156 research outputs found
Separating the BL Lac and Cluster X-ray Emissions in Abell 689 with Chandra
We present the results of a Chandra observation of the galaxy cluster Abell
689 (z=0.279). Abell 689 is one of the most luminous clusters detected in the
ROSAT All Sky Survey (RASS), but was flagged as possibly including significant
point source contamination. The small PSF of the Chandra telescope allows us to
confirm this and separate the point source from the extended cluster X-ray
emission. For the cluster we determine a bolometric luminosity of
L_{bol}=(3.3+/-0.3)x10^{44} erg s-1 and a temperature of kT=5.1^{+2.2}_{-1.3}
keV when including a physically motivated background model. We compare our
measured luminosity for A689 to that quoted in the Rosat All Sky Survey (RASS)
and find L_{0.1-2.4,keV}=2.8x10^{44} erg s-1, a value \sim10 times lower than
the ROSAT measurement. Our analysis of the point source shows evidence for
significant pileup, with a pile-up fraction of ~60%. SDSS spectra and HST
images lead us to the conclusion that the point source within Abell 689 is a BL
Lac object. Using radio and optical observations from the VLA and HST archives,
we determine {\alpha}_{ro}=0.50, {\alpha}_{ox}=0.77 and {\alpha}_{rx}=0.58 for
the BL Lac, which would classify it as being of 'High-energy peak BL Lac' (HBL)
type. Spectra extracted of A689 show a hard X-ray excess at energies above 6
keV that we interpret as inverse Compton emission from aged electrons that may
have been transported into the cluster from the BL Lac.Comment: 11 pages, 15 figures, MNRAS in pres
LoCuSS: Comparison of Observed X-ray and Lensing Galaxy Cluster Scaling Relations with Simulations
The Local Cluster Substructure Survey (LoCuSS, Smith et al.) is a systematic
multi-wavelength survey of >100 X-ray luminous galaxy clusters (0.14<z<0.3)
selected from the ROSAT all sky survey. We used data on 37 LoCuSS clusters from
the XMM-Newton archive to investigate the global scaling relations of galaxy
clusters. The scaling relations based solely on the X-ray data obey empirical
self-similarity and reveal no additional evolution beyond the LSS growth. Weak
lensing mass measurements are also available in the literature for 19 of the
clusters with XMM-Newton data. The average of the weak lensing mass to X-ray
based mass ratio is 1.09+/-8, setting the limit of the non-thermal pressure
support to 9+/-8%. The mean of the weak lensing mass to X-ray based mass ratio
of these clusters is ~1 with 31-51% scatter. The scatter in the
mass--observable relations (M-Y_X, M-M_{gas} and M-T) is smaller using X-ray
based masses than using weak lensing masses by a factor of 2. Using the scaled
radius defined by the Y_X profile, we obtain lower scatter in the weak lensing
mass based mass--observable relations. The normalization of the M-Y_X relation
(also M-M_{gas} and M-T relations) using X-ray (weak lensing) mass estimates is
lower than the one from simulations by up to 20% at ~3 sigma (~2 sigma)
significance. Despite the large scatter in the X-ray to lensing comparison, the
agreement between these two completely independent observational methods is an
important step towards controlling astrophysical and measurement systematics in
cosmological scaling relations.Comment: 56 pages, 32 figure, 2008A&A...482..451Z, typos corrected in Table
A.
