Southern Radio Lobe Research Articles

Chasing ICM cooling and AGN feedback from the macro to the meso scales in the galaxy cluster ZwCl 235

Aims. We aim to investigate the interplay between the intracluster medium (ICM) and the active galactic nucleus (AGN) in ZwCl 235, a galaxy cluster with high X-ray flux, an extended central radio galaxy, and evidence of multiphase gas at its center. Methods. Using archival data from the Chandra telescope, the Very Large Array Sky Survey (VLASS), the LOFAR Two-metre Sky Survey (LOTSS), and the VLBA telescope, we performed a complete study of ZwCl 235, dissecting the dynamics of the ICM, the thermodynamic state of the central gas, and the properties of the brightest cluster galaxy (BCG). By means of radial profiles and 2D spectral maps, we measured the temperature, entropy, and cooling time of the ICM, and we compared the morphology of the central radio galaxy with the surrounding medium. Results. We find evidence that ZwCl 235 is a sloshing cool core cluster in which the activity of the central galaxy has excavated a pair of cavities and possibly uplifted enriched gas to an altitude of ∼30 kpc. In the cluster core, the lowest entropy ICM is preferentially found in a 20 kpc-long filament tangential to the southern radio lobe of the AGN. We argue that the observed cool (∼1.3 keV) filament is likely produced by a combination of sloshing and stimulated ICM cooling, which may be fueling the central supermassive black hole. Additionally, we determined that the X-ray emission of the BCG originates from a ∼1.4 keV plasma kernel, which extends for 5 kpc in radius and has a short cooling time (∼240 Myr), and it could represent the thermal corona of the BCG. Conclusions. Overall, we propose that several sources (the large-scale ICM, the low entropy filament, and the ∼1.4 keV kernel) of cold material are currently feeding the central AGN, and that the ICM cooling cycle expectations are met from the macro scales (between 5−100 kpc) to the meso scales (≤5 kpc) of AGN feedback.

H i absorption at z ∼ 0.7 against the lobe of the powerful radio galaxy PKS 0409−75

ABSTRACT We present results from a search for the H i 21-cm line in absorption towards 16 bright radio sources with the six-antenna commissioning array of the Australian Square Kilometre Array Pathfinder. Our targets were selected from the 2-Jy sample, a flux-limited survey of the southern radio sky with extensive multiwavelength follow-up. Two sources were detected in H i absorption including a new detection towards the bright Fanaroff–Riley Type II radio galaxy PKS 0409−75 at a redshift of $z$ = 0.674. The H i absorption line is blueshifted by ∼3300 km s−1 compared to the optical redshift of the host galaxy of PKS 0409−75 at $z$ = 0.693. Deep optical imaging and spectroscopic follow-up with the GMOS instrument on the Gemini-South telescope reveal that the H i absorption is associated with a galaxy in front of the southern radio lobe with a stellar mass of 3.2–6.8 × 1011 M⊙, a star formation rate of ∼1.24 M⊙ yr−1, and an estimated H i column density of 2.16 × 1021 cm−2, assuming a spin temperature of Tspin = 500 K and source covering factor of Cf = 0.3. Using polarization measurements of PKS 0409−75 from the literature, we estimate the magnetic field of the absorbing galaxy to be ∼14.5 $\mu$G, consistent with field strengths observed in nearby spiral galaxies but larger than expected for an elliptical galaxy. Results from this pilot study can inform future surveys as new wide-field telescopes allow us to search for 21-cm H i absorption towards all bright radio sources as opposed to smaller targeted samples.

AGN Feedback in Galaxy Groups: A Detailed Study of X-Ray Features and Diffuse Radio Emission in IC 1262

Abstract This paper reports a systematic search of X-ray cavities, density jumps, and shocks in the intergalactic environment of the galaxy group IC 1262 using Chandra, GMRT, and Very Large Array archival observations. The X-ray imaging analysis reveals a pair of X-ray cavities to the north and south of the X-ray peak, at projected distances of 6.48 kpc and 6.30 kpc respectively. Total mechanical power contained in both of these cavities is found to be ∼12.37 × 1042 erg s−1, and compares well with the X-ray luminosity, within the cooling radius, measured to be ∼3.29 × 1042 erg s−1, suggesting that the mechanical power injected by the central AGN efficiently balances the radiative loss. We detect a previously unknown X-ray cavity at the position of the southern radio lobe in the intra-group medium and find a loop of excess X-ray emission extending ∼100 kpc southwest from the central galaxy. The X-ray cavity at the position of the southern radio lobe probably represents a first generation X-ray cavity. Two surface brightness edges are evident to the west and northeast of the center of this group. The radio galaxy at the core of the IC 1262 group is a rare low-redshift ultra-steep radio galaxy, its spectral index being α ∼ −1.73 (including the central AGN) and α ∼ −2.08 (excluding the central AGN). We detect a radio phoenix embedded within the southern radio lobe, for the first time in a poor group, with a spectral index (α ≤ −1.92). The spectral index distribution across the phoenix steepens with increasing distance from its intensity peak.

