共查询到20条相似文献，搜索用时 15 毫秒
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O. Johnson P. Best D. Zaritsky D. Clowe A. Aragón-Salamanca C. Halliday P. Jablonka B. Milvang-Jensen R. Pelló B. M. Poggianti G. Rudnick R. Saglia L. Simard S. White 《Monthly notices of the Royal Astronomical Society》2006,371(4):1777-1792
We present XMM–Newton observations of three optically selected z > 0.6 clusters from the European Southern Observatory (ESO) Distant Cluster Survey (EDisCS), comprising the first results of a planned X-ray survey of the full EDisCS high-redshift sample. The EDisCS clusters were identified in the Las Campanas Distant Cluster Survey as surface brightness fluctuations in the optical sky and their masses and galaxy populations are well described by extensive photometric and spectroscopic observations. We detect two of the three clusters in the X-ray and place a firm upper limit on diffuse emission in the third cluster field. We are able to constrain the X-ray luminosity and temperature of the detected clusters and estimate their masses. We find that the X-ray properties of the detected EDisCS clusters are similar to those of X-ray-selected clusters of comparable mass and – unlike other high-redshift, optically selected clusters – are consistent with the T –σ and L X –σ relations determined from X-ray-selected clusters at low redshift. The X-ray determined mass estimates are generally consistent with those derived from weak-lensing and spectroscopic analyses. These preliminary results suggest that the novel method of optical selection used to construct the EDisCS catalogue may, like selection by X-ray luminosity, be well suited for identification of relaxed, high-redshift clusters whose intracluster medium is in place and stable by z ∼ 0.8 . 相似文献
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Stefano Ettori 《Monthly notices of the Royal Astronomical Society》2000,318(4):1041-1046
The spatial emission from the core of cooling-flow clusters of galaxies is inadequately described by a β -model. Spectrally, the central region of these clusters is well approximated with a two-temperature model, where the inner temperature represents the multiphase status of the core and the outer temperature is a measure of the ambient gas temperature. Following this observational evidence, I extend the use of the β -model to a two-phase gas emission, where the two components coexist within a boundary radius r cool and the ambient gas alone fills the volume shell at a radius above r cool . This simple model still provides an analytic expression for the total surface brightness profile (Note in the first term the different sign with respect to the standard β -model.) Based upon a physically meaningful model for the X-ray emission, this formula can be used (i) to improve significantly the modelling of the surface brightness profile of cooling flow clusters of galaxies when compared to the standard β -model results, (ii) to constrain properly the physical characteristics of the intracluster plasma in the outskirts, like, e.g., the ambient gas temperature. 相似文献
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M.J. Page J.P.D. Mittaz F.J. Carrera 《Monthly notices of the Royal Astronomical Society》2001,325(2):575-583
We have surveyed 188 ROSAT Position Sensitive Proportional Counter (PSPC) fields for X-ray sources with hard spectra ( α <0.5); such sources must be major contributors to the X-ray background at faint fluxes. In this paper we present optical identifications for 62 of these sources: 28 active galactic nuclei (AGN) which show broad lines in their optical spectra (BLAGN), 13 narrow emission line galaxies (NELGs), five galaxies with no visible emission lines, eight clusters and eight Galactic stars.
The BLAGN, NELGs and galaxies have similar distributions of X-ray flux and spectra. Their ROSAT spectra are consistent with their being AGN obscured by columns of 20.5< log( NH /cm−2 )<23 . The hard spectrum BLAGN have a distribution of X-ray to optical ratios which is similar to that found for AGN from soft X-ray surveys (1< α OX <2) . However, a relatively large proportion (15 per cent) of the BLAGN, NELGs and galaxies are radio loud. This could be because the radio jets in these objects produce intrinsically hard X-ray emission, or if their hardness is caused by absorption, it could be because radio-loud objects are more X-ray luminous than radio-quiet objects. The eight hard sources identified as clusters of galaxies are the brightest, and softest group of sources and hence clusters are unlikely to be an important component of the hard, faint population.
