Radio Ridge Research Articles

Seeing the forest and the trees: A radio investigation of the ULIRG Mrk 273

Galaxy mergers have been observed to trigger nuclear activity by feeding gas to the central supermassive black hole. One such class of objects are Ultra Luminous InfraRed Galaxies (ULIRGs), which are mostly late stage major mergers of gas-rich galaxies. Recently, large-scale (∼100 kpc) radio continuum emission has been detected in a select number of ULIRGs, all of which also harbour powerful Active Galactic Nuclei (AGN). This hints at the presence of large-scale radio emission being evidence for nuclear activity. Exploring the origin of this radio emission and its link to nuclear activity requires high sensitivity multi-frequency data. We present such an analysis of the ULIRG Mrk 273. Using the International LOFAR telescope (ILT), we detected spectacular large-scale arcs in this system. This detection includes, for the first time, a giant ∼190 kpc arc in the north. We propose these arcs are fuelled by a low power radio AGN triggered by the merger. We also identified a bright ∼45 kpc radio ridge, which is likely related to the ionised gas nebula in that region. We combined this with high sensitivity data from APERture Tile In Focus (Apertif) and archival data from the Very Large Array (VLA) to explore the spectral properties. The ILT simultaneously allowed us to probe the nucleus at a resolution of ∼0.3″, where we detected three components, and, for the first time, diffuse emission around these components. Combining this with archival high frequency VLA images of the nucleus allowed us to detect absorption in one component, and a steep spectrum radio AGN in another. We then extrapolate from this case study to the importance of investigating the presence of radio emission in more ULIRGs and what it can tell us about the link between mergers and the presence of radio activity.

MeerKAT’s discovery of a radio relic in the bimodal merging cluster A2384

ABSTRACT We present the discovery of a single radio relic located at the edge of the galaxy cluster A2384, using the MeerKAT radio telescope. A2384 is a nearby (z = 0.092), low-mass, complex bimodal, merging galaxy cluster that displays a dense X-ray filament (∼700 kpc in length) between A2384(N; northern cluster) and A2384(S; southern cluster). The origin of the radio relic is puzzling. Using the MeerKAT observation of A2384, we estimate that the physical size of the radio relic is 824 × 264 kpc2 and that it is a steep spectrum source. The radio power of the relic is $P_{1.4\mathrm{GHz}}\, \sim$ (3.87 ± 0.40) × 1023 W Hz−1. This radio relic could be the result of shock wave propagation during the passage of the low-mass A2384(S) cluster through the massive A2384(N) cluster, creating a trail appearing as a hot X-ray filament. In the previous GMRT 325 MHz observation, we detected a peculiar FR I radio galaxy interacting with the hot X-ray filament of A2384, but the extended radio relic was not detected; it was confused with the southern lobe of the FR I galaxy. This newly detected radio relic is elongated and perpendicular to the merger axis, as seen in other relic clusters. In addition to the relic, we notice a candidate radio ridge in the hot X-ray filament. The physical size of the radio ridge source is ∼182 × 129 kpc2. Detection of the diffuse radio sources in the X-ray filament is a rare phenomenon, and could be a new class of radio source found between the two merging clusters of A2384(N) and A2384(S).

A radio ridge between two galaxy clusters

Radio Astronomy Galaxy clusters contain dozens or hundreds of galaxies, vast quantities of hot gas, and large amounts of dark matter. The gas can emit at radio wavelengths if it contains electrons at relativistic speeds, which can be injected by active galaxies or accelerated during a merger between two clusters. Govoni et al. used the Low-Frequency Array (LOFAR) radio telescope to observe a ridge of radio-emitting plasma extending between two galaxy clusters that are approaching a merger. The results imply that intergalactic magnetic fields connect the two clusters and challenge theories of particle acceleration in the intergalactic medium. Science , this issue p. [981][1] [1]: /lookup/doi/10.1126/science.aat7500

A radio ridge connecting two galaxy clusters in a filament of the cosmic web

Galaxy clusters are the most massive gravitationally bound structures in the Universe. They grow by accreting smaller structures in a merging process that produces shocks and turbulence in the intracluster gas. We observed a ridge of radio emission connecting the merging galaxy clusters Abell 0399 and Abell 0401 with the Low-Frequency Array (LOFAR) telescope network at 140 megahertz. This emission requires a population of relativistic electrons and a magnetic field located in a filament between the two galaxy clusters. We performed simulations to show that a volume-filling distribution of weak shocks may reaccelerate a preexisting population of relativistic particles, producing emission at radio wavelengths that illuminates the magnetic ridge.

