Peering into the extended X-ray emission on megaparsec scale in 3C 187

Context. The diffuse X-ray emission surrounding radio galaxies is generally interpreted either as due to inverse Compton scattering of nonthermal radio-emitting electrons on the cosmic microwave background (IC/CMB), or as due to thermal emission arising from the hot gas of the intergalactic medium (IGM) permeating galaxy clusters hosting such galaxies, or as a combination of both. In this work, we present an imaging and spectral analysis of Chandra observations for the radio galaxy 3C 187 to investigate its diffuse X-ray emission and constrain the contribution of these various physical mechanisms. Aims. The main goals of this work are the following: (i) to evaluate the extension of the diffuse X-ray emission from this source; (ii) to investigate the two main processes, IC/CMB and thermal emission from the IGM, which can account for the origin of this emission; and (iii) to test the possibility that 3C 187 belongs to a cluster of galaxies, which can account for the observed diffuse X-ray emission. Methods. To evaluate the extension of the X-ray emission around 3C 187, we extracted surface flux profiles along and across the radio axis. We also extracted X-ray spectra in the region of the radio lobes and in the cross-cone region to estimate the contribution of the nonthermal (IC/CMB) and thermal (IGM) processes to the observed emission, making use of radio (VLA and GMRT) data to investigate the multiwavelength emission arising from the lobes. We collected Pan-STARRS photometric data to investigate the presence of a galaxy cluster hosting 3C 187, looking for the presence of a “red sequence” in the source field in the form of a tight clustering of galaxies in the color space. In addition, we made use of observations performed with the COSMOS spectrograph at the Victor Blanco Telescope to estimate the redshift of the sources in the field of 3C 187 to verify if they are gravitationally bound, as we would expect in a cluster of galaxies. Results. The diffuse X-ray emission around 3C 187 is found to extend in the soft 0.3 − 3 keV band up to ∼850 kpc along the radio lobe direction and ∼530 kpc in the cross-cone direction, and it appears enhanced in correspondence with the radio lobes. Spectral X-ray analysis in the cross-cones indicates a thermal origin for the emission in this region with a temperature ∼4 keV. In the radio lobes, the X-ray spectral analysis in combination with the radio data suggests a dominant IC/CMB radiation in these regions, however we do not rule out a significant thermal contribution. Assuming that the radiation observed in the radio lobes is due to the IGM, the emission from the N and S cones can be interpreted as arising from hot gas with temperatures of ∼3 keV and ∼5 keV, respectively, and found to be in pressure equilibrium with the surrounding gas. Using Pan-STARRS optical data we found that 3C 187 belongs to a red sequence of ∼40 optical sources in the field whose color distribution is significantly different from background sources. We were able to collect optical spectra for only one of these cluster candidates and for 22 field (i.e., noncluster candidates) sources. While the latter show stellar spectra, the former feature a galactic spectrum with a redshift close to 3C 187 nucleus. Conclusions. The diffuse X-ray emission around 3C 187 is elongated along the radio axis and enhanced in correspondence with the radio lobes. This indicates a morphological connection between the emission in the two energy bands and thus suggests a dominating IC/CMB mechanism in these regions. This scenario is reinforced by multiwavelength radio X-ray emission, which in these regions is compatible with IC/CMB radiation. The X-ray spectral analysis however does not rule out a significant contribution to the observed emission from thermal gas, which would be able to emit over tens of gigayears and in pressure equilibrium with the surroundings. Optical data indicate that 3C 187 may belong to a cluster of galaxies, whose IGM would contribute to the X-ray emission observed around the source. Additional X-ray and optical spectroscopic observations are however needed to secure these results and get a more clear picture of the physical processes at play in 3C 187

Powerful Radio Sources in the Southern Sky. III. First Results of the Optical Spectroscopic Campaign

We recently built the G4Jy-3CRE catalog of extragalactic radio sources. This catalog lists 264 powerful radio sources selected with similar criteria to those of the revised Third Cambridge Catalog, but visible from the Southern Hemisphere. A literature search revealed that 119 sources in the G4Jy-3CRE catalog (i.e., 45%) lack a firm spectroscopic redshift measurement. Here, we present a campaign aimed at acquiring optical spectra of G4Jy-3CRE sources and measuring their redshifts. We used single-slit observations obtained with the Víctor Blanco Telescope, the New Technology Telescope, the Southern Astrophysical Research Telescope, and the 2.1 m telescope of the Observatorio Astronómico Nacional at San Pedro Mártir, Mexico. In addition, we analyzed Very Large Telescope/MUSE archival observations. From these observations, we report the spectra and redshifts of 93 sources, 42 of which are the first optical spectra and redshift determinations for the respective sources. With our new data, approximately 71% of the sources in the G4Jy-3CRE catalog now have firm spectroscopic redshift measurements. This data set will be the basis of our future analysis of the optical properties of the G4Jy-3CRE catalog

