572 research outputs found
Details of the mass--temperature relation for clusters of galaxies
We present results on the total mass and temperature determination using two
samples of clusters of galaxies. One sample is constructed with emphasis on the
completeness of the sample, while the advantage of the other is the use of the
temperature profiles, derived with ASCA. We obtain remarkably similar fits to
the M-T relation for both samples, with the normalization and the slope
significantly different from both prediction of self-similar collapse and
hydrodynamical simulations. We discuss the origin of these discrepancies and
also combine the X-ray mass with velocity dispersion measurements to provide a
comparison with high-resolution dark matter simulations. Finally, we discuss
the importance of a cluster formation epoch in the observed M-T relation.Comment: 12 pages, A&A 2001 in pres
XMM-Newton and Gemini Observations of Eight RASSCALS Galaxy Groups
We study the distribution of gas pressure and entropy in eight groups of
galaxies belonging to the ROSAT All-Sky Survey / Center for Astrophysics Loose
Systems (RASSCALS). We use archival and proprietary XMM-Newton observations,
supplementing the X-ray data with redshifts derived from the literature; we
also list 127 new redshifts measured with the Gemini North telescope. The
groups show remarkable self-similarity in their azimuthally averaged entropy
and temperature profiles. The entropy increases with radius; the behavior of
the entropy profiles is consistent with an increasing broken power law with
inner and outer slope 0.92+0.04-0.05 and 0.42+0.05-0.04 (68% confidence),
respectively. There is no evidence of a central, isentropic core, and the
entropy distribution in most of the groups is flatter at large radii than in
the inner region, challenging earlier reports as well as theoretical models
predicting large isentropic cores or asymptotic slopes of 1.1 at large radii.
The pressure profiles are consistent with a self-similar decreasing broken
power law in radius; the inner and outer slopes are -0.78+0.04-0.03 and
-1.7+0.1-0.3, respectively. The results suggest that the larger scatter in the
entropy distribution reflects the varied gasdynamical histories of the groups;
the regularity and self-similarity of the pressure profiles is a sign of a
similarity in the underlying dark matter distributions.Comment: Accepted for publication in the Astrophysical Journa
Probing Turbulence in the Coma Galaxy Cluster
Spatially-resolved gas pressure maps of the Coma galaxy cluster are obtained
from a mosaic of XMM-Newton observations in the scale range between a
resolution of 20 kpc and an extent of 2.8 Mpc. A Fourier analysis of the data
reveals the presence of a scale-invariant pressure fluctuation spectrum in the
range between 40 and 90 kpc and is found to be well described by a projected
Kolmogorov/Oboukhov-type turbulence spectrum. Deprojection and integration of
the spectrum yields the lower limit of percent of the total
intracluster medium pressure in turbulent form. The results also provide
observational constraints on the viscosity of the gas.Comment: 12 pages, 13 figures (low resolution), version accepted by Astron.
Astrophy
Structure of the hepatitis C virus IRES bound to the human 80S ribosome: Remodeling of the HCV IRES
Use of Urinary Pregnanediol 3-glucuronide to Confirm Ovulation
Objective Urinary hormonal markers may assist in increasing the efficacy of Fertility Awareness Based Methods (FABM). This study uses urinary pregnanediol-3a-glucuronide (PDG) testing to more accurately identify the infertile phase of the menstrual cycle in the setting of FABM. Methods Secondary analysis of an observational and simulation study, multicentre, European study. The study includes 107 women and tracks daily first morning urine (FMU), observed the changes in cervical mucus discharge, and ultrasonography to identify the day of ovulation over 326 menstrual cycles. The following three scenarios were tested: (A) use of the daily pregnandiol-3a-glucuronide (PDG) test alone; (B) use of the PDG test after the first positive urine luteinizing hormone (LH) kit result; (C) use of the PDG test after the disappearance of fertile type mucus. Two models were used: (1) one day of PDG positivity; or (2) waiting for three days of PDG positivity before declaring infertility. Results After the first positivity of a LH test or the end of fertile mucus, three consecutive days of PDG testing over a threshold of 5 μg/mL resulted in a 100% specificity for ovulation confirmation. They were respectively associated an identification of an average of 6.1 and 7.6 recognized infertile days. Conclusions The results demonstrate a clinical scenario with 100% specificity for ovulation confirmation and provide the theoretical background for a future development of a competitive lateral flow assay for the detection of PDG in the urine
The effect of soil moisture and atmospheric conditions on the development of shallow cumulus convection: A coupled large-eddy simulation-land surface model study
Many processes and feedback mechanisms are involved in land-atmosphere interactions that play an important role in determining the boundary layer structure throughout the diurnal cycle. Here, the effect of soil moisture on the development of shallow cumulus convection is investigated using a coupled large-eddy simulation (LES)-land surface model (LSM) framework. First, the coupled model is run for an idealised case based on measurements at the ARM Southern Great Plain site on 21 June 1997 to demonstrate that many characteristics of the subcloud layer turbulence and of the cumulus layer can be modelled successfully. Moreover, an extensive sensitivity study is performed with different amounts of soil moisture and varying atmospheric conditions. Our results support the hypothesis that the response of shallow cumulus clouds due to a change of soil moisture severely depends on the thermal stability conditions. Furthermore, they also point out that the atmospheric moisture content is as important as the static stability in determining the boundary layer characteristics and in particular the fractional cloud cover. The results demonstrate that the soil moisture-cloud cover coupling is positive in most of the cases. However, we show that under specific conditions (a less stably stratified moist atmosphere) convective activity and cloud formation is stronger over dry soils, where the principle driving mechanism for cloud development is the boundary layer growth that tends to increase relative humidity by adiabatic cooling of the air at the top of the boundary layer. This leads to a soil moisture cloud cover relationship in which the cloud cover fraction decreases with an increase of soil moisture. Moreover, our findings suggest that in the limiting case of a water saturated soil the mean cloud cover is independent of static stability, but only depends on the vertical integrated atmospheric moisture content
Reproducing the entropy structure in galaxy groups
We carry out a comparison between observations and hydrodynamic simulations
of entropy profiles of groups and clusters of galaxies. We use the Tree+SPH
GADGET code to simulate four halos of sizes in the M_500 = 1.0 - 16.e13 h^-1
Msun range, corresponding to poor groups up to Virgo-like clusters. We
concentrate on the effect of introducing radiative cooling, star formation, and
a variety of non-gravitational heating schemes on the entropy structure and the
stellar fraction. We show that all the simulations result in a correct entropy
profile for the Virgo-like cluster. With the heating energy budget of ~0.7
keV/particle injected at z_h=3, we are also able to reproduce the entropy
profiles of groups. We obtain the flat entropy cores as a combined effect of
preheating and cooling, while we achieve the high entropy at outskirts by
preheating. The resulting baryon fraction locked into stars is in the 25-30%
range, compared to 35-40% in the case of no preheating. Heating at higher
redshift, z_h=9, strongly delays the star-formation, but fails to produce a
sufficiently high specific entropy.Comment: 5 page, A&A in pres
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