THE COMPLEX NORTH TRANSITION REGION OF CENTAURUS A: RADIO STRUCTURE

We present deep radio images of the inner 50 kpc of Centaurus A, taken with the Karl G. Jansky Very Large Array (VLA) at 90cm. We focus on the Transition Regions between the inner galaxy - including the active nucleus, inner radio lobes, and star-forming disk - and the outer radio lobes. We detect previously unknown extended emission around the Inner Lobes, including radio emission from the star-forming disk. We find that the radio-loud part of the North Transition Region, known as the North Middle Lobe, is significantly overpressured relative to the surrounding ISM. We see no evidence for a collimated flow from the Active Galactic Nucleus (AGN) through this region. Our images show that the structure identified by Morganti et al. (1999) as a possible large-scale jet appears to be part of a narrow ridge of emission within the broader, diffuse, radio-loud region. This knotty radio ridge is coincident with other striking phenomena: compact X-ray knots, ionized gas filaments, and streams of young stars. Several short-lived phenomena in the North Transition Region, as well as the frequent re-energization required by the Outer Lobes, suggest that energy must be flowing through both Transition Regioins at the present epoch. We suggest that the energy flow is in the form of a galactic wind.

GSH 90-28-17: a possible old supernova remnant

GSH 90-28-17 is a high-latitude galactic HI supershell, identified in the HI supershell catalogs with a velocity of $v_{lsr}\sim-17$ \kms. We used the new Arecibo GALFA-HI survey data which have much higher resolution and sensitivity than what were previously available to re-examine the properties of the supershell. We derived a new distance of 400 pc for GSH 90-28-17 and suggested that it is related to the Lac OB1 association. The radius of GSH 90-28-17 is 66.0$\pm$3.5 pc. The HI mass of the shell is (3.1$\pm0.1)\times10^{4}$ M$_{\odot}$. It has an age of $\sim4.5$ Myr and a total kinetic energy of (8.2$\pm0.3)\times10^{48}$ ergs. We extracted radio continuum data for the GSH 90-28-17 region from the 408 MHz all-sky Survey and Bonn 1420 MHz survey, and filtered the diffuse background Galactic emission. A radio loop-like ridge is found to be associated with the HI shell at both frequencies, and shows a nonthermal origin with a TT-plot index of $\alpha$=-1.35$\pm$0.69. In addition, the pulsar J2307+2225 with a similar distance is found in the shell region. We conclude that GSH 90-28-17 is probably an old, type II supernova remnant in the solar neighborhood.

DEEPCHANDRAOBSERVATIONS OF A2199: THE INTERPLAY BETWEEN MERGER-INDUCED GAS MOTIONS AND NUCLEAR OUTBURSTS IN A COOL CORE CLUSTER

We present new Chandra observations of Abell 2199 that show evidence of gas sloshing due to a minor merger, as well as impacts of the radio source, 3C 338, hosted by the central galaxy, NGC 6166, on the intracluster gas. The new data are consistent with previous evidence of a Mach 1.46 shock 100" from the cluster center, although there is still no convincing evidence for the expected temperature jump. Other interpretations of this feature are possible, but none is fully satisfactory. Large scale asymmetries, including enhanced X-ray emission 200" southwest of the cluster center and a plume of low entropy, enriched gas reaching 50" to the north of the center, are signatures of gas sloshing induced by core passage of a merging subcluster about 400 Myr ago. An association between the unusual radio ridge and low entropy gas are consistent with this feature being the remnant of a former radio jet that was swept away from the AGN by gas sloshing. A large discrepancy between the energy required to produce the 100" shock and the enthalpy of the outer radio lobes of 3C 338 suggests that the lobes were formed by a more recent, less powerful radio outburst. Lack of evidence for shocks in the central 10" indicates that the power of the jet now is some two orders of magnitude smaller than when the 100" shock was formed.

