3,956 research outputs found
The jet-ISM interaction in the Outer Filament of Centaurus A
The interaction between the radio plasma ejected by the active nucleus of a
galaxy and the surrounding medium is a key process that can have a strong
impact on the interstellar medium of the galaxy and hence on galaxy evolution.
The closest laboratory where we can observe and investigate this phenomenon is
the radio galaxy Centaurus A. About 15 kpc north-east of this galaxy, a
particularly complex region is found: the so-called Outer Filament where
jet-cloud interactions have been proposed to occur. We investigate the presence
of signatures of jet-ISM interaction by a detailed study of the kinematics of
the ionized gas, expanding on previous results obtained from the HI. We
observed two regions of the outer filament with VLT/VIMOS in the IFU observing
mode. Emission from Hbeta and [OIII]4959,5007\AA\ is detected in both
pointings. We found two distinct kinematical components of ionized gas that
well match the kinematics of the nearby HI cloud. One component follows the
regular kinematics of the rotating gas while the second shows similar
velocities to those of the nearby HI component thought to be disturbed by an
interaction with the radio jet. We suggest that the ionized and atomic gas are
part of the same dynamical gas structure originating as result of the merger
that shaped Centaurus A and which is regularly rotating around Centaurus A as
proposed by other authors. The gas (ionized and HI) with anomalous velocities
is tracing the interaction of the Large-Scale radio Jet with the ISM,
suggesting that, although poorly collimated as structure, the jet is still
active. However, we can exclude that a strong shock is driving the ionization
of the gas. It is likely that a combination of jet entrainment and
photoionization by the UV continuum from the central engine is needed in order
to explain both the ionization and the kinematics of the gas in the Outer
Filament.Comment: 6 pages, 6 figures, 1 table. Final version accepted for publication
on A&
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
The fast molecular outflow in the Seyfert galaxy IC5063 as seen by ALMA
We use high-resolution (0.5 arcsec) CO(2-1) observations performed with ALMA
to trace the kinematics of the molecular gas in the Seyfert 2 galaxy IC5063. A
fast outflow of molecular gas extends along the entire radio jet, with the
highest outflow velocities about 0.5kpc from the nucleus, at the location of
the brighter hot-spot in the W lobe. The data show that a massive, fast outflow
with velocities up to 650 km/s of cold molecular gas is present, in addition to
one detected earlier in warm H2, HI and ionised gas. Both the central AGN and
the radio jet could energetically drive the outflow. However, the
characteristics of the outflowing gas point to the radio jet being the main
driver. This is important, because IC5063, although one of the most powerful
Seyfert galaxies, is a relatively weak radio source (P = 3x10^23 W/Hz). All the
observed characteristics can be described by a scenario of a radio plasma jet
expanding into a clumpy medium, interacting directly with the clouds and
inflating a cocoon that drives a lateral outflow into the interstellar medium.
This model is consistent with results obtained by recent simulations such as
those of Wagner et al.. A stronger, direct interaction between the jet and a
gas cloud is present at the location of the brighter W lobe. Even assuming the
most conservative values for the conversion factor CO-to-H2, the mass of the
outflowing gas is between 1.9 and 4.8x10^7 Msun. These amounts are much larger
than those of the outflow of warm gas (molecular and ionized) and somewhat
larger than of the HI outflow. This suggests that most of the observed cold
molecular outflow is due to fast cooling after being shocked. This gas is the
end product of the cooling process. Our CO observations demonstrate that fast
outflows of molecular gas can be driven by relativistic jets.Comment: Accepted for publication in A&A. 11 pages, 8 figure
Gas outflows in radio galaxies
We present a summary of our recent results on gas outflows in radio galaxies.
Fast outflows (up to 2000 km/s) have been detected both in ionized and neutral
gas. The latter is particularly surprising as it shows that, despite the
extremely energetic phenomena occurring near an AGN, some of the outflowing gas
remains, or becomes again, neutral. These results are giving new and important
insights on the physical conditions of the gaseous medium around an AGN.Comment: To appear in the proceedings of the IAU Symposium #217, Recycling
Intergalactic and Interstellar Matter, eds. P.-A. Duc, J. Braine, and E.
Brinks, 6 pages. The full paper with high resolution images can be downloaded
from http://www.astron.nl/~morganti/Papers/outflows.ps.g
The outer filament of Centaurus A as seen by MUSE
We investigate signatures of a jet-interstellar medium (ISM) interaction
using optical integral-field observations of the so-called outer filament near
Centaurus A, expanding on previous results obtained on a more limited area.
