Astronomy and Astrophysics – Astrophysics
Scientific paper
1997-07-16
Astronomy and Astrophysics
Astrophysics
ApJ, in press. Substantial revision and a new figure included
Scientific paper
10.1086/305458
If the universe was reionized by O and B stars in an early population of galaxies, the associated supernovae should have enriched the universe to a mean metallicity $\bar Z = 10^{-5} (1+ n_{rec})$, where $n_{rec}$ is the mean number of times that each baryon recombined during the reionization era. This is consistent with recent observations of the metallicity in the Lya forest at $z\simeq 3$. The mean surface brightness observable at present from the galaxies that produced these heavy elements, in the rest-frame wavelengths $1216\AA < \lambda \lesssim 2500\AA$, should be $\sim 10^{-6} (\bar Z/10^{-4}) (\Omega_b h^2/0.02) ~ photons \cm^{-2} s^{-1} arcsec^{-2}$. Most of this radiation was emitted at $z>5$, before reionization was complete. These high-redshift galaxies may be detectable in near-infrared photometric surveys, identifying them via the Gunn-Peterson trough (analogous to the use of the Lyman limit cutoff to search for galaxies at $z\sim 3$, where the Lya forest blanketing is smaller). Their spectrum may also be characterized by a strong Lya emission line. However, the spectra of galaxies seen behind intervening gas that is still neutral should show the red damping wing of the Gunn-Peterson trough, with a predictable profile that obstructs part of the Lya emission. The low-mass galaxies formed before reionization might constitute a distinctive population; we discuss the signature that this population could have in the faint number counts. Although most of these galaxies should have merged into larger ones, those that survived to the present could be dwarf spheroidals.
Miralda-Escude' Jordi
Rees Martin J.
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