Peering into the extended X-ray emission on megaparsec scale in 3C 187

Context. The diffuse X-ray emission surrounding radio galaxies is generally interpreted either as due to inverse Compton scattering of nonthermal radio-emitting electrons on the cosmic microwave background (IC/CMB), or as due to thermal emission arising from the hot gas of the intergalactic medium (IGM) permeating galaxy clusters hosting such galaxies, or as a combination of both. In this work, we present an imaging and spectral analysis of Chandra observations for the radio galaxy 3C 187 to investigate its diffuse X-ray emission and constrain the contribution of these various physical mechanisms. Aims. The main goals of this work are the following: (i) to evaluate the extension of the diffuse X-ray emission from this source; (ii) to investigate the two main processes, IC/CMB and thermal emission from the IGM, which can account for the origin of this emission; and (iii) to test the possibility that 3C 187 belongs to a cluster of galaxies, which can account for the observed diffuse X-ray emission. Methods. To evaluate the extension of the X-ray emission around 3C 187, we extracted surface flux profiles along and across the radio axis. We also extracted X-ray spectra in the region of the radio lobes and in the cross-cone region to estimate the contribution of the nonthermal (IC/CMB) and thermal (IGM) processes to the observed emission, making use of radio (VLA and GMRT) data to investigate the multiwavelength emission arising from the lobes. We collected Pan-STARRS photometric data to investigate the presence of a galaxy cluster hosting 3C 187, looking for the presence of a "red sequence"in the source field in the form of a tight clustering of galaxies in the color space. In addition, we made use of observations performed with the COSMOS spectrograph at the Victor Blanco Telescope to estimate the redshift of the sources in the field of 3C 187 to verify if they are gravitationally bound, as we would expect in a cluster of galaxies. Results. The diffuse X-ray emission around 3C 187 is found to extend in the soft 0.3  -  3  keV band up to ∼850  kpc along the radio lobe direction and ∼530  kpc in the cross-cone direction, and it appears enhanced in correspondence with the radio lobes. Spectral X-ray analysis in the cross-cones indicates a thermal origin for the emission in this region with a temperature ∼4  keV. In the radio lobes, the X-ray spectral analysis in combination with the radio data suggests a dominant IC/CMB radiation in these regions, however we do not rule out a significant thermal contribution. Assuming that the radiation observed in the radio lobes is due to the IGM, the emission from the N and S cones can be interpreted as arising from hot gas with temperatures of ∼3  keV and ∼5  keV, respectively, and found to be in pressure equilibrium with the surrounding gas. Using Pan-STARRS optical data we found that 3C 187 belongs to a red sequence of ∼40 optical sources in the field whose color distribution is significantly different from background sources. We were able to collect optical spectra for only one of these cluster candidates and for 22 field (i.e., noncluster candidates) sources. While the latter show stellar spectra, the former feature a galactic spectrum with a redshift close to 3C 187 nucleus. Conclusions. The diffuse X-ray emission around 3C 187 is elongated along the radio axis and enhanced in correspondence with the radio lobes. This indicates a morphological connection between the emission in the two energy bands and thus suggests a dominating IC/CMB mechanism in these regions. This scenario is reinforced by multiwavelength radio X-ray emission, which in these regions is compatible with IC/CMB radiation. The X-ray spectral analysis however does not rule out a significant contribution to the observed emission from thermal gas, which would be able to emit over tens of gigayears and in pressure equilibrium with the surroundings. Optical data indicate that 3C 187 may belong to a cluster of galaxies, whose IGM would contribute to the X-ray emission observed around the source. Additional X-ray and optical spectroscopic observations are however needed to secure these results and get a more clear picture of the physical processes at play in 3C 187

