Table of Contents
| Talks |
| Posters |
Session II. Evolutionary Endpoints
| Talks |
| Blundell | Evolutionary Endpoints of Radio Galaxies | |
| De Young | Magnetic Field Amplification in FR II Hotspots |
| Posters |
Session III. Radio Galaxy Environments
| Talks |
| Posters |
Session IV. The Central Regions
| Talks |
| Posters |
| Talks |
| Posters |
Session VI. Compact Radio Galaxies
| Talks |
| Posters |
Session VII. FR I vs. FR II Radio Galaxies
| Talks |
| Posters |
| Talks |
| Posters |
Session IX. The Lives of FR I Radio Galaxies
| Talks |
| Posters |
Ruth Daly (Bucknell)
The general properties of models developed to describe powerful, extended
(FR II) radio sources will be reviewed, with an eye toward the underlying
assumptions, and choices about assumptions, that are a necessary part of any
model. Observational constraints that each model must satisfy will be covered,
with an emphasis on those that are often neglected. The role of projection
effects in comparing model predictions with observations will be mentioned; it
will be suggested that radio galaxies and radio loud quasars be studied
separately. Ways in which detailed radio observations may be used to determine
the fundamental physical variables describing the properties of a given radio
source and its environment will be reviewed. It will be shown that the Mach
number of a source, its beam power, total lifetime, and total energy pumped
into the source over its lifetime can be estimated, as well as the ambient gas
pressure, ambient gas density, and ambient gas temperature. Some recent
results will be presented.
Ignas Snellen (Cambridge University) et al.
GPS sources are the objects of choice to study the initial evolution of
extragalactic radio sources, since it is most likely that they are the young
counterparts of large scale radio sources. Correlations found between their
peak frequency, peak flux density and angular size provide strong evidence that
synchrotron self absorption is the cause of the spectral turnovers, and
indicate that young radio sources evolve in a self-similar way. The difference
in redshift distribution between young and old radio sources must be due to a
difference in slope of their luminosity functions, and we argue that this slope
is strongly affected by the luminosity evolution of the individual sources. A
luminosity evolution scenario is proposed in which GPS sources increase in
luminosity and large scale radio sources decrease in luminosity with time.
C. R. Kaiser (Max-Planck-Institut für Astrophysik, Garching)
Virtually all models of the evolution of powerful (FRII) radio galaxies depend
on the source environments. In general, and particularly at higher redshift,
the properties of the gas surrounding FRII sources are not well known. Even for
those objects for which X-ray observations give an indication of the density of
their environments, further complications arise from their unknown physical
size. Here I present a model which allows the determination of the viewing
angle, the density of the environment and the rate at which energy is
transported along the jets from spectral index maps of the extended radio
structure of FRII sources. Additionally, the model also improves age estimates
from spectral aging arguments.
J. P. Leahy (STScI/University of Manchester), T. W. B. Muxlow & R. A. Laing
We have mapped nine classical double radio galaxies at 7 to 10 radio
frequencies spanning a range of two decades. We have fit standard synchrotron
loss models to the data to assess the reliability of spectral aging
calculations. The hotspots (unresolved in our images) are usually well fitted
by continuous injection models, as expected. In two cases the implied
injection index is flatter than a0= 0.5,
which is too flat to be produced by standard Fermi acceleration in a
non-relativistic shock. The bridge spectra are reasonably well fit by
single-burst models, but in some objects the injection index is not constant
across the lobes, but shows a tendency to steepen in the inner bridge, where
the break frequencies are lowest. This result suggests that the true spectral
shape is actually a more gradual curve than the standard models, possibly
because of mixing of electron populations with different ages.
Lawrence Rudnick (Univ. of Minnesota)
I will present a brief overview of observational, modeling and theoretical
issues related to ageing calculations based on spectral steepening. These
include both commonly understood problems such as the use of equipartition
estimates as well as poorly understood problems such as the importance of
inhomogeneous magnetic fields, diffusion of relativistic particles, confusion
from multiple particle populations and particle acceleration. Although some of
the effects are only of order unity, others call into question the entire
ageing paradigm. I will show some data illustrating these problems, and make a
few recommendations about how we should proceed given these uncertainties.
