765 research outputs found
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 First Data Release of the KODIAQ Survey
We present and make publicly available the first data release (DR1) of the
Keck Observatory Database of Ionized Absorption toward Quasars (KODIAQ) survey.
The KODIAQ survey is aimed at studying galactic and circumgalactic gas in
absorption at high-redshift, with a focus on highly-ionized gas traced by OVI,
using the HIRES spectrograph on the Keck-I telescope. KODIAQ DR1 consists of a
fully-reduced sample of 170 quasars at 0.29 < z_em < 5.29 observed with HIRES
at high resolution (36,000 <= R <= 103,000) between 2004 and 2012. DR1 contains
247 spectra available in continuum normalized form, representing a sum total
exposure time of ~1.6 megaseconds. These co-added spectra arise from a total of
567 individual exposures of quasars taken from the Keck Observatory Archive
(KOA) in raw form and uniformly processed using a HIRES data reduction package
made available through the XIDL distribution. DR1 is publicly available to the
community, housed as a higher level science product at the KOA. We will provide
future data releases that make further QSOs, including those with pre-2004
observations taken with the previous-generation HIRES detectors.Comment: 14 pages, 9 figures, Submitted to AJ. All data products available at
the Keck Observatory Archive beginning May 15, 2015. URL:
https://koa.ipac.caltech.edu/applications/KODIA
Developmental evolution of flowering plant pollen tube cell walls: callose synthase (CalS) gene expression patterns
<p>Abstract</p> <p>Background</p> <p>A number of innovations underlie the origin of rapid reproductive cycles in angiosperms. A critical early step involved the modification of an ancestrally short and slow-growing pollen tube for faster and longer distance transport of sperm to egg. Associated with this shift are the predominantly callose (1,3-β-glucan) walls and septae (callose plugs) of angiosperm pollen tubes. Callose synthesis is mediated by callose synthase (CalS). Of 12 <it>CalS </it>gene family members in <it>Arabidopsis</it>, only one (<it>CalS5</it>) has been directly linked to pollen tube callose. <it>CalS5 </it>orthologues are present in several monocot and eudicot genomes, but little is known about the evolutionary origin of <it>CalS5 </it>or what its ancestral function may have been.</p> <p>Results</p> <p>We investigated expression of <it>CalS </it>in pollen and pollen tubes of selected non-flowering seed plants (gymnosperms) and angiosperms within lineages that diverged below the monocot/eudicot node. First, we determined the nearly full length coding sequence of a <it>CalS5 </it>orthologue from <it>Cabomba caroliniana </it>(<it>CcCalS5</it>) (Nymphaeales). Semi-quantitative RT-PCR demonstrated low <it>CcCalS5 </it>expression within several vegetative tissues, but strong expression in mature pollen. <it>CalS </it>transcripts were detected in pollen tubes of several species within Nymphaeales and Austrobaileyales, and comparative analyses with a phylogenetically diverse group of sequenced genomes indicated homology to <it>CalS5</it>. We also report <it>in silico </it>evidence of a putative <it>CalS5 </it>orthologue from <it>Amborella</it>. Among gymnosperms, <it>CalS5 </it>transcripts were recovered from germinating pollen of <it>Gnetum </it>and <it>Ginkgo</it>, but a novel <it>CalS </it>paralog was instead amplified from germinating pollen of <it>Pinus taeda</it>.</p> <p>Conclusion</p> <p>The finding that CalS5 is the predominant callose synthase in pollen tubes of both early-diverging and model system angiosperms is an indicator of the homology of their novel callosic pollen tube walls and callose plugs. The data suggest that <it>CalS5 </it>had transient expression and pollen-specific functions in early seed plants and was then recruited to novel expression patterns and functions within pollen tube walls in an ancestor of extant angiosperms.</p
Andromeda's Parachute: A Bright Quadruply Lensed Quasar at z=2.377
We present Keck Cosmic Web Imager spectroscopy of the four putative images of
the lensed quasar candidate J014709+463037 recently discovered by Berghea et
al. (2017). The data verify the source as a quadruply lensed, broad
absorption-line quasar having z_S = 2.377 +/- 0.007. We detect intervening
absorption in the FeII 2586, 2600, MgII 2796, 2803, and/or CIV 1548, 1550
transitions in eight foreground systems, three of which have redshifts
consistent with the photometric-redshift estimate reported for the lensing
