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1.
We have discovered a radio source (B2114+022) with a unique structure during the course of the JVAS gravitational lens survey. VLA, MERLIN, VLBA and MERLIN+EVN radio maps reveal four compact components, in a configuration unlike that of any known lens system, or, for that matter, any of the ∼15 000 radio sources in the JVAS and CLASS surveys. Three of the components are within 0.3 arcsec of each other while the fourth is separated from the group by 2.4 arcsec. The widest separation pair of components have similar radio structures and spectra. The other pair also have similar properties. This latter pair have spectra which peak at ∼5 GHz. Their surface brightnesses are much lower than expected for synchrotron self-absorbed components.
Ground-based and Hubble Space Telescope optical observations show two galaxies ( z =0.3157 and 0.5883) separated by 1.25 arcsec. The lower redshift galaxy has a post-starburst spectrum and lies close to, but not coincident with, the compact group of three radio components. No optical or infrared emission is detected from any of the radio components down to I =25 and H =23 . We argue that the most likely explanation of the B2114+022 system is that the post-starburst galaxy, assisted by the second galaxy, lenses a distant radio source producing the two wide-separation images. The other two radio components are then associated with the post-starburst galaxy. The combination of the angular sizes of these components, their radio spectra and their location with respect to their host galaxy still remains puzzling.  相似文献   

2.
We present new continuum VLA observations of the nearby Sy 1.5 galaxy NGC 5033, made at 4.9 and 8.4 GHz on 2003 April 8. Combined with VLA archival observations at 1.4- and 4.9-GHz made on 1993 August 7, 1999 August 29 and 1999 October 31, we sample the galaxy radio emission at scales ranging from the nuclear regions (≲100 pc) to the outer regions of the disc (∼40 kpc). The high-resolution VLA images show a core–jet structure for the Sy 1.5 nucleus. While the core has a moderately steep non-thermal radio spectrum ( S ν∝να; α4.91.5≈−0.4), the inner kpc region shows a steeper spectrum (α8.41.5≈−0.9). This latter spectrum is typical of galaxies where energy losses are high, indicating that the escape rate of cosmic ray electrons in NGC 5033 is low. The nucleus contributes little to the total 1.4-GHz radio power of NGC 5033 and, based on the radio to far-infrared (FIR) relation, it appears that the radio and FIR emission from NGC 5033 are dominated by a starburst that during the last 10 Myr produced stars at a rate of 2.8 M⊙ yr−1 yielding a supernova (type Ib/c and II) rate of 0.045 yr−1. This supernova rate corresponds to about 1 SN event every 22 yr. Finally, from our deep 8.4-GHz VLA-D image, we suggest the existence of a radio spur in NGC 5033, which could have been due to a hot superbubble formed as a consequence of sequential supernova explosions occurring during the lifetime of a giant molecular cloud.  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.
S5 2007+777是一个典型的低峰值频率的蝎虎天体,该天体具有kpc尺度的X射线喷流,文献中利用模型估算的方法,得出X射线波段的多普勒因子达到13.0,从而喷流尺度可以达到Mpc量级.在此,搜集了有关S5 2007+777的欧洲甚长基线射电干涉网(European VLBI Network, EVN)高分辨率档案数据、美国甚长基线射电干涉网(Very Long Baseline Array, VLBA) 15 GHz观测数据等,研究了喷流的射电结构、亮温度、自行等方面的性质,发现该源的甚长基线干涉测量(Very Long Baseline Interferometry,VLBI)不同波段的喷流方向一致,但与文献中给出的kpc尺度的X射线喷流和甚大阵(Very Large Array, VLA)射电喷流方向存在一定的差异,说明该源的喷流辐射存在多普勒增亮效应.由VLBI观测得到的亮温度,估算了该源的射电多普勒因子的平均值及中值均为5.0,此值小于文献中X射线波段的多普勒因子,但与文献中利用其他方法得到的射电波段多普勒因子是一致的;另外,对多历元观测数据的拟合发现此源相同波段的各个成分在长历元上没有明显的自行,短历元上的自行甚至是视超光速运动.这可能是由低表面亮度成分中心位置的转移造成的.这同时也验证了之前估算的射电多普勒因子不是很大,小于X射线波段多普勒因子的结论.利用所得到的射电多普勒因子,发现该源具有较大尺度的本征射电喷流,可达到0.5 Mpc,由于这里使用的是均值,因此说明该源也有可能具有接近巨射电星系尺度的喷流.  相似文献   