Katherine Blundell (Oxford University)
I will describe the pitfalls encountered in deducing from classical double
radio source observables (luminosity, spectral index, redshift,
linear size and axial ratio) the essential nature of how these objects
evolve.
I will discuss the key role played by hotspots in governing the energy
distribution of their lobes, and subsequent spectral losses. Incorporating
this role, and correctly accounting for the sampling of the radio source
population by our survey flux-limits and light-cone, reproduces the
inter-dependencies of the above observables found in
spectroscopically-identified complete samples.
D. S. De Young (NOAO)
A key assumption in some models of radio source evolution is that the magnetic
field in the hotspots is always equal to the equipartition value and that this
value is proportional to the jet energy flux (e.g., Blundell et al. 1999).
This assumption is tested by following the evolution of the magnetic field in
the turbulent hotspot flow via a series of three dimensional, time dependent
and fully nonlinear calculations of MHD turbulence in the hotspots. Turbulent
amplification of the magnetic field is examined for a variety of energy spectra
that might occur in the hotspots (e.g., Meisenheimer et al. 1989). It is found
that equipartition is reached in the time required only for a subset of
possible initial conditions. Implications for FR-II evolution is discussed.
Diana Worrall (Bristol)
In this talk I will discuss the importance of the X-ray emission of radio
galaxies as a tracer of their gaseous environments, with an emphasis on whether
the X-ray emitting gas plays an active role in the radio galaxy's life and
whether the environments of radio-loud AGN are special. Issues to do with
observational biases will be discussed, and the multi-component nature of the
X-ray emission will be examined. I will use recent work to contrast the X-ray
emission and environments of FRIs, radio-quiet ellipticals, high-z FRIIs, more
local FRIIs, and GPS radio galaxies. The trends in external gas density and
pressure near extended radio structures will be reviewed. There are many open
issues, and I will identify these and the potential for resolving them using
imminently-available X-ray measurements with vastly improved resolution and
sensitivity.
Jack O. Burns (University of Missouri)
The environments of radio galaxies have changed dramatically between z=5 and
the present. Galaxies in general form within a large-scale cosmic web which
contain >100 Mpc-length filaments, composed of dark and baryonic matter, and
huge voids of comparable size. Groups and clusters, where most galaxies
reside, form at the intersections of filaments. Clusters continue to evolve to
the present day by accreting gas and galaxies from connecting filaments and
occasional mergers (about every 2 Gyrs) with other clusters. This accretion
process produces shocks, turbulence, and transonic bulk flows within the
intracluster medium -- a kind of "stormy cluster weather". The low density
plasmas associated with extended radio sources embedded within groups and
clusters act as windsocks and barometers of this cluster weather. They change
in size and shape as the cluster gaseous environment evolves with time. I will
use new high spatial dynamic range adaptive mesh refinement numerical
simulations along with x-ray and radio observations to demonstrate the
important role that environment plays in extended radio sources. I will use
particular classes of radio sources to illustrate these effects including wide
and narrow angle tailed galaxies, cluster radio halos, and radio sources within
cluster cooling flows.
Brian R. McNamara (CfA)
FR I radio sources are found frequently in the bright central galaxies in
cluster cooling flows. In some clusters the radio source is interacting with
the intracluster gas, and may be triggering short but relatively frequent
bursts of star formation. There is evidence that the star formation, and
perhaps the radio source itself, is being fueled by the accretion of cooling,
intracluster gas, and in some cases by infalling cold material that was
stripped from galaxies.
Douglas Richstone (University of Michigan)
A population of massive black holes in the present
universe is predicted by the luminosity function
of quasars in the z \gtsim 2 universe. We believe
members of this population have been discovered and
that at least the upper end of its mass function can
be characterized.
