Abstract
We present the first results of the Chandra Cool Targets (CCT) survey of the Second Bologna Catalog (B2CAT) of powerful radio sources, aimed at investigating the extended X-ray emission ...surrounding these sources. For the first 33 sources observed in the B2CAT CCT survey, we performed both imaging and spectral X-ray analysis, producing multiband Chandra images, and compared these images with radio observations. To evaluate the presence of extended emission in the X-rays, we extracted surface flux profiles comparing them with simulated ACIS point-spread functions. We detected X-ray nuclear emission for 28 sources. In addition, we detected eight regions of increased X-ray flux originating from radio hot spots or jet knots, and a region of decreased flux, possibly associated with an X-ray cavity. We performed X-ray spectral analysis for 15 nuclei and found intrinsic absorption significantly larger than the Galactic values in four of them. We detected significant extended X-ray emission in five sources, and fitted their spectra with thermal models with gas temperatures ∼2 keV. In the case of B2.1 0742+31, the surrounding hot gas is compatible with the intracluster medium of low-luminosity clusters of galaxies, while the X-ray diffuse emission surrounding the highly disturbed wide-angle-tailed radio galaxy B2.3 2254+35 features a luminosity similar to those of relatively bright galaxy groups, although its temperature is similar to those of low-luminosity galaxy clusters. These results highlight the power of low-frequency radio selection, combined with short Chandra snapshot observations, for investigating the properties of X-ray emission from radio sources.
In our previous analysis we investigated the large-scale environment of two samples of radio galaxies (RGs) in the local universe (i.e., with redshifts zsrc ≤ 0.15), classified as FR I and FR II on ...the basis of their radio morphology. The analysis was carried out using (i) extremely homogeneous catalogs and (ii) a new method, known as cosmological overdensity, to investigate their large-scale environments. We concluded that, independently of the shape of their radio extended structure, RGs inhabit galaxy-rich large-scale environments with similar characteristics and richness. In the present work, we first highlight additional advantages of our procedure, which does not suffer cosmological biases and/or artifacts, and then we carry out an additional statistical test to strengthen our previous results. We also investigate properties of RG environments using those of the cosmological neighbors. We find that large-scale environments of both FR Is and FR IIs are remarkably similar and independent of the properties of central RG. Finally, we highlight the importance of comparing radio sources in the same redshift bins to obtain a complete overview of their large-scale environments.
This paper presents the analysis of Chandra X-ray snapshot observations of a subsample of the extragalactic sources listed in the revised Third Cambridge radio catalog (3CR), previously lacking X-ray ...observations and thus observed during Chandra Cycle 15. This data set extends the current Chandra coverage of the 3CR extragalactic catalog up to redshift z = 1.0. Our sample includes 22 sources consisting of 1 compact steep spectrum source, 3 quasars (QSOs), and 18 FR II radio galaxies. As in our previous analyses, here we report the X-ray detections of radio cores and extended structures (i.e., knots, hotspots, and lobes) for all sources in the selected sample. We measured their X-ray intensities in three energy ranges, soft (0.5-1 keV), medium (1-2 keV), and hard (2-7 keV), and we also performed standard X-ray spectral analysis for brighter nuclei. All radio nuclei in our sample have an X-ray counterpart. We also discovered X-ray emission associated with the eastern knot of 3CR 154, with radio hotspots in 3CR 41, 3CR 54, and 3CR 225B, and with the southern lobe of 3CR 107. Extended X-ray radiation around the nuclei 3CR 293.1 and 3CR 323 on a scale of few tens of kiloparsecs was also found. X-ray extended emission, potentially arising from the hot gas in the intergalactic medium and/or due to the high-energy counterpart of lobes, is detected for 3CR 93, 3CR 154, 3CR 292, and 3CR 323 over a scale of a few hundred kiloparsecs. Finally, this work also presents an update on the state-of-the-art of Chandra and XMM-Newton observations for the entire 3CR sample.
The aim of this paper is to present an analysis of newly acquired X-ray observations of 16 extragalactic radio sources listed in the Third Cambridge Revised (3CR) catalog and not previously observed ...by Chandra. Observations were performed during Chandra Cycle 17, extending X-ray coverage for the 3CR extragalactic catalog up to z = 1.5. Among the 16 targets, two lie at z < 0.5 (3CR 27 at z = 0.184 and 3CR 69 at z = 0.458); all of the remaining 14 have redshifts between 1.0 and 1.5. In the current sample, there are three compact steep spectrum (CSS) sources, three quasars, and an FR I radio galaxy, while the other nine are FR II radio galaxies. All radio sources have an X-ray counterpart. We measured nuclear X-ray fluxes as well as X-ray emission associated with radio jet knots, hotspots, or lobes in three energy bands: soft (0.5-1 keV), medium (1-2 keV), and hard (2-7 keV). We also performed standard X-ray spectral analysis for the four brightest nuclei. We discovered X-ray emission associated with the radio lobe of 3CR 124, a hotspot of the quasar 3CR 220.2, another hotspot of the radio galaxy 3CR 238, and the jet knot of 3CR 297. We also detected extended X-ray emission around the nuclear region of 3CR 124 and 3CR 297 on scales of several tens of kiloparsecs. Finally, we present an update on the X-ray observations performed with Chandra and XMM-Newton on the entire 3CR extragalactic catalog.
