首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Using published flux densitiesS at low frequenciesv, radio spectra were constructed for 3C, 4C, and 4CT radio sources in Abell clusters of galaxies, radio galaxies outside Abell clusters, and quasars with known redshifts. About half the sources in rich Abell clusters (richness classesR>-2) have steep spectra between 38 and 178 MHz with spectral indices 38 178 > whereSv –. However, radio galaxies outside clusters have values of 38 178 1.2, and no steep spectra were found among 170 quasars. The radio sources in rich clusters are probably confined by intergalactic gas, and the steep spectra develop over a period of 109 yr as relativistic electrons lose energy. The absence of steep spectra among quasars does not necessarily mean that quasars never occur in rich clusters of galaxies, since quasars are probably being observed only in their early high-luminosity phases. The possibility that some quasar events occur in the nuclei of the dominant cD galaxies in clusters is discussed, but quasar events may occur in more than one type of galaxy.  相似文献   

2.
A radio survey, using the Very Large Array at 20 and 90 cm λ has been carried out in the direction of 46 distant Abell clusters (0.1 ≲ z ≲ 0.3) dominated by a cD galaxy (clusters classified to be Bautz-Morgan I type). A radio source coincident with the cD galaxy was detected in 16 clusters. We find that the radio luminosity function of the cD galaxies at 20cm λ, and below the luminosityP 1.4ghz ≲ 1024.5 W Hz-1, is similar to that of brightest ellipticals in less clustered environments. Above this luminosity, the cDs seem to have a higher probability of becoming radio sources. The effect of optical brightness on radio emission is shown to be the same for the two classes. No significantly large population of very-steep-spectrum sources with spectral index α >1.2 (flux density ∝ frequency-α) was found to be associated with cD galaxies. A significant negative correlation is found between the radio luminosity of the cD galaxy and the cooling-time of the intra cluster medium near the galaxy. We also present evidence that the probability of radio emission from first-ranked galaxies is dependent upon their location relative to the geometrical centres of clusters and thus related to the morphological class and the evolutionary state of the clusters. We argue that both these effects are primarily caused by the dynamical evolution of these distant clusters of galaxies.  相似文献   

3.
The location of galaxies in 377 rich Abell galaxy clusters is discussed. We compared the distributions of galaxies in the sample containing all galaxies with the sample compiled from the 20 brightest objects. Counts in circular sectors with angle width equal to 30î show isotropy. Only in the case of BM I clusters and the coordinate system related to the cluster major axis did we find anisotropic distributions. We investigated also the distributions of galaxy position angles within clusters exhibiting isotropy. The structure position angles for both samples have been studied as well. They appeared to be different. The difference in location of galaxies in the case of cD clusters, as well as the more elliptical shape and different position angles of samples containing bright galaxies is observed.  相似文献   

4.
analysis of new X-ray and optical data confirms that the X-ray luminosityL x of a cluster of galaxies is strongly dependent on its richness. The radio powerP 1445 of clusters at 1445 MHz is independent of richness, but is greater on the average for clusters with dominant cD galaxies than for those withou. The radio emission depends on the activity of one of the brightest galaxies; dominant cD galaxies are often responsible for radio emission, especially if they have double or multiple nuclei. For a given richness, high values ofL x andP 1445 sometimes occur together, but no strict correlation betweenL x andP 1445 exists. Possible tests of thermal-bremsstrahlung and inverse-Compton theories for the X-ray emission are mentioned.  相似文献   

5.
We present 5.5 and 9.0 GHz Australia Telescope Compact Array (ATCA) observations of the cluster MACSJ0417.5-1154, one of the most massive galaxy clusters and one of the brightest in X-ray in the Massive Cluster Survey (MACS). We estimate diffuse emission at 5.5 and 9.0 GHz from our ATCA observations, and compare the results with the 235 MHz and 610 MHz GMRT observations and 1575 MHz VLA observations. We also estimate the diffuse emission at low frequencies from existing GLEAM survey data (using the MWA telescope (http://www.mwatelescope.org)), and find that the steepening reported in earlier studies may have been an artefact of underestimates of diffuse emission at low frequencies. High-frequency radio observations of galaxy cluster mergers therefore provide an important complement to low-frequency observations, not only for a probing the ‘on’ and ‘off’ state of radio halos in these mergers, but also to constrain energetics of cluster mergers. We comment on the future directions that further studies of this cluster can take.  相似文献   