5.
A radio source with a spectral index of −2.2 between 0.08 and 1.425 GHz has been observed at the Very Large Array (VLA) at 1.425 GHz with resolution ∼ 3 arcsec. The projected linear length of the source is 56 kpc with an average projected distance of 42 kpc from the centroid of the rich southern cluster Abell 4038, assuming the source is in the cluster. The physical parameters of the source include a high minimum-energy field ( B me) of 38 μG, which is unusual for a source of low surface brightness and relaxed appearance, but is explained by its unusually steep spectrum. Although its radio morphology has some characteristics of a narrow-angle-tail source (NAT), the absence of an identified host galaxy ( m R ≥ 23.0) makes it unlikely that the source is a working radio galaxy. The relic is probably the remains of an FR II radio galaxy that was once energized by a particular bright cluster elliptical now 18 kpc to its east. The density of the intracluster gas has been sufficient to confine the source and preserve its morphology, permitting the source to age and its spectrum to steepen through synchrotron and inverse Compton energy losses.  相似文献   

6.
We present 8.4-GHz VLA A-configuration observations of 87 sources from the mid-infrared-selected AGN sample of Rush et al. These 0.25-arcsec-resolution observations allow elongated radio structures tens of pc in size to be resolved, and enable radio components smaller than 3.5 arcsec to be isolated from diffuse galactic disc emission. When combined with previous data, matched radio observations covering 90 per cent of the sample have been collected, and these represent the largest subarcsecond–resolution radio imaging survey of a homogeneously selected sample of Seyfert galaxies to date.
We use our observations to identify five radio-loud AGN in the sample. The nature of the radio emission from Seyfert nuclei will be discussed in subsequent papers.  相似文献   

7.
We present optical identifications for a sample of 20 previously unknown X-ray/radio sources that are present both in the source catalogue of ROSAT PSPC pointed observations ( ROSAT SRC) and in the NRAO VLA Sky Survey (NVSS). The optical spectroscopy was carried out with the 2.1-m telescope at San Pedro Martir (Mexico) during 1995 April and September. We have identified 15 active galactic nuclei [including 12 broad-emission-line (FWHM >1000 km s−1) objects, one bona fide BL Lac, one BL Lac candidate and one narrow-line (FWHM < 1000 km s−1) radio galaxy] and five radio galaxies. We derive the X-ray fluxes and luminosities by analysing the PSPC exposures, and show the radio morphology from the NVSS maps.  We find that the correlation between the monochromatic X-ray luminosity at 2 keV and the core radio luminosity at 5 GHz for the radio galaxies in our sample follows that found for the 3CR radio galaxies, suggesting a possible nuclear origin for the X-ray emission in these sources. This correlation is weaker in the case of broad-line objects, indicating the presence of another (unbeamed) mechanism for the X-ray emission only weakly related to the radio emission.  相似文献   

8.
We have analysed VSOP and global VLBI data at 5 GHz and VLBA + Effelsberg data at 15 GHz for 2021+614. By identifying the core as being between two bright hotspots, we show that 2021+614 is a compact symmetric object of size 40 pc. From comparison with earlier observations we deduce an apparent age of 375 yr for 2021+614. This provides additional support for the contention that compact symmetric radio objects associated with galaxies are in fact young radio sources and the possible precursors of the classical FR I or FR II radio galaxies.  相似文献   

