We present constraints on the mean matter density, Ωm, the normalization of the density fluctuation power spectrum, σ8, and the dark energy equation of state parameter, w, obtained from measurements ...of the X-ray luminosity function of the largest known galaxy clusters at redshifts z < 0.7, as compiled in the Massive Cluster Survey (MACS) and the local Brightest Cluster Sample (BCS) and ROSAT–ESO Flux Limited X-Ray (REFLEX) galaxy cluster sample. Our analysis employs an observed mass–luminosity relation, calibrated by hydrodynamical simulations, including corrections for non-thermal pressure support and accounting for the presence of intrinsic scatter. Conservative allowances for all known systematic uncertainties are included, as are standard priors on the Hubble constant and mean baryon density. We find Ωm= 0.28+0.11−0.07 and σ8= 0.78+0.11−0.13 for a spatially flat, cosmological constant model, and Ωm= 0.24+0.15−0.07, σ8= 0.85+0.13−0.20 and w=−1.4+0.4−0.7 for a flat, constant w model (marginalized 68 per cent confidence intervals). Our findings constitute the first determination of the dark energy equation of state from measurements of the growth of cosmic structure in galaxy clusters, and the consistency of our result with w=−1 lends additional support to the cosmological constant model. Future work improving our understanding of redshift evolution and observational biases affecting the mass–X-ray luminosity relation have the potential to significantly tighten these constraints. Our results are consistent with those from recent analyses of Type Ia supernovae, cosmic microwave background anisotropies, the X-ray gas mass fraction of relaxed galaxy clusters, baryon acoustic oscillations and cosmic shear. Combining the new X-ray luminosity function data with current supernova, cosmic microwave background and cluster gas fraction data yields the improved constraints Ωm= 0.269 ± 0.016, σ8= 0.82 ± 0.03 and w=−1.02 ± 0.06.
Uncertainty in the mass-observable scaling relations is currently the limiting factor for galaxy cluster based cosmology. Weak gravitational lensing can provide a direct mass calibration and reduce ...the mass uncertainty. We present new ground-based weak lensing observations of 19 South Pole Telescope (SPT) selected clusters and combine them with previously reported space-based observations of 13 galaxy clusters to constrain the cluster mass scaling relations with the Sunyaev-Zel'dovich effect (SZE), the cluster gas mass $M_\mathrm{gas}$, and $Y_\mathrm{X}$, the product of $M_\mathrm{gas}$ and X-ray temperature. We extend a previously used framework for the analysis of scaling relations and cosmological constraints obtained from SPT-selected clusters to make use of weak lensing information. Here, we introduce a new approach to estimate the effective average redshift distribution of background galaxies and quantify a number of systematic errors affecting the weak lensing modelling. These errors include a calibration of the bias incurred by fitting a Navarro-Frenk-White profile to the reduced shear using $N$-body simulations. We blind the analysis to avoid confirmation bias. We are able to limit the systematic uncertainties to 6.4% in cluster mass (68% confidence). Our constraints on the mass-X-ray observable scaling relations parameters are consistent with those obtained by earlier studies, and our constraints for the mass-SZE scaling relation are consistent with the the simulation-based prior used in the most recent SPT-SZ cosmology analysis. We can now replace the external mass calibration priors used in previous SPT-SZ cosmology studies with a direct, internal calibration obtained on the same clusters.
Abstract
We study the overdensity of point sources in the direction of X-ray-selected galaxy clusters from the meta-catalogue of X-ray-detected clusters of galaxies (MCXC; 〈z〉 = 0.14) at South Pole ...Telescope (SPT) and Sydney University Molonglo Sky Survey (SUMSS) frequencies. Flux densities at 95, 150 and 220 GHz are extracted from the 2500 deg2 SPT-SZ survey maps at the locations of SUMSS sources, producing a multifrequency catalogue of radio galaxies. In the direction of massive galaxy clusters, the radio galaxy flux densities at 95 and 150 GHz are biased low by the cluster Sunyaev–Zel’dovich Effect (SZE) signal, which is negative at these frequencies. We employ a cluster SZE model to remove the expected flux bias and then study these corrected source catalogues. We find that the high-frequency radio galaxies are centrally concentrated within the clusters and that their luminosity functions (LFs) exhibit amplitudes that are characteristically an order of magnitude lower than the cluster LF at 843 MHz. We use the 150 GHz LF to estimate the impact of cluster radio galaxies on an SPT-SZ like survey. The radio galaxy flux typically produces a small bias on the SZE signal and has negligible impact on the observed scatter in the SZE mass–observable relation. If we assume there is no redshift evolution in the radio galaxy LF then 1.8 ± 0.7 per cent of the clusters with detection significance ξ ≥ 4.5 would be lost from the sample. Allowing for redshift evolution of the form (1 + z)2.5 increases the incompleteness to 5.6 ± 1.0 per cent. Improved constraints on the evolution of the cluster radio galaxy LF require a larger cluster sample extending to higher redshift.
