137 research outputs found
Radiative pressure feedback by a quasar in a galactic bulge
We show that Eddington-limited black hole luminosities can be sufficient to
deplete a galaxy bulge of gas through radiation pressure, when the ionization
state of the gas and the presence of dust are properly taken into account. Once
feedback starts to be effective it can consistently drive all the gas out of
the whole galaxy. We estimate the amount by which the effect of radiation
pressure on dusty gas boosts the mass involved in the Eddington limit and
discuss the expected column density at which the gas is ejected. An example is
shown of the predicted observed nuclear spectrum of the system at the end of an
early, obscured phase of growth when the remaining column density NH ~ f * 1e24
cm^-2 where f is the gas fraction in the bulge.Comment: correct corrupted figures in pdf version, MNRAS accepted, 5 pages, 3
figure
Inverse Compton X-rays from Giant Radio Galaxies at z~1
We report XMM-Newton observations of three FR II radio galaxies at redshifts
between 0.85 and 1.34, which show extended diffuse X-ray emission within the
radio lobes, likely due to inverse-Compton up-scattering of the cosmic
microwave background. Under this assumption, through spectrum-fitting together
with archival VLA radio observations, we derive an independent estimate of the
magnetic field in the radio lobes of 3C 469.1 and compare it with the
equipartition value. We find concordance between these two estimates as long as
the turnover in the energy distribution of the particles occurs at a Lorentz
factor in excess of ~ 250. We determine the total energy in relativistic
particles in the radio emitting lobes of all three sources to range between
3e59 and 8e59 erg. The nuclei of these X-ray sources are heavily-absorbed
powerful AGN.Comment: 5 pages, 7 figures, 2 tables. Accepted for publication in MNRA
The Compton-thick quasar at the heart of the high-redshift giant radio galaxy 6C 0905+39
Our XMM-Newton spectrum of the giant, high-redshift (z=1.88) radio galaxy 6C
0905+39 shows that it contains one of the most powerful, high-redshift,
Compton-thick quasars known. Its spectrum is very hard above 2 keV. The steep
XMM spectrum below that energy is shown to be due to extended emission from the
radio bridge using Chandra data. The nucleus of 6C 0905+39 has a column density
of 3.5 (+1.4,-0.4) X 10^24 cm^-2 and absorption-corrected X-ray luminosity of
1.7 (+0.9,-0.1) X 10^45 erg/s in the 2-10 keV band. A lower redshift active
galaxy in the same field, SDSS J090808.36+394313.6, may also be Compton-thick.Comment: 5 pages, 5 figures, accepted to MNRA
The luminous X-ray hotspot in 4C 74.26: synchrotron or inverse-Compton emission?
We report the discovery of an X-ray counterpart to the southern radio hotspot
of the largest-known radio quasar 4C 74.26 (whose redshift is z=0.104). Both
XMM-Newton and Chandra images reveal the same significant (10arcsec, i.e.
