2,773 research outputs found
The evolutionary sequence of post-starburst galaxies
© 2017 The Authors. There are multiple ways in which to select post-starburst galaxies in the literature. In this work, we present a study into how two well-used selection techniques have consequences on observable post-starburst galaxy parameters, such as colour, morphology and environment, and how this affects interpretations of their role in the galaxy duty cycle. We identify a master sample of Hδ strong (EWHδ> 3Å) post-starburst galaxies from the value-added catalogue in the seventh data release of the Sloan Digital Sky Survey (SDSS DR7) over a redshift range 0.01 -2.5Å) but one having an additional cut onEWHα (> -3Å).We examine the differences in observables and AGN fractions to see what effect the Hα cut has on the properties of post-starburst galaxies and what these differing samples can tell us about the duty cycle of post-starburst galaxies. We find that Hδ strong galaxies peak in the 'blue cloud', E+As in the 'green valley' and pure E+As in the 'red sequence'.We also find that pure E+As have a more early-type morphology and a higher fraction in denser environments compared with the Hδ strong and E+A galaxies. These results suggest that there is an evolutionary sequence in the post-starburst phase from blue discy galaxies with residual star formation to passive red early-types
Hemostatic function and progressing ischemic stroke: D-dimer predicts early clinical progression
<p><b>Background and Purpose:</b> Early clinical progression of ischemic stroke is common and is associated with increased risk of death and dependency. We hypothesized that activation of the coagulation system is an important contributor in some cases of deterioration. We aimed to characterize alterations in circulating hemostatic markers in patients with progressing stroke.</p>
<p><b>Methods:</b> Consecutive acute ischemic stroke admissions were recruited. Progressing stroke was defined by deterioration in components of the Scandinavian Stroke Scale. Hemostatic markers (coagulation factors VIIc, VIIIc, and IXc, prothrombin fragments 1+2 [F1+2], thrombin-antithrombin complexes [TAT], D- dimer, fibrinogen, von Willebrand factor [vWF] and tissue plasminogen activator) were measured within 24 hours of symptom recognition.</p>
<p><b>Results:</b> Fifty-four (25%) of the 219 patients met criteria for progressing stroke. F1+2 (median 1.28 versus 1.06 nmol/L, P=0.01), TAT (5.28 versus 4.07 mug/L, P lt 0.01), D-dimer ( 443 versus 194 ng/mL, P lt 0.001) and vWF (216 versus 198 IU/dL, P lt 0.05) levels were higher in these patients than in stable/improving patients. In logistic regression analysis, with all important clinical and laboratory variables included, only natural log D-dimer (odds ratio [OR]: 1.87; 95% confidence interval [CI]: 1.38 to 2.54; P=0.0001) and mean arterial blood pressure (OR: 1.26 per 10 mm Hg change; 95% CI: 1.05 to 1.51; P=0.01) remained independent predictors of progressing stroke.</p>
<p><b>Conclusions:</b> There is evidence of excess thrombin generation and fibrin turnover in patients with progressing ischemic stroke. Measurement of D-dimer levels can identify patients at high risk for stroke progression. Further research is required to determine whether such patients benefit from acute interventions aimed at modifying hemostatic function.</p>
Environments and Morphologies of Red Sequence Galaxies with Residual Star Formation in Massive Clusters
We present a photometric investigation into recent star formation in galaxy
clusters at z ~ 0.1. We use spectral energy distribution templates to quantify
recent star formation in large X-ray selected clusters from the LARCS survey
using matched GALEX NUV photometry. These clusters all have signs of red
sequence galaxy recent star formation (as indicated by blue NUV-R colour),
regardless of cluster morphology and size. A trend in environment is found for
these galaxies, such that they prefer to occupy low density, high cluster
radius environments. The morphology of these UV bright galaxies suggests that
they are in fact red spirals, which we confirm with light curves and Galaxy Zoo
voting percentages as morphological proxies. These UV bright galaxies are
therefore seen to be either truncated spiral galaxies, caught by ram pressure
in falling into the cluster, or high mass spirals, with the photometry
dominated by the older stellar population.Comment: Accepted for publication in MNRAS, 11 pages, 11 figure
IMPACT: an implicit time integration scheme for chemical species and families