The Extraordinary Linear Polarisation Structure of the Southern Centaurus A Lobe Revealed by ASKAP

We present observations of linear polarisation in the southern radio lobe of Centaurus A, conducted during commissioning of the Australian Square Kilometre Array Pathfinder (ASKAP) telescope. We used 16 antennas to observe a 30 square degree region in a single 12-h pointing over a 240 MHz band centred on 913 MHz. Our observations achieve an angular resolution of 26 × 33 arcseconds (480 parsecs), a maximum recoverable angular scale of 30 arcminutes, and a full-band sensitivity of 85 μ Jy beam − 1 . The resulting maps of polarisation and Faraday rotation are amongst the most detailed ever made for radio lobes, with order 10 5 resolution elements covering the source. We describe several as-yet unreported observational features of the lobe, including its detailed peak Faraday depth structure, and intricate networks of depolarised filaments. These results demonstrate the exciting capabilities of ASKAP for widefield radio polarimetry.

A Multi-band Study of the Remarkable Jet in Quasar 4C+19.44

Abstract We present arcsecond-resolution data in the radio, IR, optical, and X-ray for 4C+19.44 (=PKS 1354+195), the longest and straightest quasar jet with deep X-ray observations. We report results from radio images with half to one arcsecond angular resolution at three frequencies, plus Hubble Space Telescope and Spitzer data. The Chandra data allow us to measure the X-ray spectral index in 10 distinct regions along the 18″ jet and compare with the radio index. The radio and X-ray spectral indices of the jet regions are consistent with a value of throughout the jet, to within uncertainties. The X-ray jet structure to the south extends beyond the prominent radio jet and connects to the southern radio lobe, and there is extended X-ray emission, both in the direction of the unseen counter-jet, and also coincident with the northern radio lobe. This jet is remarkable because its straight appearance over a large distance allows the geometry factors to be taken as fixed along the jet. Using the model of inverse Compton scattering of the cosmic microwave background (iC/CMB) by relativistic electrons, we find that the magnetic field strengths and Doppler factors are relatively constant along the jet. If instead the X-rays are synchrotron emission, they must arise from a population of electrons distinct from the particles producing the radio synchrotron spectrum.

CHANG-ES. III. UGC 10288—AN EDGE-ON GALAXY WITH A BACKGROUND DOUBLE-LOBED RADIO SOURCE

This 3rd paper in the CHANG-ES series shows the first results from our regular data taken with the Karl G. Jansky Very Large Array (JVLA). The edge-on galaxy, UGC 10288, has been observed in the B, C, and D configurations at L-band (1.5 GHz) and in the C and D configurations at C-band (6 GHz) in all polarization products. We show the first spatially resolved images in these bands,the first polarization images, and the first composed image at an intermediate frequency (4.1 GHz) which has been formed from a combination of all data sets. A surprising new result is the presence of a strong, polarized, double-lobed extragalactic radio source ({\it CHANG-ES A}) almost immediately behind the galaxy and perpendicular to its disk. The core of {\it CHANG-ES A} has an optical counterpart at a photometric redshift of $z_{phot}\,=\,0.39$; the southern radio lobe is behind the disk of UGC 10288 and the northern lobe is behind the halo region. This background `probe' has allowed us to do a preliminary Faraday Rotation analysis of the foreground galaxy, putting limits on the regular magnetic field and electron density in the halo of UGC 10288 in regions in which there is no direct detection of a radio continuum halo. We have revised the flux densities of the two sources individually as well as the star formation rate (SFR) for UGC 10288. UGC 10288 would have fallen well below the CHANG-ES flux density cutoff, had it been considered without the brighter contribution of the background source. UGC 10288 shows discrete high-latitude radio continuum features, but it does not have a {\it global} radio continuum halo. The total minimum magnetic field strength at a sample position in the arc is $\sim$ 10 $\mu$G. Thus, this galaxy still appears to be able to form substantial high latitude, localized features in spite of its relatively low SFR.

