1,882 research outputs found
Shock heating in the nearby radio galaxy NGC 3801
Original article can be found at: http://www.journals.uchicago.edu/ApJ/--Copyright American Astronomical SocietyPeer reviewe
The Disturbed 17 keV Cluster Associated with the Radio Galaxy 3C 438
We present results from a {\em Chandra} observation of the cluster gas
associated with the FR II radio galaxy 3C 438. This radio galaxy is embedded
within a massive cluster with gas temperature 17 keV and bolometric
luminosity of 6 ergs s. It is unclear if this high
temperature represents the gravitational mass of the cluster, or if this is an
already high ( 11 keV) temperature cluster that has been heated
transiently. We detect a surface brightness discontinuity in the gas that
extends 600 kpc through the cluster. The radio galaxy 3C 438 is too small
(110 kpc across) and too weak to have created this large disturbance in
the gas. The discontinuity must be the result of either an extremely powerful
nuclear outburst or the major merger of two massive clusters. If the observed
features are the result of a nuclear outburst, it must be from an earlier epoch
of unusually energetic nuclear activity. However, the energy required
( ergs) to move the gas on the observed spatial scales strongly
supports the merger hypothesis. In either scenario, this is one of the most
extreme events in the local Universe.Comment: 13 pages, 4 figures, 1 table - accepted for publication in the
Astrophysical Journal Letter
Numerical modelling of the lobes of radio galaxies in cluster environments -- IV. Remnant radio galaxies
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.We examine the remnant phase of radio galaxies using three-dimensional hydrodynamical simulations of relativistic jets propagating through cluster environments. By switching the jets off once the lobes have reached a certain length we can study how the energy distribution between the lobes and shocked intra-cluster medium compares to that of an active source, as well as calculate synchrotron emission properties of the remnant sources. We see that as a result of disturbed cluster gas beginning to settle back into the initial cluster potential, streams of dense gas are pushed along the jet axis behind the remnant lobes, causing them to rise out of the cluster faster than they would due to buoyancy. This leads to increased adiabatic losses and a rapid dimming. The rapid decay of total flux density and surface brightness may explain the small number of remnant sources found in samples with a high flux density limit and may cause analytic models to overestimate the remnant fraction expected in sensitive surveys such as those now being carried out with LOFAR.Peer reviewedFinal Accepted Versio
A Chandra study of particle acceleration in the multiple hotspots of nearby radio galaxies
We present Chandra observations of a small sample of nearby classical double
radio galaxies which have more than one radio hotspot in at least one of their
lobes. The X-ray emission from the hotspots of these comparatively low-power
objects is expected to be synchrotron in origin, and therefore to provide
information about the locations of high-energy particle acceleration. In some
models of the relationship between the jet and hotspot the hotspots that are
not the current jet termination point should be detached from the energy supply
from the active nucleus and therefore not capable of accelerating particles to
high energies. We find that in fact some secondary hotspots are X-ray sources,
and thus probably locations for high-energy particle acceleration after the
initial jet termination shock. In detail, though, we show that the spatial
structures seen in X-ray are not consistent with naive expectations from a
simple shock model: the current locations of the acceleration of the
highest-energy observable particles in powerful radio galaxies need not be
coincident with the peaks of radio or even optical emission.Comment: Accepted for ApJ. 33 pages, 8 figures inc. 2 in colo
A Chandra Study of the Lobe/ISM Interactions Around the Inner Radio Lobes of Centaurus A: Constraints on the Temperature Structure and Transport Processes
We present results from deeper {\em Chandra} observations of the southwest
radio lobe of Centaurus A, first described by Kraft et al. (2003). We find that
the sharp X-ray surface brightness discontinuity extends around 75% of
the periphery of the radio lobe, and detect significant temperature jumps in
the brightest regions of this discontinuity nearest to the nucleus. This
demonstrates that this discontinuity is indeed a strong shock which is the
result of an overpressure which has built up in the entire lobe over time.
