Models for High-Redshift Lyman Alpha Emitters

We present models for dusty high-redshift Lyman alpha emitting galaxies by combining the Press-Schechter formalism with a treatment of inhomogeneous dust distribution inside galaxies. These models reproduce the surface density of emitters inferred from recent observations, and also agree with previous non-detections. Although a detailed determination of the individual model parameters is precluded by uncertainties, we find that (i) the dust content of primordial galaxies builds up in no more than 5x10^8 years, (ii) the galactic HII regions are inhomogeneous with a cloud covering factor of order unity, and (iii) the overall star formation efficiency is at least 5 percent. Future observations should be able to detect Lyman alpha galaxies upto redshifts of about z=8. If the universe is reionized at z(reion)<8, the corresponding decline in the number of Lyman alpha emitters at z>z(reion) could prove to be a useful probe of the reionization epoch.Comment: 4 pages, poster contribution to Proc. of 9th Annual October Astrophysics Conference in Maryland, "After the Dark Ages: When Galaxies Were Young (the Universe at 2 < z < 5", College Park, October 199

Empirical Constraints on the First Stars and Quasars

Empirical studies of the first generation of stars and quasars in the Universe will likely become feasible over the next decade. The Next Generation Space Telescope will provide direct imaging and photometry of sub-galactic objects at redshifts above z=10, while microwave anisotropy experiments, such as MAP or Planck, will set constraints on the ionization history of the intergalactic medium due to these sources. We describe the expected signals that will be detectable with these future instruments.Comment: 14 pages, invited contribution to Proc. of 9th Annual October Astrophysics Conference in Maryland, "After the Dark Ages: When Galaxies Were Young (the Universe at 2 < z < 5", College Park, October 199

Quasar Str\"omgren Spheres Before Cosmological Reionization

Ionizing sources embedded in the neutral intergalactic medium (IGM) before cosmological reionization generate discrete HII regions. We show that a sufficiently bright quasar (for example, one tenth as luminous as that recently discovered by Fan et al.) can ionize a large volume, allowing the transmission of a substantial fraction of the flux of its intrinsic Lyman alpha emission line on both sides of the Lyman alpha wavelength. The observed line profile is richly informative. We show that a sufficiently accurate, high spectral resolution ($R\approx 10^4$) measurement of the line profile of a bright quasar is feasible using the Next Generation Space Telescope (NGST) as well as large ground-based telescopes. Such a measurement has two potentially important applications. First, the red side of the Lyman alpha emission line provides a way to measure the quasar lifetime. Second, the blue side provides a direct measure of the density fluctuations of the intergalactic medium at the quasar redshift. The estimate of the absorption of the red side is limited by the accuracy to which the intrinsic profile of the Lyman alpha emission line is known. The blue side, however, does not sensitively depend on the intrinsic profile, because the former is much narrower than the latter.Comment: revised, accepted to ApJ Letter