Glucose enhancement of human memory: A comprehensive research review of the glucose memory facilitation effect
The brain relies upon glucose as its primary fuel. In recent years, a rich literature has developed from both human and animal studies indicating that increases in circulating blood glucose can facilitate cognitive functioning. This phenomenon has been termed the ‘glucose memory facilitation effect’. The purpose of this review is to discuss a number of salient studies which have investigated the influence of glucose ingestion on neurocognitive performance in individuals with (a) compromised neurocognitive capacity, as well as (b) normally functioning individuals (with a focus on research conducted with human participants). The proposed neurocognitive mechanisms purported to underlie the modulatory effect of glucose on neurocognitive performance will also be considered. Many theories have focussed upon the hippocampus, given that this brain region is heavily implicated in learning and memory. Further, it will be suggested that glucose is a possible mechanism underlying the phenomenon that enhanced memory performance is typically observed for emotionally laden stimuli
Halo mass - concentration relation from weak lensing
We perform a statistical weak lensing analysis of dark matter profiles around
tracers of halo mass from galactic- to cluster-size halos. In this analysis we
use 170,640 isolated ~L* galaxies split into ellipticals and spirals, 38,236
groups traced by isolated spectroscopic Luminous Red Galaxies (LRGs) and 13,823
MaxBCG clusters from the Sloan Digital Sky Survey (SDSS) covering a wide range
of richness. Together these three samples allow a determination of the density
profiles of dark matter halos over three orders of magnitude in mass, from
10^{12} M_{sun} to 10^{15} M_{sun}. The resulting lensing signal is consistent
with an NFW or Einasto profile on scales outside the central region. We find
that the NFW concentration parameter c_{200b} decreases with halo mass, from
around 10 for galactic halos to 4 for cluster halos. Assuming its dependence on
halo mass in the form of c_{200b} = c_0 [M/(10^{14}M_{sun}/h)]^{\beta}, we find
c_0=4.6 +/- 0.7 (at z=0.22) and \beta=0.13 +/- 0.07, with very similar results
for the Einasto profile. The slope (\beta) is in agreement with theoretical
predictions, while the amplitude is about two standard deviations below the
predictions for this mass and redshift, but we note that the published values
in the literature differ at a level of 10-20% and that for a proper comparison
our analysis should be repeated in simulations. We discuss the implications of
our results for the baryonic effects on the shear power spectrum: since these
are expected to increase the halo concentration, the fact that we see no
evidence of high concentrations on scales above 20% of the virial radius
suggests that baryonic effects are limited to small scales, and are not a
significant source of uncertainty for the current weak lensing measurements of
the dark matter power spectrum. [ABRIDGED]Comment: 17 pages, 5 figures, accepted to JCAP pending minor revisions that
are included in v2 here on arXi
TEMPLATES: Direct Abundance Constraints for Two Lensed Lyman-Break Galaxies
Using integrated spectra for two gravitationally lensed galaxies from the
JWST TEMPLATES Early Release Science program, we analyze faint auroral lines,
which provide direct measurements of the gas-phase chemical abundance. For the
brighter galaxy, SGAS172334 (), we detect the
[OIII], [SIII], and [OII]7320,7330
auroral emission lines, and set an upper limit for the [NII] line.
For the second galaxy, SGAS122621 (), we do not detect any
auroral lines, and report upper limits. With these measurements and upper
limits, we constrain the electron temperatures in different ionization zones
within both of these galaxies. For SGAS172334, where auroral lines are
detected, we calculate direct oxygen and nitrogen abundances, finding an N/O
ratio consistent with observations of nearby () galaxies. These
observations highlight the potent combination of JWST and gravitational lensing
to measure faint emission lines in individual distant galaxies and to directly
study the chemical abundance patterns in those galaxies.Comment: Submitted to the Astrophysical Journal's Focus Issue on the TEMPLATES
JWST Early Release Science Program. 15 pages, 6 figures. Comments welcom
Cluster Lenses
Clusters of galaxies are the most recently assembled, massive, bound
structures in the Universe. As predicted by General Relativity, given their
masses, clusters strongly deform space-time in their vicinity. Clusters act as
some of the most powerful gravitational lenses in the Universe. Light rays
traversing through clusters from distant sources are hence deflected, and the
resulting images of these distant objects therefore appear distorted and
magnified. Lensing by clusters occurs in two regimes, each with unique
observational signatures. The strong lensing regime is characterized by effects
readily seen by eye, namely, the production of giant arcs, multiple-images, and
arclets. The weak lensing regime is characterized by small deformations in the
shapes of background galaxies only detectable statistically. Cluster lenses
have been exploited successfully to address several important current questions
in cosmology: (i) the study of the lens(es) - understanding cluster mass
distributions and issues pertaining to cluster formation and evolution, as well
as constraining the nature of dark matter; (ii) the study of the lensed objects
- probing the properties of the background lensed galaxy population - which is
statistically at higher redshifts and of lower intrinsic luminosity thus
enabling the probing of galaxy formation at the earliest times right up to the
Dark Ages; and (iii) the study of the geometry of the Universe - as the
strength of lensing depends on the ratios of angular diameter distances between
the lens, source and observer, lens deflections are sensitive to the value of
cosmological parameters and offer a powerful geometric tool to probe Dark
Energy. In this review, we present the basics of cluster lensing and provide a
current status report of the field.Comment: About 120 pages - Published in Open Access at:
http://www.springerlink.com/content/j183018170485723/ . arXiv admin note:
text overlap with arXiv:astro-ph/0504478 and arXiv:1003.3674 by other author
Gefitinib and <i>EGFR</i> Gene Copy Number Aberrations in Esophageal Cancer
Purpose: The cancer esophagus gefitinib (COG) trial demonstrated improved progression free survival with the Epidermal Growth Factor Receptor (EGFR) tyrosine kinase inhibitor (TKI), gefitinib relative to placebo in advanced esophageal cancer patients with disease progression after chemotherapy. Rapid and durable responses were observed in a minority. We hypothesised that genetic aberration of the EGFR pathway would identify patients benefitting from gefitinib.
