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Register a new userTesting the Reliability of Cluster Mass Indicators with a Systematics Limited Dataset
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Adrienne M. Juett
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We present the mass-X-ray observable scaling relationships for clusters of galaxies using the XMM-Newton cluster catalog of Snowden et al. Our results are roughly consistent with previous observational and theoretical work, with one major exception. We find 2-3 times the scatter around the best fit mass scaling relationships as expected from cluster simulations or seen in other observational studies. We suggest that this is a consequence of using hydrostatic mass, as opposed to virial mass, and is due to the explicit dependence of the hydrostatic mass on the gradients of the temperature and gas density profiles. We find a larger range of slope in the cluster temperature profiles at r_{500} than previous observational studies. Additionally, we find only a weak dependence of the gas mass fraction on cluster mass, consistent with a constant. Our average gas mass fraction results argue for a closer study of the systematic errors due to instrumental calibration and analysis method variations. We suggest that a more careful study of the differences between various observational results and with cluster simulations is needed to understand sources of bias and scatter in cosmological studies of galaxy clusters.
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We investigate the occurrence of radio minihalos --- diffuse radio sources of unknown origin observed in the cores of some galaxy clusters --- in a statistical sample of 58 clusters drawn from the Planck Sunyaev-Zeldovich cluster catalog using a mass cut ($M_{500}>6times 10^{14} M_{odot}$). We supplement our statistical sample with a similarly-sized non-statistical sample mostly consisting of clusters in the ACCEPT X-ray catalog with suitable X-ray and radio data, which includes lower-mass clusters. Where necessary (for 9 clusters), we reanalyzed the Very Large Array archival radio data to determine if a mihinalo is present. Our total sample includes all 28 currently known and recently discovered radio minihalos, including 6 candidates. We classify clusters as cool-core or non-cool core according to the value of the specific entropy floor in the cluster center, rederived or newly derived from the Chandra X-ray density and temperature profiles where necessary (for 27 clusters). Contrary to the common wisdom that minihalos are rare, we find that almost all cool cores - at least 12 out of 15 (80%) - in our complete sample of massive clusters exhibit minihalos. The supplementary sample shows that the occurrence of minihalos may be lower in lower-mass cool-core clusters. No minihalos are found in non-cool-cores or warm cores. These findings will help test theories of the origin of minihalos and provide information on the physical processes and energetics of the cluster cores.
We study the reliability of dark-matter halo detections with three different linear filters applied to weak-lensing data. We use ray-tracing in the multiple lens-plane approximation through a large cosmological simulation to construct realizations of cosmic lensing by large-scale structures between redshifts zero and two. We apply the filters mentioned above to detect peaks in the weak-lensing signal and compare them with the true population of dark matter halos present in the simulation. We confirm the stability and performance of a filter optimized for suppressing the contamination by large-scale structure. It allows the reliable detection of dark-matter halos with masses above a few times 1e13 M_sun/h with a fraction of spurious detections below ~10%. For sources at redshift two, 50% of the halos more massive than ~7e13 M_sun/h are detected, and completeness is reached at ~2e14 M_sun/h.
We present the observations of the afterglow of gamma-ray burst GRB 090102. Optical data taken by the TAROT, REM, GROND, together with publicly available data from Palomar, IAC and NOT telescopes, and X-ray data taken by the XRT instrument on board the Swift spacecraft were used. This event features an unusual light curve. In X-rays, it presents a constant decrease with no hint of temporal break from 0.005 to 6 days after the burst. In the optical, the light curve presents a flattening after 1 ks. Before this break, the optical light curve is steeper than that of the X-ray. In the optical, no further break is observed up to 10 days after the burst. We failed to explain these observations in light of the standard fireball model. Several other models, including the cannonball model were investigated. The explanation of the broad band data by any model requires some fine tuning when taking into account both optical and X-ray bands.
Joint lensing and dynamical mass profile determinations of galaxy clusters are an excellent tool to constrain modification of gravity at cosmological scales. However, search for tiny departures from General Relativity calls for an accurate control of the systematics affecting the method. In this analysis we concentrate on the systematics in the reconstruction of mass profiles from the dynamics of cluster member galaxies, while assuming that lensing provides unbiased mass profile reconstructions. In particular, in the case study of linear $f(R)$ gravity, we aim at veryfying whether in realistic simulations of cluster formation a spurious detection of departure from GR can be detected due to violation of the main assumptions (e.g. dynamical equilibrium and spherical symmetry) on which the method is based. We aim at identifying and calibrating the impact of those systematics by analyzing a set of Dark Matter halos taken from $Lambda$CDM N-body cosmological simulations performed with the GADGET-3 code. [...] If no selection criteria are applied, $sim 60%$ of clusters in a $Lambda$CDM Universe (where GR is assumed) produce a spurious detection of modified gravity. We find that the probability of finding cluster in agreement with GR predictions $P_{GR}$ mainly depends on the properties of the halos projected phase-space and on shape orientation of the cluster along the line-of-sight projection. We define two observational criteria which correlate with the probability to find clusters in agreement with GR predictions and which can be used to select [...] those objects that are more suitable for the application of the proposed method. In particular, we find that according to these criteria the percentage of spurious detection can be lowered down to $sim 20%$ in the best case. Our results are relevant in view of data that will be available with the next generation surveys.
In the past decade, the properties of annihilating dark matter models were examined by various kinds of data, including the data of gamma rays, radio waves, X-ray, positrons, electrons, antiprotons and neutrinos. In particular, most of the studies focus on the data of our Galaxy, nearby galaxies (e.g. M31 galaxy) or nearby galaxy clusters (e.g. Fornax cluster). In this article, we examine the archival radio continuum spectral data of a relatively high-redshift galaxy cluster (A697 cluster) to constrain the properties of annihilating dark matter. We find that leptophilic annihilation channels ($e^+e^-$, $mu^+mu^-$ and $tau^+tau^-$) can give very good fits to the radio continuum spectrum of the A697 cluster.
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