We review the evidence for massive dark objects in the
centers of ~20 normal galaxies. The numbers and masses
of these objects are consistent with our expectations for
the population of fossil quasars. The masses of these objects
appear to correlate with the mass of the spheroid of its host
galaxy.
We have devised a technique to estimate the frequency of
these objects, including data from nondetections, in an
unbiased way. An analysis of ~25 objects suggests that
approximately all galaxies host massive black holes.
If this is the case, these objects must play a major role
in the formation and evolution of galaxies.
We compare the results of this work to counts of quasars
at high redshifts and to estimates of black hole masses
in Seyfert galaxies at low redshift. There are some interesting
problems.
There are many remaining important mysteries. What is the
formation mechanism for supermassive black holes? How
are they coupled to the cores of their host galaxies,
and how do the galaxies and black holes co-evolve? What
is the merger rate of black holes in our lightcone?
R. Sambruna, M. Eracleous (PSU) & R. Mushotzky (GSFC)
We present a spectral survey of radio-loud (RL) AGN in X-rays using ASCA
(astro-ph/9905365) and RXTE, with the goal of clarifying their central engine
structure and compare to their radio-quiet (RQ) counterparts. Systematic
differences are observed at X-rays between the two AGN classes. At harder
energies, RL exhibit weaker Fe lines and reflection components than RQ,
indicating smaller solid angles subtended by the reprocessor to the X-ray
source. The circumnuclear environs of RL differ from RQ: large amounts of cold
gas are measured in Broad Line Radio Galaxies and Quasars, which are not seen
in RQ of similar X-ray luminosity. We discuss implications for the origin of
the RL/RQ AGN dichotomy.
Mark Lacy (University of Oxford) & Susan Ridgway
Although radio-loud objects are only a minority of AGN when all luminosities
are considered, recent studies of the quasar fraction in optically-selected
quasar surveys have shown that they constitute a substantial fraction, and
perhaps even a majority, of the most luminous AGN at high redshifts. This is
consistent with recent claims of a correlation of black hole mass with the mass
of the spheroidal components of galaxies, as most radio sources have giant
elliptical hosts. We will use constraints on the numbers of very massive
(>~3´109 Msun) black
holes in the local Universe to place constraints on radio source lifetimes and
duty cycles independent of radio source models.
David L. Meier (Jet Propulsion Laboratory)
While attempts to unify certain classes of AGN using orientation and
environmental effects have been successful, it is widely recognized that
intrinsic properties of the accreting black hole system also must play a role
in determining the appearance of such an object. In addition to mass and
accretion rate, the angular momentum (or spin) of the black hole can play a
crucial role in determining the power of a relativistic jet that is generated
by magnetohydrodynamic acceleration near the hole. In this talk a scenario is
presented, based on accretion theory and recent models of MHD jet production,
in which the primary (although not only) parameter differentiating between
radio loud and quiet objects is the black hole spin, and that determining
quasar vs. radio galaxy is the accretion rate. A surprising number of
desirable features result from these simple concepts and the accompanying
equations. In addition, there are several testable predictions that can
determine whether this grand unification scheme has further merit.
Wolfgang Kundt (Institut für Astrophysik, University of Bonn)
The centers of galactic disks can repeatedly reach high (stellar) densities,
such that they start nuclear burning in their midplanes, and appear as
supermassive point sources at present-day resolutions. Near their cores,
main-sequence burning evolves into nuclear detonations, whose ejecta are
observed in the form of the broad-line region. Coronal magnetic reconnections
generate (relativistic) pair plasma which rams twin-jets perpendicular to the
disk whenever it succeeds in escaping fast enough from the (lossful) BLR;
otherwise we deal with a radio-quiet QSO.
