Thomas A. Barlow

Abundances at High Redshifts: The Chemical Enrichment History of Damped Lyα Galaxies

We study the elemental abundances of C, N, O, Al, Si, S, Cr, Mn, Fe, Ni, and Zn in a sample of 14 damped Lyα systems (galaxies) with H I column density N(H I) ≥ 1020 cm−2, using high-quality spectra quasars obtained with the 10 m Keck telescope. To ensure accuracy, only weak, unsaturated absorption lines are used to derive ion column densities and elemental abundances. Combining these abundance measurements with similar measurements in the literature, we investigate the chemical evolution of damped Lyα galaxies based on a sample of 23 systems in the redshift range 0.7 3 in our sample have (Fe/H) around 1/100 solar or less. In comparison, a large fraction of the damped Lyα galaxies at z < 3 have reached 10 times higher metallicity. This suggests that the time around z = 3 may be the epoch of galaxy formation in the sense that galaxies are beginning to form the bulk of their stars. Several other lines of evidence appear to point to the same conclusion, including the evolution of the neutral baryon content of damped Lyα galaxies, the evolution in the quasar space density, and the morphology of z < 3 galaxies. 4. The relative abundance patterns of the elements studied here clearly indicate that the bulk of heavy elements in these high-redshift galaxies were produced by Type II supernovae; there is little evidence for significant contributions from stellar mass loss of low- to intermediate-mass stars or from Type Ia supernovae. 5. Although earlier studies have attributed the overabundance of Zn relative to Cr or Fe found in damped Lyα galaxies to selective depletion of Cr and Fe by dust grains, such an interpretation is inconsistent with many of the other elemental abundance ratios seen in these galaxies, most notably N/O and Mn/Fe. Several other tests also indicate that thereis no significant evidence for dust depletion in these galaxies. We suggest that the overabundance of Zn relative to Cr in damped Lyα galaxies may be intrinsic to their stellar nucleosynthesis. If this interpretation is correct, it will provide important new information to the theory of stellar nucleosynthesis. 6. The absorption profiles of Al III in damped Lyα galaxies are found to resemble those of the low ionization lines. The profiles of Si IV and C IV absorption, while resembling each other in general, are almost always different from those of the low-ionization absorption lines. These results suggest that Al III is probably produced in the same physical region as the low-ionization species in the absorbing galaxies, while the high-ionization species (Si IV and C IV) mostly likely come from distinct physical regions. 7. We discuss possible ways to obtain information on the history of star formation (i.e., continuous or episodic) in damped Lyα galaxies and on the shapes of the stellar initial mass functions. 8. We review the evidence for, and against, the hypothesis that damped Lyα galaxies are disks or protodisks at high redshifts and discuss the implications. 9. We determine upper limits on the temperature of the cosmic microwave background radiation at several redshifts using absorption from the fine-structure level of the C II ion. These upper limits are consistent with the predicted increase of TCMBwith redshift.

Keck High Resolution Spectroscopy of PKS 0123+257: Intrinsic Absorption in a Radio-Loud Quasar

We present results from Keck I high resolution spectroscopy of the radio loud quasar PKS 0123+257 (

Time-variable Intrinsic Absorption Lines in the Quasi-stellar Object Q2343+125

z_e

The N/Si Abundance Ratio in 15 Damped Lyα Galaxies: Implications for the Origin of Nitrogen*

=2.364, V=17.5). In this object we detect Ly

THE N/SI ABUNDANCE RATIO IN 15 DAMPED LYALPHA GALAXIES : IMPLICATIONS FORTHE ORIGIN OF NITROGEN

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Behavior of Sulfur Abundances in Metal-poor Giants and Dwarfs

, N V 1238,1242, Si IV 1393,1402, and C IV 1548,1550 in an absorption system at a redshift of 2.369. The Ly

Are AGN broad emission lines formed by discrete clouds? Analysis of Keck high-resolution spectroscopy of NGC 4151

