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1.
We present deep near-infrared images, taken with the Subaru Telescope, of the region around the   z =1.08  radio source 3C 356 which show it to be associated with a poor cluster of galaxies. We discuss evidence that this cluster comprises two subclusters traced by the two galaxies previously proposed as identifications for 3C 356, which both seem to harbour active galactic nuclei, and which have the disturbed morphologies expected if they underwent an interpenetrating collision at the time the radio jets were triggered. We explain the high luminosity and temperature of the diffuse X-ray emission from this system as the result of shock heating of intracluster gas by the merger of two galaxy groups. Taken together with the results on other well-studied powerful radio sources, we suggest that the key ingredient for triggering a powerful radio source, at least at epochs corresponding to   z ∼1  , is a galaxy–galaxy interaction which can be orchestrated by the merger of their parent subclusters. This provides an explanation for the rapid decline in the number density of powerful radio sources since   z ∼1  . We argue that attempts to use distant radio-selected clusters to trace the formation and evolution of the general cluster population must address ways in which X-ray properties can be influenced by the radio source, both directly, by mechanisms such as inverse Compton scattering, and indirectly, by the fact that the radio source may be preferentially triggered at a specific time during the formation of the cluster.  相似文献   

2.
In this paper we present a detailed study of the radio galaxy J1324–3138, located at a projected distance of 2 arcmin from the centre of the Abell cluster of galaxies A3556, belonging to the core of the Shapley Concentration, at an average redshift of z  = 0.05. We have observed J1324–3138 over a wide range of frequencies: at 327 MHz (VLA), 843 MHz (MOST), and at 1376, 2382, 4790 and 8640 MHz (ATCA).   Our analysis suggests that J1324–3138 is a remnant of a tailed radio galaxy, in which the nuclear engine has switched off and the radio source is now at a late stage of its evolution, confined by the intracluster gas. The radio galaxy is not in pressure equilibrium with the external medium, as is often found for extended radio sources in clusters of galaxies. We favour the hypothesis that the lack of observed polarized radio emission in the source is a result of Faraday rotation by a foreground screen, i.e. the source is seen through a dense cluster gas, characterized by a random magnetic field.   An implication of the head–tail nature of the source is that J1324–3138 is moving away from the core of A3556 and that, possibly, a major merging event between the core of A3556 and the subgroup hosting J1324–3138 has already taken place.  相似文献   

3.
We present neutral hydrogen absorption observations of the luminous infrared merger NGC 6240 using MERLIN with a resolution of 0.2 arcsec. Broad absorption (a few hundred km s−1) has been found against two compact radio sources within the central kpc providing dynamical information about the neutral gas components in front of these sources. A narrow absorption component is also detected superimposed upon this broad absorption and additionally against some of the extended L -band continuum. From these results we deduce that the broad component is a result of absorption by a highly disturbed disc-like structure of neutral gas aligned along the position angle of the two compact radio sources, similar to the model previously proposed by Tacconi et al. at the end of the last century based on spectral CO emission data. The narrow component is likely to arise from absorption by less disturbed neutral gas at much larger scales within the system.
Continuum observations presented here at 1.4 and 5 GHz support the view that NGC 6240 contains a double nucleus resulting from a galactic merger event and show these as two compact radio sources separated by 1.52 arcsec. We have also applied luminosity and morphological considerations to the continuum results to determine the most feasible source of radio emission for this luminous merger galaxy. We conclude that the most likely source of the radio flux found in NGC 6240 is a combination of starburst emission from radio luminous supernova remnants, similar to those found in Arp 220, and emission from a weak AGN probably triggered by a merger event.  相似文献   

4.
We present an investigation into the spatial variation of the rest-frame ultraviolet (UV) and optical line and continuum emission along the radio axis of the z ∼ 2.6 radio galaxy 0828+193, using long-slit spectra from the Keck II and Subaru telescopes. Line brightnesses, line ratios and electron temperatures are examined, and their relationship with the arm-length asymmetry of the radio source is also investigated. We find that on the side of the nucleus with the shortest radio lobe, the gas covering factor is higher, and the ionization parameter is lower. The contrasts in environmental density required to explain the asymmetries in the line brightness and the radio arm-length asymmetries are in fair agreement with each other. These results add further weight to the conclusion of McCarthy, van Breugel & Kapahi – lobe distance asymmetries in powerful radio sources are the result of an asymmetry in the environmental density.
We also note that the brightness of both the UV and optical continuum emission shows a similar spatial asymmetry to that shown by the line emission. While the UV continuum asymmetry can be wholly explained by the expected asymmetry in the nebular continuum, the optical continuum asymmetry cannot. We argue that, at least at optical wavelengths, the starlight and/or the scattered light must also be strongly spatially asymmetric.  相似文献   

