103 research outputs found
The Deuterium to Hydrogen Abundance Ratio Towards the QSO SDSS1558-0031
We present a measurement of the D/H abundance ratio in a metal-poor damped
Lyman alpha (DLA) system along the sightline of QSO SDSS1558-0031. The DLA
system is at redshift z = 2.70262, has a neutral column density of
log(NHI)=20.67+/-0.05 cm^2, and a gas-phase metallicity [O/H]= -1.49 which
indicates that deuterium astration is negligible. Deuterium absorption is
observed in multiple Lyman series with a column density of
log(NDI)=16.19+/-0.04 cm^2, best constrained by the deuterium Lyman-11 line. We
measure log(D/H) = -4.48+/-0.06, which when combined with previous measurements
along QSO sightlines gives a best estimate of log(D/H) = -4.55+/-0.04, where
the 1-sigma error estimate comes from a jackknife analysis of the weighted
means. Using the framework of standard big bang nucleosynthesis, this value of
D/H translates into a baryon density of Omega_b h^2 = 0.0213 +/- 0.0013 +/-
0.0004 where the error terms represent the 1-sigma errors from D/H and the
uncertainties in the nuclear reaction rates respectively. Combining our new
measurement with previous measurements of D/H, we no longer find compelling
evidence for a trend of D/H with NHI.Comment: 13 pages, 3 figures, 1 table. Accepted to the Astrophysical Journal
Letter
The Keck+Magellan Survey for Lyman Limit Absorption II: A Case Study on Metallicity Variations
We present an absorption line analysis of the Lyman limit system (LLS) at
z=3.55 in our Magellan/MIKE spectrum of PKS2000-330. Our analysis of the Lyman
limit and full HI Lyman series constrains the total HI column density of the
LLS (N_HI = 10^[18.0 +/- 0.25] cm^{-2} for b_HI >= 20 km/s) and also the N_HI
values of the velocity subsystems comprising the absorber. We measure ionic
column densities for metal-line transitions associated with the subsystems and
use these values to constrain the ionization state (>90% ionized) and relative
abundances of the gas. We find an order of magnitude dispersion in the
metallicities of the subsystems, marking the first detailed analysis of
metallicity variations in an optically thick absorber. The results indicate
that metals are not well mixed within the gas surrounding high galaxies.
Assuming a single-phase photoionization model, we also derive an N_H-weighted
metallicity, = -1.66 +/- 0.25, which matches the mean metallicity in
the neutral ISM in high z damped Lya systems (DLAs). Because the line density
of LLSs is ~10 times higher than the DLAs, we propose that the former dominate
the metal mass-density at z~3 and that these metals reside in the galaxy/IGM
interface. Considerations of a multi-phase model do not qualitatively change
these conclusions. Finally, we comment on an anomalously large O^0/Si^+ ratio
in the LLS that suggests an ionizing radiation field dominated by soft UV
sources (e.g. a starburst galaxy). Additional abundance analysis is performed
on the super-LLS systems at z=3.19.Comment: 20 pages, 7 figures (most in color). Accepted to Ap
The Ucsd/Keck Damped Lya Abundance Database: A Decade of High Resolution Spectroscopy
We publish the Keck/HIRES and Keck/ESI spectra that we have obtained during
the first 10 years of Keck observatory operations. Our full sample includes 42
HIRES spectra and 39 ESI spectra along 65 unique sightlines providing abundance
measurements on ~85 damped Lya systems. The normalized data can be downloaded
from the journal or from our supporting website:
http://www.ucolick.org/~xavier/DLA/. The database includes all of the
sightlines that have been included in our papers on the chemical abundances,
kinematics, and metallicities of the damped Lya systems. This data has also
been used to argue for variations in the fine-structure constant. We present
new chemical abundance measurements for 10 damped Lya systems and a summary
table of high-resolution metallicity measurements (including values from the
literature) for 153 damped Lya systems at z>1.6. We caution, however, that this
metallicity sample (and all previous ones) is biased to higher N(HI) values
than a random sample.Comment: 55 pages, 11 figures. Accepted to ApJS. See
http://www.ucolick.org/~xavier/DLA/ for the dat
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