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On The Origin Of Metallicity In Lyman-Alpha Forest Systems | | Masashi Chiba
; Biman B. Nath
; | | Date: |
5 Feb 1997 | | Journal: | Astrophys.J. 483 (1997) 638 | | Subject: | astro-ph | | Affiliation: | NAOJ, Japan) and Biman B. Nath (IUCAA, India | | Abstract: | We investigate the hypothesis that $lyal$ absorption lines arise in two populations of halos --- minihalos of small circular velocity ($V_c la 55$ km s$^{-1}$) in which star formation and metal production are inhibited by photoionization of the UV background radiation, and large galactic halos ($55 la V_c la 250$ km s$^{-1}$) which possess stars and metals. Based on the model of $lyal$-absorbing gas confined in both populations of halos, we attempt to explain the recent observations of (1) associations of visible galaxies with $lyal$ lines at low redshifts $z la 1$, and (2) metal lines associated with a non-negligible fraction of low H I column density $lyal$ lines at $z sim 3$. For galactic halos, we find that photoionized gas clouds confined in the pressure of ambient hot gas can produce $lyal$ absorptions with H I column density as low as $10^{14}$ cm$^{-2}$, and that the impact parameter of a sightline for such absorptions matches well with the observed radius of gaseous envelope in a typical luminous galaxy. Using the Press- Schechter prescription for the mass function of halos, we also show that the fraction of $lyal$ lines with associated metal lines can be understood in terms of the fraction of $lyal$ absorbers that are associated with galactic halos. In particular, the reported fraction of $sim 0.5--0.75$ at $z sim 3$ is reproduced when the boundary value of $V_c$ to separate mini or galactic halos is $40 sim 60$ km s$^{-1}$, which is consistent with the theoretical prediction of galaxy formation under photoionization. ..... | | Source: | arXiv, astro-ph/9702049 | | Services: | Forum | Review | PDF | Favorites | |
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