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1.
Our Chandra observation of the FR I radio galaxy 3C 66B has resulted in the first detection of an X-ray counterpart to the previously known radio, infrared and optical jet. The X-ray jet is detected up to 7 arcsec from the core and has a steep X-ray spectrum, α ≈1.3±0.1 . The overall X-ray flux density and spectrum of the jet are consistent with a synchrotron origin for the X-ray emission. However, the inner knot in the jet has a higher ratio of X-ray to radio emission than the others. This suggests that either two distinct emission processes are present or differences in the acceleration mechanism are required; there may be a contribution to the emission from the inner knot from an inverse Compton process or it may be the site of an early strong shock in the jet. The peak of the brightest radio and X-ray knot is significantly closer to the nucleus in the X-ray than in the radio, which may suggest that the knots are privileged sites for high-energy particle acceleration. 3C 66B's jet is similar both in overall spectral shape and in structural detail to those in more nearby sources such as M87 and Centaurus A.  相似文献   

2.
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   

3.
We report on new optical, infrared and radio observations of the Seyfert galaxy Markarian 315. We confirm the detection at all wavelengths of a secondary peak of emission, which lies ≈ 2 arcsec east of the Seyfert nucleus. Moreover, we detect a chain-like structure which surrounds the active nucleus, with peculiar behaviour westward of the nucleus. We consider different interpretations for the origin of the secondary peak emission.  相似文献   

4.
We present the wide-field imaging and polarimetry at  ν= 20 GHz  of seven most extended, bright  ( S total≥ 0.50 Jy)  , high-frequency selected radio sources in the southern sky with declinations  δ < −30°  . Accompanying the data are brief reviews of the literature for each source. The results presented here aid in the statistical completeness of the Australia Telescope 20-GHz Survey: the Bright Source Sample. The data are of crucial interest for future cosmic microwave background missions as a collection of information about candidate calibrator sources. We were able to obtain data for seven of the nine sources identified by our selection criteria. We report that Pictor A is thus far the best extragalactic calibrator candidate for the Low Frequency Instrument of the Planck European Space Agency mission due to its high level of integrated polarized flux density  (∼0.50 ± 0.06 Jy)  on a scale of 10 arcmin. Six out of the seven sources have a clearly detected compact radio core in our images, with either a null detection or less than 2 per cent detection of polarized emission from the nuclei. Most sources with detected jets have magnetic field alignments running in a longitudinal configuration, however, PKS 1333−33 exhibits transverse fields and an orthogonal change in field geometry from nucleus to jets.  相似文献   

5.
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   

6.
We present 0.15-arcsec (25-pc) resolution MERLIN observations of neutral hydrogen absorption detected towards the nuclear region of the type 2 Seyfert galaxy NGC 5929. Absorption is detected only towards the north-eastern radio component with a column density of (6.5 ± 0.6) × 1021 cm−2. Based on comparison with an HST WFPC2 continuum image, we propose that the absorption is caused by a 1.5-arcsec structure of neutral gas and dust offset 0.3 arcsec south-east of the nucleus and running NE–SW. A separate cloud of dust is apparent 1.5 arcsec to the south-west of the nucleus in the HST image. A comparison of the centroid velocity (2358 ± 5 km s−1) and full width at half-maximum (43 ± 6 km s−1) of the absorbing gas with previous [O  III ] observations suggests that both the neutral and ionized gas are undergoing galactic rotation towards the observer in the north-east and away from the observer in the south-west. The main structure is consistent with an inclined ring of gas and dust encircling the active galactic nucleus (AGN); alternatively it may be a bar or inner spiral arm. We do not detect neutral hydrogen absorption or dust obscuration against the radio nucleus (column density < 3.1 × 1021 cm−2) expected by a torus of neutral gas and dust in unified models of AGNs for a type 2 Seyfert galaxy.  相似文献   

7.
We use the results from a constrained, cosmological magnetohydrodynamic simulation of the Local Universe to predict the radio halo and the γ-ray flux from the Coma cluster and compare it to current observations. The simulated magnetic field within the Coma cluster is the result of turbulent amplification of the magnetic field during the build-up of the cluster. The magnetic seed field originates from starburst driven, galactic outflows. The synchrotron emission is calculated assuming a hadronic model. We follow four approaches with different distributions for the cosmic ray proton population within galaxy clusters. The radial profile of the radio halo can only be reproduced with a radially increasing energy fraction within the cosmic ray proton population, reaching >100 per cent of the thermal-energy content at ≈1 Mpc, for example the edge of the radio-emitting region. Additionally, the spectral steepening of the observed radio halo in Coma cannot be reproduced, even when accounting for the negative flux from the thermal Sunyaev–Zeldovich effect at high frequencies. Therefore, the hadronic models are disfavoured from the present analysis. The emission of γ-rays expected from our simulated Coma is still below the current observational limits (by a factor of ∼6) but would be detectable by FERMI observations in the near future.  相似文献   

