1,329 research outputs found
The construction of a workbook for enrichment of multi-meaning words.
Thesis (M.Ed.)--Boston Universit
A New Measurement of the Temperature Density Relation of the IGM From Voigt Profile Fitting
We decompose the Lyman-{\alpha} (Ly{\alpha}) forest of an extensive sample of
74 high signal-to-noise ratio and high-resolution quasar spectra into a
collection of Voigt profiles. Absorbers located near caustics in the peculiar
velocity field have the smallest Doppler parameters, resulting in a low-
cutoff in the - set by the thermal state of intergalactic
medium (IGM). We fit this cutoff as a function of redshift over the range
, which allows us to measure the evolution of the IGM
temperature-density () relation parameters
and . We calibrate our measurements against Ly forest
simulations, using 21 different thermal models of the IGM at each redshift,
also allowing for different values of the IGM pressure smoothing scale. We
adopt a forward-modeling approach and self-consistently apply the same
algorithms to both data and simulations, propagating both statistical and
modeling uncertainties via Monte Carlo. The redshift evolution of shows a
suggestive peak at , while our evolution of is consistent with
and disfavors inverted temperature-density relations. Our
measured evolution of and are generally in good agreement with
previous determinations in the literature. Both the peak in the evolution of
at , as well as the high temperatures K
that we observe at , strongly suggest that a significant episode
of heating occurred after the end of HI reionization, which was most likely the
cosmic reionization of HeII.Comment: Accepted for publication in ApJ, 23 pages, 26 figures, machine
readable tables available onlin
The Incidence of Low-Metallicity Lyman-Limit Systems at z~3.5: Implications for the Cold-Flow Hypothesis of Baryonic Accretion
Cold accretion is a primary growth mechanism of simulated galaxies, yet
observational evidence of "cold flows" at redshifts where they should be most
efficient (-4) is scarce. In simulations, cold streams manifest as
Lyman-limit absorption systems (LLSs) with low heavy-element abundances similar
to those of the diffuse IGM. Here we report on an abundance survey of 17 H
I-selected LLSs at -4.4 which exhibit no metal absorption in SDSS
spectra. Using medium-resolution spectra obtained at Magellan, we derive
ionization-corrected metallicities (or limits) with a Markov-Chain Monte Carlo
sampling that accounts for the large uncertainty in measurements
typical of LLSs. The metal-poor LLS sample overlaps with the IGM in metallicity
and is best described by a model where are drawn from the
IGM chemical abundance distribution. These represent roughly half of all LLSs
at these redshifts, suggesting that 28-40 of the general LLS population at
could trace unprocessed gas. An ancillary sample of ten LLSs without
any a priori metal-line selection is best fit with of
metallicities drawn from the IGM. We compare these results with regions of a
moving-mesh simulation; the simulation finds only half as many baryons in
IGM-metallicity LLSs, and most of these lie beyond the virial radius of the
nearest galaxy halo. A statistically significant fraction of all LLSs have low
metallicity and therefore represent candidates for accreting gas; large-volume
simulations can establish what fraction of these candidates actually lie near
galaxies and the observational prospects for detecting the presumed hosts in
emission.Comment: 19 pages, 17 figures; Submitted to ApJ; Corrected figure 16
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
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