2,282 research outputs found
Metal abundances at z<1.5: new measurements in sub-Damped Lyman-alpha Absorbers
Damped Lyman-alpha systems (DLAs) and sub-DLAs seen toward background quasars
provide the most detailed probes of elemental abundances. Somewhat
paradoxically these measurements are more difficult at lower redshifts due to
the atmospheric cut-off, and so a few years ago our group began a programme to
study abundances at z < 1.5 in quasar absorbers. In this paper, we present new
UVES observations of six additional quasar absorption line systems at z < 1.5,
five of which are sub-DLAs. We find solar or above solar metallicity, as
measured by the abundance of zinc, assumed not to be affected by dust, in two
sub-DLAs: one, towards Q0138-0005 with [Zn/H]=+0.28 +/- 0.16; the other towards
Q2335+1501 with [Zn/H]=+0.07 +/- 0.34. Relatively high metallicity was observed
in another system: Q0123-0058 with [Zn/H]=-0.45 +/- 0.20. Only for the one DLA
in our sample, in Q0449-1645, do we find a low metallicity, [Zn/H]=-0.96 +/-
0.08. We also note that in some of these systems large relative abundance
variations from component to component are observed in Si, Mn, Cr and Zn.Comment: 7 figures and 10 tables. Accepted for publication in MNRA
A GBT Survey for HI 21 cm Absorption in the Disks and Halos of Low-Redshift Galaxies
We present an HI 21 cm absorption survey with the Green Bank Telescope (GBT)
of galaxy-quasar pairs selected by combining data from the Sloan Digital Sky
Survey (SDSS) and the Faint Images of the Radio Sky at Twenty-Centimeters
(FIRST) survey. Our sample consists of 23 sightlines through 15 low-redshift
foreground galaxy - background quasar pairs with impact parameters ranging from
1.7 kpc up to 86.7 kpc. We detected one absorber in the GBT survey from the
foreground dwarf galaxy, GQ1042+0747, at an impact parameter of 1.7 kpc and
another possible absorber in our follow-up Very Large Array (VLA) imaging of
the nearby foreground galaxy, UGC 7408. Both of the absorbers are narrow (FWHM
of 3.6 and 4.8 km/s), have sub Damped Lyman alpha column densities, and most
likely originate in the disk gas of the foreground galaxies. We also detected H
I emission from three foreground galaxies, including UGC 7408. Although our
sample contains both blue and red galaxies, the two H I absorbers as well as
the H I emissions are associated with blue galaxies. We discuss the physical
conditions in the 21 cm absorbers and some drawbacks of the large GBT beam for
this type of survey.Comment: 15 pages, 6 figures, 3 table
Community-engaged primary care medical education
BACKGROUND: Community-engaged medical education (CEME) requires medical schools to partner with local communities to help address community priorities, whilst enhancing the learning experiences of students. Current literature on CEME has focused on evaluating its effects on students; however, there remains a gap in exploring whether CEME initiatives can have a sustainable impact for communities. APPROACH: The Community Action Project (CAP) at Imperial College London, is an eight-week, community-engaged, quality improvement project for Year 3 medical students. Students initially consult with clinicians, patients and wider community stakeholders to understand local needs and assets, and identify a health priority to address. They then work with relevant stakeholders to design, implement and evaluate a project to help address their identified priority. EVALUATION: All CAPs (n = 264) completed in the 2019-2021 academic years were evaluated for evidence of several key areas, including community engagement and sustainability. 91% of projects evidenced a needs analysis, 71% demonstrated patient involvement in their development, and 64% demonstrated sustainable impacts from their projects. Analysis revealed the topics frequently addressed, and the formats used by students. Two CAPs are described in more detail to demonstrate their community impact. IMPLICATIONS: The CAP demonstrates how the principles of CEME (meaningful community engagement and social accountability) can lead to sustainable benefits for local communities through purposeful collaboration with patients and local communities. Strengths, limitations and future directions are highlighted
The Large, Oxygen-Rich Halos of Star-Forming Galaxies Are A Major Reservoir of Galactic Metals
The circumgalactic medium (CGM) is fed by galaxy outflows and accretion of
intergalactic gas, but its mass, heavy element enrichment, and relation to
galaxy properties are poorly constrained by observations. In a survey of the
outskirts of 42 galaxies with the Cosmic Origins Spectrograph onboard the