9.
We present radio observations at frequencies ranging from 240 to 8460 MHz of the radio galaxy 4C 29.30 (J0840+2949) using the Giant Metrewave Radio Telescope (GMRT), the Very Large Array (VLA) and the Effelsberg telescope. We report the existence of weak extended emission with an angular size of ∼520 arcsec (639 kpc) within which a compact edge-brightened double-lobed source with a size of 29 arcsec (36 kpc) is embedded. We determine the spectrum of the inner double from 240 to 8460 MHz and show that it has a single power-law spectrum with a spectral index of ∼0.8. Its spectral age is estimated to be ≲33 Myr. The extended diffuse emission has a steep spectrum with a spectral index of ∼1.3 and a break frequency ≲240 MHz. The spectral age is ≳200 Myr, suggesting that the extended diffuse emission is due to an earlier cycle of activity. We re-analyse archival X-ray data from Chandra and suggest that the X-ray emission from the hotspots consists of a mixture of non-thermal and thermal components, the latter being possibly due to gas which is shock heated by the jets from the host galaxy.  相似文献   

10.
We present observations of CLASS B2108+213, the widest separation gravitational lens system discovered by the Cosmic Lens All-Sky Survey. Radio imaging using the VLA at 8.46 GHz and MERLIN at 5 GHz shows two compact components separated by 4.56 arcsec with a faint third component in between which we believe is emission from a lensing galaxy. 5-GHz VLBA observations reveal milliarcsecond-scale structure in the two lensed images that is consistent with gravitational lensing. Optical emission from the two lensed images and two lensing galaxies within the Einstein radius is detected in Hubble Space Telescope imaging. Furthermore, an optical gravitational arc, associated with the strongest lensed component, has been detected. Surrounding the system is a number of faint galaxies which may help explain the wide image separation. A plausible mass distribution model for CLASS B2108+213 is also presented.  相似文献   

11.
Three supernova remnants (SNR) have been mapped in the galaxy M33 with the Very Large Array* (VLA) at 20 cm. The angular resolution is ∼1.3 arcsec or ∼4 pc at a distance of 600 kpc and the rms noise is ∼0.04 mJy /beam. One of the radio sources shows evidence for a shell structure with a size of ∼15 pc, confirming the SNR nature of this source. The second object is extended and may well be a thick-shell SNR of size ∼12 pc. The third object is a small, presumably young SNR with a size of ∼4 pc.  相似文献   

12.
We present Chandra data from a 31.7-ks observation of the Centaurus cluster, using the ACIS-S detector. Images of the X-ray emission show a plume-like feature at the centre of the cluster, of extent 60 arcsec (20 kpc in projection). The feature has the same metallicity as gas at a similar radius, but is cooler. Using adaptive binning, we generate temperature, abundance and absorption maps of the cluster core. The radial abundance profile shows that the previously known, steep abundance gradient peaks with a metallicity of  1.3–1.8 Z⊙  at a radius of about 45 arcsec (15 kpc), before falling back to 0.4 Z⊙ at the centre of the cluster. A radial temperature profile shows that the temperature decreases inwards. We determine the spatial distributions of each of two temperature components, where applicable. The radiative cooling time of the cooler component within the inner 10 arcsec (3 kpc) is less than  2×107 yr  . X-ray holes in the image coincident with the radio lobes are seen, as well as two outer sharp temperature drops, or cold fronts. The origin of the plume is unclear. The existence of the strong abundance gradient is a strong constraint on extensive convection or gas motion driven by a central radio source.  相似文献   

13.
Using a deep Chandra observation of the Perseus cluster of galaxies, we find a high-abundance shell 250 arcsec (93 kpc) from the central nucleus. This ridge lies at the edge of the Perseus radio mini-halo. In addition we identify two Hα filaments pointing towards this shell. We hypothesize that this ridge is the edge of a fossil radio bubble, formed by entrained enriched material lifted from the core of the cluster. There is a temperature jump outside the shell, but the pressure is continuous indicating a cold front. A non-thermal component is mapped over the core of the cluster with a morphology similar to the mini-halo. Its total luminosity is  4.8 × 1043 erg s−1  , extending in radius to ∼75 kpc. Assuming the non-thermal emission to be the result of inverse Compton scattering of the cosmic microwave background and infrared emission from NGC 1275, we map the magnetic field over the core of the cluster.  相似文献   