6.
As part of an extensive radio–IR–optical–X-ray study of ROSAT clusters of galaxies in the Hydra region we have observed the bimodal Abell cluster A3528, located in the core of the Shapley Supercluster ( z  ≃ 0.053), with the Molonglo Observatory Synthesis Telescope at 843 MHz and the Australia Telescope Compact Array at 1.4 and 2.4 GHz. This is part I in a series of papers which looks at the relationship between the radio and X-ray emission in samples of ROSAT selected clusters.   The radio source characteristics — tailed morphologies and steep spectra — are consistent with the effects of a dense intracluster medium and the pre-merging environment of A3528. In particular, we present evidence that the minor member of the radio-loud dumbbell galaxy located at the centre of the northern component of A3528 is on a plunging orbit. We speculate that this orbit may have been induced by the tidal interactions between the merging components of A3528. In addition, the radio source associated with the dominant member of the dumbbell galaxy exhibits many of the characteristics of compact steep spectrum sources. We argue that the radio emission from this source was triggered ∼ 106 yr ago by tidal interactions between the two members of the dumbbell galaxy, strengthening the argument that compact steep spectrum (CSS) sources are young.   Re-analysis of archive pointed Position Sensitive Proportional Counter (PSPC) data using multiresolution filtering suggests the presence of an AGN and/or a cooling flow in the southern component of A3528.  相似文献   

7.
We report the serendipitous detection of a Wide-Angle Tail (WAT) radio galaxy at 240 and 610 MHz, using the Giant Metrewave Radio Telescope (GMRT). This WAT is hosted by a cD galaxy PGC 1519010 whose photometric redshift given in the SDSS DR6 catalogue is close to the spectroscopic redshifts (0.105, 0.106 and 0.107) of three galaxies found within 4′ of the cD. Using the SDSS DR6, we have identified a total of 37 galaxies within 15′ of the cD, whose photometric redshifts are between 0.08 and 0.14. This strongly suggests that the cD is associated with a group of galaxies whose conspicuous feature is a north-south chain of galaxies (filament) extending to at least 2.6 Mpc. The ROSAT all-sky survey shows a faint, diffuse X-ray source in this direction, which probably marks the hot intracluster gas in the potential well of this group. We combine the radio structural information for this WAT with the galaxy clustering in that region to check its overall consistency with the models of WAT formation. The bending of the jet before and after its disruption forming the radio plume, are found to be correlated in this WAT, as seen from the contrasting morphological patterns on the two sides of the core. Probable constraints imposed by this on the models of WAT formation are pointed out. We also briefly report on the other interesting radio sources found in the proximity of the WAT. These include a highly asymmetric double radio source and an ultra-steep spectrum radio source for which no optical counterpart is detected in the SDSS.  相似文献   

8.
We investigate current problems connected with the formation of cD galaxies. The subject of the present paper is to compare internal properties of the cD galaxy Zw162010 with cluster properties of Abell 1795. This consideration is a first attempt to find commonly valid essential correlations between peculiarities of brightest cluster members as structures and active phenomena and global cluster properties as for instance galaxy populations and concentration degrees. The colours, the X-ray emission, and the velocity of the cD galaxy are used to discuss the obvious influence of the environment on the evolution of the active nucleus. In a second paper (Kirchner et al. 1992) the radio structure is used to investigate the influence of the surrounding cluster medium onto the development of the active nucleus. Furtheron, various jet ejection scenarios will be quantitatively examined.  相似文献   