We present new constraints on the evolution of dark energy from an analysis of cosmic microwave background, supernova and X-ray galaxy cluster data. Our analysis employs a minimum of priors and ...exploits the complementary nature of these data sets. We examine a series of dark energy models with up to three free parameters: the current dark energy equation of state w0, the early-time equation of state wet, and the scalefactor at transition at. From a combined analysis of all three data sets, assuming a constant equation of state and that the Universe is flat, we measure w0=−1.05+0.10−0.12. Including wet as a free parameter and allowing the transition scalefactor to vary over the range 0.5 < at < 0.95 where the data sets have discriminating power, we measure w0=−1.27+0.33−0.39 and wet=−0.66+0.44−0.62. We find no significant evidence for evolution in the dark energy equation-of-state parameter with redshift. Marginal hints of evolution in the supernovae data become less significant when the cluster constraints are also included in the analysis. The complementary nature of the data sets leads to a tight constraint on the mean matter density Ωm and alleviates a number of other parameter degeneracies, including that between the scalar spectral index ns, the physical baryon density Ωbh2 and the optical depth τ. This complementary nature also allows us to examine models in which we drop the prior on the curvature. For non-flat models with a constant equation of state, we measure w0=−1.09+0.12−0.15 and obtain a tight constraint on the current dark energy density Ωde= 0.70 ± 0.03. For dark energy models other than a cosmological constant, energy–momentum conservation requires the inclusion of spatial perturbations in the dark energy component. Our analysis includes such perturbations, assuming a sound speed c2s= 1 in the dark energy fluid as expected for quintessence scenarios. For our most general dark energy model, not including such perturbations would lead to spurious constraints on wet, which would be tighter than those mentioned above by approximately a factor of 2 with the current data.
Ghrelin, the endogenous ligand for GH secretagogue receptors, has been reported to influence acid gastric secretion and motility, but its potential gastroprotective effect is unknown. The aims of ...this study were 1) to examine the effects of central and peripheral administration of ghrelin on ethanol-induced gastric ulcers in conscious rats, and 2) to investigate the possible roles of nitric oxide (NO), vagal nerve, and sensory fibers in the gastric effects of ghrelin.
Ghrelin was administered either intracerebroventricularly or sc 30 min before ethanol, and mucosal lesions were examined macroscopically. Additionally, rats were either treated with the inhibitor of NO synthesis Nω-nitro-l-arginine methyl ester (L-NAME) or underwent bilateral cervical vagotomy or capsaicin-induced sensory denervation. Conventional histology and immunohistochemistry for ghrelin, gastrin, and somatostatin were performed on gastric specimens from representative rats.
Central ghrelin (4–4000 ng/rat) dose-dependently reduced ethanol-induced gastric ulcers by 39–77%. Subcutaneous ghrelin administration (80 μg/kg) reduced ulcer depth only. L-NAME and capsaicin, but not vagotomy, prevented the gastroprotective effect of central ghrelin (4000 ng/rat).
This is the first evidence that ghrelin exerts a potent central gastroprotective activity against ethanol-induced lesions. The gastroprotective effect of ghrelin is mediated by endogenous NO release and requires the integrity of sensory nerve fibers.
Background and purpose:
Ghrelin, a gut‐brain peptide, is considered a gastroprotective factor in gastric mucosa. We investigated the role of prostaglandins (PG) and the possible interplay between PGs ...and nitric oxide (NO) in ghrelin gastroprotection against ethanol (EtOH)‐induced gastric lesions.
