arXiv subjects

Sabine Schindler

Publications and source records attributed to Sabine Schindler.

At least 37 records · Page 2Linked to original sources

arXiv2004

Feedback from Intra-Cluster Supernovae on the ICM in Cooling Flow Galaxy Clusters

We study the effect of heating and metal enrichment from supernovae (SNe) residing between galaxies on the Intra-Cluster Medium (ICM). Recent observations indicate that a considerable fraction (~20 %) of the SN Ia parent stellar population in galaxy clusters is intergalactic. By considering their effect on the relaxed progenitors of cooling flow clusters we propose that intra-cluster SNe can act as a distributed heating source which may influence the initial stages of the formation of cooling flows. We investigate the increase in cooling time as a function of the energy input supplied by SNe and their assumed spatial distribution, and conclude that intra-cluster SNe represent a heating source which in some clusters can cause a delay of the formation of cooling flows. This would imply that some cooling flows are younger than previously thought. We also discuss the impact that a large population of intra-cluster SNe could have on the chemical evolution of the ICM in cooling flow clusters.

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arXiv2003

Automatic detection of arcs and arclets formed by gravitational lensing

We present an algorithm developed particularly to detect gravitationally lensed arcs in clusters of galaxies. This algorithm is suited for automated surveys as well as individual arc detections. New methods are used for image smoothing and source detection. The smoothing is performed by so-called anisotropic diffusion, which maintains the shape of the arcs and does not disperse them. The algorithm is much more efficient in detecting arcs than other source finding algorithms and the detection by eye.

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arXiv2003

Keys to Cosmology - Clusters of Galaxies

We review several aspects of clusters of galaxies and their application to cosmology. We present first results of numerical simulations of the dynamics of the intra-cluster gas and of different interaction processes between cluster galaxies and the intra-cluster gas. In particular metallicity maps are very useful to determine the importance of the different interaction processes. Also mass determination methods and possible sources for uncertainties in the measurements are shown.

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arXiv2003

Galaxy and hot gas distributions in the z=0.52 galaxy cluster RBS380 from CHANDRA and NTT observations

We present CHANDRA X-ray and NTT optical observations of the distant z=0.52 galaxy cluster RBS380 -- the most distant cluster of the ROSAT Bright Source (RBS) catalogue. We find diffuse, non-spherically symmetric X-ray emission with a X-ray luminosity of L_X(0.3-10 keV)=1.6 10^(44) erg/s, which is lower than expected from the RBS. The reason is a bright AGN in the centre of the cluster contributing considerably to the X-ray flux. This AGN could not be resolved with ROSAT. In optical wavelength we identify several galaxies belonging to the cluster. The galaxy density is at least 2 times higher than expected for such a X-ray faint cluster, which is another confirmation of the weak correlation between X-ray luminosity and optical richness. The example of the source confusion in this cluster shows how important high-resolution X-ray imaging is for cosmological research.

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arXiv2003

Clusters of galaxies: a fundamental pillar of cosmology

Clusters of galaxies are used in a variety of ways to do cosmology. Some of them are presented here. Their X-ray emitting gas allows us to determine the baryon fraction, dark matter distribution and the matter density $Ω_{m}$ of the universe. Another interesting component is relativistic particles whose radio emission provide the measure of the magnetic fields ($\approx μG$) in the intra-cluster medium (ICM). The observation of distant clusters of galaxies is also important for cosmology. In particular the new X-ray satellites CHANDRA and XMM yield exciting new results for galaxy cluster physics and cosmology.

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arXiv2003

Clusters of Galaxies in X-rays: Dark Matter

We present the analysis of baryonic and non-baryonic matter distribution in a sample of ten nearby clusters ($0.03<z<0.09$) with temperatures between 4.7 and 9.4 keV. These galaxy clusters have been studied in detail using X-ray data and global physical properties have been determined. Correlations between these quantities have been analysed and compared with the results for distant clusters. We found an interesting dependence between the relative gas extent (expressed as the ratio of gas mass fractions at $r_{500}$ and $0.5\times r_{500}$) and the total cluster mass. The extent of the gas relative to the extent of the dark matter tends to be larger in less massive clusters. This dependence might give us some hints about non-gravitational processes in clusters. The new X-ray satellites Chandra and XMM yield exciting new results for galaxy cluster physics and cosmology. We show the interesting X-ray observations of two intermediate redshift clusters, RBS797 ($z=0.35$) and CL 0939+4713 ($z=0.41$) taken with Chandra and XMM respectively.