We propose that BLAGN are likely to constitute a significant fraction of the faint, hard, 0.5–2 keV population and could be important to reproducing the shape of the X-ray background, because they are the most numerous type of object in our sample (comprising almost half the identified sources), and because all our high redshift ( z >1) identified hard sources have broad lines. 相似文献
The BLAGN, NELGs and galaxies have similar distributions of X-ray flux and spectra. Their ROSAT spectra are consistent with their being AGN obscured by columns of 20.5< log( N
We propose that BLAGN are likely to constitute a significant fraction of the faint, hard, 0.5–2 keV population and could be important to reproducing the shape of the X-ray background, because they are the most numerous type of object in our sample (comprising almost half the identified sources), and because all our high redshift ( z >1) identified hard sources have broad lines. 相似文献
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E. O'Sullivan J. M. Vrtilek A. M. Read L. P. David T. J. Ponman 《Monthly notices of the Royal Astronomical Society》2003,346(2):525-539
We present an X-ray study of the galaxy group or poor cluster MKW 4. Working with XMM–Newton data we examine the distribution and properties of the hot gas which makes up the group halo. The inner halo shows some signs of structure, with circular or elliptical beta models providing a poor fit to the surface brightness profile. This may be evidence of large-scale motion in the inner halo, but we do not find evidence of sharp fronts or edges in the emission. The temperature of the halo declines in the core, with deprojected spectral fits showing a central temperature of ∼1.3 keV compared to ∼3 keV at 100 kpc. In the central ∼30 kpc of the group, multitemperature spectral models are required to fit the data, but they indicate a lack of gas at low temperatures. Steady-state cooling flow models provide poor fits to the inner regions of the group and the estimated cooling time of the gas is long except within the central dominant galaxy, NGC 4073. Abundance profiles show a sharp increase in the core of the group, with mean abundance rising by a factor of 2 in the centre of NGC 4073. Fitting individual elements shows the same trend, with high values of Fe, Si and S in the core. We estimate that ∼50 per cent of the Fe in the central 40 kpc was injected by Type Ia supernovae, in agreement with previous ASCA studies. Using our best-fitting surface brightness and temperature models, we calculate the mass, gas fraction, entropy and mass-to-light ratio of the group. At 100 kpc (∼0.1 virial radius) the total mass and gas entropy of the system ( ∼2 × 1013 M⊙ and ∼300 keV cm2 ) are quite comparable to those of other systems of similar temperature, but the gas fraction is rather low (∼1 per cent). We conclude that MKW 4 is a fairly relaxed group, which has developed a strong central temperature gradient but not a large-scale cooling flow. 相似文献
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Stefano Ettori 《Monthly notices of the Royal Astronomical Society》2000,311(2):313-316
I suggest that the β -model used to fit the X-ray surface brightness profiles of extended sources, like groups and clusters of galaxies, has to be corrected when the counts are collected in a wide energy band comparable to the mean temperature of the source, and a significant gradient in the gas temperature is observed. I present a revised version of the β -model for the X-ray brightness that applies to an intracluster gas with temperature and density related by a polytropic equation and extends the standard version that is strictly valid for an isothermal gas. Given a temperature gradient observed through an energy window of 1–10 keV typical for the new generation of X-ray observatories, the β parameter can change systematically by up to 20 per cent from the value obtained under isothermal assumption, i.e. by an amount larger than any statistical uncertainty obtained from the present data. Within the virial regions of typical clusters of galaxies, these systematic corrections affect the total gravitating mass estimate by 5–10 per cent, the gas mass by 10–30 per cent and the gas fraction value up to 50 per cent, when compared with the measurements obtained under the isothermal assumption. 相似文献
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M. Vivekanand 《Monthly notices of the Royal Astronomical Society》2001,326(2):L33-L36
We report the discovery of a 40 arcsec long X-ray filament in the core of the cluster of galaxies Abell 1795. The feature coincides with an H α +N ii filament found by Cowie et al. in the early 1980s and resolved into at least two U -band filaments by McNamara et al. in the mid-1990s. The (emission-weighted) temperature of the X-ray emitting gas along the filament is 2.5–3 keV, as revealed by X-ray colour ratios. The deprojected temperature will be less. A detailed temperature map of the core of the cluster presented. The cD galaxy at the head of the filament is probably moving through or oscillating in the cluster core. The radiative cooling time of the X-ray emitting gas in the filament is about which is similar to the age of the filament obtained from its length and velocity. This suggests that the filament is produced by cooling of the gas from the intracluster medium. The filament, much of which is well separated from the body of the cD galaxy and its radio source, is potentially of great importance in helping to understand the energy and ionization source of the optical nebulosity common in cooling flows. 相似文献