Experimental approach:
We examined the effects of (1) central ghrelin (4 μg per rat) injection on PGE2 accumulation in normal or EtOH–lesioned gastric mucosa, (2) pretreatment with indomethacin (10 mg kg−1, p.o.), a non‐selective cyclooxygenase (COX) inhibitor, and with a selective COX‐1, SC560 (5 mg kg−1, p.o.) or COX‐2 inhibitor, celecoxib (3.5 mg kg−1, p.o.) on ghrelin gastroprotection against 50% EtOH (1 mL per rat)‐induced gastric lesions, (3) the NO synthase inhibitor, L‐NAME (70 mg kg−1, s.c), on gastric PGE2 content in ghrelin‐treated rats and (4) central ghrelin on the expression of constitutive and inducible NOS and COX mRNA and on the localization of the immunoreactivity for COX‐2 in the gastric mucosa exposed to EtOH.
Key results:
Ghrelin increased PGE2 in normal mucosa, whereas, it reversed the EtOH‐induced PGE2 surge. Ghrelin had no effect on mucosal COX‐1 expression but reduced the EtOH‐induced increase in COX‐2 expression and immunoreactivity. Indomethacin and SC560, but not celecoxib, removed ghrelin gastroprotection. L‐NAME prevented the PGE2 surge induced by ghrelin and, like indomethacin, reduced EtOH‐induced PGE2 increase. Ghrelin enhanced eNOS expression and reduced iNOS mRNA.
Conclusions and implications:
This study shows that COX‐1‐derived PGs are mainly involved in ghrelin gastroprotection and that the constitutive‐derived NO together with PGE2 are involved in ghrelin gastroprotective activity.
British Journal of Pharmacology (2008) 154, 688–697; doi:10.1038/bjp.2008.120; published online 14 April 2008
Obestatin is a recently discovered 23 amino acids peptide derived from the ghrelin gene. As opposed to ghrelin, obestatin was shown to inhibit food intake in mice. The aims of this research were to ...study the effects of acute obestatin treatment on feeding behavior in the rat and its effects on GH and corticosterone secretion. Our results demonstrate that in young-adult male rats, obestatin effectively blunts the hunger caused by short-term starvation. Obestatin did not modify GH secretion in 10-day-old rats and did not antagonize the GH-releasing effects of hexarelin. Moreover, obestatin administration had no effects on spontaneous corticosterone secretion. In conclusion, these data demonstrate that in young-adult male rats the newly discovered obestatin can inhibit feeding but does not modify GH and corticosterone release in infant rats.
Context.
The opacity of the ionosphere prevents comprehensive Earth-based surveys of low frequency
ν
≲ 10 MHz astrophysical radio emissions. The limited available data in this frequency regime show a ...downturn in the mean sky brightness at
ν
≲ 3 MHz in a divergence from the synchrotron emission power-law that is observed at higher frequencies. The turning over of the spectrum coincides with a shift in the region of maximum brightness from the Galactic plane to the poles. This implicates free-free absorption by interstellar ionized gas, whose concentration in the plane causes radiation that propagates in this region to suffer stronger absorption than radiation from the poles.
Aims.
Using observations from Parker Solar Probe (PSP), we evaluate the
l
= 0 and
l
= 2 spherical harmonic expansion coefficients of the radio brightness distribution at 56 frequencies between 0.5 and 7 MHz. These data quantify free-free absorption’s global effects on the brightness distribution, which provides new constraints on the distribution of free electrons in the Galaxy.
Methods.
The auto and cross spectra of the voltages induced on crossed short dipole antennas by radiation from a nonpolarized extended brightness distribution are linear combinations of the distribution’s
l
= 0 and
l
= 2 expansion coefficients. We extracted the least squares solution to these coefficients from PSP’s measurements of the radio background. Also, we generated hypothetical low frequency brightness maps that incorporated free-free absorption and tested their compatibility with the data. The maps primarily depended on models of the Galactic emissivity and distribution of free electrons. A comparison of the maps’ expansion coefficients with the empirical coefficients provided an indication of these input models’ accuracies.
Results.
An average reduced
x
2
≈ 1.04 of the spherical harmonic analysis between 0.5 and 7 MHz indicates that PSP’s antennas act approximately as ideal short dipoles in this frequency band. The best-fit expansion coefficients show that, with decreasing frequency, the mean sky brightness decreases at
ν
< 3 MHz and the Galactic plane darkens relative to the poles. At
ν
> 0.6 MHz, these observations can be reproduced in synthetic brightness maps in which the Galactic emissivity maintains a power-law form and free-free absorption is modeled using free electron distributions derived from pulsar measurements. At lower frequencies, the empirical mean brightness falls below the mean in this model, possibly signifying a cutoff in the synchrotron power-law.
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