8.
We report the first detection of an inverse Compton X-ray emission, spatially correlated with a very steep spectrum radio source (VSSRS), 0038-096, without any detected optical counterpart, in cluster Abell 85. The ROSAT PSPC data and its multiscale wavelet analysis reveal a large-scale (linear diameter of the order of 500 h −150 kpc), diffuse X-ray component, in addition to the thermal bremsstrahlung, overlapping an equally large-scale VSSRS. The primeval 3 K background photons, scattering off the relativistic electrons, can produce the X-rays at the detected level. The inverse Compton flux is estimated to be (6.5 ± 0.5) × 10−13 erg s−1 cm−2 in the 0.5–2.4 keV X-ray band. A new 327-MHz radio map is presented for the cluster field. The synchrotron emission flux is estimated to be (6.6 ± 0.90) × 10−14 erg s−1 cm−2 in the 10–100 MHz radio band. The positive detection of both radio and X-ray emission from a common ensemble of relativistic electrons leads to an estimate of (0.95 ± 0.10) × 10−6 G for the cluster-scale magnetic field strength. The estimated field is free of the 'equipartition' conjecture, the distance, and the emission volume. Further, the radiative fluxes and the estimated magnetic field imply the presence of 'relic' (radiative lifetime ≳ 109 yr) relativistic electrons with Lorentz factors γ ≈ 700–1700; this would be a significant source of radio emission in the hitherto unexplored frequency range ν ≈ 2–10 MHz.  相似文献   

9.
Radio jet and core data for a complete sample of 98 Fanaroff–Riley type II sources with   z < 1  are analysed with a Markov Chain Monte Carlo model fitting method to obtain constraints on bulk-flow speeds in the beam. The Bayesian parameter-inference method is described and demonstrated to be capable of providing meaningful constraints on the Lorentz factor at both kpc and parsec scales. For both jets and cores, we show that models in which some intrinsic dispersion is present in the features' intrinsic prominence, bulk-flow speeds or both provide the best fit to the data. The constraints on the Lorentz factor on parsec scales are found to be consistent with the expected values given very long baseline interferometry observations and other evidence, with     . On kpc scales, the Lorentz factor is found to be ≈1.18–1.49, in agreement with the results of previous analyses of radio jet data. These values are clearly not consistent with the  γ≈ 10  speeds required by beamed inverse-Compton models of X-ray emission from quasar jets; our results therefore support models that require velocity structure in powerful jets.  相似文献   

10.
We investigate the brightest regions of the kpc-scale jet in the powerful radio galaxy 3C 346, using new optical Hubble Space Telescope ( HST ) ACS/F606W polarimetry together with Chandra X-ray data and 14.9 and 22.5 GHz Very Large Array (VLA) radio polarimetry. The jet shows a close correspondence between optical and radio morphology, while the X-ray emission shows a  0.80 ± 0.17 kpc  offset from the optical and radio peak positions. Optical and radio polarimetry show the same apparent magnetic field position angle and fractional polarization at the brightest knot, where the jet undergoes a large kink of almost 70° in the optical and radio images. The apparent field direction here is well aligned with the new jet direction, as predicted by earlier work that suggested the kink was the result of an oblique shock. We have explored models of the polarization from oblique shocks to understand the geometry of the 3C 346 jet, and find that the upstream flow is likely to be highly relativistic  (βu= 0.91+0.05−0.07)  , where the plane of the shock front is inclined at an angle of  η= 51°± 11°  to the upstream flow which is at an angle  θ= 14+8−7  deg to our line of sight. The actual deflection angle of the jet in this case is only 22°.  相似文献   