AN ACTIVE GALACTIC NUCLEUS DRIVEN SHOCK IN THE INTRACLUSTER MEDIUM AROUND THE RADIO GALAXY 3C 310

We present results from a 57.6 ks Chandra observation of the cluster gas associated with the fat-double radio galaxy 3C 310. We find a surface brightness discontinuity in the gas outside the southern radio lobe that we attribute to a shock driven by the supersonic inflation of this lobe ~180 kpc from the nucleus. Modeling the surface brightness/density jump, the shock has Mach number 1.5-1.9, depending on the assumptions one makes about the density profile and the nature of the energy input. There are not sufficient counts in the image to detect conclusively the temperature jump associated with the shock. The total mechanical energy of the outburst is 5 × 1060 erg. Assuming a Mach 1.9 shock, the age of the outburst is ~100 million yrs, and the time-averaged power of the outburst is ~1.3 × 1045 erg s–1. The power input is 100 times greater than the radiative losses of the gas within the radius of the shock. Most importantly, the equivalent heat input due to the entropy increase is roughly 10% of the thermal energy of the gas to the radius of the shock. 3C 310 is another example where regular outbursts of the observed strength with a duty cycle of 0.1 could offset the radiative losses of the gas near the Bondi radius and regulate feedback. We also detect a cool filamentary X-ray arm along the eastern periphery of the southern radio lobe. This arm is probably composed of low-entropy gas dredged up in the inflation of the radio plasma, similar to features seen in M87.

CHANDRAANDROSATOBSERVATIONS OF A194: DETECTION OF AN X-RAY CAVITY AND MAPPING THE DYNAMICS OF THE CLUSTER

Based on Chandra and ROSAT observations, we investigated the nearby poor cluster Abell 194, which hosts two luminous radio galaxies, NGC547 (3C 40B) and NGC541 (3C 40A). We demonstrated the presence of a large X-ray cavity (r~34 kpc) formed by the giant southern radio lobe arising from 3C 40B in NGC547. The estimated age of the cavity is t=7.9 x 10^7 years and the total work of the AGN is 3.3 x 10^59 erg, hence the cavity power is P_cav=1.3 x 10^44 erg/s. Furthermore, in the Chandra images of NGC545 and NGC541 we detected sharp surface brightness edges, identified as merger cold fronts, and extended tails. Using the pressure ratios between inside and outside the cold fronts we estimated that the velocities of NGC545 and NGC541 correspond to Mach-numbers of M=1.0^{+0.3}_{-0.5} and M=0.9^{+0.2}_{-0.5}, respectively. The low radial velocities of these galaxies relative to the mean radial velocity of Abell 194 imply that their motion is oriented approximately in the plane of the sky. Based on these and earlier observations, we concluded that NGC545 and NGC541 are falling through the cluster, whose center is NGC547, suggesting that Abell 194 is undergoing a significant cluster merger event. Additionally, we detected 20 bright X-ray sources around NGC547 and NGC541, a surprisingly large number, since the predicted number of resolved LMXBs and CXB sources is 2.2 and 4.1, respectively. To explain the nature of additional sources, different possibilities were considered, none of which are satisfactory. We also studied the origin of X-ray emission in Minkowski's Object, and concluded that it is most likely dominated by the population of HMXBs rather than by hot diffuse ISM. Moreover, in view of the galaxy dynamics in Abell 194, we explored the possibility that the starburst in Minkowski's Object was triggered by its past interaction with NGC541, and concluded that it may be a viable path.

CAVITIES AND SHOCKS IN THE GALAXY GROUP HCG 62 AS REVEALED BYCHANDRA,XMM-NEWTON, AND GIANT METREWAVE RADIO TELESCOPE DATA

We report on the results of an analysis of Chandra, XMM-Newton and new GMRT data of the X-ray bright compact group of galaxies HCG 62, which is one of the few groups known to possess clear, small X-ray cavities in the inner regions. This is part of an ongoing X-ray/low-frequency radio study of 18 groups, initially chosen for the availability of good-quality X-ray data and evidence for AGN/hot gas interaction. At higher frequency (1.4 GHz), the HCG 62 cavity system shows minimal if any radio emission, but the new GMRT observations at 235 MHz and 610 MHz clearly detect extended low-frequency emission from radio lobes corresponding to the cavities. By means of the synergy of X-ray and low-frequency radio observations, we compare and discuss the morphology, luminosity and pressure of the gas and of the radio source. We find that the radio source is radiatively inefficient, with a ratio of radio luminosity to mechanical cavity power of $\sim 10^{-4}$, and that the radio pressure of the lobes is about one order of magnitude lower than the X-ray pressure of the surrounding thermal gas. Thanks to the high spatial resolution of the Chandra surface brightness and temperature profiles, we also identify a shock front located at 36 kpc to the south-west of the group center, close to the southern radio lobe, with a Mach number $\sim 1.5$ and a total power which is about one order of magnitude higher than the cavity power. Such a shock may have heated the gas in the southern region, as indicated by the temperature map. The shock may also explain the arc-like region of enriched gas seen in the iron abundance map, as this may be produced by a non-Maxwellian electron distribution near its front.