Peering Into the Extended X-ray Emission on Megaparsec Scale in 3C 187

Context. The diffuse X-ray emission surrounding radio galaxies is generally interpreted either as due to inverse Compton scattering of non-thermal radio-emitting electrons on the Cosmic Microwave Background (IC/CMB), or as the thermal emission arising from the hot gas of the intergalactic medium (IGM) permeating galaxy clusters hosting such galaxies, or as a combination of both. In this work we present an imaging and spectral analysis of Chandra observations for the radio galaxy 3C 187 to investigate its diffuse X-ray emission and constrain the contribution of these different physical mechanisms. Aims. The main goals of this work are: (i) to evaluate the extension of the diffuse X-ray emission from this source, (ii) to investigate the two main processes that can account for its origin - IC/CMB and thermal emission from the IGM - and (iii) to test the possibility for 3C 187 to belong to a cluster of galaxies, that can account for the observed diffuse X-ray emission. Methods. To evaluate the extension of the X-ray emission around 3C 187 we extracted surface flux profiles along and across the radio axis. We also extracted X-ray spectra in the region of the radio lobes and in the cross-cone region to estimate the contribution of the non-thermal (IC/CMB) and thermal (IGM) processes to the observed emission, making use of radio (VLA and GMRT) data to investigate the multi-wavelength emission arising from the lobes. We collected Pan-STARRS photometric data to investigate the presence of a galaxy cluster hosting 3C 187, looking for the presence of a "red sequence" in the source field in the form of a tight clustering of the galaxies in the color space...Comment: 32 pages, 13 figures, accepted for publication on A&A on 12/19/202

Powerful Radio Sources in the Southern Sky. II. A SWIFT X-Ray Perspective

We recently constructed the G4Jy-3CRE, a catalog of extragalactic radio sources based on the GLEAM 4-Jy (G4Jy) sample, with the aim of increasing the number of powerful radio galaxies and quasars with similar selection criteria to those of the revised release of the Third Cambridge catalog (3CR). The G4Jy-3CRE consists of a total of 264 radio sources mainly visible from the Southern Hemisphere. Here, we present an initial X-ray analysis of 89 G4Jy-3CRE radio sources with archival X- ray observations from the Neil Gehrels Swift Observatory. We reduced a total of 615 Swift observations, for about 0.89 Msec of integrated exposure time, we found X-ray counterparts for 61 radio sources belonging to the G4Jy-3CRE, 11 of them showing extended X-ray emission. The remaining 28 sources do not show any X-ray emission associated with their radio cores. Our analysis demonstrates that X-ray snapshot observations, even if lacking uniform exposure times, as those carried out with Swift, allow us to (i) verify and/or re ne the host galaxy identi cation; (ii) discover the extended X-ray emission around radio galaxies of the intracluster medium when harbored in galaxy clusters, as the case of G4Jy 1518 and G4Jy 1664, and (iii) detect X-ray radiation arising from their radio lobes, as for G4Jy 1863.Comment: 35 pages, 17 figures, 2 tables; second paper of a series, pre-proof versio

Disentangling the nature of the prototype radio weak BL Lac: Contemporaneous multifrequency observations of WISE J141046.00 + 740511.2

Context. The gamma-ray emitting source WISE J141046.00+740511.2 has been associated with a Fermi-LAT detection by crossmatching with Swift/XRT data. It has shown all the canonical observational characteristics of a BL Lac source, including a power-law, featureless optical spectrum. However, it was only recently detected at radio frequencies and its radio flux is significantly low. Aims. Given that a radio detection is fundamental to associate lower-energy counterparts to Fermi-LAT sources, we aim to unambiguously classify this source by performing a multiwavelength analysis based on contemporaneous data. Methods. By using multifrequency observations at the Jansky Very Large Array, Giant Metrewave Radio Telescope, Gran Telescopio Canarias, Gemini, William Herschel Telescope and Liverpool observatories, together with Fermi-LAT and Swift data, we carried out two kinds of analyses. On one hand, we studied several known parameters that account for the radio loudness or weakness characterization and their application to blazars (in general) and to our source (in particular). And, on the other hand, we built and analyzed the observed spectral energy distribution (SED) of this source to try to explain its peculiar characteristics. Results. The multiwavelength analysis indicates that WISE J141046.00+740511.2 is a blazar of the high-frequency peaked (HBL) type that emits highly polarized light and that is likely located at a low redshift. In addition, the one-zone model parameters that best fit its SED are those of an extreme HBL (EHBL); this blazar type has been extensively predicted in theory to be lacking in the radio emission that is otherwise typical of canonical gamma-ray blazars. Conclusions. We confirm that WISE J141046.00+740511.2 is indeed a highly polarized BL Lac of the HBL type. Further studies will be conducted to explain the atypical low radio flux detected for this source.Comment: accepted for publication in A&A, in pres

