686 research outputs found
The Discovery of Extended Thermal X-ray Emission from PKS 2152-699: Evidence for a `Jet-cloud' Interaction
A Chandra ACIS-S observation of PKS 2152-699 reveals thermal emission from a
diffuse region around the core and a hotspot located 10" northeast from the
core. This is the first detection of thermal X-ray radiation on kiloparsec
scales from an extragalactic radio source. Two other hotspots located 47"
north-northeast and 26" southwest from the core were also detected. Using a
Raymond-Smith model, the first hotspot can be characterized with a thermal
plasma temperature of 2.6 K and an electron number density of 0.17
cm. These values correspond to a cooling time of about 1.6
yr. In addition, an emission line from the hotspot, possibly Fe xxv, was
detected at rest wavelength 10.04\AA.
The thermal X-ray emission from the first hotspot is offset from the radio
emission but is coincident with optical filaments detected with broadband
filters of HST/WFPC2. The best explanation for the X-ray, radio, and optical
emission is that of a `jet-cloud' interaction.
The diffuse emission around the nucleus of PKS 2152-699 can be modeled as a
thermal plasma with a temperature of 1.2 K and a luminosity of
1.8 erg s. This emission appears to be asymmetric with a
small extension toward Hotspot A, similar to a jet. An optical hotspot (EELR)
is seen less than an arcsecond away from this extension in the direction of the
core. This indicates that the extension may be caused by the jet interacting
with an inner ISM cloud, but entrainment of hot gas is unavoidable. Future
observations are discussed.Comment: To appear in the Astrophysical Journal 21 pages, 5 Postscript
figures, 1 table, AASTeX v. 5.
The location of the broad HI absorption in 3C305: clear evidence for a jet-accelerated neutral outflow
We present high-spatial resolution 21-cm HI VLA observations of the radio
galaxy 3C305 (z=0.041). These new high-resolution data show that the ~1000 km/s
broad HI absorption, earlier detected in low-resolution WSRT observations, is
occurring against the bright, eastern radio lobe, about 1.6 kpc from the
nucleus. We use new optical spectra taken with the WHT to make a detailed
comparison of the kinematics of the neutral hydrogen with that of the ionised
gas. The striking similarity between the complex kinematics of the two gas
phases suggests that both the ionised gas and the neutral gas are part of the
same outflow. Earlier studies of the ionised gas had already found evidence for
a strong interaction between the radio jet and the interstellar medium at the
location of the eastern radio lobe. Our results show that the fast outflow
produced by this interaction also contains a component of neutral atomic
hydrogen. The most likely interpretation is that the radio jet ionises the ISM
and accelerates it to the high outflow velocities observed. Our observations
demonstrate that, following this strong jet-cloud interaction, not all gas
clouds are destroyed and that part of the gas can cool and become neutral. The
mass outflow rate measured in 3C~305 is comparable, although at the lower end
of the distribution, to that found in Ultra-Luminous IR galaxies. This suggests
that AGN-driven outflows, and in particular jet-driven outflows, can have a
similar impact on the evolution of a galaxy as starburst-driven superwinds.Comment: Accepted for publication in A&A. 7 pages, 4 figure
BeppoSAX Observations of 2 Jy Lobe-dominated Broad-Line Sources: the Discovery of a Hard X-ray Component
We present new BeppoSAX LECS, MECS, and PDS observations of five
lobe-dominated, broad-line active galactic nuclei selected from the 2 Jy sample
of southern radio sources. These include three radio quasars and two broad-line
radio galaxies. ROSAT PSPC data, available for all the objects, are also used
to better constrain the spectral shape in the soft X-ray band. The collected
data cover the 0.1 - 10 keV energy range, reaching 40 keV for one source.