NGC 3627: a galaxy-dwarf collision?

Group galaxies very often show distinct signs of interaction with both companion galaxies and the intragroup medium. X-ray observations are particularly helpful because they provide information on the temperatures and the densities of the hot gas in galaxies and intergalactic space. This can put important constraints on the nature and timescales of these interactions. We use the XMM-Newton X-ray observations of NGC 3627 in the Leo Triplet galaxy group to explain peculiar features visible in the polarized radio maps. We analyzed soft X-ray (0.2-1 keV) emission from NGC 3627 to study the distribution of the hot gas and its temperature in different areas of the galaxy. Any change throughout the disk can reflect distortions visible in the radio polarized emission. We also studied two bright point sources that are probably tightly linked to the evolution of the galaxy. We find an increase in the temperature of the hot gas in the area of the polarized radio ridge in the western arm of the galaxy. In the eastern part of the disk we find two ultra-luminous X-ray sources. We note a large hot gas temperature difference (by a factor of 2) between the two bar ends. The polarized radio ridge in the western arm of NGC 3627 is most likely formed by ram-pressure effects caused by the movement of the galaxy through the intragroup medium. To explain the distortions visible in the eastern part of the disk in polarized radio maps, the asymmetry of the bar, and the distortion of the eastern arm, we propose a recent collision of NGC 3627 with a dwarf companion galaxy.

Deep optical observations of the interaction of the SS 433 microquasar jet with the W50 radio continuum shell

Four mosaics of deep, continuum-subtracted, CCD images have been obtained over the extensive Galactic radio continuum shell, W50, which surrounds the remarkable stellar system SS 433. Two of these mosaics in the and [O iii] 5007 Å emission lines, respectively, cover a field of which contains all of W50 but at a low angular resolution of 5 arcsec. The third and fourth mosaics cover the eastern (in [O iii] 5007 Å) and western (in 6548, 6584 Å) filamentary nebulosity, respectively, but at an angular resolution of 1 arcsec. These observations are supplemented by new low-dispersion spectra and long-slit, spatially resolved echelle spectra. The [O iii] 5007 Å images show for the first time the distribution of this emission in both the eastern and western filaments while new emission features are also found in both of these regions. Approaching flows of faintly emitting material from the bright eastern filaments of up 100 km s−1 in radial velocity are detected. The present observations also suggest that the heliocentric systemic radial velocity of the whole system is 56 ± 2 km s−1. Furthermore, very deep imagery and high-resolution spectroscopy of a small part of the northern radio ridge of W50 has revealed for the first time the very faint optical nebulosity associated with this edge. It is suggested that patchy foreground dust along the ≈5 kpc sightline is inhibiting the detection of all of the optical nebulosity associated with W50. The interaction of the microquasar jets of SS 433 with the W50 shell is discussed.

Far-Ultraviolet Observations of the Loop I/North Polar Spur Region

The results of diffuse far-ultraviolet observations of the Loop I/North Polar Spur (NPS) region are presented in this Letter. Several important ionic emission lines, including C IV, Si II*, Si IV, and Al II, were detected. Fluorescent emission lines from hydrogen molecules were also seen in the spectra. A spectral image made with C IV emission shows a shell-like feature colocated with the X-ray NPS. This feature is located just inside the Loop I radio ridges. Another interesting C IV feature is seen at the inner edge of the interaction ring, where the cold interstellar medium is in direct contact with the X-ray-bright hot gas. The present observation is in good agreement with a model of recent supernova explosion in an inhomogeneous medium, possibly disturbed by previous multiple supernova explosions.