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Alastair J. R. Sanderson Ewan O'Sullivan Trevor J. Ponman 《Monthly notices of the Royal Astronomical Society》2009,395(2):764-776
We investigate the thermodynamic and chemical structure of the intracluster medium (ICM) across a statistical sample of 20 galaxy clusters analysed with the Chandra X-ray satellite. In particular, we focus on the scaling properties of the gas density, metallicity and entropy and the comparison between clusters with and without cool cores (CCs). We find marked differences between the two categories except for the gas metallicity, which declines strongly with radius for all clusters ( Z ∝ r −0.31 ) , outside ∼0.02 r 500 . The scaling of gas entropy is non-self-similar and we find clear evidence of bimodality in the distribution of logarithmic slopes of the entropy profiles. With only one exception, the steeper sloped entropy profiles are found in CC clusters whereas the flatter slope population are all non-CC clusters. We explore the role of thermal conduction in stabilizing the ICM and conclude that this mechanism alone is sufficient to balance cooling in non-CC clusters. However, CC clusters appear to form a distinct population in which heating from feedback is required in addition to conduction. Under the assumption that non-CC clusters are thermally stabilized by conduction alone, we find the distribution of Spitzer conduction suppression factors, f c , to be lognormal, with a log (base 10) mean of −1.50 ± 0.03 (i.e. f c = 0.032 ) and log standard deviation 0.39 ± 0.02 . 相似文献
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R. Gilmour P. Best O. Almaini 《Monthly notices of the Royal Astronomical Society》2009,392(4):1509-1531
We present an analysis of the X-ray point source populations in 182 Chandra images of galaxy clusters at z > 0.1 with exposure time >10 ks, as well as 44 non-cluster fields. The analysis of the number and flux of these sources, using a detailed pipeline to predict the distribution of non-cluster sources in each field, reveals an excess of X-ray point sources associated with the galaxy clusters. A sample of 148 galaxy clusters at 0.1 < z < 0.9 , with no other nearby clusters, shows an excess of 230 cluster sources in total, an average of ∼1.5 sources per cluster. The lack of optical data for these clusters limits the physical interpretation of this result, as we cannot calculate the fraction of cluster galaxies hosting X-ray sources. However, the fluxes of the excess sources indicate that over half of them are very likely to be active galactic nuclei (AGN), and the radial distribution shows that they are quite evenly distributed over the central 1 Mpc of the cluster, with almost no sources found beyond this radius. We also use this pipeline to successfully reproduce the results of previous studies, particularly the higher density of sources in the central 0.5 Mpc of a few cluster fields, but show that these conclusions are not generally valid for this larger sample of clusters. We conclude that some of these differences may be due to the sample properties, such as the size and redshift of the clusters studied, or a lack of publications for cluster fields with no excess sources. This paper also presents the basic X-ray properties of the galaxy clusters, and in subsequent papers in this series the dependence of the AGN population on these cluster properties will be evaluated.
In addition the properties of over 9500 X-ray point sources in the fields of galaxy clusters are tabulated in a separate catalogue available online or at http://www.sc.eso.org~rgilmour . 相似文献
In addition the properties of over 9500 X-ray point sources in the fields of galaxy clusters are tabulated in a separate catalogue available online or at http://www.sc.eso.org~rgilmour . 相似文献
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We examine the effects of cooling flows on the T X – L Bol relation for a sample of the most X-ray luminous ( L Bol > 1045 erg s−1 ) clusters of galaxies known. Using high-quality ASCA X-ray spectra and ROSAT images we explicitly account for the effects of cooling flows on the X-ray properties of the clusters and show that this reduces the previously noted dispersion in the T X – L Bol relationship. More importantly, the slope of the relationship is flattened from L Bol ∝ T 3 X to approximately L Bol ∝ T 2 X , in agreement with recent theoretical models which include the effects of shocks and pre-heating on the X-ray gas. We find no evidence for evolution in the T X – L Bol relation within z ∼ 0.3. Our results demonstrate that the effects of cooling flows must be accounted for before cosmological parameters can be determined from X-ray observations of clusters. The results presented here should provide a reliable basis for modelling the T X – L Bol relation at high X-ray luminosities. 相似文献