共查询到20条相似文献，搜索用时 46 毫秒
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S. Bardelli A. Pisani M. Ramella E. Zucca & G. Zamorani 《Monthly notices of the Royal Astronomical Society》1998,300(2):589-598
The 'algorithm driven by the density estimate for the identification of clusters' ( DEDICA ) is applied to the A3558 cluster complex in order to find substructures. This complex, located at the centre of the Shapley Concentration supercluster, is a chain formed by the ACO clusters A3556, A3558 and A3562 and the two poor clusters SC 1327-312 and SC 1329-313. We find a large number of clumps, indicating that strong dynamical processes are active. In particular, it is necessary to use a fully three-dimensional sample (i.e. using the galaxy velocity as third coordinate) in order also to recover the clumps superimposed along the line of sight. Even though a large number of detected substructures was already found in a previous analysis, this method is more efficient and faster when compared with a wide battery of tests, and permits the direct estimate of the detection significance. Almost all subclusters previously detected by the wavelet analyses found in the literature are recognized by DEDICA . On the basis of the substructure analysis, we also briefly discuss the origin of the A3558 complex by comparing two hypotheses: (i) the structure is a cluster–cluster collision seen just after the first core–core encounter; or (ii) this complex is the result of a series of incoherent group–group and cluster–group mergings, focused in that region by the presence of the surrounding supercluster. We studied the fraction of blue galaxies in the detected substructures and found that the bluest groups reside between A3562 and A3558, i.e. in the expected position for the scenario of cluster–cluster collision. 相似文献
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T. Venturi S. Bardelli G. Zambelli R. Morganti R.W. Hunstead 《Monthly notices of the Royal Astronomical Society》2001,324(4):1131-1146
We report and discuss the results of a 22-cm radio survey carried out with the Australia Telescope Compact Array (ATCA) covering the A3528 complex, a chain formed by the merging ACO clusters A3528–A3530–A3532 , located in the central region of the Shapley Concentration. Simultaneous 13-cm observations are also presented. Our final catalogue includes a total of 106 radio sources above the flux density limit of 0.8 mJy. By cross-correlation with optical and spectroscopic catalogues we found 32 optical counterparts, nine of them belonging to the A3528 complex.
We explored the effects of cluster mergers on the radio emission properties of radio galaxies by means of the radio luminosity function (RLF) and radio source counts. We found that the radio source counts are consistent with the background counts, as already found for the A3558 complex. The RLF for this complex is consistent, in both shape and normalization, with the general cluster luminosity function for early-type galaxies derived by Ledlow & Owen. This result is different from the one we obtained for the A3558 merging complex, the RLF of which is significantly lower than that derived by Ledlow & Owen.
We propose that the different stage of the merger is responsible for the different RLFs in the two cluster complexes in the core of the Shapley Concentration. The early stage of merger for the A3528 complex, proposed by many authors, may not yet have affected the radio properties of cluster galaxies, while in the more much advanced merger in the A3558 region we actually see the effects of this process on the radio emission. 相似文献
We explored the effects of cluster mergers on the radio emission properties of radio galaxies by means of the radio luminosity function (RLF) and radio source counts. We found that the radio source counts are consistent with the background counts, as already found for the A3558 complex. The RLF for this complex is consistent, in both shape and normalization, with the general cluster luminosity function for early-type galaxies derived by Ledlow & Owen. This result is different from the one we obtained for the A3558 merging complex, the RLF of which is significantly lower than that derived by Ledlow & Owen.
We propose that the different stage of the merger is responsible for the different RLFs in the two cluster complexes in the core of the Shapley Concentration. The early stage of merger for the A3528 complex, proposed by many authors, may not yet have affected the radio properties of cluster galaxies, while in the more much advanced merger in the A3558 region we actually see the effects of this process on the radio emission. 相似文献
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T. Venturi S. Bardelli R. Morganti R. W. Hunstead 《Monthly notices of the Royal Astronomical Society》2000,314(3):594-610
We present the results of a 22-cm radio survey carried out with the Australia Telescope Compact Array (ATCA) covering the A3558 complex, a chain formed by the merging ACO clusters A3556–A3558–A3562 and the two groups SC 1327−312 and SC 1323−313, located in the central region of the Shapley Concentration. The purpose of our survey is to study the effects of cluster mergers on the statistical properties of radio galaxies and to investigate the connection between mergers and the presence of radio haloes and relic sources.
