82 research outputs found
Classical radio source propagating into outer HI disc in NGC 3801
We present observations of a large-scale disc of neutral hydrogen (HI) in the
nearby Fanaroff & Riley type-I radio galaxy NGC 3801 with the Westerbork
Synthesis Radio Telescope. The HI disc (34 kpc in diameter and with M_HI = 1.3
x 10^9 M_sun) is aligned with the radio jet axis. This makes NGC 3801 an ideal
system for investigating the evolution of a small radio source through its host
galaxy's cold ISM. The large-scale HI disc is perpendicular to a known inner CO
disc and dust-lane. We argue that the formation history of the large-scale HI
disc is in agreement with earlier speculation that NGC 3801 was involved in a
past gas-rich galaxy-galaxy merger (although other formation histories are
discussed). The fact that NGC 3801 is located in an environment of several
HI-rich companions, and shows indications of ongoing interaction with the
nearby companion NGC 3802, strengthens this possibility. The large amounts of
ambient cold ISM, combined with X-ray results by Croston et al (2007) on the
presence of over-pressured radio jets and evidence for an obscuring torus, are
properties that are generally not, or no longer, associated with more evolved
FR-I radio sources. We do show, however, that the HI properties of NGC 3801 are
comparable to those of a significant fraction of nearby low-power compact radio
sources, suggesting that studies of NGC 3801 may reveal important insight into
a more general phase in the evolution of at least a significant fraction of
nearby radio galaxies.Comment: Accepted for publication in MNRAS (6 figure, 2 tables
Cold gas & mergers: fundamental difference in HI properties of different types of radio galaxies?
We present results of a study of large-scale neutral hydrogen (HI) gas in
nearby radio galaxies. We find that the early-type host galaxies of different
types of radio sources (compact, FR-I and FR-II) appear to contain
fundamentally different large-scale HI properties: enormous regular rotating
disks and rings are present around the host galaxies of a significant fraction
of low power compact radio sources, while no large-scale HI is detected in low
power, edge-darkened FR-I radio galaxies. Preliminary results of a study of
nearby powerful, edge-brightened FR-II radio galaxies show that these systems
generally contain significant amounts of large-scale HI, often distributed in
tail- or bridge-like structures, indicative of a recent galaxy merger or
collision. Our results suggest that different types of radio galaxies may have
a different formation history, which could be related to a difference in the
triggering mechanism of the radio source. If confirmed by larger studies with
the next generation radio telescopes, this would be in agreement with previous
optical studies that suggest that powerful FR-II radio sources are likely
triggered by galaxy mergers and collisions, while the lower power FR-I sources
are fed in other ways (e.g. through the accretion of hot IGM). The giant HI
disks/rings associated with some compact sources could - at least in some cases
- be the relics of much more advanced mergers.Comment: 5 pages, 3 figures - to appear in PoS, "The Modern Radio Universe:
From Planets to Dark Energy Conference", Manchester UK, eds: Beswick, Diamond
& Schilizz
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
QSO2 outflow characterization using data obtained with OSIRIS at the Gran Telescopio Canarias
Ionized outflows are ubiquitous in non radio-loud obscured quasars (QSO2s) at
different redshifts. We search for large-scale ionized outflows associated with
six optically selected QSO2 (five non-radio-loud and one radio-loud) at
0.2-0.5, targeting objects with extended radio structures. We have obtained
OSIRIS/GTC optical long slit spectroscopy data for these six QSO2 with the slit
located along the radio axis. We traced the gas kinematics with the
[OIII]4959,5007 lines to investigate ionized outflows and characterize
the dynamical state of the host galaxies. This second study has been
complemented with previously published FORS2/VLT spectroscopic data of 13 more
QSO2 at similar z. We identify ionized outflows in four out of the six QSO2
observed with the GTC. The outflows are spatially unresolved in two QSO2 and
compact in a third (radial size of R=0.80.3 kpc). Of particular interest
is the radio-quiet QSO2 SDSS 0741+3020 at z=0.47, associated with a giant
112 kpc nebula. An ionized outflow probably induced by the radio
structures has been detected along the axis defined by the central
1\arcsec\ radio structure, extending up to at least 4 kpc from the
active galactic nucleus (AGN). Turbulent gas (130 km s) has
also been detected across the giant gas nebula up to 40 kpc from the AGN.
This turbulence may have been induced by outflows triggered by the interaction
between a so-far undetected large-scale radio source and the nebula. Regarding
the dynamical state of the host galaxies, we find that the majority of the QSO2
show v/ 1, implying that they are dominated by random motions
(so-called dispersion-dominated systems). Most (17 of 19) fall in the area of
the E/S0 galaxies in the dynamical diagram v/ versus . None are
consistent with spiral or disk galaxies.Comment: 27 pages, 11+8 figures, accepted for publication in A&
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
Jet-ISM Interaction in the Radio Galaxy 3C293: Jet-driven Shocks Heat ISM to Power X-ray and Molecular H2 emission
We present a 70ks Chandra observation of the radio galaxy 3C293. This galaxy
belongs to the class of molecular hydrogen emission galaxies (MOHEGs) that have
very luminous emission from warm molecular hydrogen. In radio galaxies, the
molecular gas appears to be heated by jet-driven shocks, but exactly how this
mechanism works is still poorly understood. With Chandra, we observe X-ray
emission from the jets within the host galaxy and along the 100 kpc radio jets.
We model the X-ray spectra of the nucleus, the inner jets, and the X-ray
features along the extended radio jets. Both the nucleus and the inner jets
show evidence of 10^7 K shock-heated gas. The kinetic power of the jets is more
than sufficient to heat the X-ray emitting gas within the host galaxy. The
thermal X-ray and warm H2 luminosities of 3C293 are similar, indicating similar
masses of X-ray hot gas and warm molecular gas. This is consistent with a
picture where both derive from a multiphase, shocked interstellar medium (ISM).
We find that radio-loud MOHEGs that are not brightest cluster galaxies (BCGs),
like 3C293, typically have LH2/LX~1 and MH2/MX~1, whereas MOHEGs that are BCGs
have LH2/LX~0.01 and MH2/MX~0.01. The more massive, virialized, hot atmosphere
in BCGs overwhelms any direct X-ray emission from current jet-ISM interaction.
On the other hand, LH2/LX~1 in the Spiderweb BCG at z=2, which resides in an
unvirialized protocluster and hosts a powerful radio source. Over time, jet-ISM
interaction may contribute to the establishment of a hot atmosphere in BCGs and
other massive elliptical galaxies.Comment: Accepted by ApJ 21 pages in ApJ format, 9 figures, 8 table
Fast neutral outflows in nearby radio galaxies: a major source of feedback
Fast (~1000 km/s) outflows of neutral gas (from 21-cm HI absorption) are
detected in strong radio sources. The outflows occur, at least in some cases,
at distances from the radio core that range between few hundred parsecs and
kpc. These HI outflows likely originate from the interaction between radio jets
and the dense surrounding medium. The estimated mass outflow rates are
comparable to those of moderate starburst-driven superwinds. The impact on the
evolution of the host galaxies is discussed.Comment: 4 pages, 2 figures. Conference proceedings to appear in "The Central
Engine of Active Galactic Nuclei", ed. L. C. Ho and J.-M. Wang (San
Francisco: ASP
- …