Searcharxiv⌕ Search

arXiv subjects

Hans Boehringer

Publications and source records attributed to Hans Boehringer.

66 records · Page 4Linked to original sources
arXiv2001

Galaxy Clusters: Cosmic High-Energy Laboratories to Study the Structure of Our Universe

This contribution illustrates the study of galaxy clusters as astrophysical laboratories as well as probes for the large-scale structure of the Universe. Using the REFLEX Cluster Survey, the measurement of the statistics of the large-scale structure on scales up to 500 $h^{-1}$ Mpc is illustrated. The results clearly favour a low density Universe. Clusters constitute, in addition, well defined astrophysical laboratory environments in which some very interesting large-scale phenomena can be studied. As an illustration we show some spectacular new XMM X-ray spectroscopic results on the thermal structure of cooling flows and the interaction effects of AGN with this hot intracluster medium. The X-ray observations with XMM-Newton show a lack of spectral evidence for large amounts of cooling and condensing gas in the centers of galaxy clusters believed to harbour strong cooling flows. To explain these findings we consider the heating of the core regions of clusters by jets from a central AGN. We find that the power output the AGN jets is well sufficient. The requirements such a heating model has to fulfill are explored and we find a very promising scenario of self-regulated Bondi accretion of the central black hole.

astro-ph↗
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.

astro-ph↗
arXiv2000

Relating Galaxy Cluster X-Ray Luminosities to Gravitational Masses in Wide Angle Surveys

It is shown that galaxy cluster surveys selecting clusters by their X-ray luminosity effectively select by cluster mass. It is shown that a selection based solely on Abell galaxy richness is less efficient in terms of mass. Furthermore the empirical X-ray luminosity - gravitational mass relation and its scatter is quantified and the relation is compared to predicted relations.

astro-ph↗
arXiv1999

Relations of Physical Properties for a Large Sample of X-Ray Galaxy Clusters

One hundred and six galaxy clusters have been studied in detail using X-ray data and important global physical properties have been determined. Correlations between these properties are studied with respect to the description of clusters as a self-similar class of objects. The results support the self-similar picture only partly and significant deviations are found for some correlations.

astro-ph↗
arXiv1999

The Mass Function of an X-Ray Flux-Limited Sample of Galaxy Clusters

Using the brightest clusters in the ROSAT All-Sky Survey we compiled an X-ray flux-limited sample of galaxy clusters. The clusters have been reanalysed using ROSAT PSPC pointed observations if possible. The gravitational mass has been determined individually for each cluster in a homogeneous way assuming hydrostatic equilibrium. The mass function has been derived. We present the preliminary results and a comparison to previous determinations.

astro-ph↗
arXiv1999

X-ray properties of LINERs

We present an investigation of the X-ray properties of 13 LINERs based on ROSAT all-sky survey and pointed PSPC and HRI observations. Several sources are studied for the first time in X-rays. The X-ray spectra are best described by a powerlaw with photon index Gamma ~ -2.0 or thermal emission from gas with very subsolar abundances. The luminosities range between log L_x = 37.7 (NGC 404) and 40.8 (NGC 4450). No X-ray variability on the timescale of hours/days is detected. This is in line with the suggestion that LINERs may accrete in the advection-dominated mode. On a longer term, one of the objects, NGC 2768, turns out to be slightly variable. Some sources appear to be extended at weak emission levels whereas the bulk of the X-ray emission is consistent with arising from a point source within the PSPC instrumental resolution. L_x/L_B ratios are derived and emission mechanisms that potentially contribute to the observed X-ray luminosities are discussed. We also examine the presence of second X-ray sources near the target sources both in terms of instrumental effects and in terms of `real' sources within the LINER galaxies.

astro-ph↗
arXiv1999

X-ray emission mechanisms of LINERs

We present here an analysis of the X-ray properties of a sample of LINER galaxies observed with the ROSAT PSPC and HRI instruments. A spatial analysis shows that the bulk of the X-ray emission is consistent with arising from a point source; some extended emission appears at weak emission levels. The X-ray spectra are formally best described by a powerlaw with photon index Gamma_x ~ -2 or thermal emission from a Raymond-Smith plasma with highly subsolar abundances (Z < 0.1). Several emission mechanisms that might contribute to the observed X-ray spectra are discussed. In particular, we take the very subsolar abundances derived from Raymond-Smith fits as an indication of a more complex emission mechanism, like the presence of a second hard component or plasma out of collisional-ionization equilibrium.

astro-ph↗
arXiv1999

The central radio source in the NGC 383 group: jet - IGM interaction ?