Powerful Radio Sources in the Southern Sky. I. Optical Identifications

Since the early sixties, our view of radio galaxies and quasars has been drastically shaped by discoveries made thanks to observations of radio sources listed in the Third Cambridge catalog and its revised version (3CR). However, the largest fraction of data collected to date on 3CR sources was performed with relatively old instruments, rarely repeated and/or updated. Importantly, the 3CR contains only objects located in the Northern Hemisphere thus having limited access to new and innovative astronomical facilities. To mitigate these limitations we present a new catalog of powerful radio sources visible from the Southern Hemisphere, extracted from the GLEAM 4-Jy (G4Jy) catalog and based on equivalent selection criteria as the 3CR. This new catalog, named G4Jy- 3CRE, where the E stands for "equivalent", lists a total of 264 sources at declination below -5 degrees and with 9 Jy limiting sensitivity at ~178 MHz. We explored archival radio maps obtained with different surveys and compared then with optical images available in the Pan-STARRS, DES and DSS databases to search for optical counterparts of their radio cores. We compared mid-infrared counterparts, originally associated in the G4Jy, with the optical ones identified here and we present results of a vast literature search carried out to collect redshift estimates for all G4Jy-3CRE sources resulting in a total of 145 reliable z measurements.Comment: 72 pages, 35 figures, 5 Table

The cavity of 3CR 196.1: Hα\alpha emission spatially associated with an X-ray cavity

We present a multifrequency analysis of the radio galaxy 3CR 196.1 ($z = 0.198$), associated with the brightest galaxy of the cool core cluster CIZAJ0815.4-0303. This nearby radio galaxy shows a hybrid radio morphology and an X-ray cavity, all signatures of a turbulent past activity, potentially due to merger events and AGN outbursts. We present results of the comparison between $Chandra$ and VLT/MUSE data for the inner region of the galaxy cluster, on a scale of tens of kpc. We discovered H$\alpha$ + [N II]$\lambda6584$ emission spatially associated with the X-ray cavity (at $\sim$10 kpc from the galaxy nucleus) instead of with its rim. This result differs from previous discoveries of ionized gas surrounding X-ray cavities in other radio galaxies harbored in galaxy clusters and could represent the first reported case of ionized gas filling an X-ray cavity, either due to different AGN outbursts or to the cooling of warm ($10^4<T\leq10^7$ K) AGN outflows. We also found that the H$\alpha$, [N II]$\lambda\lambda6548,6584$ and [S II]$\lambda\lambda6718,6733$ emission lines show an additional redward component, at $\sim$1000 km$\,$s$^{-1}$ from rest frame, with no detection in H$\beta$ or [O III]$\lambda\lambda4960,5008$. We believe the most likely explanation for this redward component is the presence of a background gas cloud since there appears to be a discrete difference in velocities between this component and the rest frame.Comment: 15 pages, 8 figures, ApJ accepted, pre-proof versio

Extended X-ray emission around FR II radio galaxies: Hot spots, lobes, and galaxy clusters

We present a systematic analysis of the extended X-ray emission discovered around 35 FR II radio galaxies from the revised Third Cambridge Catalog (3CR) Chandra Snapshot Survey with redshifts between 0.05 and 0.9. We aimed to (i) test for the presence of extended X-ray emission around FR II radio galaxies, (ii) investigate whether the extended emission origin is due to inverse Compton (IC) scattering of seed photons arising from the cosmic microwave background (CMB) or thermal emission from an intracluster medium (ICM), and (iii) test the impact of this extended emission on hot-spot detection. We investigated the nature of the extended X-ray emission by studying its morphology and compared our results with low-frequency radio observations (i.e., ~150 MHz) in the TGSS and LOFAR archives, as well as with optical images from Pan-STARRS. In addition, we optimized a search for X-ray counterparts of hot spots in 3CR FR II radio galaxies. We found statistically significant extended emission (&gt;3s confidence level) along the radio axis of ~90% and in the perpendicular direction of ~60% of the galaxies in our sample. We confirmed the detection of seven hot spots in the 0.5-3 keV energy range. In the cases where the emission in the direction perpendicular to the radio axis is comparable to that along the radio axis, we suggest that the underlying radiative process is thermal emission from the ICM. Otherwise, the dominant radiative process is likely nonthermal IC/CMB emission from lobes. We found that nonthermal IC/CMB is the dominant process in ~70% of the sources in our sample, while thermal emission from the ICM dominates in ~15% of them