We present the analysis of nine radio sources belonging to the Third Cambridge Revised catalog (3CR) observed with Chandra during Cycle 20 in the redshift range between 1.5 and 2.5. This study ...completes the 3CR Chandra Snapshot Survey thus guaranteeing the X-ray coverage of all 3CR sources identified to date. This sample lists two compact steep spectrum sources, four radio galaxies, and three quasars. We detected X-ray emission from all nuclei, with the only exception of 3C 326.1 and 3C 454.1 and from radio lobes in six out of nine sources at a level of confidence larger than ∼5 . We measured X-ray fluxes and luminosities for all nuclei and lobes in the soft (0.5-1 keV), medium (1-2 keV), and hard (2-7 keV) X-ray bands. Since the discovered X-ray extended emission is spatially coincident with the radio structure in all cases, its origin could be due to inverse Compton (IC) scattering of the cosmic microwave background (CMB) occurring in radio lobes.
Abstract
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 (>3
σ
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.
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.
Abstract
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 active galactic nuclei (AGN) outbursts. We present results of the comparison between Chandra and Very Large Telescope Multi-Unit Spectroscopic Explorer data for the inner region of the galaxy cluster, on a scale of tens of kpc. We discovered H
α
+ N
ii
λ
6584 emission spatially associated with the X-ray cavity (at ∼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
≤ 10
7
K) AGN outflows. We also found that the H
α
, N
ii
λ
λ
6548, 6584, and S
ii
λ
λ
6718, 6733 emission lines show an additional redward component, at ∼1000 km s
−1
from rest frame, with no detection in H
β
or O
iii
λ
λ
4960, 5008. We believe the most likely explanation for this redward component is the presence of a background gas cloud as there appears to be a discrete difference of velocities between this component and the rest frame.
Abstract
We present the analysis of multiwavelength observations of seven extragalactic radio sources, listed as unidentified in the Third Cambridge Revised Catalog (3CR). X-ray observations, ...performed during Chandra Cycle 21, were compared to Very Large Array (VLA), Wide-field Infrared Survey Explorer, and Pan-STARRS observations in the radio, infrared, and optical bands, respectively. All sources in this sample lack a clear optical counterpart, and are thus missing their redshift and optical classification. In order to confirm the X-ray and infrared radio counterparts of core and extended components, here we present for the first time radio maps obtained manually reducing VLA archival data. As in previous papers on the Chandra X-ray snapshot campaign, we report X-ray detections of radio cores and two sources, out of the seven presented here, are found to be members of galaxy clusters. For these two cluster sources (namely, 3CR 409 and 3CR 454.2), we derived surface brightness profiles in four directions. For all seven sources, we measured X-ray intensities of the radio sources and we also performed standard X-ray spectral analysis for the four sources (namely, 3CR 91, 3CR 390, 3CR 409, and 3CR 428) with the brightest nuclei (more than 400 photons in the 2″ nuclear region). We also detected extended X-ray emission around 3CR 390 and extended X-ray emission associated with the northern jet of 3CR 158. This paper represents the first attempt to give a multiwavelength view of the unidentified radio sources listed in the 3CR catalog.
Abstract
We present the analysis of X-ray and optical observations of gas filaments observed in the radio source 3CR 318.1, associated with NGC 5920, the brightest cluster galaxy (BCG) of MKW 3 s, a ...nearby cool core galaxy cluster. This work is one of the first X-ray and optical analyses of filaments in cool core clusters carried out using MUSE observations. We aim at identifying the main excitation processes responsible for the emission arising from these filaments. We complemented the optical VLT/MUSE observations, tracing the colder gas phase, with X-ray Chandra observations of the hotter highly ionized gas phase. Using the MUSE observations, we studied the emission line intensity ratios along the filaments to constrain the physical processes driving the excitation, and, using the Chandra observations, we carried out a spectral analysis of the gas along these filaments. We found a spatial association between the X-ray and optical morphology of these filaments, which are colder and have lower metal abundance than the surrounding intracluster medium (ICM), as already seen in other BCGs. Comparing with previous results from the literature for other BCGs, we propose that the excitation process that is most likely responsible for these filaments emission is a combination of star formation and shocks, with a likely contribution from self-ionizing, cooling ICM. Additionally, we conclude that the filaments most likely originated from AGN-driven outflows in the direction of the radio jet.
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