14.
We present new 1.6-GHz (18-cm) MERLIN maps of 15 Seyfert galaxies, with angular resolutions typically 0.1 to 0.3 arcsec. These and previous observations are used to investigate the properties of 19 of the 24 CfA Seyfert galaxies brighter than 2 mJy at 8.4 GHz. This is the first time a significant fraction of the CfA sample has been mapped at this frequency with subarcsecond resolution, and our observations provide the highest resolution radio maps available for several sources. We use our observations to measure the two-point spectral indices of compact radio components, and we investigate the correlation between infrared and radio emission shown by Seyfert galaxies.
Our results can be summarized as follows. Resolved structures as small as 20 pc are found in three previously unresolved radio sources, and only four sources show single, unresolved radio components. The mean 1.6 to 8.4 GHz spectral index of 31 radio components is         , and approximately 25 per cent of the components have a spectral index flatter than     . The spectral index distributions of type 1 and type 2 Seyferts are statistically indistinguishable. The cores of multiple-component sources tend to have flatter radio spectra than secondary components. The low-resolution infrared ( IRAS ) emission from Seyfert galaxies is usually dominated by kiloparsec-scale, extranuclear emission regions.  相似文献   

15.
The radio properties of 11 obscured 'radio-intermediate' quasars at redshifts   z ≳ 2  have been investigated using the European Very-Long-Baseline-Interferometry Network (EVN) at 1.66 GHz. A sensitivity of  ∼25 μJy per 17 × 14 mas2 beam  was achieved, and in seven out of 11 sources unresolved radio emission was securely detected. The detected radio emission of each source accounts for ∼30–100 per cent of the total source flux density. The physical extent of this emission is ≲150 pc, and the derived properties indicate that this emission originates from an active galactic nucleus (AGN). The missing flux density is difficult to account for by star formation alone, so radio components associated with jets of physical size ≳150 pc and ≲40 kpc are likely to be present in most of the sources. Amongst the observed sample steep, flat, gigahertz-peaked and compact-steep spectrum sources are all present. Hence, as well as extended and compact jets, examples of beamed jets are also inferred, suggesting that in these sources, the obscuration must be due to dust in the host galaxy, rather than the torus invoked by the unified schemes. Comparing the total to core (≲150 pc) radio luminosities of this sample with different types of AGN suggests that this sample of   z ≳ 2  radio-intermediate obscured quasars shows radio properties that are more similar to those of the high-radio-luminosity end of the low-redshift radio-quiet quasar population than those of Fanaroff–Riley type I (FR I) radio galaxies. This conclusion may reflect intrinsic differences, but could be strongly influenced by the increasing effect of inverse-Compton cooling of extended radio jets at high redshift.  相似文献   

16.
We present Chandra , Very Large Array (VLA) and Very Long Baseline Array (VLBA) observations of the nucleus of NGC 4696, a giant elliptical in the Centaurus cluster of galaxies. Like M87 in the Virgo cluster, PKS 1246−410 in the Centaurus cluster is a nearby example of a radio galaxy in a dense cluster environment. In analysing the new X-ray data, we have found a compact X-ray feature coincident with the optical and radio core. While nuclear emission from the X-ray source is expected, its luminosity is low,  <1040 erg s−1  . We estimate the Bondi accretion radius to be 30 pc and the accretion rate to be  0.01 M⊙ yr−1  , which under the canonical radiative efficiency of 10 per cent would overproduce by 3.5 orders of magnitude the radiative luminosity. Much of this energy can be directed into the kinetic energy of the jet, which over time inflates the observed cavities seen in the thermal gas. The VLBA observations reveal a weak nucleus and a broad, one-sided jet extending over 25 pc in position angle −150°. This jet is deflected on the kiloparsec-scale to a more east–west orientation (position angle of −80°).  相似文献   