5.
Images of neutral hydrogen 21 cm absorption and radio continuum emission at 1.4 GHz from Mrk 273 were made using the Very Long Baseline Array and Very Large Array. These images reveal a gas disk associated with the northern nuclear region with a diameter 0&farcs;5 (370 pc) at an inclination angle of 53 degrees. The radio continuum emission is composed of a diffuse component plus a number of compact sources. This morphology resembles those of nearby, lower luminosity starburst galaxies. These images provide strong support for the hypothesis that the luminosity of the northern source is dominated by an extreme compact starburst. The H i 21 cm absorption shows an east-west gradient in velocity of 450 km s-1 across 0&farcs;3 (220 pc), which implies an enclosed mass of 2x109 M middle dot in circle, comparable to the molecular gas mass. The brightest of the compact sources may indicate radio emission from an active nucleus, but this source contributes only 3.8% to the total flux density of the northern nuclear regions. The H i 21 cm absorption toward the southeast radio nucleus suggests infall at 200 km s-1 on scales 相似文献   

6.
We present X-ray imaging spectroscopy of the extremely luminous infrared galaxy IRAS 09104+4109     obtained with the Chandra X-ray Observatory. With the arcsec resolution of Chandra , an unresolved source at the nucleus is separated from the surrounding cluster emission. A strong iron K line at 6.4 keV on a very hard continuum is detected from the nuclear source, rendering IRAS 09104+4109 the most distant reflection-dominated X-ray source known. Combined with the BeppoSAX detection of the excess hard X-ray emission, it provides further strong support for the presence of a hidden X-ray source of quasar luminosity in this infrared galaxy. Also seen is a faint linear structure to the north, which coincides with the main radio jet. An X-ray deficit in the corresponding region suggests an interaction between the cluster medium and the jet driven by the active nucleus.  相似文献   

7.
Measurements of the velocities of galaxies thought to be associated with the giant radio galaxy NGC 6251 confirm the presence of a poor cluster with a systemic redshift of and a line-of-sight velocity dispersion of z =283(+109,52) km s1. This suggests a cluster atmosphere temperature of T =0.7(+0.6,0.2) keV, which is not enough to confine the radio jet by gas pressure. The core of NGC 6251 shows strong emission lines of [O  iii ] and H +[N  ii ], but there is no evidence for line emission from the jet (detected in optical continuum by Keel).  相似文献   

8.
The low-frequency radio luminosity is believed to be an indicator of jet power, while the optical/ultraviolet (UV) emission is probably from accretion discs in the nuclei of steep-spectrum radio quasars. We present a correlation between the ratio of radio-to-optical luminosities and the continuum spectral index in blue/UV bands, which might indicate that the continuum shape in blue/UV bands is related to the ratio of jet to accretion power. The results may imply that the spectra and structure of accretion discs are probably affected by the interactions between jets and discs.  相似文献   

9.
Multiwavelength imaging and spectroscopy of the z =0.708 radio galaxy 3C 441 and a red aligned optical/infrared component are used to show that the most striking aspect of the radio–optical 'alignment effect' in this object is due to the interaction of the radio jet with a companion galaxy in the same group or cluster. The stellar population of the red aligned continuum component is predominantly old, but with a small post-starburst population superposed, and it is surrounded by a low-surface-brightness halo, possibly a face-on spiral disc. The [O iii ] 500.7/[O ii ] 372.7 emission-line ratio changes dramatically from one side of the component to the other, with the low-ionization material apparently having passed through the bow shock of the radio source and been compressed. A simple model for the interaction is used to explain the velocity shifts in the emission-line gas, and to predict that the ISM of the interacting galaxy is likely to escape once the radio source bow shock has passed through. We also discuss another, much fainter, aligned component, and the subarcsecond-scale alignment of the radio source host galaxy. Finally, we comment on the implications of our explanation of 3C 441 on theories for the alignment effect.  相似文献   

