Sloan Fellows

About: Sloan Fellows is a based out in . It is known for research contribution in the topics: Galaxy & Star formation. The organization has 55 authors who have published 253 publications receiving 35008 citations. The organization is also known as: Sloan Fellows.

Metallicities and Physical conditions in Star-forming Galaxies at z~1.0-1.5

Abstract: We present a study of the mass-metallicity (M-Z) relation and H II region physical conditions in a sample of 20 star-forming galaxies at 1.0

The Nature of Damped Lyman-α and Mg II Absorbers Explored through Their Dust Contents

Abstract: We estimate the abundance of dust in damped Lyman-α absorbers (DLAs) by statistically measuring the excess reddening they induce on their background quasars. We detect systematic reddening behind DLAs consistent with the SMC-type reddening curve and inconsistent with the Milky Way type. We find that the derived dust-to-gas ratio is, on average, inversely proportional to the column density of neutral hydrogen, implying that the amount of dust is constant, regardless of the column density of hydrogen. It means that the average metallicity is inversely proportional to the column density of hydrogen, unless the average dust-to-metal ratio varies with the hydrogen column density. This indicates that the prime origin of metals seen in DLAs is not by in situ star formation, with which is expected from the empirical star formation law, contrary to our observation. We interpret the metals observed in absorbers to be deposited dominantly from nearby galaxies by galactic winds ubiquitous in intergalactic space. When extrapolating the relation between dust-to-gas ratio and H I column density to lower column density, we find a value that is consistent with what is observed for Mg II absorbers.

Accelerating Compact Object Mergers in Triple Systems with the Kozai Resonance: A Mechanism for "Prompt" Type Ia Supernovae, Gamma-Ray Bursts, and Other Exotica

Abstract: White dwarf-white dwarf (WD-WD) and neutron star-neutron star (NS-NS) mergers may produce Type Ia supernovae and gamma-ray bursts (GRBs), respectively. A general problem is how to produce binaries with semi-major axes small enough to in significantly less than the Hubble time (t_H), and thus accommodate the observation that these events closely follow episodes of star formation. I explore the possibility that such systems are not binaries at all, but actually coeval, or dynamical formed, triple systems. The tertiary induces Kozai oscillations in the inner binary, driving it to high eccentricity, and reducing its gravitational wave (GW) merger timescale. This effect significantly increases the allowed range of binary period P such that the merger time is t_merge < t_H. In principle, Chandrasekhar-mass binaries with P ~ 300 days can merge in < t_H if they contain a prograde solar-mass tertiary at high enough inclination. For retrograde tertiaries, the maximum P such that t_merge < t_H is yet larger. In contrast, P < 0.3 days is required in the absence of a tertiary. I discuss implications of these findings for the production of transients formed via compact object binary mergers. Based on the statistics of solar-type binaries, I argue that many such binaries should be in triple systems affected by the Kozai resonance. If true, expectations for the mHz GW signal from individual sources, the diffuse background, and the foreground for GW experiments like LISA are modified. This work motivates future studies of triples systems of A, B,and O stars, and new types of searches for WD-WD binaries in triple systems.

Foregrounds and Forecasts for the Cosmic Microwave Background

Abstract: One of the main challenges facing upcoming CMB experiments will be to distinguish the cosmological signal from foreground contamination. We present a comprehensive treatment of this problem and study how foregrounds degrade the accuracy with which the Boomerang, MAP and Planck experiments can measure cosmological parameters. Our foreground model includes not only the normalization, frequency dependence and scale dependence for each physical component, but also variations in frequency dependence across the sky. When estimating how accurately cosmological parameter can be measured, we include the important complication that foreground model parameters (we use about 500) must be simultaneously measured from the data as well. Our results are quite encouraging: despite all these complications, precision measurements of most cosmological parameters are degraded by less than a factor of 2 for our main foreground model and by less than a factor of 5 in our most pessimistic scenario. Parameters measured though large-angle polarization signals suffer more degradation: up to 5 in the main model and 25 in the pessimistic case. The foregrounds that are potentially most damaging and therefore most in need of further study are vibrating dust emission and point sources, especially those in the radio frequencies. It is well-known that E and B polarization contain valuable information about reionization and gravity waves, respectively. However, the cross-correlation between polarized and unpolarized foregrounds also deserves further study, as we find that it carries the bulk of the polarization information about most other cosmological parameters.

The Extinction Distribution in the Galaxy UGC 5041

Abstract: We probe the dust extinction through the foreground disk of the overlapping galaxy pair UGC 5041 by analyzing B-, I-, and H-band images. The inclined foreground disk of this infrared-selected pair is almost opaque in B at a projected distance of ~8 kpc. From the images, we directly estimate the area-weighted distribution of differential near-IR extinction: it is nearly Gaussian, with τI - τH = 0.6 and σ = 0.27. For a homogenous dust distribution and a Milky Way extinction curve, this corresponds to a face-on distribution p(τ) with a mean of τV = 0.34 and σV = 0.15. For a clumpy dust model, the optical depth estimate increases to τV = 0.41 and σV = 0.19. Even though the galaxy pair is subject to different selection biases and our analysis is subject to different systematics, the result is consistent with existing case studies, indicating that τV ~ 0.3 is generic for late-type spirals near their half-light radii. We outline how to estimate from p(τ) by how much background quasars are underrepresented, where projected within ~10 kpc of nearby spirals, such as damped Lyα absorbers or gravitational lenses; from our data we derive a factor of 2 deficit for flux-limited, optical surveys.