Can simulations reproduce the observed temperature-mass relation for clusters of galaxies?

It has become increasingly apparent that traditional hydrodynamical simulations of galaxy clusters are unable to reproduce the observed properties of galaxy clusters, in particular overpredicting the mass corresponding to a given cluster temperature. Such overestimation may lead to systematic errors in results using galaxy clusters as cosmological probes, such as constraints on the density perturbation normalization sigma_8. In this paper we demonstrate that inclusion of additional gas physics, namely radiative cooling and a possible preheating of gas prior to cluster formation, is able to bring the temperature-mass relation in the innermost parts of clusters into good agreement with recent determinations by Allen, Schmidt & Fabian using Chandra data.Comment: 5 pages, submitted to MNRA

The Organization of the Primate Insular Cortex

Long perceived as a primitive and poorly differentiated brain structure, the primate insular cortex recently emerged as a highly evolved, organized and richly connected cortical hub interfacing bodily states with sensorimotor, environmental, and limbic activities. This insular interface likely substantiates emotional embodiment and has the potential to have a key role in the interoceptive shaping of cognitive processes, including perceptual awareness. In this review, we present a novel working model of the insular cortex, based on an accumulation of neuroanatomical and functional evidence obtained essentially in the macaque monkey. This model proposes that interoceptive afferents that represent the ongoing physiological status of all the organs of the body are first being received in the granular dorsal fundus of the insula or “primary interoceptive cortex,” then processed through a series of dysgranular poly-modal “insular stripes,” and finally integrated in anterior agranular areas that serve as an additional sensory platform for visceral functions and as an output stage for efferent autonomic regulation. One of the agranular areas hosts the specialized von Economo and Fork neurons, which could provide a decisive evolutionary advantage for the role of the anterior insula in the autonomic and emotional binding inherent to subjective awareness

The X-ray Cluster Normalization of the Matter Power Spectrum

The number density of galaxy clusters provides tight statistical constraints on the matter fluctuation power spectrum normalization, traditionally phrased in terms of sigma_8, the root mean square mass fluctuation in spheres with radius 8 h^-1 Mpc. We present constraints on sigma_8 and the total matter density Omega_m0 from local cluster counts as a function of X-ray temperature, taking care to incorporate and minimize systematic errors that plagued previous work with this method. In particular, we present new determinations of the cluster luminosity - temperature and mass - temperature relations, including their intrinsic scatter, and a determination of the Jenkins mass function parameters for the same mass definition as the mass - temperature calibration. Marginalizing over the 12 uninteresting parameters associated with this method, we find that the local cluster temperature function implies sigma_8 (Omega_m0/0.32)^alpha = 0.86+/-0.04 with alpha = 0.30 (0.41) for Omega_m0 < 0.32 (Omega_mo > 0.32) (68% confidence for two parameters). This result agrees with a wide range of recent independent determinations, and we find no evidence of any additional sources of systematic error for the X-ray cluster temperature function determination of the matter power spectrum normalization. The joint WMAP5 + cluster constraints are: Omega_m0 = 0.30+0.03/-0.02 and sigma_8 = 0.85+0.04/-0.02 (68% confidence for two parameters).Comment: 31 pages, 16 figures, accept for publication in ApJ 609, Jan. 10, 200

The mean density of the Universe from cluster evolution

The determination of the mean density of the Universe is a long standing problem of modern cosmology. The number density evolution of x-ray clusters at a fixed temperature is a powerful cosmological test, new in nature (Oukbir and Blanchard, 1992), somewhat different from standard analyses based on the dynamical measurement of individual objects. However, the absence of any available sample of x-ray selected clusters with measured temperatures at high redshift has prevented this test from being applied earlier. Recently, temperature measurements of ten EMSS clusters at $0.3 \le z \le 0.4$ have allowed the application of this test (Henry, 1997). In this work, we present the first results of a new analysis we have performed of this data set as well as a new estimation of the local temperature distribution function of clusters: a likelihood analysis of the temperature distribution functions gives a preferred value for the mean density of the universe which corresponds to 75% of the critical density. An open model with a density smaller than 30% of the critical density is rejected with a level of significance of 95%.Comment: 4 pages, shortened. To be published in Les Comptes Rendus de l'Academie des Science

Performance of a Nonelectric Infant Warmer in Rwandan Health Centers.

Background. Neonatal hypothermia remains a challenge in resource-limited settings. Methods. We conducted a prospective mixed-methods cohort study in rural Rwandan health centers to assess the performance of an infant warmer we designed for low-resource settings. All hypothermic infants were eligible for enrollment. Outcomes. Safety: incidence of adverse reactions. Effectiveness: attainment of euthermia, rate of temperature rise. Feasibility: correct use of warmer, signs of wear. Interviews of caregivers and nurses. Findings. Of 102 encounters, there were no adverse reactions. Of 80 encounters for hypothermia when infants on warmer for ≥1 hour, 79 achieved euthermia; 73 in ≤2 hours. Of the 80 encounters, 64 had temperature rise ≥0.5°C/h. Of the 102 encounters, there were no instances of the warmer being prepared, used, or cleaned incorrectly. Five out of the 12 warmers exhibited wear. Interview participants were predominantly positive; some found time for readiness of warmer challenging. Interpretation. The warmer performed well. It is appropriate to study in larger scale

