52 research outputs found
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
The location and impact of jet-driven outflows of cold gas: the case of 3C293
The nearby radio galaxy 3C293 is one of a small group of objects where
extreme outflows of neutral hydrogen have been detected. However, due to the
limited spatial resolution of previous observations, the exact location of the
outflow was not able to be determined. In this letter, we present new higher
resolution VLA observations of the central regions of this radio source and
detect a fast outflow of HI with a FWZI velocity of \Delta v~1200 km/s
associated with the inner radio jet, approximately 0.5 kpc west of the central
core. We investigate possible mechanisms which could produce the observed HI
outflow and conclude that it is driven by the radio-jet. However, this outflow
of neutral hydrogen is located on the opposite side of the nucleus to the
outflow of ionised gas previously detected in this object. We calculate a mass
outflow rate in the range of 8-50 solar masses/yr corresponding to a kinetic
energy power injected back into the ISM of 1.38x10^{42} - 1.00x10^{43} erg/s or
0.01 - 0.08 percent of the Eddington luminosity. This places it just outside
the range required by some galaxy evolution simulations for negative feedback
from the AGN to be effective in halting star-formation within the galaxy.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
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
Outflow densities and ionisation mechanisms in the NLRs of the prototypical Seyfert galaxies NGC 1068 and NGC 4151
Despite being thought to play an important role in galaxy evolution, the true
impact of outflows driven by active galactic nuclei (AGN) on their host
galaxies is unclear. In part, this may be because electron densities of
outflowing gas are often underestimated: recent studies that use alternative
diagnostics have measured much higher densities than those from commonly used
techniques, and consequently find modest outflow masses and kinetic powers.
Furthermore, outflow ionisation mechanisms - which are often used to probe
acceleration mechanisms - are also uncertain. To address these issues, we have
analysed archival HST/STIS spectra of the inner regions (r<160pc) of the nearby
prototypical Seyfert galaxies NGC 1068 and NGC 4151, which show evidence of
warm-ionised outflows driven by the central AGN. We derive high electron
densities (<<cm) using the transauroral [OII]
and [SII] emission lines ratios for the first time with spatially-resolved
observations. Moreover, we find evidence that the gas along the radio axis in
NGC 1068 has a significant AGN-photoionised matter-bounded component, and there
is evidence for shock-ionisation and/or radiation-bounded AGN-photoionisation
along the radio axis in NGC 4151. We also note that the outflow extents are
similar to those of the radio structures, consistent with acceleration by
jet-induced shocks. Taken together, our investigation demonstrates the
diversity of physical and ionisation conditions in the narrow line regions of
Seyfert galaxies, and hence reinforces the need for robust diagnostics of
outflowing gas densities and ionisation mechanisms.Comment: 21 pages, 13 figures, accepted for publication in MNRA
HI on large and small scales in starburst radio galaxies
The study of the optical continuum of radio galaxies shows that about 30%
have a young stellar population component. Among them are the most far-IR
bright radio galaxies. A further indication of the relatively gas rich
environment of these galaxies (possibly related to the recent merger from which
they originate) is the high fraction being detected in HI. Here we present
recent results obtained from the study of neutral hydrogen (detected either in
emission or absorption) in a group of starburst radio galaxies. In some
objects, large-scale (tens of kpc) structures involving HI masses exceeding
10^9 M_sun are observed. In these cases, the HI can be used to study the origin
and evolution of these systems and the timescales involved. In this respect,
the parameters obtained from the study of the stellar populations and from the
HI can be complementary. In other objects, very broad (> 1000 km/s), mostly
blueshifted HI is detected in absorption. This result shows that, despite the
extremely energetic phenomena occurring near an AGN - including the powerful
radio jet - some of the outflowing gas remains, or becomes again, neutral. This
can give new and important insights in the physical conditions of the gaseous
medium around an AGN. The possible origin of the extreme kinematics is
discussed.Comment: Invited review to appear in the proceedings of the conference
"Neutral ISM in Starburst Galaxies", eds. S.Aalto, S.Huttemeister & A.Pedlar.
12 pages, Figs.2,4,5 are in separate gif files. The full paper with high
resolution images can be downloaded from
http://www.nfra.nl/~morganti/Papers/starburst.ps.g
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