Lyman edges in supermassive black hole binaries

We propose a new spectral signature for supermassive black hole binaries (SMBHBs) with circumbinary gas disks: a sharp drop in flux blueward of the Lyman limit. A prominent edge is produced if the gas dominating the emission in the Lyman continuum region of the spectrum is sufficiently cold (T < 20,000 K) to contain significant neutral hydrogen. Circumbinary disks may be in this regime if the binary torques open a central cavity in the disk and clear most of the hot gas from the inner region, and if any residual UV emission from the individual BHs is either dim or intermittent. We model the vertical structure and spectra of circumbinary disks using the radiative transfer code TLUSTY, and identify the range of BH masses and binary separations producing a Lyman edge. We find that compact supermassive binaries with orbital periods of ~0.1 - 10 yr, whose gravitational waves (GWs) are expected to be detectable by pulsar timing arrays (PTAs), could have prominent Lyman edges. Such strong spectral edge features are not typically present in AGN spectra and could serve as corroborating evidence for the presence of a SMBHB.Comment: Published in MNRASL. 6 pages. 4 figure

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

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