9.
The radio properties ofUhuru X-ray sources with fairly certain extragalactic identifications are described briefly. Radio to X-ray flux ratios are low for rich clusters of galaxies and high for double radio sources. There is some evidence from the Abell 426 (Perseus) and Abell 1367 clusters that a radio galaxy in a rich cluster may be the centre of extended X-ray emission. Nuclei of galaxies have an enormous range in X-ray luminosity; the known range is from 1030 W for our galaxy to 3×1038 W for 3C 273. Unidentified X-ray sources at high galactic latitudes may include new classes of objects with very low radio to X-ray flux ratios or hard X-ray emission.  相似文献   

10.
High sensitivity observations of radio halos in galaxy clusters at frequencies ν ≤ 330 MHz are still relatively rare, and very little is known compared to the classical 1.4 GHz images. The few radio halos imaged down to 150–240 MHz show a considerable spread in size, morphology and spectral properties. All clusters belonging to the GMRT Radio Halo Survey with detected or candidate cluster-scale diffuse emission have been imaged at 325 MHz with the GMRT. Few of them were also observed with the GMRT at 240 MHz and 150 MHz. For A 1682, imaging is particularly challenging due to the presence of strong and extended radio galaxies at the center. Our data analysis suggests that thew radio galaxies are superposed to very low surface brightness radio emission extended on the cluster scale, which we present here.  相似文献   

11.
We measured metal abundances of the intracluster medium in the central regions of 34 nearby clusters of galaxies, using ASCA data. Clusters that have a sharp X-ray emission centred on a cD galaxy are commonly found to exhibit a central increment in the Fe abundance, which is more pronounced in lower temperature clusters; +(0.1–0.2) solar at kT >5 keV, compared with +(0.2–0.3) solar at 1.5< kT <4 keV. These central excess metals are thought to be ejected from cD galaxies. Several low-temperature cD type clusters also show significant Si abundance increase by +(0.1–0.2) solar at the central region. Compared with the Si-rich abundances observed in the outer regions of rich clusters, the Si to Fe abundance ratio of central excess metals tends to be near the solar ratio, implying that type Ia products from cD galaxies are dominant for the central excess metals. On the other hand, some other clusters do not show the central Fe abundance increase. As these clusters tend to contain two or three central giant galaxies, it is suggested that galaxy interactions have removed the central abundance increase.  相似文献   

12.
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   

13.
We study the stellar mass assembly of the Spiderweb galaxy  (MRC 1138−262)  , a massive   z = 2.2  radio galaxy in a protocluster and the probable progenitor of a brightest cluster galaxy. Nearby protocluster galaxies are identified and their properties are determined by fitting stellar population models to their rest-frame ultraviolet to optical spectral energy distributions. We find that within 150 kpc of the radio galaxy the stellar mass is centrally concentrated in the radio galaxy, yet most of the dust-uncorrected, instantaneous star formation occurs in the surrounding low-mass satellite galaxies. We predict that most of the galaxies within 150 kpc of the radio galaxy will merge with the central radio galaxy by   z = 0  , increasing its stellar mass by up to a factor of ≃2. However, it will take several hundred Myr for the first mergers to occur, by which time the large star formation rates are likely to have exhausted the gas reservoirs in the satellite galaxies. The tidal radii of the satellite galaxies are small, suggesting that stars and gas are being stripped and deposited at distances of tens of kpc from the central radio galaxy. These stripped stars may become intracluster stars or form an extended stellar halo around the radio galaxy, such as those observed around cD galaxies in cluster cores.  相似文献   

14.
A submillimetre survey of the star formation history of radio galaxies   总被引：1，自引：0，他引：1  
We present the results of the first major systematic submillimetre survey of radio galaxies spanning the redshift range 1< z <5. The primary aim of this work is to elucidate the star formation history of this sub class of elliptical galaxies by tracing the cosmological evolution of dust mass. Using SCUBA on the JCMT, we have obtained 850-μm photometry of 47 radio galaxies to a consistent rms depth of 1 mJy, and have detected dust emission in 14 cases. The radio galaxy targets have been selected from a series of low-frequency radio surveys of increasing depth (3CRR, 6CE, etc.), in order to allow us to separate the effects of increasing redshift and increasing radio power on submillimetre luminosity. Although the dynamic range of our study is inevitably small, we find clear evidence that the typical submillimetre luminosity (and hence dust mass) of a powerful radio galaxy is a strongly increasing function of redshift; the detection rate rises from ≃15 per cent at z <2.5 to ≳75 per cent at z >2.5, and the average submillimetre luminosity rises at a rate ∝(1+ z )3 out to z ≃4. Moreover, our extensive sample allows us to argue that this behaviour is not driven by underlying correlations with other radio galaxy properties such as radio power, radio spectral index, or radio source size/age. Although radio selection may introduce other more subtle biases, the redshift distribution of our detected objects is in fact consistent with the most recent estimates of the redshift distribution of comparably bright submillimetre sources discovered in blank field surveys. The evolution of submillimetre luminosity found here for radio galaxies may thus be representative of massive ellipticals in general.  相似文献   