10.
We present the results of Giant Metrewave Radio Telescope (GMRT) observations of the interacting system Arp86 in both neutral atomic hydrogen, H  i , and in radio continuum at 240 606 and 1394 MHz. In addition to H  i emission from the two dominant galaxies, NGC 7752 and NGC 7753, these observations show a complex distribution of H  i tails and bridges due to tidal interactions. The regions of highest column density appear related to the recent sites of intense star formation. H  i column densities  ∼1–1.5 × 1021 cm−2  have been detected in the tidal bridge which is bright in Spitzer image as well. We also detect H  i emission from the galaxy 2MASX J23470758+2926531, which is shown to be a part of this system. We discuss the possibility that this could be a tidal dwarf galaxy. The radio continuum observations show evidence of a non-thermal bridge between NGC 7752 and NGC 7753, and a radio source in the nuclear region of NGC 7753 consistent with it having a low-ionization nuclear emission region nucleus.  相似文献   

11.
We present a Chandra observation of the candidate BL Lac object EXO 0423.4−0840. The X-ray emission from EXO 0423.4−0840 is clearly extended, and is associated with an optical early-type galaxy, MCG-01-12-005, at the centre of cluster ClG 0422-09. We do not detect a point source that can be associated with a BL Lac, but we found a small radio source in the centre of MCG-01-12-005. The cluster gas temperature mapped by the Chandra observation drops continuously from 80 kpc towards the centre, and is locally single phase. We measure a metallicity profile that declines outwards with a value  0.8 Z⊙  in the centre, dropping to  0.35 Z⊙  at larger radius, which we interpret as a superposition of cluster gas and a dense interstellar medium (ISM) in the central galaxy. Although the temperature profile suggests that conduction is not efficient, the ISM and intra-cluster medium seem not to have mixed. The entropy profile declines continuously towards the centre, in agreement with recent results on groups and clusters. The radio source appears to have had some effect in terms of gas heating, as seen in the small-scale (∼10 kpc) entropy core, and the asymmetric hard emission on the same scale.  相似文献   

12.
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   

13.
Investigating the spatial correlation between different emissions in an extended astrophysical source can provide crucial insights into their physical connection, hence it can be the key to understand the nature of the system. The point-to-point analysis of surface brightness is a reliable method to do such an analysis. In this work we present PT-REX, a software to carry out these studies between radio and X-ray emission in extended sources. We discuss how to reliably carry out this analysis and its limitation and we introduce the Monte Carlo point-to-point analysis, which allows to extend this approach to poorly-resolved sources. Finally we present and discuss the application of our tool to study the diffuse radio emission in a galaxy cluster.  相似文献   

14.
We present Chandra X-ray observations of the Hydra A cluster of galaxies, and we report the discovery of structure in the central 80 kpc of the cluster's X-ray-emitting gas. The most remarkable structures are depressions in the X-ray surface brightness, approximately 25-35 kpc in diameter, that are coincident with Hydra A's radio lobes. The depressions are nearly devoid of X-ray-emitting gas, and there is no evidence for shock-heated gas surrounding the radio lobes. We suggest that the gas within the surface brightness depressions was displaced as the radio lobes expanded subsonically, leaving cavities in the hot atmosphere. The gas temperature declines from 4 keV at 70 kpc to 3 keV in the inner 20 kpc of the brightest cluster galaxy (BCG), and the cooling time of the gas is approximately 600 Myr in the inner 10 kpc. These properties are consistent with the presence of an approximately 34 M middle dot in circle yr-1 cooling flow within a 70 kpc radius. Bright X-ray emission is present in the BCG surrounding a recently accreted disk of nebular emission and young stars. The star formation rate is commensurate with the cooling rate of the hot gas within the volume of the disk, although the sink for the material that may be cooling at larger radii remains elusive. A bright, unresolved X-ray source is present in the BCG's nucleus, coincident with the radio core. Its X-ray spectrum is consistent with a power law absorbed by a foreground NH approximately 4x1022 cm-2 column of hydrogen. This column is roughly consistent with the hydrogen column seen in absorption toward the less, similar24 pc diameter VLBA radio source. Apart from the point source, no evidence for excess X-ray absorption above the Galactic column is found.  相似文献   