The NGC 383 group is a rich group of galaxies that harbours the central radio source 3C 31 = NGC 383. After presenting results from the X-ray analysis of the extended intra-group medium and the central radio galaxy, we discuss the spatial morphology of X-ray emitting gas as compared to the radio plasma and perform a comparison of the pressures of both components.

astro-ph↗
arXiv1999

X-ray study of the NGC 383 group of galaxies and the source 1E0104+3153

(abridged) We present results from an analysis of the X-ray properties of the NGC 383 galaxy group based on ROSAT PSPC and HRI data. X-ray emission can be traced out to ~ 1 Mpc, the estimated virial radius of the system. We determine a total mass of 6x10^{13} M_sun for the group inside this radius with a gas mass fraction of 21%. The intragroup-gas temperature of 1.5 keV is both consistent with the galaxy velocity dispersion and the X-ray luminosity-temperature relation of groups and clusters suggesting that the group is fairly relaxed. This is also indicated by the almost spherically symmetric appearance of the group's X-ray halo. The X-ray properties of the radio galaxy NGC 383 (3C 31) which is located near the center of the group are discussed. Its spectrum is best described by a two-component model, consisting of emission from a low-temperature Raymond-Smith plasma, and a hard tail. The possible interaction of the radio jets of 3C 31 with the IGM is studied. A spatial, spectral and temporal analysis of the Einstein source 1E0104+3153 located within the field of view is performed, one goal being the identification of the optical counterpart (with both, a high-redshift BAL quasar and a nearby elliptical galaxy, member of a small group, located within the Einstein X-ray error circle). We find evidence that the IGM of the small group contributes significantly to the X-ray emission of 1E0104, which can be described by a Raymond-Smith model of kT ~ 2 keV and a soft X-ray luminosity of L_x ~ 3 10^{43} erg/s.

astro-ph↗
arXiv1996

X-ray properties of the distant cluster Cl0016+16

We present X-ray data on the distant cluster Cl0016+16 (z=0.5545) from ROSAT PSPC and HRI observations and use them to study the physics of the intracluster medium (ICM) and the dynamical state of the cluster. The surface brightness distribution is not only described by a spherically symmetric model but also by a two-dimensional $β$-model fit. Subtracting an elliptical model cluster as defined by the best fit parameters of the two-dimensional model we find significant residuals, indicating an additional, extended X-ray source within the cluster. This source, likely to be a merging subcomponent of the cluster, coincides with a peak in the weak lensing mass map of Smail et. al. (1995). In the course of this analysis we present a new approach to quantify the significance of substructure in cluster X-ray images dominated by Poisson noise and smoothed with a Gauss filter. We determine the radial mass profile integrated out to a radius of 3Mpc and find for the total mass of the cluster a value of $\sim 1.4-3.3 \times 10^{15}$ \msun and $\sim 4.5 \times 10^{14}$ \msun for the gas mass, yielding a gas-to-total mass ratio of 14-32\%. There is no significant radial dependence of the gas-to-total mass ratio in the cluster.

astro-ph↗
arXiv1995

ROSAT observations of the galaxy group AWM7

We present results of ROSAT/PSPC and HRI observations of the AWM7 group of galaxies, which is a poor galaxy cluster and forms part of the Perseus-Pisces filament. The X-ray emission originates from intracluster gas at temperatures of 1.7 to 4.5 keV. The cluster obviously is elliptical with a position angle perpendicular to the position angle of the dominant elliptical galaxy NGC1129, which is offset from the cluster X-ray centre by 30 kpc. The analysis of the PSPC imaging and spectral data yield a gravitational mass of 2--5$\cdot10^{14}$\msun within a radius of 1.2 Mpc and a cooling flow with a mass deposition rate of up to 60--66 \msun y$^{-1}$.

astro-ph↗