15.
The study of galaxy protoclusters is beginning to fill in unknown details of the important phase of the assembly of clusters and cluster galaxies. This review describes the current status of this field and highlights promising recent findings related to galaxy formation in the densest regions of the early universe. We discuss the main search techniques and the characteristic properties of protoclusters in observations and simulations, and show that protoclusters will have present-day masses similar to galaxy clusters when fully collapsed. We discuss the physical properties of galaxies in protoclusters, including (proto-)brightest cluster galaxies, and the forming red sequence. We highlight the fact that the most massive halos at high redshift are found in protoclusters, making these objects uniquely suited for testing important recent models of galaxy formation. We show that galaxies in protoclusters should be among the first galaxies at high redshift making the transition from a gas cooling regime dominated by cold streams to a regime dominated by hot intracluster gas, which could be tested observationally. We also discuss the possible connections between protoclusters and radio galaxies, quasars, and \(\hbox {Ly}\alpha \) blobs. Because of their early formation, large spatial sizes and high total star-formation rates, protoclusters have also likely played a crucial role during the epoch of reionization, which can be tested with future experiments that will map the neutral and ionized cosmic web. Lastly, we review a number of promising observational projects that are expected to make significant impact in this growing, exciting field.  相似文献   

16.
We study the variations of the properties of groups of galaxies with dynamical masses of 1013 M ⊙<M 200<1014 M ⊙, represented by two samples: one has redshifts of z < 0.027 and is located in the vicinity of the Coma cluster, the other has z > 0.027, and is located in the regions of the following superclusters of galaxies: Hercules, Leo, Bootes, Ursa Major, and Corona Borealis. Using the archived data of the SDSS and 2MASX catalogs, we determined the concentration of galaxies in the systems by measuring it as the inner density of the group within the distance of the fifth closest galaxy from the center brighter than M K = ?23. m 3. We also measured the magnitude gap between the first and the fourth brightest galaxies ΔM 14 located within one half of the selected radius R 200, the fraction of early-type galaxies, and the ratio of bright dwarf galaxies (Mr = [?18. m 5,?16. m 5]) to giant galaxies (M r < ?18. m 5) (DGR) within the radius R 200. The main aim of the investigation is to find among these characteristics the ones that reflect the evolution of groups of galaxies.We determined that the ratio of bright dwarf galaxies to early-type giant galaxies on the red sequence depends only on the x-ray luminosity: the DGR increases with luminosity. The fraction of early-type galaxies in the considered systems is equal, on average, to 0.65 ± 0.01, and varies significantly for galaxies with σ200 < 300 kms?1. Based on the luminosity of the brightest galaxy, the magnitude gap between the first and the fourth brightest galaxies in the groups, and on model computations of these parameters, we selected four fossil group candidates: AWM4, NGC0533, NGC0741, and NGC6098 (where the brightest galaxy is a double).We observe no increase in the number of faint galaxies (the α parameter of the Schechter function is less than 1) in our composite luminosity function (LF) for galaxy systems with z < 0.027 in the M K = [?26m,?21. m 5] range, whereas earlier we obtained α > 1 for the LF of the Hercules and Leo superclusters of galaxies.  相似文献   

