ABSTRACT
Double lobe radio sources associated with active galactic nuclei represent one of the longest studied groups in radio astronomy. A particular subgroup of double radio sources comprises the ...compact symmetric objects (CSOs). CSOs are distinguished by their prominent double structure and subkpc total size. It has been argued that the vast majority of high-luminosity CSOs (CSO 2s) represent a distinct class of active galactic nuclei with its own morphological structure and lifecycle. In this work, we present theoretical considerations regarding CSO 2s. We develop a semi-analytic evolutionary model, inspired by the results of large-scale numerical simulations of relativistic jets, that reproduces the features of the radio source population. We show that CSO 2s may be generated by finite energy injections and propose stellar tidal disruption events as a possible cause. We find that tidal disruption events of giant branch stars with masses ≳1 M⊙ can fuel these sources and discuss possible approaches to confirming this hypothesis. We predict that if the tidal disruption scenario holds, CSO 2s with sizes less than 400 pc should outnumber larger sources by more than a factor of 10. Our results motivate future numerical studies to determine whether the scenarios we consider for fuelling and source evolution can explain the observed radio morphologies. Multiwavelength observational campaigns directed at these sources will also provide critical insight into the origins of these objects, their environments, and their lifespans.
We present the new Very Large Array 22 GHz and extended Multi-Element Remote-Linked Interferometer Network 5 GHz observations of CLASS B1030+074, a two-image strong gravitational lens system whose ...background source is a compact flat-spectrum radio quasar. In such systems we expect a third image of the background source to form close to the centre of the lensing galaxy. The existence and brightness of such images is important for investigation of the central mass distributions of lensing galaxies, but only one secure detection has been made so far in a galaxy-scale lens system. The noise levels achieved in our new B1030+074 images reach 3 μJy beam−1 and represent an improvement in central image constraints of nearly an order of magnitude over previous work, with correspondingly better resulting limits on the shape of the central mass profile of the lensing galaxy. Simple models with an isothermal outer power-law slope now require either the influence of a central supermassive black hole (SMBH), or an inner power-law slope very close to isothermal, in order to suppress the central image below our detection limit. Using the central mass profiles inferred from light distributions in Virgo galaxies, moved to z = 0.5, and matching to the observed Einstein radius, we now find that 45 per cent of such mass profiles should give observable central images, 10 per cent should give central images with a flux density still below our limit, and the remaining systems have extreme demagnification produced by the central SMBH. Further observations of similar objects will therefore allow proper statistical constraints to be placed on the central properties of elliptical galaxies at high redshift.
AGN feedback in the FR II galaxy 3C 220.1 Liu, Wenhao; Sun, Ming; Nulsen, Paul E J ...
Monthly Notices of the Royal Astronomical Society,
03/2020, Volume:
492, Issue:
3
Journal Article
Peer reviewed
Open access
ABSTRACT
We present results from a deep (174 ks) Chandra observation of the FR-II radio galaxy 3C 220.1, the central brightest cluster galaxy (BCG) of a kT ∼ 4 keV cluster at z = 0.61. The ...temperature of the hot cluster medium drops from ∼5.9 to ∼3.9 keV at ∼35 kpc radius, while the temperature at smaller radii may be substantially lower. The central active galactic nucleus (AGN) outshines the whole cluster in X-rays, with a bolometric luminosity of 2.0 × 1046 erg s−1 (∼10 per cent of the Eddington rate). The system shows a pair of potential X-ray cavities ∼35 kpc east and west of the nucleus. The cavity power is estimated within the range of 1.0 × 1044 and 1.7 × 1045 erg s−1, from different methods. The X-ray enhancements in the radio lobes could be due to inverse Compton emission, with a total 2–10 keV luminosity of ∼8.0 × 1042 erg s−1. We compare 3C 220.1 with other cluster BCGs, including Cygnus A, as there are few BCGs in rich clusters hosting an FR-II galaxy. We also summarize the jet power of FR-II galaxies from different methods. The comparison suggests that the cavity power of FR-II galaxies likely underestimates the jet power. The properties of 3C 220.1 suggest that it is at the transition stage from quasar-mode feedback to radio-mode feedback.