We found that the radio source counts in the A3558 complex are consistent with the background source counts. The much higher optical density compared with the background is not reflected as a higher density of radio sources. Furthermore, we found that no correlation exists between the local density and the radio source power, and that steep-spectrum radio galaxies are not segregated in denser optical regions.
The radio luminosity function for elliptical and S0 galaxies is significantly lower than for cluster early-type galaxies and for those not selected to be in clusters at radio powers log P1.4 ≳22.5, implying that the probability of a galaxy becoming a radio source above this power limit is lower in the Shapley Concentration compared with any other environment. Possible explanations will be presented.
The detection of a head–tail source in the centre of A3562, coupled with careful inspection of the 20-cm NRAO VLA Sky Survey (NVSS) and of 36-cm MOST observations, allowed us to spot two extended sources in the region between A3562 and SC 1329−313, i.e. a candidate radio halo at the centre of A3562 and low brightness extended emission around a 14.96-mag Shapley galaxy. The relation between these two extended galaxies and the ongoing group merger in this region of the Shapley Concentration are discussed. 相似文献
We found that the radio source counts in the A3558 complex are consistent with the background source counts. The much higher optical density compared with the background is not reflected as a higher density of radio sources. Furthermore, we found that no correlation exists between the local density and the radio source power, and that steep-spectrum radio galaxies are not segregated in denser optical regions.
The radio luminosity function for elliptical and S0 galaxies is significantly lower than for cluster early-type galaxies and for those not selected to be in clusters at radio powers log P
The detection of a head–tail source in the centre of A3562, coupled with careful inspection of the 20-cm NRAO VLA Sky Survey (NVSS) and of 36-cm MOST observations, allowed us to spot two extended sources in the region between A3562 and SC 1329−313, i.e. a candidate radio halo at the centre of A3562 and low brightness extended emission around a 14.96-mag Shapley galaxy. The relation between these two extended galaxies and the ongoing group merger in this region of the Shapley Concentration are discussed. 相似文献
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Ho Seong Hwang † Myung Gyoon Lee 《Monthly notices of the Royal Astronomical Society》2009,397(4):2111-2122
We present the results of a study of galaxy activity in two merging binary clusters (A168 and A1750) using the Sloan Digital Sky Survey (SDSS) data supplemented with the data in the literature. We have investigated the merger histories of A168 and A1750 by combining the results from a two-body dynamical model and X-ray data. In A168, two subclusters appear to have passed each other and to be coming together from the recent maximum separation. In A1750, two major subclusters appear to have started interaction and to be coming together for the first time. We find an enhanced concentration of the galaxies showing star formation (SF) or active galactic nuclei (AGN) activity in the region between two subclusters in A168, which were possibly triggered by the cluster merger. In A1750, we do not find any galaxies with SF/AGN activity in the region between two subclusters, indicating that two major subclusters are in the early stage of merging. 相似文献
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S. Ettori S. W. Allen A. C. Fabian 《Monthly notices of the Royal Astronomical Society》2001,322(1):187-194
We present an analysis of BeppoSAX observations of three clusters of galaxies that are amongst the most luminous in the Universe: RXJ1347−1145, Zwicky 3146 and Abell 2390. Using data from both the Low Energy (LECS) and Medium Energy (MECS) Concentrator Spectrometers, and a joint analysis with the Phoswich Detection System (PDS) data above 10 keV, we constrain, with a relative uncertainty of between 7 and 42 per cent (90 per cent confidence level), the mean gas temperature in the three clusters. These measurements are checked against any possible non-thermal contribution to the plasma emission and are shown to be robust.
We confirm that RXJ1347−1145 has a gas temperature that lies in the range between 13.2 and 22.3 keV at the 90 per cent confidence level, and is larger than 12.1 keV at 3 σ level. The existence of such a hot galaxy cluster at redshift of about 0.45 implies an upper limit on the mean mass density in the Universe, Ωm , of 0.5.