XMM‐NewtonDetection of X‐Ray Emission from the Compact Steep‐Spectrum Radio Galaxy 3C 303.1

Using XMM-Newton we detect faint unresolved X-ray emission from the compact steep-spectrum radio galaxy 3C 303.1. We detect a thermal component at kT 0.8 keV, which seems likely to be produced in the interstellar medium (ISM) of the host galaxy. There is evidence for a second component in the spectrum whose nature is currently ambiguous. Plausible hypotheses for the second component include (1) hot gas shocked by the expansion of the radio source, and (2) synchrotron self-Compton emission from the southern radio lobe if the magnetic field is below the equipartition value by a factor of ~3.5.

Discovery of an X-Ray Jet and Extended Jet Structure in the Quasar PKS 1055+201

This Letter reports rich X-ray jet structures found in the Chandra observation of PKS 1055+201. In addition to an X-ray jet coincident with the radio jet, we detect a region of extended X-ray emission surrounding the jet as far from the core as the radio hot spot to the north, and a similar extended X-ray region along the presumed path of the unseen counterjet to the southern radio lobe. Both X-ray regions show a similar curvature to the west, relative to the quasar. We interpret this as the first example in which we separately detect the X-ray emission from a narrow jet and extended, residual jet plasma over the entire length of a powerful FR II jet.

Dynamics of the radio galaxy 3C 449

We present ROSAT PSPC observations of the twin-jet radio galaxy 3C 449. The soft X-ray emission from this object is dominated by an extended halo with a scale comparable to that of the radio source. The asymmetry of the X-ray emission is reflected in that of the radio lobes, providing evidence that the behaviour of the jets is strongly influenced by the external medium. A region of reduced X-ray surface brightness coincident with the southern radio lobe of 3C 449 suggests that the radio source has displaced thermal plasma from the X-ray-emitting halo. However, the minimum pressure in the radio lobe is considerably lower than our estimates of the pressure in the external medium. We discuss the implications for the dynamics of the radio source.

Optical, radio, and X-ray structure in NGC 1275.

view Abstract Citations (49) References (63) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical, radio, and X-ray structure in NGC 1275. McNamara, Brian R. ; O'Connell, Robert W. ; Sarazin, Craig L. Abstract We have compiled U, I, Hα, radio, and x-ray maps of NGC 1275 in order to study the galaxy's structure and color distribution. There are strong indications that the radio source is interacting with the gaseous medium in NGC 1275. A ~2 mag spread in U-I color is found across the face of the galaxy. The brightest and bluest structure in the U-band image is located along the northern radio lobes and cavity walls in the x-ray emission. Correspondingly bright features are absent along the southern radio lobe. The low velocity Hα emission avoids the cavities in the x-ray emission occupied by the radio lobes. The global distribution of excess blue light, Hα emission, and brightest x-ray emission occur over similar spatial scales (~30-40 kpc). However, the x-ray and optical structures are not correlated in detail. We have detected a faint blue continuum from the outer, "crab-like" low velocity filaments, which may signal ongoing star formation there. In addition, we have detected blue continuum toward the high velocity emission regions, perhaps from stars associated with the high velocity gas. Dark features, probably associated with dust, surround the nucleus and extend in filaments to the north- west. We suggest the dust surrounding the nucleus is associated with NGC 1275 itself, whereas the dust to the north-west may be associated with the high velocity system. The color distribution is consistent with population ages ranging from ~10 Myr to 1 Gyr superposed on an older, elliptical background population. The formation of the youngest (brightest, bluest) population along the radio lobes may have been induced by shock compression of cold gas along the northern radio lobe. This interpretation is complicated, however, by the superposition of light toward both high and low velocity gas to the north-west of the nucleus and the pole-on aspect of the radio source. The cooling rate of the x-ray-emitting gas in the central 20 kpc or so is comparable to the estimated star formation rates over the past several hundred Myr. However, the x-ray structure is more complicated than simple cooling flow models would predict, and there are indications that the dense x-ray structures are falling into the galaxy and have not had time to cool. A merger with a gas-enriched galaxy [Holtzman et al. AJ, 103,691(1992)] may have contributed to the structure. Publication: The Astronomical Journal Pub Date: July 1996 DOI: 10.1086/117991 Bibcode: 1996AJ....112...91M Keywords: GALAXIES: INDIVIDUAL: NGC 1275; X-RAYS: GALAXIES; RADIO LINES: GALAXIES; GALAXIES: ACTIVE full text sources ADS | data products SIMBAD (3) NED (1)

Resolution of the southern radio lobe of 3C 33 at 660 nm

A strand of emission coincident with the peak in the radio emission at 2 and 6 cm was revealed by an HST planetary camera image of the southern radio lobe of 3C 33. The detailed morphological similarity between the optical and radio data conclusively confirms the common origin of the radio and optical emission. The question of whether or not the detailed correlations in emission seen in the jets can also be observed on the larger scales of radio lobes is addressed.