Abstract
Low-frequency radio selection finds radio-bright galaxies regardless of the amount of obscuration by gas and dust. We report Chandra observations of a complete 178 MHz–selected, and so ...orientation-unbiased, sample of 44 0.5 <
z
< 1 3CRR sources. The sample is comprised of quasars and narrow-line radio galaxies (NLRGs) with similar radio luminosities, and the radio structure serves as both an age and an orientation indicator. Consistent with unification, intrinsic obscuration (measured by
N
H
, X-ray hardness ratio, and X-ray luminosity) generally increases with inclination. However, the sample includes a population not seen in high-
z
3CRR sources: NLRGs viewed at intermediate inclination angles with
N
H
< 10
22
cm
−2
. Multiwavelength analysis suggests that these objects have lower
L
/
L
Edd
than typical NLRGs at similar orientation. Thus, both orientation and
L
/
L
Edd
are important, and a “radiation-regulated unification” provides a better explanation of the sample’s observed properties. In comparison with the 3CRR sample at 1 <
z
< 2, our lower-redshift sample shows a higher fraction of Compton-thin NLRGs (45% versus 29%) but a similar Compton-thick fraction (20%), implying a larger covering factor of Compton-thin material at intermediate viewing angles and thus a more “puffed-up” torus atmosphere. We posit that this is due to a range of
L
/
L
Edd
extending to lower values in this sample. In contrast, at high redshifts, the narrower range and high
L
/
L
Edd
values allowed orientation (and so simple unification) to dominate the sample’s observed properties.
The XXL Survey Smolčić, Vernesa; Intema, Huib; Šlaus, Bruno ...
Astronomy and astrophysics (Berlin),
12/2018, Volume:
620
Journal Article
Peer reviewed
Open access
We present the 25 square-degree GMRT-XXL-N 610 MHz radio continuum survey, conducted at 50 cm wavelength with the Giant Metrewave Radio Telescope (GMRT) towards the XXL Northern field (XXL-N). We ...combined previously published observations of the XMM-Large Scale Structure (XMM-LSS) field, located in the central part of XXL-N, with newly conducted observations towards the remaining XXL-N area, and imaged the combined data-set using the Source Peeling and Atmospheric Modeling (SPAM) pipeline. The final mosaic encompasses a total area of 30.4 square degrees, with rms <150
μ
Jy beam
−1
over 60% of the area. The rms achieved in the inner 9.6 square degree area, enclosing the XMM-LSS field, is about 200
μ
Jy beam
−1
, while that over the outer 12.66 square degree area (which excludes the noisy edges) is about 45
μ
Jy beam
−1
. The resolution of the final mosaic is 6.5 arcsec. We present a catalogue of 5434 sources detected at ≥7 ×rms. We verify, and correct the reliability of, the catalog in terms of astrometry, flux, and false detection rate. Making use of the (to date) deepest radio continuum survey over a relatively large (2 square degree) field, complete at the flux levels probed by the GMRT-XXL-N survey, we also assess the survey’s incompleteness as a function of flux density. The radio continuum sensitivity reached over a large field with a wealth of multi-wavelength data available makes the GMRT-XXL-N 610 MHz survey an important asset for studying the physical properties, environments and cosmic evolution of radio sources, in particular radio-selected active galactic nuclei (AGN).
We use 2.0 Msec of Chandra observations to investigate the cocoon shocks of Cygnus A and some implications for its lobes and jet. Measured shock Mach numbers vary in the range 1.18-1.66 around the ...cocoon. We estimate a total outburst energy of , with an age of . The average postshock pressure is found to be , which agrees with the average pressure of the thin rim of compressed gas between the radio lobes and shocks, as determined from X-ray spectra. However, average rim pressures are found to be lower in the western lobe than in the eastern lobe by 20%. Pressure estimates for hotspots A and D from synchrotron self-Compton models imply that each jet exerts a ram pressure 3 times its static pressure, consistent with the positions of the hotspots moving about on the cocoon shock over time. A steady, one-dimensional flow model is used to estimate jet properties, finding mildly relativistic flow speeds within the allowed parameter range. Models in which the jet carries a negligible flux of rest mass are consistent with the observed properties of the jets and hotspots. This favors the jets being light, implying that the kinetic power and momentum flux are carried primarily by the internal energy of the jet plasma rather than by its rest mass.