19kpc) offset between the X-ray hotspot and the radio hotspot imaged with
MERLIN. The peak of the X-ray emission may be due to synchrotron or
inverse-Compton emission. If synchrotron emission, the hotspot represents the
site of particle acceleration and the offset arises from either the jet
exhibiting Scheuer's `dentist's drill' effect or a fast spine having less
momentum than the sheath surrounding it, which creates the radio hotspot. If
the emission arises from the inverse-Compton process, it must be
inverse-Compton scattering of the CMB in a decelerating relativistic flow,
implying that the jet is relativistic (Gamma >= 2) out to a distance of at
least 800kpc. Our analysis, including optical data from the Liverpool
Telescope, rules out a background AGN for the X-ray emission and confirms its
nature as a hotspot, making it the most X-ray luminous hotspot yet detected.Comment: 9 pages, 9 figures, definitive version published by MNRA
The X-ray and radio-emitting plasma lobes of 4C23.56: further evidence of recurrent jet activity and high acceleration energies
New Chandra observations of the giant (0.5 Mpc) radio galaxy 4C23.56 at z =
2.5 show X-rays in a linear structure aligned with its radio emission, but
anti-correlated with the detailed radio structure. Consistent with the
powerful, high-z giant radio galaxies we have studied previously, X-rays seem
to be invariably found where the lobe plasma is oldest even where the radio
emission has long since faded. The hotspot complexes seem to show structures
resembling the double shock structure exhibited by the largest radio quasar
4C74.26, with the X-ray shock again being offset closer to the nucleus than the
radio synchrotron shock. In the current paper, the offsets between these shocks
are even larger at 35kpc. Unusually for a classical double (FRII) radio source,
there is smooth low surface-brightness radio emission associated with the
regions beyond the hotspots (further away from the nucleus than the hotspots
themselves), which seems to be symmetric for the ends of both jets. We consider
possible explanations for this phenomenon, and conclude that it arises from
high-energy electrons, recently accelerated in the nearby radio hotspots that
are leaking into a pre-existing weakly-magnetized plasma that are symmetric
relic lobes fed from a previous episode of jet activity. This contrasts with
other manifestations of previous epochs of jet ejection in various examples of
classical double radio sources namely (1) double-double radio galaxies by e.g.
Schoenmakers et al, (2) the double-double X-ray/radio galaxies by Laskar et al
and (3) the presence of a relic X-ray counter-jet in the prototypical classical
double radio galaxy, Cygnus A by Steenbrugge et al. The occurrence of
multi-episodic jet activity in powerful radio galaxies and quasars indicates
that they may have a longer lasting influence on the on-going structure
formation processes in their environs than previously presumed.Comment: Accepted by MNRAS; 6 page
The inverse-Compton X-ray-emitting lobes of the high-redshift giant radio galaxy 6C 0905+39
We present new XMM-Newton data of the high-redshift (z=1.883), Mpc-sized
giant radio galaxy 6C 0905+39. The larger collecting area and longer
observation time for our new data means that we can better characterise the
extended X-ray emission, in particular its spectrum, which arises from cosmic
microwave background photons scattered into the X-ray band by the energetic
electrons in the spent synchrotron plasma of the (largely) radio-quiet lobes of
6C 0905+39. We calculate the energy that its jet-ejected plasma has dumped into
its surroundings in the last 3 X 10^7 years and discuss the impact that
similar, or even more extreme, examples of spent, radio-quiet lobes would have
on their surroundings. Interestingly, there is an indication that the emission
from the hotspots is softer than the rest of the extended emission and the
core, implying it is due to synchrotron emission. We confirm our previous
detection of the low-energy turnover in the eastern hotspot of 6C 0905+39.Comment: 7 pages, 7 figures, accepted by MNRA
Two types of shock in the hotspot of the giant quasar 4C74.26: a high-resolution comparison from Chandra, Gemini & MERLIN
New Chandra observations have resolved the structure of the X-ray luminous
southern hotspot in the giant radio quasar 4C74.26 into two distinct features.