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The galaxy evolution explorer

line has a square- bottomed profile suggesting a high column density of gas, yet the line does not reach zero intensity. The resolved C IV doublet ratio also clearly demonstrates that the absorbing clouds at this redshift do not fully occult the background light source along our line-of-sight. The absorption lines are positioned near the centers of the broad emission- lines and the coverage fraction of the strongest absorption lines varies inversely proportionally with the strength of the corresponding emission lines. This implies that although the absorption-line region may obscure the continuum source, it does not completely occult the broad emission-line region. This effect suggests that the lines are formed close to the QSO central region. A model is proposed in which the apparent coverage fraction derived for the weaker absorption lines may vary with the column density of the lines. Broad absorption-lines (which are known to be intrinsic) are found nearly exclusively in radio-quiet objects. Intrinsic narrow absorption lines have previously been found in radio quiet QSOs; it is therefore significant that an intrinsic absorption system has been verified in a radio loud quasar.

Broad absorption-line time variability in the QSO CSO 203

We discuss high-resolution Keck Observatory spectra of an intrinsic absorption-line system at redshift za ≈ 2.24 in the radio-quiet QSO Q2343+125 (ze = 2.515). The absorbers physical relationship to the QSO is confirmed by time-variable line strengths and partial line-of-sight coverage of the QSO continuum source. The N V, C IV, and Si IV doublets varied in unison by factors of 4 in less than 0.3 yr in the QSO rest frame. The resolved C IV doublet ratios show that the absorber occults 20% of the QSO continuum source; therefore, the absorbing clouds are likely to have characteristic sizes less than 0.01 pc. There is evidence for smaller coverage fractions when the lines were weaker, which could explain the line-strength changes. Lower ionization species such as C II and Si II are not detected. The Lyα line at za ≈ 2.24 is contaminated by the dense forest of cosmologically intervening absorption lines, but also appears to be weak or absent. The large uncertainties in the H I column prevent reliable constraints on the metal abundances. The za ≈ 2.24 lines clearly form in high-velocity ejecta from the QSO. The line profiles are smooth and rounded, with FWHM ~ 400 km s-1 and centroids shifted -24,000 km s-1 from the QSO emission redshift. Several narrow-line systems are present inside the broader absorption profiles, but they did not vary in strength and may be due to intervening gas. The large-amplitude variability, low coverage fractions, and large ratio of centroid to FWHM velocities imply different outflow properties than those inferred from the broad absorption lines (BALs) in other sources. Nonetheless, the ejecta identified by the za ≈ 2.24 absorber could be related to the BAL phenomenon and could be ubiquitous in QSOs if the gas subtends a small fraction of the sky as seen from the emission source(s).

Temperature and Kinematics of C IV Absorption Systems

?????Calculations derived from Galactic chemical evolution models indicate that there should be considerable scatter in the observed N/O ratios at a fixed metallicity (O/H) for galaxies with very low metallicities, due to the delayed release of primary N from intermediate-mass stars relative to that of O from short-lived massive stars. Moreover, the scatter should increase progressively as metallicity decreases. Such effects have not been convincingly demonstrated by observations of H II regions in nearby metal-poor galaxies, raising doubts about the time-delay model of primary N production. Pettini et al. and Lipman et al. realized the utility of high-redshift damped Ly? galaxies for gaining further insights into the origin of N, and discussed abundances in three damped Ly? galaxies. Since abundance measurements for O are generally unavailable for damped Ly? galaxies, they used N/Si or N/S in place of N/O, under the reasonable assumption that the abundance ratios O/Si and O/S are the same as solar in damped Ly? galaxies. We discuss observations of heavy-element abundances in 15 high-redshift (z > 2) damped Ly? galaxies, many of which have metallicities comparable to or lower than the lowest metallicity galaxy known locally (I Zw 18). We find that the N/Si ratios in damped Ly? galaxies exhibit a very large scatter (~1 dex) at [Si/H] ~ -2 and that there is some indication that the scatter increases with decreasing metallicity. Consideration of various sources of uncertainty suggests that they are not likely the main causes of the large scatter. These results provide strong support for the time-delay model of primary N production in intermediate-mass stars if, indeed, O/Si solar in damped Ly? galaxies.