International audienceThe implicit time integration scheme of Stott and Harwood (1993) was proposed as an efficient scheme for use in three-dimensional chemical models of the atmosphere. The scheme was designed for chemistry schemes using `chemical families', in which species with short lifetimes are grouped into longer-lived families. Further study with more complex chemistry, more species and reactions showed the scheme to be non-convergent and unstable under certain conditions; particularly for the perturbed chemical scenarios of polar stratospheric winters. In this work the scheme has been improved by revising the treatment of families and the convergence properties of the scheme. The new scheme has been named IMPACT (IMPlicit Algorithm for Chemical Time-stepping). It remains easy to implement and produces simulations that compare well with integrations using more accurate higher order schemes
Analytical modeling of micelle growth. 2. Molecular thermodynamics of mixed aggregates and scission energy in wormlike micelles
Hypotheses: Quantitative molecular-thermodynamic theory of the growth of
giant wormlike micelles in mixed nonionic surfactant solutions can be developed
on the basis of a generalized model, which includes the classical phase
separation and mass action models as special cases. The generalized model
describes spherocylindrical micelles, which are simultaneously multicomponent
and polydisperse in size. Theory: The model is based on explicit analytical
expressions for the four components of the free energy of mixed nonionic
micelles: interfacial-tension, headgroup-steric, chain-conformation components
and free energy of mixing. The radii of the cylindrical part and the spherical
endcaps, as well as the chemical composition of the endcaps, are determined by
minimization of the free energy. Findings: In the case of multicomponent
micelles, an additional term appears in the expression for the micelle growth
parameter (scission free energy), which takes into account the fact that the
micelle endcaps and cylindrical part have different compositions. The model
accurately predicts the mean mass aggregation number of wormlike micelles in
mixed nonionic surfactant solutions without using any adjustable parameters.
The endcaps are enriched in the surfactant with smaller packing parameter that
is better accommodated in regions of higher mean surface curvature. The model
can be further extended to mixed solutions of nonionic, ionic and zwitterionic
surfactants used in personal-care and house-hold detergency
Measurement of the intracluster light at z ~ 1
A significant fraction of the total photospheric light in nearby galaxy
clusters is thought to be contained within the diffuse intracluster light
(ICL), which extends 100s of kpc from cluster cores. The study of the ICL can
reveal details of the evolutionary histories and processes occurring within
galaxy clusters, however since it has a very low surface brightness it is often
difficult to detect. We present here the first measurements of the ICL as a
fraction of total cluster light at z \sim 1 using deep J-band (1.2 {\mu}m)
imaging from HAWK-I on the VLT. We investigate the ICL in 6 X-ray selected
galaxy clusters at 0.8< z <1.2 and find that the ICL below isophotes {\mu}(J) =
22 mag/arcsec2 constitutes 1-4% of the total cluster light within a radius
R500. This is broadly consistent with simulations of the ICL at a similar
redshift and when compared to nearby observations suggests that the fraction of
the total cluster light that is in the ICL has increased by a factor 2 - 4
since z\sim1. We also find the fraction of the total cluster light contained
within the Brightest Cluster Galaxy (BCG) to be 2.0-6.3% at these redshifts,
which in 5 out of 6 cases is larger than the fraction of the ICL component, in
contrast to results from nearby clusters. This suggests that the evolution in
cluster cores involves substantial stripping activity at late times, in
addition to the early build up of the BCG stellar mass through merging. The
presence of significant amounts of stellar light at large radii from these BCGs
may help towards solving the recent disagreement between the semi-analytic
model predictions of BCG mass growth (e.g. De Lucia & Blaziot, 2007) and the
observed large masses and scale sizes reported for BCGs at high redshift.Comment: 12 pages, 12 figures. Accepted for publication in MNRA
Early Quenching of Massive Protocluster Galaxies Around <i>z</i>=2.2 Radio Galaxies
Radio galaxies are among the most massive galaxies in the high-redshift Universe and are known to often lie in protocluster environments. We have studied the fields of seven z = 2.2 radio galaxies with High Acuity Wide field K-band Imager (HAWK-I) narrow-band and broad-band imaging in order to map out their environment using Hα emitters (HAEs). The results are compared to the blank field HAE survey HiZELS. All of the radio galaxy fields are overdense in HAEs relative to a typical HiZELS field of the same area and four of the seven are richer than all except one of 65 essentially random HiZELS subfields of the same size. The star formation rates of the massive HAEs are lower than those necessary to have formed their stellar population in the preceding Gyr – indicating that these galaxies are likely to have formed the bulk of their stars at higher redshifts, and are starting to quench
- …