Patients and Methods: A pre-specified blinded molecular analysis of COG trial tumours was conducted to compare efficacy of gefitinib to placebo according to EGFR copy number gain (CNG) and EGFR, KRAS, BRAF and PIK3CA mutation status. EGFR CNG was determined by fluorescent insitu hybridisation (FISH) using pre-specified criteria and EGFR FISH positive defined as high polysomy or amplification.
Results: Biomarker data were available for 340 patients. In EGFR FISH positive tumours (20.2%) overall survival was improved with gefitinib compared to placebo (hazard ratio [HR] for death, 0.59; 95% confidence interval [CI], 0.35, 1.00 p=0.05). In EGFR FISH negative tumours there was no difference in overall survival with gefitinib compared to placebo (HR for death, 0.90, 95% CI 0.69, 1.18 p=0.46). EGFR amplification (7.2%) patients gained greatest benefit from gefitinib (HR for death, 0.21; 95% CI 0.07-0.64; p=0.006). There was no difference in overall survival for gefitinib versus placebo for patients with EGFR, KRAS, BRAF and PIK3CA mutations, or for any mutation versus none.
Conclusion: EGFR CNG assessed by FISH appears to identify a subgroup of esophageal cancer patients who may benefit from gefitinib as a second line treatment, and suggests that anti-EGFR 3 therapies should be investigated in prospective clinical trials in different settings in EGFR FI SH positive, and in particular EGFR amplified, esophageal cancer
Gravitational Lensing
Gravitational lensing has developed into one of the most powerful tools for
the analysis of the dark universe. This review summarises the theory of
gravitational lensing, its main current applications and representative results
achieved so far. It has two parts. In the first, starting from the equation of
geodesic deviation, the equations of thin and extended gravitational lensing
are derived. In the second, gravitational lensing by stars and planets,
galaxies, galaxy clusters and large-scale structures is discussed and
summarised.Comment: Invited review article to appear in Classical and Quantum Gravity, 85
pages, 15 figure
COOL-LAMPS VI: Lens model and New Constraints on the Properties of COOL J1241+2219, a Bright z = 5 Lyman Break Galaxy and its z = 1 Cluster Lens
We present a strong lensing analysis of COOL J1241+2219, the brightest known
gravitationally lensed galaxy at , based on new multi-band Hubble
Space Telescope (HST) imaging data. The lensed galaxy has a redshift of
z=5.043, placing it shortly after the end of the Epoch of Reionization, and an
AB magnitude z_AB=20.47 mag (Khullar et al. 2021). As such, it serves as a
touchstone for future research of that epoch. The high spatial resolution of
HST reveals internal structure in the giant arc, from which we identify 15
constraints and construct a robust lens model. We use the lens model to extract
cluster mass and lensing magnification. We find that the mass enclosed within
the Einstein radius of the z=1.001 cluster lens is
M(<5.77'')=, significantly lower than other known
strong lensing clusters at its redshift. The average magnification of the giant
arc is , a factor of greater
than previously estimated from ground-based data; the flux-weighted average
magnification is We update the current
measurements of the stellar mass and star formation rate (SFR) of the source
for the revised magnification, and yr. The powerful lensing
magnification acting upon COOL J1241+2219 resolves the source and enables
future studies of the properties of its star formation on a clump-by-clump
basis. The lensing analysis presented here will support upcoming
multiwavelength characterization with HST and JWST data of the stellar mass
assembly and physical properties of this high-redshift lensed galaxy.Comment: Submitted to Ap
A hypothetico-deductive approach to assessing the social function of chemical signalling in a non-territorial solitary carnivore
The function of chemical signalling in non-territorial solitary carnivores is still relatively unclear. Studies on territorial solitary and social carnivores have highlighted odour capability and utility, however the social function of chemical signalling in wild carnivore populations operating dominance hierarchy social systems has received little attention. We monitored scent marking and investigatory behaviour of wild brown bears Ursus arctos, to test multiple hypotheses relating to the social function of chemical signalling. Camera traps were stationed facing bear ‘marking trees’ to document behaviour by different age sex classes in different seasons. We found evidence to support the hypothesis that adult males utilise chemical signalling to communicate dominance to other males throughout the non-denning period. Adult females did not appear to utilise marking trees to advertise oestrous state during the breeding season. The function of marking by subadult bears is somewhat unclear, but may be related to the behaviour of adult males. Subadults investigated trees more often than they scent marked during the breeding season, which could be a result of an increased risk from adult males. Females with young showed an increase in marking and investigation of trees outside of the breeding season. We propose the hypothesis that females engage their dependent young with marking trees from a young age, at a relatively ‘safe’ time of year. Memory, experience, and learning at a young age, may all contribute towards odour capabilities in adult bears
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