11.
We present detailed observations of MRC 0116+111, revealing a luminous, miniradio halo of ∼240-kpc diameter located at the centre of a cluster of galaxies at redshift   z = 0.131  . Our optical and multiwavelength Giant Metrewave Radio Telescope and Very Large Array radio observations reveal a highly unusual radio source: showing a pair of giant (∼100-kpc diameter) bubble-like diffuse structures, that are about three times larger than the analogous extended radio emission observed in M87 – the dominant central radio galaxy in the Virgo cluster. However, in MRC 0116+111 we do not detect any ongoing active galactic nucleus (AGN) activity, such as a compact core or active radio jets feeding the plasma bubbles. The radio emitting relativistic particles and magnetic fields were probably seeded in the past by a pair of radio jets originating in the AGN of the central cD galaxy. The extremely steep high-frequency radio spectrum of the north-western bubble, located ∼100 kpc from cluster centre, indicates radiation losses, possibly because having detached, it is rising buoyantly and moving away into the putative hot intracluster medium. The other bubble, closer to the cluster centre, shows signs of ongoing particle re-acceleration. We estimate that the radio jets which inflated these two bubbles might have also fed enough energy into the intracluster medium to create an enormous system of cavities and shock fronts, and to drive a massive outflow from the AGN, which could counter-balance and even quench a cooling flow. Therefore, this source presents an excellent opportunity to understand the energetics and the dynamical evolution of radio jet inflated plasma bubbles in the hot cluster atmosphere.  相似文献   

12.
We studied the radio source associated with the ultraluminous X-ray source in NGC 5408  ( L X≈ 1040 erg s−1)  . The radio spectrum is steep (index  ≈−1  ), consistent with optically thin synchrotron emission, not with flat-spectrum core emission. Its flux density (≈0.28 mJy at 4.8 GHz, at a distance of 4.8 Mpc) was the same in the March 2000 and December 2004 observations, suggesting steady emission rather than a transient outburst. However, it is orders of magnitude higher than expected from steady jets in stellar-mass microquasar. Based on its radio flux and spectral index, we suggest that the radio source is either an unusually bright supernova remnant, or, more likely, a radio lobe powered by a jet from the black hole (BH). Moreover, there is speculative evidence that the source is marginally resolved with a radius ∼30 pc. A faint H  ii region of similar size appears to coincide with the radio and X-ray sources, but its ionization mechanism remains unclear. Using a self-similar solution for the expansion of a jet-powered electron–positron plasma bubble, in the minimum-energy approximation, we show that the observed flux and (speculative) size are consistent with an average jet power  ≈ 7 × 1038 erg s−1∼ 0.1 L X∼ 0.1 L Edd  , an age ≈105 yr, a current velocity of expansion ≈80 km s−1. We briefly discuss the importance of this source as a key to understand the balance between luminosity and jet power in accreting BHs.  相似文献   

13.
We announce the discovery of an extended emission-line region associated with a high-redshift type-2 quasi-stellar object (QSO). The halo, which was discovered in our new wide-field narrow-band survey, resides at   z = 2.85  in the Spitzer First Look Survey region and is extended over ∼80 kpc. Deep very long baseline interferometry (VLBI) observations imply that approximately 50 per cent of the radio emission is extended on scales >200 pc. The inferred active galactic nuclei (AGN) luminosity is sufficient to ionize the extended halo, and the optical emission is consistent with being triggered coevally with the radio source. The Lyα halo is as luminous as those found around high-redshift radio galaxies; however, the active nucleus is several orders of magnitude less luminous at radio wavelengths than those Fanarof–Riley type II (FRIIs) more commonly associated with extended emission-line regions. AMS05 appears to be a high-redshift analogue to the radio-quiet quasar E1821+643 which is core dominated, but which also exhibits extended Fanarof–Riley type I (FRI)-like structure and contains an optically powerful AGN. We also find evidence for more quiescent kinematics in the Lyα emission line in the outer regions of the halo, reminiscent of the haloes around the more powerful FRIIs. The optical to mid-infrared spectral energy distribution is well described by a combination of an obscured QSO  ( L bol∼ 3.4 ± 0.2 × 1013 L⊙)  and a 1.4 Gyr old simple stellar population with mass  ∼3.9 ± 0.3 × 1011 M⊙  .  相似文献   

14.
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   

15.
We have used a deep Chandra observation of the central regions of the twin-jet Fanaroff–Riley class I (FRI) radio galaxy 3C 31 to resolve the thermal X-ray emission in the central few kpc of the host galaxy, NGC 383, where the jets are thought to be decelerating rapidly. This allows us to make high-precision measurements of the density, temperature and pressure distributions in this region, and to show that the X-ray emitting gas in the centre of the galaxy has a cooling time of only  5×107 yr  . In a companion paper, these measurements are used to place constraints on models of the jet dynamics.
A previously unknown one-sided X-ray jet in 3C 31, extending up to 8 arcsec from the nucleus, is detected and resolved. Its structure and steep X-ray spectrum are similar to those of X-ray jets known in other FRI sources, and we attribute the radiation to synchrotron emission from a high-energy population of electrons. In situ particle acceleration is required in the region of the jet where bulk deceleration is taking place.
We also present X-ray spectra and luminosities of the galaxies in the Arp 331 chain of which NGC 383 is a member. The spectrum and spatial properties of the nearby bright X-ray source 1E 0104+3153 are used to argue that the soft X-ray emission is mostly due to a foreground group of galaxies rather than to the background broad absorption-line quasar.  相似文献   