17.
We present Very Long Baseline Array (VLBA) observations of the nucleus of NGC 1275, the central, dominant galaxy in the Perseus cluster of galaxies. These are the first observations to resolve the linearly polarized emission from 3C 84, and from them we determine a Faraday rotation measure (RM) ranging from 6500 to 7500 rad m−2 across the tip of the bright southern jet component. At 22 GHz some polarization is also detected from the central pc of 3C 84, indicating the presence of even more extreme RMs that depolarize the core at lower frequencies. The nature of the Faraday screen is most consistent with being produced by magnetic fields associated with the optical filaments of ionized gas in the Perseus cluster.  相似文献   

18.
We present and discuss observations of the radio galaxy 0755+379 made with the VLA at 1.4 and 5.0 GHz and with MERLIN at 1.7 GHz. These data allow us to image the radio jets over two orders of magnitude in linear size and to investigate the hypothesis that jets in low-luminosity radio galaxies start with velocities close to c and then slow down to subrelativistic speeds. We apply a model for an adiabatically expanding relativistic jet to the observed surface brightness and derive velocity profiles along the jet for various assumed starting conditions. We show that these profiles are consistent with the observed jet/counter-jet brightness ratios provided that the angle to the line of sight θ ≃27°. The inferred velocity at a distance of 0.5 kpc from the nucleus is ≃0.9 c . Finally, we show that the predicted velocity at 10 kpc from the nucleus is consistent with that obtained independently from energy-balance arguments.  相似文献   

19.
We present multifrequency observations of a sample of 15 radio-emitting broad absorption-line quasars (BAL QSOs), covering a spectral range between 74 MHz and 43 GHz. They mostly display convex radio spectra which typically peak at about 1–5 GHz (in the observer's rest frame), flatten at MHz frequencies, probably due to synchrotron self-absorption, and become steeper at high frequencies, i.e. ν≳ 20 GHz. Very Large Array (VLA) 22-GHz maps (HPBW ∼80 mas) show unresolved or very compact sources, with linear projected sizes of ≤1 kpc. About two-thirds of the sample looks unpolarized or weakly polarized at 8.4 GHz, frequency in which reasonable upper limits could be obtained for polarized intensity. Statistical comparisons have been made between the spectral index distributions of samples of BAL and non-BAL QSOs, both in the observed and in the rest frame, finding steeper spectra among non-BAL QSOs. However, constraining this comparison to compact sources results in no significant differences between both distributions. This comparison is consistent with BAL QSOs not being oriented along a particular line of sight. In addition, our analysis of the spectral shape, variability and polarization properties shows that radio BAL QSOs share several properties common to young radio sources like compact steep spectrum or gigahertz peaked spectrum sources.  相似文献   

20.
We present MERLIN and VLA observations at 1.4 and 5 GHz of the diffuse radio emission in the centre of M82. We detect a large expanding shell of ionized gas surrounding the brightest supernova remnant 41.95+57.5 with a diameter of ∼100 pc and an expansion velocity of ∼100 km s−1. We observe a 50-pc-scale 'blow-out' from this region, in the form of a 'cone' of missing 5-GHz continuum emission, which appears to be an excellent example of a galactic chimney.
On larger radio scales, we observe four chimney structures extending out to the north ∼100–200 pc along the minor axis. One of these features is almost certainly related to the 50-pc-scale blow-out from 41.95+57.5, although this is not the most prominent feature. The other features have also been traced to expulsion of material from the very centre by using an 'unsharp masked' image from 5-GHz VLA B-array observations, with the supernova remnant removed.
We interpret these chimney features as the base of the superwind, which implies that the ejection of material into the halo does not occur smoothly over the starburst region. Instead, very localized venting of hot gas is clearly in evidence.  相似文献   

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