The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopic survey that will eventually cover approximately one-quarter of the celestial sphere and collect spectra of %10 6 galaxies, 100,000 quasars, 30,000 stars, and 30,000 serendipity targets. In 2001 June, the SDSS released to the general astronomical community its early data release, roughly 462 deg 2 of imaging data including almost 14 million detected objects and 54,008 follow-up spectra. The imaging data were collected in drift-scan mode in five bandpasses (u, g, r, i, and z); our 95% completeness limits for stars are 22.0, 22.2, 22.2, 21.3, and 20.5, respectively. The photometric calibration is reproducible to 5%, 3%, 3%, 3%, and 5%, respectively. The spectra are flux-and wavelength-calibrated, with 4096 pixels from 3800 to 9200 Å at R % 1800. We present the means by which these data are distributed to the astronomical community, descriptions of the hardware used to obtain the data, the software used for processing the data, the measured quantities for each observed object, and an overview of the properties of this data set.

We present the results of 2D hydrodynamical simulations of circumbinary disk accretion using the finite-volume code DISCO. This code solves the 2D viscous Navier-Stokes equations on a highresolution moving mesh which shears with the fluid flow, greatly reducing advection errors in comparison with a fixed grid. We perform a series of simulations for binary mass ratios in the range 0.026 ≤ q ≤ 1.0, each lasting longer than a viscous time so that we reach a quasi-steady accretion state. In each case, we find that gas is efficiently stripped from the inner edge of the circumbinary disk and enters the cavity along accretion streams, which feed persistent "mini-disks" surrounding each black hole. We find that for q 0.1, the binary excites eccentricity in the inner region of the circumbinary disk, creating an overdense lump which gives rise to enhanced periodicity in the accretion rate. The dependence of the periodicity on mass ratio may provide a method for observationally inferring mass ratios from measurements of the accretion rate. We also find that for all mass ratios studied, the magnitude of the accretion onto the secondary is sufficient to drive the binary toward larger mass ratio. This suggests a mechanism for biasing mass ratio distributions toward equal mass.

We present Monte Carlo calculations of Lyα radiative transfer through optically thick, spherically symmetric, collapsing gas clouds. These represent simplified models of proto-galaxies that are caught in the process of their assembly. Such galaxies produce Lyα flux over an extended solid angle, either from a spatially extended Lyα emissivity, or from scattering effects, or both. We present a detailed study of the effect of the gas distribution and kinematics, and of the Lyα emissivity profile, on the emergent spectrum and surface brightness distribution. The emergent Lyα spectrum is typically double-peaked and asymmetric. In practice, however, we find that energy transfer from the infalling gas to the Lyα photons -together with a reduced escape probability for photons in the red wing-causes the blue peak to be significantly enhanced and the red peak, in most cases, to be undetectable. This results in an effective blueshift, which, combined with scattering in the intergalactic medium, will render extended Lyα emission from collapsing protogalaxies difficult to detect beyond redshift z ∼ > 4. We find that scattering flattens the surface brightness profile in clouds with large line center optical depths (τ 0 > 10 5 ). A strong wavelength dependence of the slope of the surface brightness distribution (with preferential flattening at the red side of the line) would be a robust indication that Lyα photons are being generated (rather than just scattered) in a spatially extended, collapsing region around the galaxy. We also find that for self-ionized clouds whose effective Lyα optical depth is ∼ < 10 3 , infall and outflow models can produce nearly identical spectra and surface brightness distributions, and are difficult to distinguish from one another. The presence of deuterium with a cosmic abundance may produce a narrow but detectable dip in the spectra of systems with moderate hydrogen column densities, in the range 10 18 − 10 20 cm −2 . Finally, we present a new analytic solution for the emerging Lyα spectrum in the limiting case of a static uniform sphere, extending previous solutions for static plane-parallel slabs.

In hierarchical models of structure formation, an early cosmic UV background (UVB) is produced by the small (T_vir < 10^4 K) halos that collapse before reionization. The UVB at energies below 13.6eV suppresses the formation of stars or black holes inside small halos, by photo-dissociating their only cooling agent, molecular H2. We self-consistently compute the buildup of the early UVB in Press-Schechter models, coupled with H2 photo-dissociation both in the intergalactic medium (IGM), and inside virialized halos. We find that the intergalactic H2 has a negligible effect on the UVB, both because its initial optical depth is small (tau<0.1), and because it is photo-dissociated at an early stage. If the UV sources in the first collapsed halos are stars, then their UV flux suppresses further star-formation inside small halos. This results in a pause in the buildup of the UVB, and reionization is delayed until larger halos (T_vir> 10^4 K) collapse. If the small halos host mini-quasars with hard spectra extending to approximately 1 keV, then their X-rays balance the effects of the UVB, the negative feedback does not occur, and reionization can be caused by the small halos.Comment: 16 pages, 16 figures included, uses emulateapj.sty. Submitted to Ap

In the absence of H 2 molecules, the primordial gas in early dark matter haloes with virial temperatures just above T vir 10 4 K cools by collisional excitation of atomic H. Although it cools efficiently, this gas remains relatively hot, at a temperature near T ∼ 8000 K, and consequently might be able to avoid fragmentation and collapse directly into a supermassive black hole. In order for H 2 formation and cooling to be strongly suppressed, the gas must be irradiated by a sufficiently intense ultraviolet (UV) flux. We performed a suite of threedimensional hydrodynamical adaptive mesh refinement (AMR) simulations of gas collapse in three different protogalactic haloes with T vir 10 4 K, irradiated by a UV flux with various intensities and spectra. We determined the critical specific intensity, J crit 21 , required to suppress H 2 cooling in each of the three haloes. For a hard spectrum representative of metal-free stars, we find (in units of 10 −21 erg s −1 Hz −1 sr −1 cm −2 ) 10 4 < J crit 21 < 10 5 , while for a softer spectrum, which is characteristic of a normal stellar population, and for which H − dissociation is important, we find 30 < J crit 21 < 300. These values are a factor of 3-10 lower than previous estimates. We attribute the difference to the higher, more accurate H 2 collisional dissociation rate we adopted. The reduction in J crit 21 exponentially increases the number of rare haloes exposed to supercritical radiation. When H 2 cooling is suppressed, gas collapse starts with a delay, but it ultimately proceeds more rapidly. The infall velocity is near the increased sound speed, and an object as massive as M ∼ 10 5 M may form at the centre of these haloes, compared to the M ∼ 10 2 M stars forming when H 2 cooling is efficient.