An FeLoBAL Binary Quasar

In an ongoing infrared imaging survey of quasars at Keck Observatory, we have discovered that the z=1.285 quasar SDSS J233646.2-010732.6 comprises two point sources with a separation of 1.67". Resolved spectra show that one component is a standard quasar with a blue continuum and broad emission lines; the other is a broad absorption line (BAL) quasar, specifically, a BAL QSO with prominent absorption from MgII and metastable FeII, making it a member of the ``FeLoBAL'' class. The number of known FeLoBALs has recently grown dramatically from a single example to more than a dozen, including a gravitationally lensed example and the binary member presented here, suggesting that this formerly rare object may be fairly common. Additionally, the presence of this BAL quasar in a relatively small separation binary adds to the growing evidence that the BAL phenomenon is not due to viewing a normal quasar at a specific orientation, but rather that it is an evolutionary phase in the life of many, if not all, quasars, and is particularly associated with conditions found in interacting systems.Comment: AASTEX 13 pp., 4 figs; accepted by ApJ Letter

C, N, O Abundances in the Most Metal-Poor Damped Lyman alpha Systems

This study focuses on some of the most metal-poor damped Lyman alpha absorbers known in the spectra of high redshift QSOs, using new and archival observations obtained with UV-sensitive echelle spectrographs on the Keck and VLT telescopes. The weakness and simple velocity structure of the absorption lines in these systems allows us to measure the abundances of several elements, and in particular those of C, N, and O, a group that is difficult to study in DLAs of more typical metallicities. We find that when the oxygen abundance is less than about 1/100 of solar, the C/O ratio in high redshift DLAs and sub-DLAs matches that of halo stars of similar metallicity and shows higher values than expected from galactic chemical evolution models based on conventional stellar yields. Furthermore, there are indications that at these low metallicities the N/O ratio may also be above simple expectations and may exhibit a minimum value, as proposed by Centurion and her collaborators in 2003. Both results can be interpreted as evidence for enhanced production of C and N by massive stars in the first few episodes of star formation, in our Galaxy and in the distant proto-galaxies seen as QSO absorbers. The higher stellar yields implied may have an origin in stellar rotation which promotes mixing in the stars' interiors, as considered in some recent model calculations. We briefly discuss the relevance of these results to current ideas on the origin of metals in the intergalactic medium and the universality of the stellar initial mass function.Comment: 17 pages, 9 Figures, Accepted for publication in Monthly Notices of the Royal Astronomical Societ

Emission-Line Properties of z > 4 Quasars

We present results of a program of high signal-to-noise spectroscopy for 44 QSOs at redshifts > 4 using the MMT and Keck observatories. The quasar spectra cover 1100 -- 1700 A in the rest frame for sources spanning a luminosity range of approximately 2 orders of magnitude. Comparisons between these data and spectra of lower redshift quasars reveal a high degree of similarity, although differences are present in the profiles and the strengths of some emission features. An examination of the luminosity dependence of the emission lines reveals evidence for a weak or absent Baldwin effect among z > 4 QSOs. We compare measurements for objects in our sample with results from other high redshift surveys characterized by different selection techniques. Distributions of equivalent widths for these different ensembles are consistent with a common parent population, suggesting that our sample is not strongly biased, or in any case, subject to selection effects that are not significantly different from other surveys, including the Sloan Digital Sky Survey. Based on this comparison, we tentatively conclude that the trends identified here are representative of high z QSOs. In particular, the data bolster indications of supersolar metallicities in these luminous, high-z sources, which support scenarios that assume substantial star formation at epochs preceding or concurrent with the QSO phenomena.Comment: 26 pages (incl. 9 figures), AASTeX v5.0, to appear in The Astrophysical Journa

The Metallicity of the Redshift 4.16 Quasar BR2248-1242

We estimate the metallicity in the broad emission-line region of the redshift z=4.16 quasar, BR2248-1242, by comparing line ratios involving nitrogen to theoretical predictions. BR2248-1242 has unusually narrow emission lines with large equivalent widths, thus providing a rare opportunity to measure several line-ratio abundance diagnostics. The combined diagnostics indicate a metallicity of ~2 times solar. This result suggests that an episode of vigorous star formation occurred near BR2248-1242 prior to the observed z=4.16 epoch. The time available for this enrichment episode is only ~1.5 Gyr at z=4.16 (for H_{0}=65 km s^-1 Mpc^-1, Omega_{m}=0.3 and Omega_Lambda ~< 1). This evidence for high metallicities and rapid star formation is consistent with the expected early-epoch evolution of dense galactic nuclei.Comment: 8 pages, 3 figures. Prepared in AAStex. Submitted to the Astrophysical Journal Revised version: added 1 referenc