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arXiv2002

Gas in Groups and Clusters of Galaxies

Groups and clusters contain a large fraction of hot gas which emits X-ray radiation. This gas yields information on the dynamical state and on the total mass of these systems. X-ray spectra show that heavy elements are present in the gas. As these metals must have been produced in the cluster/group galaxies and later transported into the gas, the metallicity is a good tracer for the transport processes. Several possible processes, that transport gas from the small potential wells of the galaxies into the clusters and groups, are discussed.

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arXiv2002

Aspherical galaxy clusters: effects on cluster masses and gas mass fractions

We present an investigation of the effects of asphericity on the estimates of total mass and gas mass fraction in galaxy clusters from X-ray observations. We model the aspherical shape of galaxy clusters by a triaxial model and compare the true total mass and the true total gas mass fraction with the corresponding quantities obtained with the assumption of spherical symmetry. In the triaxial model we allow the extent along the line of sight to vary in order to describe elongated and compressed cluster shapes. Using a sample of 10 ROSAT clusters and a recent CHANDRA observation we find the following results. For prolate or oblate shapes the difference between triaxial and spherical model both in the mass and in the gas mass fraction are negligible (less than 3 %). For more aspherical shapes the total mass is underestimated (overestimated) in the centre, if the cluster is compressed (elongated). The gas mass fraction is overestimated for compressed clusters and slightly underestimated for elongated clusters. Comparing X-ray masses with gravitational lensing estimates, we find that elongations along the line of sight can resolve discrepancies of masses determined by the two different methods of up to ~30 %. The combination of Sunyaev-Zel'dovich and X-ray observations is useful to measure the elongation of the cluster along the line of sight. As an application, we estimate the elongation of the cluster CL0016+16 with two different approaches, Sunyaev-Zel'dovich measurements and comparison of weak lensing and X-ray masses, and find reasonable agreement.

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arXiv2002

Cluster-Group Interaction in the Virgo Cluster

We present two projects related to interaction in the Virgo cluster. In the first section we draw a quantitative comparison of the distribution of the galaxies and the intra-cluster gas taking into account that the Virgo cluster has an irregular structure consisting of several subclusters. In the second section we show hydrodynamic simulations of the interaction (ram pressure stripping) of a galaxy like M86 with the intra-cluster gas.

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arXiv2001

Clusters of Galaxies - Keys to Cosmology

Various cosmological applications of galaxy clusters are presented. Clusters are used to determine the baryon fraction, dark matter distribution and the matter density of the universe. They also contain a wealth of information about structure formation and evolution on different scales: large-scale structure, cluster formation and also galaxy formation via the interaction of cluster galaxies with the intra-cluster medium. In particular, the X-ray satellites CHANDRA and XMM yield exciting new results for galaxy cluster physics and cosmology.

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arXiv2001

Intra-Cluster Medium Enrichment and the Dynamical State of Galaxy Clusters

The effects of cluster mergers on the metal enrichment of the intra-cluster gas in clusters of galaxies are reviewed. Mergers can influence the metal production as well as the gas ejection processes, which transport the gas from the galaxy potential wells into the intra-cluster gas. Several processes are discussed: ram-pressure stripping, galactic winds and star formation activity. Simulations on different scales ranging from galaxy size to large-scale structure are presented.

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arXiv2001

Omega_m - Different Ways to Determine the Matter Density of the Universe

A summary of various measurements of the mean matter density in the universe, Omega_m, is presented. Results from very different kinds of methods using various astronomical objects -- from supernovae to large-scale structure -- are shown. There is a remarkable preference for Omega_m values around 0.3, but there are also some measurements that favour a higher or a smaller value.

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arXiv2001

Simulations of Clusters of Galaxies

Numerical simulations of clusters of galaxies provide a unique way to follow the dynamics of these systems. The models reveal many characteristics of the merging process of subclusters: shock structure and strength, temperature distribution and gas distribution. From the models detailed observational signatures of the dynamical state can be derived. The simulations also show that mergers have effects on the magnetic field, on the X-ray luminosity, on the metal enrichment and other physical processes. Furthermore, observational methods like the mass determination can be tested.