Magnetic fields in barred galaxies

We present λ3.5 cm and A6.2 cm radio continuum maps in total and polarized intensity of the barred galaxies NGC 1097 (at 2-15 resolution) and NGC 1365 (at 9-25 resolution). A previously unknown radio galaxy southwest of NGC 1097 is reported. Apart from a smooth faint envelope and a bright central region, both galaxies exhibit radio ridges roughly overlapping with the massive dust lanes in the bar region. The contrast in total intensity across the radio ridges is compatible with compression and shear of an isotropic random magnetic field, where the gas density compression ratio is approximately equal to 4 and the cosmic ray density is constant across the ridges. The contrast in polarized intensity is significantly smaller than that expected from compression and shearing of the regular magnetic field: this could be the result of decoupling of the regular field from the dense molecular clouds. The regular field in the ridge is probably strong enough to reduce significantly shear in the diffuse gas (to which it is coupled) and hence to reduce magnetic field amplification by shearing. This contributes to the misalignment of the observed field orientation with respect to the velocity vectors of the dense gas. Our observations, for the first time, indicate that magnetic forces can control the flow of the diffuse inlerstellar gas at kilopursec scales. The total radio intensity reaches its maximum in the circumnuclear starburst regions, where the equipartition field strength is about 60μG, amongst the strongest fields detected in spiral galaxies so far. The regular field in the inner region has a spiral shape with large pitch angle, indicating the action of a dynamo. Magnetic stress leads to mass inflow towards the centre, sufficient to feed the active nucleus in NGC 1097. - We detected diffuse X-ray emission, possibly forming a halo of hot gas around NGC 1097.

ChandraImaging of the X‐Ray Core of the Virgo Cluster

We report subarcsecond X-ray imaging spectroscopy of M87 and the core of the Virgo Cluster with the Chandra X-Ray Observatory. The X-ray morphology shows structure on arcsecond (~100 pc) to 10' (~50 kpc) scales, the most prominent feature being an arc running from the east, across the central region of M87, and off to the southwest. A ridge in the radio map, ending in an ear-shaped structure, follows the arc to the east. Depressions in the X-ray surface brightness correspond to the inner radio lobes, and there is no evidence of shock-heated gas surrounding them. There are also at least two approximately circular (centered near the nucleus) edges in the X-ray brightness distribution, the radii of which are slightly larger than the nuclear distances of the inner radio lobes and intermediate radio ridges. We speculate that these discontinuities may be spherical pulses or fronts driven by the same jet activity as is responsible for the radio structure; such pulses are found in recent numerical simulations. All these results provide good evidence that the nuclear activity affects the intracluster medium. We present a temperature map of the intracluster medium and obtain the temperature, pressure, and cooling time as a function of nuclear distance for the arcs and the ambient intracluster medium. We show that the gas in the arcs is cooler than, and probably overpressured with respect to, the ambient intracluster medium. The metal abundances of the cooler gas in the arc are somewhat enhanced relative to the ambient intracluster medium, favoring a buoyant plume origin for the X-ray arc, in which ambient gas near the nucleus is entrained by buoyant radio plasma and carried to larger nuclear distances. The gas within the inner front (nuclear distance 3.5 kpc 45'') is at least a two-temperature plasma, with the cool component at 1 keV. This cool region is concentrated to the north of the nucleus and is strongly correlated with the H?+[N II] emission line distribution.

X‐Ray Observation and Analysis of the Composite Supernova Remnant G327.1−1.1

Based on the data from the observation of the SNR G327.1-1.1 by ASCA and ROSAT, we find that G327.1-1.1 is a composite remnant with both a nonthermal emission component and a diffuse thermal emission component. The nonthermal component is well fitted by a power-law model with photon index about 2.2. This component is attributed to the emission from the synchrotron nebula powered by an undiscovered central pulsar. The thermal component has a temperature of about 0.4 keV. We attribute it to the emission from the shock-heat swept-up ISM. Its age, explosion energy and density of ambient medium are derived from the observed thermal component. Some charactistics about the synchrotron nebula are also derived. We search for the pulsed signal, but has not found it. The soft X-ray(0.4 - 2 keV) and hard X-ray(2 - 10 keV) images are different, but they both elongate in the SE-NW direction. And this X-ray SE-NW elongation is in positional coincidence with the radio ridge in MOST 843MHz radio map. We present a possibility that the X-ray nonthermal emission mainly come from the trail produced by a quickly moving undiscoverd pulsar, and the long radio ridge is formed when the pulsar is moving out of the boundary of the plerionic structure.

