrophysics , redshift , quasar , spatial distribution , ultraviolet , hydrogen molecule , molecular cloud , intensity (physics) , line (geometry) , fraction (chemistry) , spectral line , hydrogen , astronomy , optics , galaxy , stars , quantum mechanics , geometry , statistics , chemistry , organic chemistry , mathematics
To interpret H 2 quasar absorption‐line observations in damped Lyα clouds (DLAs), we model the H 2 spatial distribution within a DLA. Based on numerical simulations of disc structures with parameters similar to those derived for such absorbers, we calculate the H 2 distribution as a function of ultraviolet background (UVB) intensity and dust‐to‐gas ratio. For typical values of these two quantities we find that the area in which the H 2 fraction exceeds 10 −6 (typical observational detection limit) only covers ≲10 per cent of the disc surface, i.e. H 2 has a very inhomogeneous, clumpy distribution even at these low abundance levels. This explains the relative paucity of H 2 detections in DLAs. We also show the dependence of the covering fraction of H 2 on dust‐to‐gas ratio and UVB intensity, and we comment on the physics governing the H 2 chemical network at high redshift.