共查询到20条相似文献，搜索用时 15 毫秒
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R. J. Smith B. J. Boyle S. J. Maddox 《Monthly notices of the Royal Astronomical Society》2000,313(2):252-262
An angular correlation of low significance (2 σ ) is observed between 0.3< z <0.5 QSOs and V 23 galaxies. Overall, the cross-correlation function between 82 intermediate-redshift (0.3< z <0.7) X-ray selected QSOs and V ≲24 galaxies is investigated, but no signal is detected for the z >0.5 QSOs. After converting to an excess of galaxies physically associated with the QSO, this lack of strong correlation is shown to be consistent with the clustering of normal galaxies at the same moderate redshifts. Combined with previous observations, these results imply that the environments of radio-quiet QSOs do not undergo significant evolution with respect to the galaxy population over a wide range of redshifts (0< z <1.5). This is in marked contrast to the rapid increase in the richness of the environments associated with radio-loud QSOs over the same redshift range. 相似文献
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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 Position Sensitive Proportional Counter (PSPC) data. It is found that the new luminosities are on average 1.18±0.08 times higher than previously measured, but also 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 either has 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 Ω0 . 相似文献
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B. J. Maughan † L. R. Jones H. Ebeling C. Scharf 《Monthly notices of the Royal Astronomical Society》2006,365(2):509-529
The X-ray properties of a sample of 11 high-redshift (0.6 < z < 1.0) clusters observed with Chandra and/or XMM–Newton are used to investigate the evolution of the cluster scaling relations. The observed evolution in the normalization of the L – T , M – T , M g – T and M – L relations is consistent with simple self-similar predictions, in which the properties of clusters reflect the properties of the Universe at their redshift of observation. Under the assumption that the model of self-similar evolution is correct and that the local systems formed via a single spherical collapse, the high-redshift L – T relation is consistent with the high- z clusters having virialized at a significantly higher redshift than the local systems. The data are also consistent with the more realistic scenario of clusters forming via the continuous accretion of material.
The slope of the L – T relation at high redshift ( B = 3.32 ± 0.37) is consistent with the local relation, and significantly steeper than the self-similar prediction of B = 2 . This suggests that the same non-gravitational processes are responsible for steepening the local and high- z relations, possibly occurring universally at z ≳ 1 or in the early stages of the cluster formation, prior to their observation.
The properties of the intracluster medium at high redshift are found to be similar to those in the local Universe. The mean surface-brightness profile slope for the sample is β= 0.66 ± 0.05 , the mean gas mass fractions within R2500( z ) and R 200( z ) are 0.069 ± 0.012 and 0.11 ± 0.02 , respectively, and the mean metallicity of the sample is 0.28 ± 0.11 Z⊙ . 相似文献
The slope of the L – T relation at high redshift ( B = 3.32 ± 0.37) is consistent with the local relation, and significantly steeper than the self-similar prediction of B = 2 . This suggests that the same non-gravitational processes are responsible for steepening the local and high- z relations, possibly occurring universally at z ≳ 1 or in the early stages of the cluster formation, prior to their observation.
The properties of the intracluster medium at high redshift are found to be similar to those in the local Universe. The mean surface-brightness profile slope for the sample is β= 0.66 ± 0.05 , the mean gas mass fractions within R
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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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A. D. Chernin V. P. Dolgachev L. M. Domozhilova 《Monthly notices of the Royal Astronomical Society》2000,319(3):851-859
We study triple systems of galaxies with mean projected harmonic separation ≃0.6 h −1 Mpc We call the systems 'wide triplets', in contrast to compact triplets with mean projected harmonic separation ≃0.04 h −1 Mpc, studied by Karachentsev et al. Data are taken for 108 wide triplets from a list compiled by Trofimov & Chernin; at least one-third of them are considered to be probably isolated physical systems. With typical crossing times of about the Hubble time, the wide triplets seem to be in a state of ongoing collapse. This is confirmed by a set of computer models which simulate well the observational characteristics of the ensemble of wide triplets. The simulations also give a statistical estimate of the total mass of a typical wide triplet: it proves to be ≃1013 M⊙ . This figure indicates that the dark matter mass is 15–30 times the mass of baryonic matter in the systems. The dynamics of wide triplets, as well as their dark matter content, provide new direct cosmological constraints by establishing that hierarchical evolution is occurring on a mass scale of ∼1013 M⊙ and a spatial scale of ∼1 Mpc. 相似文献
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M. R. George † A. C. Fabian J. S. Sanders A. J. Young H. R. Russell 《Monthly notices of the Royal Astronomical Society》2009,395(2):657-666
We measure X-ray emission from the outskirts of the cluster of galaxies PKS 0745−191 with Suzaku , determining radial profiles of density, temperature, entropy, gas fraction and mass. These measurements extend beyond the virial radius for the first time, providing new information about cluster assembly and the diffuse intracluster medium out to ∼1.5 r 200 ( r 200 ≃ 1.7 Mpc ≃ 15 arcmin ). The temperature is found to decrease by roughly 70 per cent from 0.3 to 1 r 200 . We also see a flattening of the entropy profile near the virial radius and consider the implications this has for the assumption of hydrostatic equilibrium when deriving mass estimates. We place these observations in the context of simulations and analytical models to develop a better understanding of non-gravitational physics in the outskirts of the cluster. 相似文献
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Minnie Y. Mao Melanie Johnston-Hollitt Jamie B. Stevens Simon J. Wotherspoon 《Monthly notices of the Royal Astronomical Society》2009,392(3):1070-1079
Using radio data at 1.4 GHz from the Australia Telescope Compact Array (ATCA), we identify five head–tail (HT) galaxies in the central region of the Horologium–Reticulum Supercluster (HRS). Physical parameters of the HT galaxies were determined along with substructure in the HRS to probe the relationship between environment and radio properties. Using a density enhancement technique applied to 582 spectroscopic measurements in the 2°× 2° region about A3125/A3128, we find all five HT galaxies reside in regions of extremely high density (>100 galaxies Mpc−3 ). In fact, the environments surrounding HT galaxies are statistically denser than those environments surrounding non-HT galaxies and among the densest environments in a cluster. Additionally, the HT galaxies are found in regions of enhanced X-ray emission and we show that the enhanced density continues out to substructure groups of 10 members. We propose that it is the high densities that allow ram pressure to bend the HT galaxies as opposed to previously proposed mechanisms relying on exceptionally high peculiar velocities. 相似文献
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