15.
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16.
We have observed the prototypical wide-angle tail (WAT) radio galaxy 3C 465 with Chandra and XMM–Newton . X-ray emission is detected from the active nucleus and the inner radio jet, as well as a small-scale, cool component of thermal emission, a number of the individual galaxies of the host cluster (Abell 2634), and the hotter thermal emission from the cluster itself. The X-ray detection of the jet allows us to argue that synchrotron emission may be an important mechanism in other well-collimated, fast jets, including those of classical double radio sources. The bases of the radio plumes are not detected in the X-ray, which supports the model in which these plumes are physically different from the twin jets of lower-power radio galaxies. The plumes are in fact spatially coincident with deficits of X-ray emission on large scales, which argues that they contain little thermal material at the cluster temperature, although the minimum pressures throughout the source are lower than the external pressures estimated from the observed thermal emission. Our observations confirm both spatially and spectrally that a component of dense, cool gas with a short cooling time is associated with the central galaxy. However, there is no evidence for the kind of discontinuity in external properties that would be required in many models of the jet–plume transition in WATs. Although the WAT jet–plume transition appears likely to be related to the interface between this central cool component and the hotter intracluster medium, the mechanism for WAT formation remains unclear. We revisit the question of the bending of WAT plumes, and show that the plumes can be bent by plausible bulk motions of the intracluster medium, or by motion of the host galaxy with respect to the cluster, as long as the plumes are light.  相似文献   

17.
We present new Hubble Space Telescope ( HST  ) continuum and spectral line images of the radio galaxy Cygnus A. The images show much complex structure in the central kpc2. Continuum images show the central dust lane in detail, allowing detailed maps of E ( B  −  V ) to be constructed; the dust appears to follow a roughly Galactic extinction law. The emission-line components are resolved in the line images and investigated in detail. A clear 'opening cone' morphology is found, especially in the lines of Hα and [O  i ]. Blue condensations are seen in the south-eastern emission component and surrounding the central region. These are almost certainly due to star formation, which began <1 Gyr ago as deduced from the colour of the regions. More extended blue continuum is also seen and corresponds to the blue polarized component detected by other recent spectropolarimetric observations.  相似文献   

18.
We present the results of radio continuum observations of 25 luminous IRAS galaxies at 3.95 GHz and discuss the correlation between the radio continuum and far-infrared (FIR) emission. We argue that the relationship between the radio and FIR emission is different in different galaxy scale structures. The FIR-radio correlation is much closer in the core region of the galaxy than in its disk region. While the FIR luminosity is independent of the FIR-to-radio ratio, the core radio luminosity of the galaxy decreases as this ratio increases.Translated fromAstrofizika, Vol. 37, No. 3, 1994.  相似文献   

19.
The radio source 18P87, previously thought to be a point source, has been serendipitously found to be resolved into a core‐jet geometry in VLA maps. H I absorption of continuum emission (in data from the Canadian Galactic Plane Survey) appears in gas with radial velocities >+2 km/s but not in brightly emitting gas at lower radial velocity. Examination of further archival observations at radio, infrared and optical wavelengths suggests that the “obvious” interpretation as a radio galaxy requires a rather unusual object of this kind and a highly unusual local line of sight. We argue that 18P87 may be a Galactic object, a local astrophysical jet. If this is correct it could have arisen from outbursts of a microquasar (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

20.
We present a Chandra observation of the powerful radio galaxy 3C 294 showing clear evidence for a surrounding intracluster medium. At a redshift of 1.786 this is the most distant cluster of galaxies yet detected in X-rays. The radio core is detected as a point source, which has a spectrum consistent with a heavily absorbed power law, implying an intrinsic 2–10 keV luminosity of ∼1045 erg s−1. A small excess of emission is associated with the southern radio hotspots. The soft, diffuse emission from the intracluster medium is centred on the radio source. It has an hourglass shape in the north–south direction, extending to radii of at least 100 kpc, well beyond the radio source. The X-ray spectrum of this extended component is fitted by a thermal model with temperature ∼5 keV, or by gas cooling from above 7 keV at rates of ∼ 400–700 M⊙ yr−1. The rest-frame 0.3–10 keV luminosity of the cluster is ∼ 4.5×1044 erg s−1. The existence of such a cluster is consistent with a low-density universe.  相似文献   

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