Combining the BeppoSAX estimates for gas temperature and luminosity of the three clusters presented in this work with ASCA measurements available in the literature, we obtain a slope of 2.7 in the L – T relation once the physical properties are corrected from the contamination from the central cooling flows. 相似文献
We confirm that RXJ1347−1145 has a gas temperature that lies in the range between 13.2 and 22.3 keV at the 90 per cent confidence level, and is larger than 12.1 keV at 3 σ level. The existence of such a hot galaxy cluster at redshift of about 0.45 implies an upper limit on the mean mass density in the Universe, Ω
Combining the BeppoSAX estimates for gas temperature and luminosity of the three clusters presented in this work with ASCA measurements available in the literature, we obtain a slope of 2.7 in the L – T relation once the physical properties are corrected from the contamination from the central cooling flows. 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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Christopher J. Conselice & John S. Gallagher III 《Monthly notices of the Royal Astronomical Society》1998,297(2):L34-L38
We present evidence for a new morphologically defined form of small-scale substructure in the Coma cluster, which we call galaxy aggregates. Aggregates are dominated by a central galaxy, which is on average 5 mag brighter than the smaller aggregate members, nearly all of which lie to one side of the central galaxy. We have found three such galaxy aggregates: two dominated by the S0 galaxies RB 55 and RB 60, and one by the starbursting SBb NGC 4858. RB 55 and 60 are both equidistant between the two dominant D galaxies NGC 4874 and 4889, while NGC 4858 is located near the large E0 galaxy NGC 4860. All three central galaxies have redshifts consistent with Coma cluster membership. We describe the spatial structures of these unique objects, and suggest several possible mechanisms to explain their origin. These include: chance superpositions from background galaxies, interactions between other galaxies and with the cluster gravitational potential, and ram pressure. We conclude that the most probable scenario of creation is an interaction with the cluster through its gravitational potential. 相似文献
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P. Firth E. A. Evstigneeva M. J. Drinkwater 《Monthly notices of the Royal Astronomical Society》2009,394(4):1801-1811
From high signal-to-noise ratio GMOS-N and AAOmega spectra, we have measured line-strength indices in the Lick/IDS system for several luminous and spatially dispersed compact stellar systems (CSSs) located in the Virgo and Fornax galaxy clusters. We estimate their [α/Fe] ratios, ages and metallicities using a simple (single-burst) stellar population model. We confirm that the Virgo core region luminous CSSs ( ) contain ancient stellar populations with subsolar total metallicities, suggesting that they comprise the bright tail of M87's GC distribution. The two Virgo intracluster globular clusters have ages and metallicities consistent with the cluster core CSSs. Two Fornax luminous CSSs also have ancient stellar populations but are at the upper end of the Virgo CSS metallicity range, while the third (UCD3) appears to be relatively young, metal-rich and with a core + halo radial profile. Our results suggest that Fornax may contain an extra population of luminous CSSs formed more recently than the ancient GC-like systems found in both clusters. 相似文献
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Nazirah N. Jetha Irini Sakelliou Martin J. Hardcastle Trevor J. Ponman Ian R. Stevens 《Monthly notices of the Royal Astronomical Society》2005,358(4):1394-1404
We present Chandra and Very Large Array observations of two galaxy clusters, Abell 160 and Abell 2462, whose brightest cluster galaxies (BCGs) host wide angle tailed radio galaxies (WATs). We search for evidence of interactions between the radio emission and the hot, X-ray emitting gas, and we test various jet termination models. We find that both clusters have cool BCGs at the cluster centre, and that the scale of these cores (∼30–40 kpc for both sources) is of approximately the same scale as the length of the radio jets. For both sources, the jet flaring point is coincident with a steepening in the host cluster's temperature gradient, and similar results are found for 3C 465 and Hydra A. However, none of the published models of WAT formation offers a satisfactory explanation as to why this may be the case. Therefore, it is unclear what causes the sudden transition between the jet and the plume. Without accurate modelling, we cannot ascertain whether the steepening of the temperature gradient is the main cause of the transition, or merely a tracer of an underlying process. 相似文献
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Neil Trentham & Bahram Mobasher 《Monthly notices of the Royal Astronomical Society》1998,299(2):488-498
We present the K -band (2.2 μm) luminosity functions (LFs) of the X-ray-luminous clusters MS1054–0321 ( z = 0.823), MS0451–0305 ( z = 0.55), Abell 963 ( z = 0.206), Abell 665 ( z = 0.182) and Abell 1795 ( z = 0.063) down to absolute magnitudes M K = −20. Our measurements probe fainter absolute magnitudes than do any previous studies of the near-infrared LFs of clusters. All the clusters are found to have similar LFs within the errors, when the galaxy populations are evolved to redshift z = 0. It is known that the most massive bound systems in the Universe at all redshifts are X-ray-luminous clusters. Therefore, assuming that the clusters in our sample correspond to a single population seen at different redshifts, the results here imply that not only had the stars in present-day ellipticals in rich clusters formed by z = 0.8, but that they existed in as luminous galaxies then as they do today. Additionally, the clusters have K -band LFs which appear to be consistent with the K -band field LF in the range −24 < M K < −22, although the uncertainties in both the field and cluster samples are large. 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