galaxy (z_L ~ 0.57). By virtue of their positions on the sky, the source images
probe these absorbers over transverse physical scales of ~0.3-21 kpc,
permitting assessment of the variation in metal-line equivalent width W_r as a
function of sight-line separation. We measure differences in W_r,2796 of <40%
across all sight-line pairs subtending 7-21 kpc, suggestive of a high degree of
spatial coherence for MgII-absorbing material. W_r,2600 is observed to vary by
>50% over the same scales across the majority of sight-line pairs, while CIV
absorption exhibits a wide range in W_r,1548 differences of ~5-80% within
transverse distances less than ~3 kpc. J014709+463037 is one of only a handful
of z > 2 quadruply lensed systems for which all four source images are very
bright (r = 15.4-17.7 mag) and are easily separated in ground-based seeing
conditions. As such, it is an ideal candidate for higher-resolution
spectroscopy probing the spatial variation in the kinematic structure and
physical state of intervening absorbers.Comment: Submitted to ApJL. 9 pages, 3 figures. Uses aastex61 forma
Purification and properties of anionic glutathione S-transferase from bovine ciliary body
Discovery of three new near-pristine absorption clouds at -4.4
We report the discovery of three new "near-pristine" Lyman Limit Systems
(LLSs), with metallicities ~1/1000 solar, at redshifts 2.6, 3.8 and 4.0, with a
targeted survey at the Keck Observatory. High resolution echelle spectra of
eight candidates yielded precise column densities of hydrogen and weak, but
clearly detected, metal lines in seven LLSs; we previously reported the one
remaining, apparently metal-free LLS, to have metallicity <1/10000 solar.
Robust photoionisation modelling provides metallicities [Si/H] = -3.05 to
-2.94, with 0.26 dex uncertainties (95% confidence) for three LLSs, and [Si/H]
>~ -2.5 for the remaining four. Previous simulations suggest that near-pristine
LLSs could be the remnants of PopIII supernovae, so comparing their detailed
metal abundances with nucleosynthetic yields from supernovae models is an
important goal. Unfortunately, at most two different metals were detected in
each new system, despite their neutral hydrogen column densities
(10^{19.2-19.4} cm^{-2}) being two orders of magnitude larger than the two
previous, serendipitously discovered near-pristine LLSs. Nevertheless, the
success of this first targeted survey for near-pristine systems demonstrates
the prospect that a much larger, future survey could identify clear
observational signatures of PopIII stars. With a well-understood selection
function, such a survey would also yield the number density of near-pristine
absorbers which, via comparison to future simulations, could reveal the
origin(s) of these rare systems.Comment: Accepted by MNRAS. 21 pages, 27 figure
The Deuterium Abundance in the z=0.7 absorber towards QSO PG1718+4807
We report a further analysis of the ratio of deuterium to hydrogen (D/H)
using HST spectra of the z=0.701 Lyman limit system towards the QSO PG1718+481.
Initial analyses of this absorber found it gave a high D/H value, 1.8 - 3.1
\times 10^{-4} (Webb et al. 1998), inconsistent with several higher redshift
measurements. It is thus important to critically examine this measurement. By
analysing the velocity widths of the DI, HI and metal lines present in this
system, Kirkman et al. (2001) report that the additional absorption in the blue
wing of the lya line can not be DI, with a confidence level of 98%. Here we
present a more detailed analysis, taking into account possible wavelength
shifts between the three sets of HST spectra used in the analysis. We find that
the constraints on this system are not as strong as those claimed by Kirkman et
al. The discrepancy between the parameters of the blue wing absorption and the
parameters expected for DI is marginally worse than 1 sigma.
Tytler et al.(1999) commented on the first analysis of Webb et
al.(1997,1998), reporting the presence of a contaminating lower redshift Lyman
limit system, with log[N(HI)] = 16.7 at z=0.602, which biases the N(HI)
estimate for the main system. Here we show that this absorber actually has
log[N(HI)] < 14.6 and does not impact on the estimate of N(HI) in the system of
interest at z = 0.701.
The purpose of the present paper is to highlight important aspects of the
analysis which were not explored in previous studies, and hence help refine the
methods used in future analyses of D/H in quasar spectra.Comment: 11 pages, 9 figures. Accepted by MNRA
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