351 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
The impact of the warm outflow in the young (GPS) radio source & ULIRG PKS 1345+12 (4C 12.50)
(Abridged) We present new deep VLT/FORS optical spectra with intermediate
resolution and large wavelength coverage of the GPS radio source and ULIRG
PKS1345+12 (4C12.50; z=0.122), taken with the aim of investigating the impact
of the nuclear activity on the circumnuclear ISM. PKS1345+12 is a powerful
quasar and is also the best studied case of an emission line outflow in a
ULIRG. Using the density sensitive transauroral emission lines [S II]4068,4076
and [O II]7318,7319,7330,7331, we pilot a new technique to accurately model the
electron density for cases in which it is not possible to use the traditional
diagnostic [S II]6716/6731, namely sources with highly broadened complex
emission line profiles and/or high (Ne > 10^4 cm^-3) electron densities. We
measure electron densities of Ne=2.94x10^3 cm^-3, Ne=1.47x10^4 cm^-3 and
Ne=3.16x10^5 cm^-3 for the regions emitting the narrow, broad and very broad
components respectively. We calculate a total mass outflow rate of 8 M_sun
yr^-1. We estimate the total mass in the warm gas outflow is 8x10^5 M_sun. The
total kinetic power in the warm outflow is 3.4x10^42 erg s^-1. We find that
only a small fraction (0.13% of Lbol) of the available accretion power is
driving the warm outflow, significantly less than currently required by the
majority of quasar feedback models (~5-10\% of Lbol), but similar to recent
findings by Hopkins et al. (2010) for a two-stage feedback model. The models
also predict that AGN outflows will eventually remove the gas from the bulge of
the host galaxy. The visible warm outflow in PKS1345+12 is not currently
capable of doing so. However, it is entirely possible that much of the outflow
is either obscured by a dense and dusty natal cocoon and/or in cooler or hotter
phases of the ISM. This result is important not just for studies of young
(GPS/CSS) radio sources, but for AGN in general.Comment: Accepted for publication in MNRAS. 11 pages, 4 figure
Fast Outflows of Neutral Hydrogen in Radio Galaxies
AGN activity is known to drive fast outflows of gas. We report the discovery
of fast outflows of neutral gas with velocities over 1000 km/s in a number of
radio galaxies. In the best studied object, 3C~293, the kinematical properties
of the neutral and ionised outflows are similar, indicating a common origin.
Moreover, the outflow appears to be located near the radio lobes and not near
the nucleus. This suggests that the interaction between the radio jet and the
ISM is driving the outflow.Comment: To appear in the proceedings of IAU Symposium 222,"The Interplay
among Black Holes, Stars and ISM in Galactic Nuclei", eds Storchi-Bergmann et
al; 2 pages, 1 figur
The heating mechanism for the warm/cool dust in powerful, radio-loud AGN
The uncertainty surrounding the nature of the heating mechanism for the dust
that emits at mid- to far-IR (MFIR) wavelengths in active galaxies limits our
understanding of the links between active galactic nuclei (AGN) and galaxy
evolution, as well as our ability to interpret the prodigious infrared and
sub-mm emission of some of the most distant galaxies in the Universe. Here we
report deep Spitzer observations of a complete sample of powerful, intermediate
redshift (0.05 < z < 0.7) radio galaxies and quasars. We show that AGN power,
as traced by [OIII]5007 emission, is strongly correlated with both the mid-IR
(24 micron) and the far-IR (70 micron) luminosities, however, with increased
scatter in the 70 micron correlation. A major cause of this increased scatter
is a group of objects that falls above the main correlation and displays
evidence for prodigious recent star formation activity at optical wavelengths,
along with relatively cool MFIR colours. These results provide evidence that
illumination by the AGN is the primary heating mechanism for the dust emitting
at both 24 and 70 microns, with starbursts dominating the heating of the cool
dust in only 20 -- 30% of objects. This implies that powerful AGN are not
always accompanied by the type of luminous starbursts that are characteristic
of the peak of activity in major gas-rich mergers.Comment: 13 pages, 3 figures. Accepted for publication in astrophysical
journal letter
- …