1,177 research outputs found
The Dynamics of Radio Galaxies and Double-Double Radio Galaxies
Relativistic and magnetised plasma ejected by radio loud AGNs through jets
form the diffuse lobes of radio galaxies. The radiating particles
(electron/electron-positron) in lobes emit in radio via the synchrotron process
and X-ray via inverse-Compton scattering of cosmic microwave background
photons. The thermal environment around radio galaxies emits X-rays via the
thermal bremsstrahlung process. By combining information from these processes
we can measure physical conditions in and around the radio lobes and thus study
the dynamics of radio galaxies, including double-double radio galaxies.Comment: 11 pages, 4 figures, Diffuse Radio Plasma Conference proceedings
(held in Raman Research Institute, Bangalore, India
The dynamics and environmental impact of 3C452
We present a detailed analysis of a new XMM-Newton observation of the FRII
radio galaxy 3C452 and its environment. We detect X-ray emission from the hot
intragroup medium and measure its temperature as well as obtaining the surface
brightness and pressure profiles. We provide evidence that 3C452 is currently
heating its environment, measuring a temperature of keV for the
immediate environment of the radio source compared to
keV for the outer environment. We also present evidence that the outer regions
of the lobes are overpressured (internal pressure of Pa and
external pressure of Pa at the edge of the lobes)
and therefore are driving a shock at the lobe edges (with a temperature which
we constrain to be keV), while the inner regions of the
lobes are underpressured and contracting. Taking into account the very large
amount of energy stored in the lobes, we show that this relatively low-powered
FRII radio galaxy will have an extremely significant impact on its group
environment.Comment: 10 pages, 6 figures (4 in colour). Accepted by MNRA
Brightest Cluster Galaxies and Core Gas Density in REXCESS Clusters
We investigate the relationship between brightest cluster galaxies (BCGs) and
their host clusters using a sample of nearby galaxy clusters from the
Representative XMM Cluster Structure Survey (REXCESS). The sample was imaged
with the Southern Observatory for Astrophysical Research (SOAR) in R band to
investigate the mass of the old stellar population. Using a metric radius of
12h^-1 kpc, we found that the BCG luminosity depends weakly on overall cluster
mass as L_BCG \propto M_cl^0.18+-0.07, consistent with previous work. We found
that 90% of the BCGs are located within 0.035 r_500 of the peak of the X-ray
emission, including all of the cool core (CC) clusters. We also found an
unexpected correlation between the BCG metric luminosity and the core gas
density for non-cool core (non-CC) clusters, following a power law of n_e
\propto L_BCG^2.7+-0.4 (where n_e is measured at 0.008 r_500). The correlation
is not easily explained by star formation (which is weak in non-CC clusters) or
overall cluster mass (which is not correlated with core gas density). The trend
persists even when the BCG is not located near the peak of the X-ray emission,
so proximity is not necessary. We suggest that, for non-CC clusters, this
correlation implies that the same process that sets the central entropy of the
cluster gas also determines the central stellar density of the BCG, and that
this underlying physical process is likely to be mergers.Comment: 16 pages, 8 figures, accepted Astrophysical Journa
Shocks, Seyferts and the SNR connection: a Chandra observation of the Circinus galaxy
We analyse new Chandra observations of the nearest (D=4 Mpc) Seyfert 2 active
galaxy, Circinus, and match them to pre-existing radio, infrared and optical
data to study the kpc-scale emission. The proximity of Circinus allows us to
observe in striking detail the structure of the radio lobes, revealing for the
first time edge-brightened emission both in X-rays and radio. After considering
various other possible scenarios, we show that this extended emission in
Circinus is most likely caused by a jet-driven outflow, which is driving shells
of strongly shocked gas into the halo of the host galaxy. In this context, we
estimate Mach numbers M=2.7-3.6 and M=2.8-5.3 for the W and E shells
respectively. We derive temperatures of 0.74 (+0.06, -0.05) keV and 0.8-1.8 keV
for the W and E shells, and an expansion velocity of ~900-950 km/s. We estimate
that the total energy (thermal and kinetic) involved in creating both shells is
~2x10^55 erg, and their age is ~10^6 years. Comparing these results with those
we previously obtained for Centaurus A, NGC 3801 and Mrk 6, we show that these
parameters scale approximately with the radio power of the parent AGN. The
spatial coincidence between the X-ray and edge-brightened radio emission in
Circinus resembles the morphology of some SNR shocks. This parallel has been
expected for AGN, but has never been observed before. We investigate what
underlying mechanisms both types of systems may have in common, arguing that,
in Circinus, the edge-brightening in the shells may be accounted for by a B
field enhancement caused by shock compression, but do not preclude some local
particle acceleration. These results can be extrapolated to other low-power
systems, particularly those with late type hosts.Comment: 13 pages, 9 figures, and 5 tables. Accepted for publication in Ap
A Flare in the Jet of Pictor A
A Chandra X-ray imaging observation of the jet in Pictor A showed a feature
that appears to be a flare that faded between 2000 and 2002. The feature was
not detected in a follow-up observation in 2009. The jet itself is over 150 kpc
long and a kpc wide, so finding year-long variability is surprising. Assuming a
synchrotron origin of the observed high-energy photons and a minimum energy
condition for the outflow, the synchrotron loss time of the X-ray emitting
electrons is of order 1200 yr, which is much longer than the observed
variability timescale. This leads to the possibility that the variable X-ray