We present the Giant Metrewave Radio Telescope 240 MHz observations of the nearby luminous Fanaroff–Riley type I radio source 3C 270, in the group-central elliptical NGC 4261. Combining these data ...with reprocessed Very Large Array 1.55 and 4.8 GHz observations, we produce spectral-index maps that reveal a constant spectral index along the jets and a gradual steepening from the ends of the jets through the lobes towards the nucleus. A Jaffe & Perola (JP) model fitted to the integrated spectrum of the source gives an asymptotic low-frequency index of
$\alpha _{\rm {inj}}=0.53_{-0.02}^{+0.01}$
, while JP models fitted to the observed spectral index trend along the lobes allow us to estimate radiative ages of ∼29 and ∼37 Myr for the west and east lobes, respectively. Our age estimates are a factor of 2 lower than the 75-Myr upper limit derived from X-ray data. We find unlikely the scenario of an early supersonic phase in which the lobe expanded into the ISM at approximately Mach 6 (3500 km s−1), and suggest that either the source underwent multiple active galactic nuclei outbursts with possible large changes in jet power, or possibly that the source age that we find is due to a backflow that transports young electrons from the jet tips through the lobes towards the nucleus relatively quickly. We calculate that in the lobes the energy ratio of non-radiating to radiating particles is ∼4–24 indicating significant gas entrainment. If the lobes are in pressure balance with their surroundings, the total energy required to heat the entrained material is 1058 erg, ∼40 per cent of the total enthalpy of the lobes.
Abstract We present a new machine learning (ML)-driven source-finding tool for next-generation radio surveys that performs fast source extraction on a range of source morphologies at large dynamic ...ranges with minimal parameter tuning and post-processing. The construction of the Square Kilometre Array (SKA) radio telescope will revolutionize the field of radio astronomy. However, accurate and automated source-finding techniques are required to reach SKA science goals. We have developed a novel source-finding method, ContinUNet, powered by an ML segmentation algorithm, U-Net, that has proven highly effective and efficient when tested on SKA precursor data sets. Our model was trained and tested on simulated radio continuum data from SKA Science Data Challenge 1 and proved comparable with the state-of-the-art source-finding methods, PyBDSF and ProFound. ContinUNet was then tested on the MeerKAT International GHz Tiered Extragalactic Exploration Early Science data without retraining and was able to extract point-like and extended sources with equal ease; processing a 1.6 deg$^2$ field in $\lt $13 s on a supercomputer and $\approx$2 min on a personal laptop. We were able to associate components of extended sources without manual intervention with the powerful inference capabilities learnt within the network, making ContinUNet a promising tool for enabling science in the upcoming SKA era.
The XXL Survey Farahi, Arya; Guglielmo, Valentina; Evrard, August E. ...
Astronomy and astrophysics (Berlin),
12/2018, Volume:
620
Journal Article
Peer reviewed
Open access
Context.
An X-ray survey with the
XMM-Newton
telescope, XMM-XXL, has identified hundreds of galaxy groups and clusters in two 25 deg
2
fields. Combining spectroscopic and X-ray observations in one ...field, we determine how the kinetic energy of galaxies scales with hot gas temperature and also, by imposing prior constraints on the relative energies of galaxies and dark matter, infer a power-law scaling of total mass with temperature.
Aims.
Our goals are: i) to determine parameters of the scaling between galaxy velocity dispersion and X-ray temperature,
T
300 kpc
, for the halos hosting XXL-selected clusters, and; ii) to infer the log-mean scaling of total halo mass with temperature, ⟨ln
M
200
|
T
300 kpc
,
z
⟩.
Methods.
We applied an ensemble velocity likelihood to a sample of >1500 spectroscopic redshifts within 132 spectroscopically confirmed clusters with redshifts
z
< 0.6 to model, ⟨ln
σ
gal
|
T
300 kpc
,
z
⟩, where
σ
gal
is the velocity dispersion of XXL cluster member galaxies and
T
300 kpc
is a 300 kpc aperture temperature. To infer total halo mass we used a precise virial relation for massive halos calibrated by
N
-body simulations along with a single degree of freedom summarising galaxy velocity bias with respect to dark matter.
Results.
For the XXL-N cluster sample, we find σ
gal
∝ T
300 kpc
0.63±0.05
, a slope significantly steeper than the self-similar expectation of 0.5. Assuming scale-independent galaxy velocity bias, we infer a mean logarithmic mass at a given X-ray temperature and redshift,
〈ln(
E
(
z
)
M
200
/10
14
M
⊙
)|T
300
kpc,
z
〉 = π
T
+ α
T
ln (
T
300
kpc/
T
p
) +
β
T
ln (
E
(
z
)/
E
(
z
p
)) using pivot values
kT
p
= 2.2 keV and
z
p
= 0.25, with normalization
π
T
= 0.45 ± 0.24 and slope
α
T
= 1.89 ± 0.15. We obtain only weak constraints on redshift evolution,
β
T
= −1.29 ± 1.14.
Conclusions.
The ratio of specific energies in hot gas and galaxies is scale dependent. Ensemble spectroscopic analysis is a viable method to infer mean scaling relations, particularly for the numerous low mass systems with small numbers of spectroscopic members per system. Galaxy velocity bias is the dominant systematic uncertainty in dynamical mass estimates.
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