Additionally, we demonstrate that if the mean free path for ions to transfer
energy and momentum to the electrons behind the shock is as large as the
Spitzer value, the electron and proton temperatures will not have equilibrated
along the SW boundary of the radio lobe where the shock is strongest. Thus the
proton temperature of the shocked gas could be considerably larger than the
observed electron temperature, and the total energy of the outburst
correspondingly larger as well. We investigate this using a simple
one-dimensional shock model for a two-fluid (proton/electron) plasma. We find
that for the thermodynamic parameters of the Cen A shock the electron
temperature rises rapidly from 0.29 keV (the temperature of the ambient
ISM) to 3.5 keV at which point heating from the protons is balanced by
adiabatic losses. The proton and electron temperatures do not equilibrate in a
timescale less than the age of the lobe. We note that the measured electron
temperature of similar features in other nearby powerful radio galaxies in poor
environments may considerably underestimate the strength and velocity of the
shock.Comment: 29 pages, 9 figures, 2 tables - accepted for publication in the
Astrophysical Journa
Sub-Arcsecond Imaging of 3C123:108-GHz Continuum Observations of the Radio Hotspots
We present the results of sub-arcsecond 108 GHz continuum interferometric
observations toward the radio luminous galaxy 3C123. Using multi-array
observations, we utilize the high u,v dynamic range of the BIMA millimeter
array to sample fully spatial scales ranging from 0.5" to 50". This allows us
to make one-to-one comparisons of millimeter-wavelength emission in the radio
lobes and hotspots to VLA centimeter observations at 1.4, 4.9, 8.4, and 15 GHz.
At 108 GHz, the bright, eastern double hotspot in the southern lobe is
resolved. This is only the second time that a multiple hotspot region has been
resolved in the millimeter regime. We model the synchrotron spectra of the
hotspots and radio lobes using simple broken power-law models with high energy
cutoffs, and discuss the hotspot spectra and their implications for models of
multiple hotspot formation.Comment: 16 pages, 3 Figures, ApJ Accepte
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
Remnant radio-loud AGN in the Herschel-ATLAS field
Only a small fraction of observed active galactic nuclei (AGN) display large-scale radio emission associated with jets, yet these radio-loud AGN have become increasingly important in models of galaxy evolution. In determining the dynamics and energetics of the radio sources over cosmic time, a key question concerns what happens when their jets switch off. The resulting ‘remnant' radio-loud AGN have been surprisingly evasive in past radio surveys, and therefore statistical information on the population of radio-loud AGN in their dying phase is limited. In this paper, with the recent developments of Low-Frequency Array (LOFAR) and the Very Large Array, we are able to provide a systematically selected sample of remnant radio-loud AGN in the Herschel-ATLAS field. Using a simple core-detection method, we constrain the upper limit on the fraction of remnants in our radio-loud AGN sample to 9 per cent, implying that the extended lobe emission fades rapidly once the core/jets turn off. We also find that our remnant sample has a wide range of spectral indices (−1.5 ⩽ α1400150 ⩽ −0.5), confirming that the lobes of some remnants may possess flat spectra at low frequencies just as active sources do. We suggest that, even with the unprecedented sensitivity of LOFAR, our sample may still only contain the youngest of the remnant population
The origins of X-ray emission from the hotspots of FRII radio sources
We use new and archival Chandra data to investigate the X-ray emission from a
large sample of compact hotspots of FRII radio galaxies and quasars from the 3C
catalogue. We find that only the most luminous hotspots tend to be in good
agreement with the predictions of a synchrotron self-Compton model with
equipartition magnetic fields. At low hotspot luminosities inverse-Compton
predictions are routinely exceeded by several orders of magnitude, but this is
never seen in more luminous hotspots. We argue that an additional synchrotron
component of the X-ray emission is present in low-luminosity hotspots, and that
the hotspot luminosity controls the ability of a given hotspot to produce
synchrotron X-rays, probably by determining the high-energy cutoff of the
electron energy spectrum. It remains plausible that all hotspots are close to
the equipartition condition.Comment: 49 pages, 16 figures. ApJ accepted. Revised version fixes a typo in
one of the Tables and corrects a statement about 3C27
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