An X‐Ray Temperature Map of the Merging Cluster Abell 2255

We present a spatially resolved map of intracluster gas temperatures in the rich cluster Abell 2255, using ROSAT PSPC data. The intracluster gas is strongly nonisothermal and the temperature distribution supports the conclusions of Burns and coworkers that Abell 2255 is currently undergoing a merger. The hottest regions are near the core, northwest of the center. A map of the ratio of softer to harder X-ray photons reveals an anomalously soft region northeast of the center, coincident with a radio ridge discovered by Burns and coworkers in 1995. We suggest that this cooler region is associated with an infalling group of galaxies that is giving rise to the radio ridge. Meanwhile, a much more substantial recent merger between comparably sized subcluster components can account for the more global merger signatures, which include the extensive central radio halo, the large-scale gas temperature variations, the pair of central-dominant ellipticals, elliptical X-ray isophotes offset from these dominant galaxies, and the very high velocity dispersion of galaxies in the cluster.

Excitation of the ``Arched'' Filaments near the Galactic Center

view Abstract Citations (15) References (55) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Excitation of the ``Arched'' Filaments near the Galactic Center Colgan, Sean W. J. ; Erickson, Edwin F. ; Simpson, Janet P. ; Haas, Michael R. ; Morris, Mark Abstract We present measurements of the far-infrared (FIR) fine structure lines [S III] (33 μm), [Si II] (35 μm), [O III] (52, 88 μm), [O I] (63 μm), and [C II] (158 μm) and the adjacent continua at these wavelengths in a strip crossing the E2 and W1 thermal radio filaments in the Galactic center "arc." The properties of the two filaments are similar: the line and continuum fluxes peak in the vicinity of the radio ridges, and the contrast of the ridge fluxes relative to the off-ridge fluxes is greatest for the FIR continuum and doubly ionized lines, lower for the single-dish radio measurements (Sofue et al. 1986) and smallest for the low-excitation lines. The near spatial coincidence of the line and continuum emission maxima with the radio filaments demonstrates that the same excitation source must be responsible for both the line and the continuum emission. The peak FIR luminosity of ∼2.5 x 105 Lsun per 30" beam and the association of [O III] intensity with the filaments pose difficulties for shock and MHD models. Excitation by a string of stars is also unlikely, but photoionization of molecular cloud edges by a quasi-uniform distribution of stars is the most plausible excitation source proposed. The peak ionized line intensity is shifted slightly eastward relative to the FIR continuum emission. The deduced excitation, as measured by the [O III] to [S III] line flux ratios, also peaks slightly east of the radio ridges. Together, these two measurements suggest a substantial contribution from an ionizing source to the east. The strengths of the [O I] and [C II] lines are consistent with their production in photodissociated molecular material adjacent to the photoionized gas, but the FIR luminosity and the [Si II] emission appear to originate predominantly in or very near to the ionized gas. Publication: The Astrophysical Journal Pub Date: October 1996 DOI: 10.1086/177918 Bibcode: 1996ApJ...470..882C Keywords: GALAXY: CENTER; INFRARED: ISM: LINES AND BANDS; ISM: STRUCTURE full text sources ADS | data products SIMBAD (8)

Studies of two LYNDS bright nebulae - LBN 140.77 - 1.42, a remarkable thermal ridge, and LBN 139.57 + 2.70, a radio and infrared partial ring

Observations at 408 MHz of two extended features corresponding to objects in Lynds' (1965) catalog of bright nebulae are presented. These are LBN 140.77 - 1.42, which corresponds to a linear radio ridge roughly 2 deg in extent that is approximately perpendicular to the Galactic plane, and LBN 139.57 + 2.70, which shows a partial radio ring roughly 12 arcmin in radius. The radio emission from LBN 140.77 - 1.42 has a thermal spectrum, and it coincides with the western edge of a large spur that is evident in atomic hydrogen in the Perseus arm. Part of this spur is also evident in the infrared at all IRAS wavebands. Thus, LBN 140.77 - 1.42 appears to be a remarkably large-scale ionization front penetrating a large interstellar cloud. The nature of LBN 139.57 + 2.70 is not clear. 37 refs.