16.
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   

17.
Flat radio spectra with large brightness temperatures at the core of active galactic nuclei and X-ray binaries are usually interpreted as the partially self-absorbed bases of jet flows emitting synchrotron radiation. Here we extend previous models of jets propagating at large angles to our line of sight to self-consistently include the effects of energy losses of the relativistic electrons due to the synchrotron process itself and the adiabatic expansion of the jet flow. We also take into account energy gains through self-absorption. Two model classes are presented. The ballistic jet flows, with the jet material travelling along straight trajectories, and adiabatic jets. Despite the energy losses, both scenarios can result in flat emission spectra; however, the adiabatic jets require a specific geometry. No re-acceleration process along the jet is needed for the electrons. We apply the models to observational data of the X-ray binary Cygnus X-1. Both models can be made consistent with the observations. The resulting ballistic jet is extremely narrow with a jet opening angle of only 5 arcsec. Its energy transport rate is small compared to the time-averaged jet power and therefore suggests the presence of non-radiating protons in the jet flow. The adiabatic jets require a strong departure from energy equipartition between the magnetic field and the relativistic electrons. These models also imply a jet power of two orders of magnitude higher than the Eddington limiting luminosity of a  10-M⊙  black hole. The models put strong constraints on the physical conditions in the jet flows on scales well below achievable resolution limits.  相似文献   

18.
We present millimetre photometry and submillimetre imaging of the central core and two hotspots in the radio lobes of the galaxy Cygnus A. For both hotspots and the central core, the synchrotron spectrum continues smoothly from the radio to a frequency of 677 GHz. The spectral index of the hotspots is constant over our frequency range, with a spectral index of α ≈ −1.0 ( S ν ∝ να), which is steeper than at lower frequencies and represents the emission from an aged population of electrons. The core is significantly flatter, with α = −0.6 ± 0.1, suggestive of an injected spectrum with no ageing, but some evidence for steepening exists at our highest observing frequency. Although IRAS data suggest the presence of dust in Cygnus A, our 450-μm data show no evidence of cold dust, therefore the dust component must have a temperature lying between 85 and 37 K, corresponding to dust masses of 1.4 × 106 and 1.0 × 108 M⊙ respectively.  相似文献   

19.
Centaurus B (PKS B1343−601) is one of the brightest and closest radio galaxies, with flux density ∼250 Jy at 408 MHz and redshift 0.01215, but it has not been studied much because of its position (i) close to the Galactic plane (it is also known as G309.6+1.7 and Kes 19) and (ii) in the southern sky. It has recently been suggested as the centre of a highly obscured cluster behind the Galactic plane. We present radio observations made with the Australia Telescope Compact Array and Molonglo Observatory Synthesis Telescope to study the jets and lobes. The total intensity and polarization radio images of the FR I jets are used to determine the jet brightness and width variations, magnetic field structure and fractional polarization. The equipartition pressure calculated along the jets declines rapidly over the first 1 arcmin from the galaxy reaching a constant pressure of 10−13  h −4/7 Pa in the lobes blown in the intracluster medium.  相似文献   

20.
Chandra ACIS observations of PKS 0521−365 find that the X-ray emission of this BL Lac object consists of emission from an unresolved core, a diffuse halo and a 2-arcsec jet feature coincident with the inner radio/optical jet. A comparison with a new ATCA 8.6-GHz map also finds X-ray emission from the bright hotspot south-east of the nucleus. The jet spectrum, from radio to X-ray, is probably synchrotron emission from an electron population with a broken power-law energy distribution, and resembles the spectra seen from the jets of low-power (FR I) radio galaxies. The hotspot X-ray flux is consistent with the expectations of synchrotron self-Compton emission from a plasma close to equipartition, as seen in studies of high-power (FR II) radio galaxies. While the angular structure of the halo is similar to that found by an analysis of the ROSAT High Resolution Imager image, its brightness is seen to be lower with Chandra , and the halo is best interpreted as thermal emission from an atmosphere of similar luminosity to the haloes around FR I radio galaxies. The X-ray properties of PKS 0521−365 are consistent with it being a foreshortened, beamed, radio galaxy.  相似文献   

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