4,193 research outputs found
On the population of remnant FRII radio galaxies and implications for radio source dynamics
The purpose of this work is two-fold: (1) to quantify the occurrence of
ultra-steep spectrum remnant FRII radio galaxies in a 74 MHz flux limited
sample, and (2) perform Monte-Carlo simulations of the population of active and
remnant FRII radio galaxies to confront models of remnant lobe evolution, and
provide guidance for further investigation of remnant radio galaxies. We find
that fewer than 2 of FRII radio galaxies with S Jy are
candidate ultra-steep spectrum remnants, where we define ultra-steep spectrum
as . Our Monte-Carlo simulations
demonstrate that models involving Sedov-like expansion in the remnant phase,
resulting in rapid adiabatic energy losses, are consistent with this upper
limit, and predict the existence of nearly twice as many remnants with normal
(not ultra-steep) spectra in the observed frequency range as there are
ultra-steep spectrum remnants. This model also predicts an ultra-steep remnant
fraction approaching 10 at redshifts . Importantly, this model
implies the lobes remain over-pressured with respect to the ambient medium well
after their active lifetime, in contrast with existing observational evidence
that many FRII radio galaxy lobes reach pressure equilibrium with the external
medium whilst still in the active phase. The predicted age distribution of
remnants is a steeply decreasing function of age. In other words young remnants
are expected to be much more common than old remnants in flux limited samples.
For this reason, incorporating higher frequency data GHz will be of
great benefit to future studies of the remnant population.Comment: 19 pages, 8 figures, 4 table
Is Centaurus A special? A neutral hydrogen perspective
Due to the proximity, the neutral hydrogen belonging to Centaurus A can be
observed at high resolution with good sensitivity. This allows to study the
morphology and kinematics in detail in order to understand the evolution of
this radio-loud source (e.g. merger history, AGN activity). At the same time,
it is important to compare the results to other sources of the same class (i.e.
early-type galaxies in general and radio galaxies in particular) to see how
Centaurus A fits into the global picture of early-type/radio galaxy evolution.
The amount of HI, the morphology of a warped disk with HI clouds surrounding
the disk and the regular kinematics of the inner part of the HI disk are not
unusual for early-type galaxies. The growing evidence that mergers are not
necessarily responsible for AGN activity fits with the observational result
that the recent merger event in Centaurus A is not connected to the current
phase of activity. Based on these results, we conclude that Centaurus A has
typical neutral hydrogen properties for an early-type and radio galaxy and it
can therefore - from an HI perspective - be seen as a typical example of its
class.Comment: submitted to PASA; 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
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
Tidal Remnants and Intergalactic HII Regions
We report the discovery of two small intergalactic HII regions in the loose
group of galaxies around the field elliptical NGC 1490. The HII regions are
located at least 100 kpc from any optical galaxy but are associated with a
number of large HI clouds that are lying along an arc 500 kpc in length and
that have no optical counterpart on the Digital Sky Survey. The sum of the HI
masses of the clouds is almost 10^10 M_sun and the largest HI cloud is about
100 kpc in size. Deep optical imaging reveals a very low surface brightness
counterpart to this largest HI cloud, making this one of the HI richest optical
galaxies known (M_HI/L_V~200). Spectroscopy of the HII regions indicates that
the abundance in these HII regions is only slightly sub-solar, excluding a
primordial origin of the HI clouds. The HI clouds are perhaps remnants
resulting from the tidal disruption of a reasonably sized galaxy, probably
quite some time ago, by the loose group to which NGC1490 belongs.
Alternatively, they are remnants of the merger that created the field
elliptical NGC1490. The isolated HII regions show that star formation on a very
small scale can occur in intergalactic space in gas drawn from galaxies by
tidal interactions. Many such intergalactic small star formation regions may
exist near tidally interacting galaxies.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 with low resolution figures. The full paper with high
resolution images can be downloaded from
http://www.astron.nl/~morganti/Papers/cloud.ps.g
Shock heating in the nearby radio galaxy NGC 3801
Original article can be found at: http://www.journals.uchicago.edu/ApJ/--Copyright American Astronomical SocietyPeer reviewe
Molecular Hydrogen and Paschen-alpha Emission in Cooling Flow Galaxies
We present near-infrared spectra obtained to search for Pa-alpha and
molecular hydrogen lines in edge-darkened (FR I-type) radio galaxies with
bright Halpha emission in the redshift range 0.0535<z<0.15. We find that all
three galaxies in our sample (PKS 0745-191, PKS 1346+26, & PKS2322-12) which
are associated with strong cooling flows also have strong Pa-alpha and H_2
(1-0) S(1) through S(5) emission, while other radio galaxies do not. Together
with earlier observations this confirms claims that cooling flow galaxies are
copious emitters of molecular hydrogen with large H_2 (1-0) S(3)/Pa-alpha
ratios in the range 0.5 to 2. The emission is centrally concentrated within the
inner few kiloparsec and could come from warm (T ~ 1000-1500 K) molecular
material which is being deposited by the cooling flow. We speculate that the
H_2 emission could be related to the interaction between the jets and this
molecular gas.Comment: ApJ Letters, in press, AAS LaTex, preprint also available at
http://www.astro.umd.edu/~hfalcke/publications.html#nirga
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