17.
Absorption by gas and dust in circumstellar Hii regions within primeval galaxies could seriously depress the far-ultraviolet continuum radiation emitted by primeval galaxies. This effect might account for the failure of Partridge (1974) and Davis and Wilkinson (1974) to detect the redshifted radiation from primeval galaxies at optical and near-infrared wavelengths. A primeval galaxy becomes very bright only during the final stages of contraction. Provided that dust can form by the time the primeval galaxy reaches peak luminosity, a significant fraction of the stellar far-ultraviolet radiation is converted into far-infrared. Thus an appropriate spectral region to search for the redshifted integrated background from primeval galaxies lies between 350 , where the 2.7 K microwave background radiation becomes important, and 150 , where other extragalactic discrete sources, such as nearby galactic nuclei, may contribute. The expected IR flux is calculated with Kaufman's (1975) model for the star formation rate in the contracting galaxy. Letz p be the redshift andT g the grain temperature when the primeval galaxy becomes very bright. Unlessz p10 orT g is fairly high, the intensity of the far-infrared radiation from primeval galaxies would be dominated by the high frequency tail of the 2.7 K microwave background. On the other hand, if dust is unimportant, we determine the spectral energy distribution of a primeval galaxy emitted in the range 912 Å to 2050 Å; we find that the luminosities are not very sensitive to the dependence of effective temperatures on metal abundance.  相似文献   

18.
A series of phenomenological similarities between activity phenomena in the microscopic world and in the world of galaxies is examined. Proceeding from the high metallicity of quasars, it is shown that the relative amount of light elements, primarily hydrogen, increases during the evolution of the universe. Evidence supporting an analogous enrichment of the world of galaxies by dwarf galaxies is presented. A variant is proposed in which cD galaxies are the generators of the clusters of galaxies in which they are located, while all the galaxies of a given cluster are products of the activity of a central supergiant galaxy. An analogous mechanism is apparently responsible for the formation of systems of globular clusters. A physical connection between activity phenomena and cosmic expansion is sought.  相似文献   

19.
A list of 750 objects has been compiled using the Astrophysical CATalogs Support System (CATS) database, by cross-identifying sources in the IRAS catalogues and the catalogue of the Texas survey at 365 MHz. We have carried out a search for optical counterparts of those objects, where the difference in positions between the two catalogues and the APM is less than 3. One of these sources, IRAS F02044+0957, was observed with the RATAN-600 radio telescope at four frequencies in April 1999. Optical spectroscopy of the components of the system was made with the 2.1-m telescope of the Guillermo Haro Observatory. The radio and optical spectra, the NVSS radio map and the optical and infrared images allow us to conclude that the steep spectrum (=–0-94 ± 0-02) radio source IRAS F02044+0957 is a pair of interacting galaxies, a LINER and a HII galaxy, at z=0.093.Published in Astrofizika, Vol. 48, No. 1, pp. 113–124 (February 2005).  相似文献   

20.
The “Big Trio” program is conducted at the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) aiming to investigate a sample of sources with steep and ultra-steep spectra fromthe RCcatalog obtained on the basis of observational data of the “Cold” survey. The population of distant FRII type radio galaxies with steep spectra is of particular interest, since new data indicate the presence of black holes with masses of more than 109 M ⊙ which already formed in these giant stellar systems in the first billion years of life of the Universe, as well as their connection with emerging clusters. There are three sources with z sp > 3 in the sample. According to the observations of the 6-m SAO RAS telescope, the archival data of Subaru and Spitzer, an increased density of objects and several Lyα-emitters have been detected near one of the most powerful radio galaxies, RCJ0311+0507 (4C+04.11) with z = 4.51, which is the second most distant of the known FRII-type galaxies. Another object— RCJ1740+0502 with z = 3.57, is a possible dual AGN candidate. The third source, RCJ0105+0501, is an FRII-type galaxy (z = 3.138) with a host galaxy of a complex structure, possibly generated by interaction in a close pair of galaxies. These radio sources have high radio luminosity (L 500MHz ≈ 1028–1029WHz?1), which requires the presence of a giant black hole with a sufficient accretion rate, and also with a rapid rotation, which in turn can be provided by major merging.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号