Detailed spectral fitting shows that all sources have a flat hard X-ray
spectrum with energy index alpha_x ~ 0.75 in the 2 - 10 keV energy range. This
is a new result, which is at variance with the situation at lower energies
where these sources exhibit steeper spectra. Spectral breaks ~0.5 at 1 - 2 keV
characterize the overall X-ray spectra of our objects. The flat, high-energy
slope is very similar to that displayed by flat-spectrum/core-dominated
quasars, which suggests that the same emission mechanism (most likely inverse
Compton) produces the hard X-ray spectra in both classes. Contrary to the
optical evidence for some of our sources, no absorption above the Galactic
value is found in our sample. Finally, a (weak) thermal component is also
present at low energies in the two broad-line radio galaxies included in our
study.Comment: 4 pages, LateX, 3 figures. Uses espcrc2.sty. To appear in: "The
Active X-ray Sky: Results from BeppoSAX and Rossi-XTE", Rome, Italy, 21-24
October, 1997, Eds.: L. Scarsi, H. Bradt, P. Giommi and F. Fior
Taking snapshots of the jet-ISM interplay with ALMA
We present an update of our on-going project to characterise the impact of
radio jets on the ISM by tracing molecular gas at high spatial resolution using
ALMA. The radio active galactic nuclei (AGN) studied show recently born radio
jets. In this stage, the plasma jets can have the largest impact on the ISM, as
also predicted by state-of-the-art simulations. The two targets have quite
different ages, allowing us to get snapshots of the effects of radio jets as
they grow. Interestingly, both also host powerful quasar emission. The largest
mass outflow rate of molecular gas is found in a radio galaxy hosting a newly
born radio jet emerging from an obscuring cocoon of gas and dust. Although the
mass outflow rate is high (few hundred Msun/yr), the outflow is limited to the
inner few hundred pc region. In a second object, the jet is larger (a few kpc)
and is in a more advanced evolutionary phase. In this object, the distribution
of the molecular gas is reminiscent of what is seen, on larger scales, in
cool-core clusters hosting radio galaxies. Gas deviating from quiescent
kinematics is not very prominent, limited only to the very inner region, and
has a low mass outflow rate. Instead, on kpc scales, the radio lobes appear
associated with depressions in the distribution of the molecular gas,
suggesting they have broken out from the dense nuclear region. The AGN does not
appear to be able at present to stop the star formation observed in this
galaxy. These results suggest that the effects of the radio source start in the
first phases by producing outflows which, however, tend to be limited to the
kpc region. After that, the effects turn into producing large-scale bubbles
which could, in the long term, prevent the surrounding gas from cooling. Our
results characterise the effect of radio jets in different phases of their
evolution, bridging the studies done for radio galaxies in clusters.Comment: 5 Pages 2 figures; Proceedings IAU Symposium No. 359, "Galaxy
evolution and feedback across different environments", T. Storchi-Bergmann,
R. Overzier, W. Forman & R. Riffel, ed
Highly extinguished emission line outflows in the young radio source PKS 1345+12
(Abridged) We present new, intermediate resolution spectra (~4A) of the
compact radio source PKS 1345+12. Our spectra clearly show extended line
emission (~20kpc) consistent with the asymmetric halo of diffuse emission
observed in optical and infra-red images. In the nucleus we observe complex
emission line profiles requiring 3 Gaussian components (narrow, intermediate
and broad). The broadest component (FWHM ~2000 km/s) is blue shifted by ~2000
km/s with respect to the galaxy halo and HI absorption. We interpret this as
material in outflow. We find evidence for high reddening and measure
E(B-V)>0.92 for the broadest component. From [S II]6716,6731 we estimate
electron densities of n_e5300 cm^{-3} and n_{e}>4200 cm^{-3}
for the regions emitting the narrow, intermediate and broad components
respectively. We calculate a total mass of line emitting gas of M_{gas}<10^6
solar masses. Not all emission line profiles can be reproduced by the same
model: [O I]6300,6363 and [S II] require separate, unique models. We argue that
PKS 1345+12 is a young radio source whose nuclear regions are enshrouded in a
dense cocoon of gas and dust. The radio jets are expanding, sweeping material
out of the nuclear regions. Emission originates from three kinematically
distinct regions though gradients (e.g. density, ionisation potential,
acceleration) must exist across the regions responsible for the emission of the
intermediate and broad components.Comment: Accepted for publication in MNRAS, 13 pages, 8 postscript figure
Spectroscopy of the near-nuclear regions of Cygnus A: estimating the mass of the supermassive black hole
We use a combination of high spatial resolution optical and near-IR
spectroscopic data to make a detailed study of the kinematics of the NLR gas in
the near-nuclear regions of the powerful, FRII radio galaxy Cygnus A
(z=0.0560), with the overall goal of placing limits on the mass of any
supermassive black hole in the core. Our K-band infrared observations (0.75
arcsec seeing) -- taken with NIRSPEC on the Keck II telescope -- show a smooth
rotation pattern across the nucleus in the Paschen alpha and H_2 emission lines
along a slit position (PA180) close to perpendicular to the radio axis,
however, there is no evidence for such rotation along the radio axis (PA105).
Higher spatial resolution observations of the [OIII]5007 emission line -- taken
with STIS on the Hubble Space Telescope (HST) -- confirm the general rotation
pattern of the gas in the direction perpendicular to the radio axis, and
provide evidence for steep velocity gradients within a radius of 0.1 arcsec of
the core. The circular velocities measured from both the Keck and HST data lead
to an estimate of the mass of the supermassive black hole of 2.5+/-0.7x10^9
solar masses. For the host galaxy properties of Cygnus A, this mass is
consistent with the global correlations between black hole mass and host galaxy
properties deduced for non-active galaxies. Therefore, despite the extreme
power of its radio source and the quasar-like luminosity of its AGN, the black
hole in Cygnus A is not unusually massive considering theluminosity of its host
galaxy. Indeed, the estimated mass of the black hole in Cygnus A is similar to
that inferred for the supermassive black hole in the FRI radio galaxy M87,
despite the fact that the AGN and radio jets of Cygnus A are 2 -- 3 orders of
magnitude more powerful.Comment: 17 pages, 12 figure
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