Using the Multi Unit Spectroscopic Explorer (MUSE) on the VLT during science
verification, we observed a significant fraction of the brighter emitting gas
across the outer filament. The ionized gas shows complex morphology with
compact blobs, arc-like structures and diffuse emission. Based on the
kinematics, we identified three main components. The more collimated component
is oriented along the direction of the radio jet. The other two components
exhibit diffuse morphology together with arc-like structures also oriented
along the radio jet direction. Furthermore, the ionization level of the gas is
found to decrease from the more collimated component to the more diffuse
components. The morphology and velocities of the more collimated component
confirm our earlier results that the outer filament and the nearby HI cloud are
likely partially shaped by the lateral expansion of the jet. The arc-like
structures embedded within the two remaining components are the clearest
evidence of a smooth jet-ISM interaction along the jet direction. This suggests
that, although poorly collimated, the radio jet is still active and has an
impact on the surrounding gas. This result indicates that the effect on the ISM
of even low-power radio jets should be considered when studying the influence
Active Galactic Nuclei can have on their host galaxy.Comment: 5 pages, 3 figures, Accepted for publication by A&
Starburst radio galaxies: general properties, evolutionary histories and triggering
In this paper we discuss the results of a programme of spectral synthesis
modelling of a sample of starburst radio galaxies in the context of scenarios
for the triggering of the activity and the evolution of the host galaxies. The
starburst radio galaxies -- comprising ~15 - 25% of all powerful extragalactic
radio sources -- frequently show disturbed morphologies at optical wavelengths,
and unusual radio structures, although their stellar masses are typical of
radio galaxies as a class. In terms of the characteristic ages of their young
stellar populations (YSP), the objects can be divided into two groups: those
with YSP ages t_ysp < 0.1 Gyr, in which the radio source has been triggered
quasi-simultaneously with the main starburst episode, and those with older YSP
in which the radio source has been triggered or re-triggered a significant
period after the starburst episode. Combining the information on the YSP with
that on the optical morphologies of the host galaxies, we deduce that the
majority of the starburst radio galaxies have been triggered in galaxy mergers
in which at least one of the galaxies is gas rich. However, the triggering (or
re-triggering) of the radio jets can occur immediately before, around, or a
significant period after the final coalescence of the merging nuclei,
reflecting the complex gas infall histories of the merger events. Overall, our
results provide further evidence that powerful radio jet activity can be
triggered via a variety of mechanisms, including different evolutionary stages
of major galaxy mergers; clearly radio-loud AGN activity is not solely
associated with a particular stage of a unique type of gas accretion event.Comment: 16 pages, 3 Figures, accepted for publication in MNRA
Large-scale HI in nearby radio galaxies: segregation in neutral gas content with radio source size
We present results of a study of neutral hydrogen (HI) in a complete sample
of nearby non-cluster radio galaxies. We find that radio galaxies with large
amounts of extended HI (M_HI >= 10^9 M_solar) all have a compact radio source.
The host galaxies of the more extended radio sources, all of Fanaroff & Riley
type-I, do not contain these amounts of HI. We discuss several possible
explanations for this segregation. The large-scale HI is mainly distributed in
disk- and ring-like structures with sizes up to 190 kpc and masses up to 2 x
10^10 M_solar. The formation of these structures could be related to past
merger events, although in some cases it may also be consistent with a
cold-accretion scenario.Comment: 4 pages, 2 figures. Accepted for publication in A&A Letters. A
version with full resolution figures can be found at
http://www.astro.rug.nl/~emonts/emonts_HIletter_jan07.pd
Young radio jets breaking free: molecular and HI outflows in their centers
Our view of the central regions of AGN has been enriched by the discovery of fast and massive outflows of H I and molecular gas. Here we present a brief summary of results obtained for young (and restarted) radio AGN. We find that H I outflows tend to be particularly common in this group of objects. This supports the idea that the jet, expanding in a clumpy medium, plays a major role in driving these outflows. The clumpiness of the medium is confirmed by VLBI and ALMA observations. The H I observations reveal that, at least part of the gas, is distributed in clouds with sizes up to a few tens of pc and mass ~104Mâ. A change of the conditions in the outflow, with an increasing fraction of diffuse components, as the radio jets grow, is suggested by the high resolution H I observations. The molecular gas completes the picture, showing that the radio plasma jet can couple well with the ISM, strongly affecting the kinematics, but also the physical conditions of the molecular gas. This is confirmed by numerical simulations reproducing, to first order, the kinematics of the gas
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