Cosmic-ray volleys from the galactic center and their recent impact on the earth environment

It is proposed that outbursts of cosmic ray electrons from the Galactic Center penetrate the Galaxy relatively undamped and are able to have a major impact on the Solar System through their ability to vaporize and inject cometary material into the interplanetary environment. It is suggested that one such ‘superwave’, passing through the Solar System toward the end of the Last Ice Age, was responsible for producing major changes in the Earth's climate and for indirectly precipitating the terminal Pleistocene extinction episode. The high concentrations of 10Be, NO3 −, Ir and Ni observed in Late Wisconsin polar ice are consistent with this scenario. The intensities of the Galactic nonthermal radio background and diffuse X-ray emission ridge are shown to vary with Galactic longitude in the same manner as electron intensity along the proposed superwave ‘event horizon’. The high luminosities and unusual structural features which characterize the Crab Nebula and Cassiopeia A are shown to be attributable to the fact that these remnants happen to coincide with this event horizon and are being externally impacted by an intense volley of relativistic electrons travelling from the Galactic Center direction. The same cosmic ray volley is also shown to be able to account for the unusual structure of the extended radio source CTB 80.

CD galaxy dynamics and an aged ridge (jet) in 3C 338

The results of VLA observations and possible models for the peculiar structure of 3C 338, a two-arcmin radio source associated with the cD galaxy NGC 6166 in Abell 2199, are presented. The optical parameters for Abell 2199 and NGc 6166 are reviewed, and the VLA observations and reductions are described. The radio structure of 3C 338 including spectral index and polarization distributions are also discussed. Two possible origins for the ridge structure located to the south of the core which has some characteristics of a jet are proposed. The first involves a cooling accretion flow of ICM material onto the cD. The ram pressure of a highly asymmetric flow seems to be sufficient to confine the radio ridge using an accretion rate of 100 solar masses/yr. The second model presumes that the ridge is actually an aged radio jet. The radio engine would have to be intermittent with a period of about ten million years.

X-ray observations of the North Polar Spur

The X-ray enhancement associated with the North Polar Spur (Radio Loop I) was observed by a soft X-ray instrument on OSO 8 during August 1975. This paper presents image-processed maps of the region scanned, a detailed analysis of the X-ray data, and interpretations of the data in terms of supernova remnant models. If the neutral hydrogen ridge, radio continuum ridge, and X-ray emission ridge are all associated, then they cannot all be fitted by a single supernova remnant model because they require different energies of explosion. A reheated supernova remnant model does appear compatible with all the available observations.

What is the compact radio source in the nucleus of M82

view Abstract Citations (11) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS What is the compact radio source in the nucleus of M82? Kronberg, P. P. ; Clarke, J. N. Abstract Interferometric observations at 8085 MHz of the strong compact radio source (designated 49.1+58) in the nucleus of M82 are reported which were performed in 1971 and repeated in 1975 to search for flux-density variations. High-sensitivity 8-GHz maps of M82 are presented, and upper limits of 3% along the main radio ridge and 0.3% for 49.1+58 are placed on the linear polarization. It is found that the flux density from 49.1+58 decreased by about 14% in four years; the relative stability of the source is taken to suggest that the source is not expanding and not dynamically confined. A very high ratio of relativistic- to cold-plasma density (no less than about 4000) is determined, indicating that the particle generator in this source is probably the strong magnetic field of a supermassive object which is presumably in a highly collapsed state. It is concluded that there is considerable disorder in the magnetic-field structure of 49.1+58. Publication: The Astrophysical Journal Pub Date: September 1978 DOI: 10.1086/182757 Bibcode: 1978ApJ...224L..51K Keywords: Galactic Nuclei; Galactic Radiation; Radio Sources (Astronomy); Astronomical Maps; Linear Polarization; Microwave Emission; Polarized Electromagnetic Radiation; Astrophysics; Galactic Nuclei:Radio Sources full text sources ADS | data products NED (1)