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arXiv2001

Gas Dynamic Stripping and X-Ray Emission of Cluster Elliptical Galaxies

Detailed 3-D numerical simulations of an elliptical galaxy orbiting in a gas-rich cluster of galaxies indicate that gas dynamic stripping is less efficient than the results from previous, simpler calculations (Takeda et al. 1984; Gaetz et al. 1987) implied. This result is consistent with X-ray data for cluster elliptical galaxies. Hydrodynamic torques and direct accretion of orbital angular momentum can result in the formation of a cold gaseous disk, even in a non-rotating galaxy. The gas lost by cluster galaxies via the process of gas dynamic stripping tends to produce a colder, chemically enriched cluster gas core. A comparison of the models with the available X-ray data of cluster galaxies shows that the X-ray luminosity distribution of cluster galaxies may reflect hydrodynamic stripping, but also that a purely hydrodynamic treatment is inadequate for the cooler interstellar medium near the centre of the galaxy.

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arXiv2000

The ROSAT-ESO Flux-Limited X-Ray (REFLEX) Galaxy Cluster Survey III: The Power Spectrum

We present a measure of the power spectrum on scales from 15 to 800 Mpc/h using the ROSAT-ESO Flux-Limited X-Ray(REFLEX) galaxy cluster catalogue. The REFLEX survey provides a sample of the 452 X-ray brightest southern clusters of galaxies with the nominal flux limit S=3.0 10^{-12}erg/s/cm2 for the ROSAT energy band (0.1-2.4)keV. Several tests are performed showing no significant incompletenesses of the REFLEX clusters with X-ray luminosities brighter than 10^{43}erg/s up to scales of about 800 Mpc/h. They also indicate that cosmic variance might be more important than previous studies suggest. We regard this as a warning not to draw general cosmological conclusions from cluster samples with a size smaller than REFLEX. Power spectra, P(k), of comoving cluster number densities are estimated for flux- and volume-limited subsamples. The most important result is the detection of a broad maximum within the comoving wavenumber range 0.022<k<0.030 h/Mpc. The data suggest an increase of the power spectral amplitude with X-ray luminosity. Compared to optically selected cluster samples the REFLEX P(k)is flatter for wavenumbers k<0.05 h/Mpc thus shifting the maximum of P(k) to larger scales. The smooth maximum is not consistent with the narrow peak detected at k=0.05 h/Mpc using the Abell/ACO richness $\ge 0$ data. In the range 0.02<k<0.4 h/Mpc general agreement is found between the slope of the REFLEX P(k) and those obtained with optically selected galaxies. A semi-analytic description of the biased nonlinear power spectrum in redshift space gives the best agreement for low-density Cold Dark Matter models with or without a cosmological constant.

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arXiv2000

Clusters of Galaxies: Diagnostic Tools for Cosmology

Clusters of galaxies can be used for very different kinds of cosmological tests. I review a few of the methods: determination of cluster masses and dark matter content, metal enrichment and its connection to the origin of the intra-cluster gas, and the dynamical state of clusters. The progress in the different fields expected from observations with the new X-ray satellites XMM and Chandra is pointed out.

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arXiv2000

The effect of magnetic fields on the mass determination of clusters of galaxies

We test the effects of magnetic fields on the mass determination of galaxy clusters with the X-ray method. As this method takes into account only thermal pressure, additional non-thermal pressure support, e.g. caused by a magnetic field, can result in an underestimation of the mass. SPH models of galaxy clusters including magnetic fields of various strengths in two different cosmologies are used for the test. We compare the true mass of the model clusters with the mass determined from simulated X-ray images of the same models. The effect of the magnetic field on the mass in relaxed clusters is found to be negligible compared to other uncertainties, even at small radii, where the strongest effects are expected. However in one model, in which the cluster is in the process of merging, we find an effect of up to a factor of 2 caused by the magnetic field. In relaxed clusters the mass estimate, averaged over many models, is at most 15% smaller in models with relatively high magnetic field of $2μ$G compared to models without a magnetic field with a small dependence on the cosmology chosen. Therefore we conclude that the presence of a magnetic field cannot be responsible for the discrepancies of a factor of 2-3 found between X-ray and lensing mass in the central regions of relaxed clusters.

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arXiv2000

Simulations of Merging Clusters of Galaxies

Numerical simulations of cluster mergers reveal many characteristics of the merging process: shock structure and strength, observational signatures of the dynamical state, effects on the mass determination, turbulence and the evolution of the X-ray luminosity and the magnetic field. In this article I review the results obtained from various simulations over the last years.

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