Comparison of Hectospec Virial Masses with SZE Measurements

We present the first comparison of virial masses of galaxy clusters with their Sunyaev-Zel'dovich Effect (SZE) signals. We study 15 clusters from the Hectospec Cluster Survey (HeCS) with MMT/Hectospec spectroscopy and published SZE signals. We measure virial masses of these clusters from an average of 90 member redshifts inside the radius $r_{100}$. The virial masses of the clusters are strongly correlated with their SZE signals (at the 99% confidence level using a Spearman rank-sum test). This correlation suggests that $Y_{SZ}$ can be used as a measure of virial mass. Simulations predict a powerlaw scaling of $Y_{SZ}\propto M_{200}^\alpha$ with $\alpha\approx$1.6. Observationally, we find $\alpha$=1.11$\pm$0.16, significantly shallower (given the formal uncertainty) than the theoretical prediction. However, the selection function of our sample is unknown and a bias against less massive clusters cannot be excluded (such a selection bias could artificially flatten the slope). Moreover, our sample indicates that the relation between velocity dispersion (or virial mass estimate) and SZE signal has significant intrinsic scatter, comparable to the range of our current sample. More detailed studies of scaling relations are therefore needed to derive a robust determination of the relation between cluster mass and SZE.Comment: 6 pages, 2 figures, accepted to ApJ Letters, minor revisions, shortened titl

A reanalysis of the luminosities of clusters of galaxies in the EMSS sample with 0.3 < z < 0.6

The X-ray luminosities of the Einstein Extended Medium Sensitivity Survey (EMSS) clusters of galaxies with redshifts 0.3<z<0.6 are remeasured using ROSAT PSPC data. It is found that the new luminosities are on average 1.18 +/- 0.08 times higher than previously measured but that this ratio depends strongly on the X-ray core radii we measure. For the clusters with small core radii, in general we confirm the EMSS luminosities, but for clusters with core radii >250 kpc (the constant value assumed in the EMSS), the new luminosities are 2.2 +/- 0.15 times the previous measurements. The X-ray luminosity function (XLF) at 0.3<z<0.6 is recalculated and is found to be consistent with the local XLF. The constraints on the updated properties of the 0.3<z<0.6 EMSS sample, including a comparison with the number of clusters predicted from local XLFs, indicate that the space density of luminous, massive clusters has either not evolved or has increased by a small factor ~2 since z=0.4. The implications of this result are discussed in terms of constraints on the cosmological parameter Omega_0.Comment: 12 pages, 7 figures. Accepted for publication in MNRA

The mass and temperature functions in a moving barrier model

In this paper, I use the extension of the excursion set model of Sheth & Tormen (2002) and the barrier shape obtained in Del Popolo & Gambera (1998) to calculate the unconditional halo mass function, and the conditional mass function in several cosmological models. I show that the barrier obtained in Del Popolo & Gambera (1998), which takes account of tidal interaction between proto-haloes, is a better description of the mass functions than the spherical collapse and is in good agreement with numerical simulations (Tozzi & Governato 1998, and Governato et al. 1999). The results are also in good agreement with those obtained by Sheth & Tormen (2002), only slight differences are observed expecially at the low mass end. I moreover calculate, and compare with simulations, the temperature function obtained by means of the mass functions previously calculated and also using an improved version of the M-T relation, which accounts for the fact that massive clusters accrete matter quasi-continuously, and finally taking account of the tidal interaction with neighboring clusters. Even in this case the discrepancy between the Press-Schecter predictions and simulations is considerably reduced.Comment: 23 pages; 11 encapsulated figures. Accepted for publication in MNRA

HIFLUGCS: Galaxy cluster scaling relations between X-ray luminosity, gas mass, cluster radius, and velocity dispersion

We present relations between X-ray luminosity and velocity dispersion (L-sigma), X-ray luminosity and gas mass (L-Mgas), and cluster radius and velocity dispersion (r500-sigma) for 62 galaxy clusters in the HIFLUGCS, an X-ray flux-limited sample minimizing bias toward any cluster morphology. Our analysis in total is based on ~1.3Ms of clean X-ray XMM-Newton data and 13439 cluster member galaxies with redshifts. Cool cores are among the major contributors to the scatter in the L-sigma relation. When the cool-core-corrected X-ray luminosity is used the intrinsic scatter decreases to 0.27 dex. Even after the X-ray luminosity is corrected for the cool core, the scatter caused by the presence of cool cores dominates for the low-mass systems. The scatter caused by the non-cool-core clusters does not strongly depend on the mass range, and becomes dominant in the high-mass regime. The observed L-sigma relation agrees with the self-similar prediction, matches that of a simulated sample with AGN feedback disregarding six clusters with <45 cluster members with spectroscopic redshifts, and shows a common trend of increasing scatter toward the low-mass end, i.e., systems with sigma<500km/s. A comparison of observations with simulations indicates an AGN-feedback-driven impact in the low-mass regime. The best fits to the $L-M_{\rm gas}$ relations for the disturbed clusters and undisturbed clusters in the observational sample closely match those of the simulated samples with and without AGN feedback, respectively. This suggests that one main cause of the scatter is AGN activity providing feedback in different phases, e.g., during a feedback cycle. The slope and scatter in the observed r500-sigma relation is similar to that of the simulated sample with AGN feedback except for a small offset but still within the scatter.Comment: 45 pages, 28 figures, A&A proof-version, high-resolution figures in Appendix F can be found in the electronic version on the A&A we