Hubble Space Telescope, we detected ubiquitous, large (150 kiloparsec) halos of
ionized oxygen surrounding star-forming galaxies, but we find much less ionized
oxygen around galaxies with little or no star formation. This ionized CGM
contains a substantial mass of heavy elements and gas, perhaps far exceeding
the reservoirs of gas in the galaxies themselves. It is a basic component of
nearly all star-forming galaxies that is removed or transformed during the
quenching of star formation and the transition to passive evolution.Comment: This paper is part of a set of three papers on circumgalactic gas
observed with the Cosmic Origins Spectrograph on HST, to be published in
Science, together with related papers by Tripp et al. and Lehner & Howk, in
the November 18, 2011 edition. This version has not undergone final
copyediting. Please see Science online for the final printed versio
The Role of Sub-damped Lyman-alpha Absorbers in the Cosmic Evolution of Metals
Observations of low mean metallicity of damped Lyman-alpha (DLA) quasar
absorbers at all redshifts studied appear to contradict the predictions for the
global mean interstellar metallicity in galaxies from cosmic chemical evolution
models. On the other hand, a number of metal-rich sub-DLA systems have been
identified recently, and the fraction of metal-rich sub-DLAs appears to be
considerably larger than that of metal-rich DLAs, especially at z < 1.5. In
view of this, here we investigate the evolution of metallicity in sub-DLAs. We
find that the mean Zn metallicity of the observed sub-DLAs may be higher than
that of the observed DLAs, especially at low redshifts, reaching a near-solar
level at z <~ 1. This trend does not appear to be an artifact of sample
selection, the use of Zn, the use of N_{HI}-weighting, or observational
sensitivity. While a bias against very low metallicity could be present in the
sub-DLA sample in some situations, this cannot explain the difference between
the DLA and sub-DLA metallicities at low z. The primary reason for the
difference between the DLAs and sub-DLAs appears to be the dearth of metal-rich
DLAs. We estimate the sub-DLA contribution to the total metal budget using
measures of their metallicity and comoving gas density. These calculations
suggest that at z <~ 1, the contribution of sub-DLAs to the total metal budget
may be several times that of DLAs. At higher redshifts also, there are
indications that the sub-DLAs may contribute significantly to the cosmic metal
budget.Comment: 9 pages, 2 figures, Accepted for Publication in the Astrophysical
Journa
Evidence for Cold Accretion: Primitive Gas Flowing onto a Galaxy at z~0.274
We present UV and optical observations from the Cosmic Origins Spectrograph
on the Hubble Space Telescope and Keck of a z= 0.27395 Lyman limit system (LLS)
seen in absorption against the QSO PG1630+377. We detect H I absorption with
log N(HI)=17.06\pm0.05 as well as Mg II, C III, Si III, and O VI in this
system. The column densities are readily explained if this is a multi-phase
system, with the intermediate and low ions arising in a very low metallicity
([Mg/ H] =-1.71 \pm 0.06) photoionized gas. We identify via Keck spectroscopy
and Large Binocular Telescope imaging a 0.3 L_* star-forming galaxy projected
37 kpc from the QSO at nearly identical redshift (z=0.27406, \Delta v = -26
\kms) with near solar metallicity ([O/ H]=-0.20 \pm 0.15). The presence of very
low metallicity gas in the proximity of a near-solar metallicity, sub-L_*
galaxy strongly suggests that the LLS probes gas infalling onto the galaxy. A
search of the literature reveals that such low metallicity LLSs are not
uncommon. We found that 50% (4/8) of the well-studied z < 1 LLSs have
metallicities similar to the present system and show sub-L_* galaxies with rho
< 100 kpc in those fields where redshifts have been surveyed. We argue that the
properties of these primitive LLSs and their host galaxies are consistent with
those of cold mode accretion streams seen in galaxy simulations.Comment: Accepted for publication in the Astrophysical Journa
Complete homochirality induced by the nonlinear autocatalysis and recycling
A nonlinear autocatalysis of a chiral substance is shown to achieve
homochirality in a closed system, if the back-reaction is included. Asymmetry
in the concentration of two enantiomers or the enantiometric excess increases
due to the nonlinear autocatalysis. Furthermore, when the back-reaction is
taken into account, the reactant supplied by the decomposition of the
enantiomers is recycled to produce more and more the dominant one, and
eventually the homochirality is established.Comment: 4 pages, 2 figure
- …