emission arises from a very small sub-volume of the jet, characterized by
magnetic field that is substantially larger than the average over the jet.Comment: 12 pages, 3 figures, to appear in Ap. J. Letter
An X-ray study of magnetic field strengths and particle content in FRII radio sources
We present a Chandra and XMM-Newton study of X-ray emission from the lobes of
33 classical double radio galaxies and quasars. We report new detections of
lobe-related X-ray emission in 11 sources. Together with previous detections we
find that X-ray emission is detected from at least one radio lobe in ~75
percent of the sample. For all of the lobe detections, we find that the
measured X-ray flux can be attributed to inverse-Compton scattering of the
cosmic microwave background radiation, with magnetic field strengths in the
lobes between (0.3 - 1.3) B_eq, where the value B_eq corresponds to
equipartition between the electrons and magnetic field assuming a filling
factor of unity. There is a strong peak in the magnetic field strength
distribution at B ~ 0.7 B_eq. We find that > 70 percent of the radio lobes are
either at equipartition or electron dominated by a small factor. The
distribution of measured magnetic field strengths differs for narrow-line and
broad-line objects, in the sense that broad-line radio galaxies and quasars
appear to be further from equipartition; however, this is likely to be due to a
combination of projection effects and worse systematic uncertainty in the X-ray
analysis for those objects. Our results suggest that the lobes of classical
double radio sources do not contain an energetically dominant proton
population, because this would require the magnetic field energy density to be
similar to the electron energy density rather than the overall energy density
in relativistic particles.Comment: 44 pages, 4 figures. Accepted for publication in Ap
Large Kinetic Power in FRII Radio Jets
We investigate the total kinetic powers (L_{j}) and ages (t_{age}) of
powerful jets of four FR II radio sources (Cygnus A, 3C 223, 3C 284, and 3C
219) by the detail comparison of the dynamical model of expanding cocoons with
observed ones. It is found that these sources have quite large kinetic powers
with the ratio of L_{j} to the Eddington luminosity (L_{Edd}) resides in . Reflecting the large kinetic powers, we also find that the
total energy stored in the cocoon (E_{c}) exceed the energy derived from the
minimum energy condition (E_{min}): . This implies that
a large amount of kinetic power is carried by invisible components such as
thermal leptons (electron and positron) and/or protons.Comment: 5 pages, accepted for publication in Astrophysics and Space Scienc
Detection of non-thermal X-ray emission in the lobes and jets of Cygnus A
This article has been published in Monthly Notices of the Royal Astronomical Society © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. 21 pages, 8 figuresWe present a spectral analysis of the lobes and X-ray jets of Cygnus A, using more than 2 Ms of observations. The X-ray jets are misaligned with the radio jets and significantly wider. We detect non-thermal emission components in both lobes and jets. For the eastern lobe and jet, we find 1 keV flux densities of nJy and nJy, and photon indices of and respectively. For the western lobe and jet, we find flux densities of nJy and nJy, and photon indices of and respectively. Using these results, we modeled the electron energy distributions of the lobes as broken power laws with age breaks. We find that a significant population of non-radiating particles is required to account for the total pressure of the eastern lobe. In the western lobe, no such population is required and the low energy cutoff to the electron distribution there needs to be raised to obtain pressures consistent with observations. This discrepancy is a consequence of the differing X-ray photon indices, which may indicate that the turnover in the inverse-Compton spectrum of the western lobe is at lower energies than in the eastern lobe. We modeled the emission from both jets as inverse-Compton emission. There is a narrow region of parameter space for which the X-ray jet can be a relic of an earlier active phase, although lack of knowledge about the jet's electron distribution and particle content makes the modelling uncertain.Peer reviewedFinal Published versio
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The nature of compact radio-loud AGN: a systematic look at the LOFAR AGN population
© 2024 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/We investigate the nature of low-luminosity radio-loud active galactic nuclei (RLAGN) selected from the LOFAR Two-metre Sky Survey (LoTSS) first data release (DR1). Using optical, mid-infrared, and radio data, we have conservatively selected 55 radiative AGN candidates from DR1 within the redshift range kpc, 42 are compact at the limiting resolution of 0.35 arcsec (taking an upper limit on the projected physical size, this corresponds to less than 1 kpc), and three are undetected. The extended objects display a wide range of radio morphologies: two-jet (5), one-jet (4), and double-lobed (1). We present the radio spectra of all detected radio sources which range from steep to flat/inverted and span the range seen for other compact radio sources such as compact symmetric objects (CSOs), compact steep spectrum (CSS) sources, and gigahertz peaked-spectrum (GPS) sources. Assuming synchrotron self-absorption (SSA) for flat/inverted radio spectrum sources, we predict small physical sizes for compact objects to range between pc. Alternatively, using free-free absorption (FFA) models, we have estimated the free electron column depth for all compact objects, assuming a homogeneous absorber. We find that these objects do not occupy a special position on the power/linear size () diagram but some share a region with radio-quiet quasars (RQQs) and so-called `FR0' sources in terms of radio luminosity and linear size.Peer reviewe
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