The nearer one to the nucleus is an extremely luminous peak, extended some 5
kpc perpendicular to the orientation of the jet; 19 kpc projected further away
from the central nucleus than this is a fainter X-ray arc having similar
symmetry. This arc is co-spatial with near-IR and optical emission imaged with
Gemini, and radio emission imaged with MERLIN. The angular separation of the
double shock structure (itself ~19 kpc or 10 arcsec in size) from the active
nucleus which fuels them of ~550 kpc is a reminder of the challenge of
connecting "unidentified" hard X-ray or Fermi sources with their origins.Comment: In press at MNRA
The extended X-ray emission around HDF130 at z=1.99: an inverse Compton ghost of a giant radio source in the Chandra Deep Field North
One of the six extended X-ray sources found in the Chandra DeepField North is
centred on HDF130, which has recently been shown to be a massive galaxy at
z=1.99 with a compact radio nucleus. The X-ray source has a roughly
double-lobed structure with each lobe about 41 arcsec long, or 345 kpc at the
redshift of HDF130. We have analyzed the 2 Ms X-ray image and spectrum of the
source and find that it is well fit by a power-law continuum of photon index
2.65 and has a 2--10 keV luminosity of 5.4x10^{43}ergps (if at z=1.99). Any
further extended emission within a radius of 60 arcsec has a luminosity less
than half this value, which is contrary to what is expected from a cluster of
galaxies. The source is best explained as an inverse Compton ghost of a giant
radio source, which is no longer being powered, and for which Compton losses
have downgraded the energetic electrons, \gamma> 10^4, required for
high-frequency radio emission. The lower energy electrons, \gamma~1000, produce
X-rays by inverse Compton scattering on the Cosmic Microwave Background.
Depending on the magnetic field strength, some low frequency radio emission may
remain. Further inverse Compton ghosts may exist in the Chandra deep fields.Comment: 4 pages, 2 figures, accepted for publication in MNRA
The inverse-Compton ghost HDF 130 and the giant radio galaxy 6C 0905+3955: matching an analytic model for double radio source evolution
We present new GMRT observations of HDF 130, an inverse-Compton (IC) ghost of
a giant radio source that is no longer being powered by jets. We compare the
properties of HDF 130 with the new and important constraint of the upper limit
of the radio flux density at 240 MHz to an analytic model. We learn what values
of physical parameters in the model for the dynamics and evolution of the radio
luminosity and X-ray luminosity (due to IC scattering of the cosmic microwave
background (CMB)) of a Fanaroff-Riley II (FR II) source are able to describe a
source with features (lobe length, axial ratio, X-ray luminosity, photon index
and upper limit of radio luminosity) similar to the observations. HDF 130 is
found to agree with the interpretation that it is an IC ghost of a powerful
double-lobed radio source, and we are observing it at least a few Myr after jet
activity (which lasted 5--100 Myr) has ceased. The minimum Lorentz factor of
injected particles into the lobes from the hotspot is preferred to be
for the model to describe the observed quantities well,
assuming that the magnetic energy density, electron energy density, and lobe
pressure at time of injection into the lobe are linked by constant factors
according to a minimum energy argument, so that the minimum Lorentz factor is
constrained by the lobe pressure. We also apply the model to match the features
of 6C 0905+3955, a classical double FR II galaxy thought to have a low-energy
cutoff of in the hotspot due to a lack of hotspot
inverse-Compton X-ray emission. The models suggest that the low-energy cutoff
in the hotspots of 6C 0905+3955 is , just slightly above
the particles required for X-ray emission.Comment: 9 pages, 3 figure
Discovery of the low-energy cutoff in a powerful giant radio galaxy
The lobes of radio galaxies and quasars, fed by jets and hotspots, represent
a significant, and currently ill-constrained, source of energy input into the
inter-galactic medium (IGM). How much energy is input into the IGM depends on
the minimum energy to which the power-law distribution of relativistic
particles is accelerated in the hotspots. This has hitherto been unknown to
within three orders of magnitude. We present direct evidence for the discovery
of this low-energy cutoff in the lobe of a Mpc-sized radio galaxy via the
existence of extended X-ray emission, inverse-Compton scattered from aged radio
plasma, and its separation by 80kpc from regions containing freshly accelerated
plasma from the hotspot. The low-energy cutoff of gamma ~ 10^4 in the hotspot
is higher than previously thought, but reconciles discrepancies with magnetic
field estimates which had been systematically lower than equipartition values.
The inverse Compton scattering of the spent synchrotron plasma is at the
expense of cosmic microwave background (CMB) photons; we comment on the
importance of such giant radio galaxies as contaminants of CMB anisotropies.Comment: Accepted by Ap J Letter
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