Matthew Lehnert (Max-Planck Institut für Astronomy)
To set the stage for subsequent talks, I review the general properties of the
host galaxies of powerful AGN. This review includes information about the
stellar populations, structure, and luminosity of host galaxies and the
possible emission mechanisms contributing to the extended emission (scattering,
nebular continuum, stellar population, etc) giving special attention to
how the relative contributions of these mechanisms may vary with radio power,
radio morphological class, and redshift. Having established the gross
properties of the host galaxies of different (broad) classes AGN, I attempt
to establish a cosmogonical setting in which to place these hosts. An
important aspect of doing so is to relate the properties of the hosts with
the growth and fueling of the "nuclear monster". I briefly review the
most recent thinking on the connection between galaxy evolution and
the "ecology of AGN" and ruminate on how we might test these ideas.
W. H. de Vries (Kapteyn Astronomical Institute), C. P. O'Dea, P. D. Barthel
& S. A. Baum
HST NICMOS observations of a sample of powerful radio sources are used to study
host galaxy properties as a function of radio source size. Detailed profile
fits and stellar synthesis modeling provided evidence for the unimpeded
expansion of the radio sources from sub-kpc to Mpc sized structures (i.e. from
GPS through CSS to FR2 sources). Differences with FR1 hosts are also discussed.
Marek J Kukula (University of Edinburgh), James Dunlop, Ross McLure, Chris
O'Dea & Stefi Baum
We summarise the results of our recently completed HST R-band study of
low-redshift (0.1<z<0.25) FRII radio galaxies along with the host
galaxies of quasars of similar redshifts and radio powers. We find that, like
radio galaxies, the hosts of all but the least luminous quasars are massive
ellipticals with relatively large scalelengths (@
10 kpc) and luminosities (>2L*). Indeed the quasar hosts are
essentially indistinguishable from the radio galaxies in our sample. Using the
HST archive, we have compiled a database of inactive ellipticals having similar
redshifts, sizes and luminosities to the AGN hosts, and utilising similar HST
filters. A detailed comparison of these active and inactive elliptical samples
reveals a surprising degree of similarity and serves to emphasize that the
presence of a powerful active nucleus cannot necessarily be deduced from the
appearance of the stellar component of the host galaxy.
John Biretta, A. Martel, M. McMaster, W. Sparks, S. Baum (STScI) &
P. McCarthy (OCIW)
We present narrow-band images of sixty-four 3CR radio sources observed in
lines of [OII] 3727, [OIII] 5007, and H-alpha using the WFPC2 camera
on-board HST. The images reveal a wide variety of emission lime
morphologies, from compact nuclear regions to large-scale emission knots,
filaments, and spiral-like structures. Many objects give evidence of
ionization cones. In general we find a close correspondence between the
emission-line and radio axes; most are aligned within 40 degrees. There is
also evidence for a positive correlation between radio luminosity and the
spatial extent of the emission-line region. Properties of interesting
individual objects are discussed.
Susan Ridgway, Tim Heckman, Daniela Calzetti, Matt Lehnert & Alan Stockton
We will present the results of a NICMOS imaging survey of a small sample of z~2
-- 3 radio-quiet quasars. We have resolved extension in at least 4 of 5 objects
and find evidence for a wide range in the morphologies and magnitudes of these
hosts. We compare the properties of these z ~ 2 - 3 radio-quiet quasar hosts
with those of radio-loud objects at similar redshifts. At least one host has a
morphology that is indicative of a merger remnant. This frequency of "merger
remnant" morphology is similar to that we have found in a WFPC2 imaging survey
of z ~ 1 radio quasars.
John Conway (Onsala Space Observatory)
The nature of the (<1 kpc) sized double lobed radio sources known as Compact
Symmetric Objects is discussed. It has been proposed that these objects are
either young objects or normal aged objects 'frustrated' by dense gas. VLBI
monitoring observations of CSOs over 10 - 20 years has now revealed the
expansion in overall size of at least 5 CSOs with hotspot advance speeds
0.1h-1 - 0.2h-1 and kinematic ages of less than 5000
years. Together with spectral aging observations and energy supply arguments
these VLBI results strongly argue that most such objects are young. What is not
yet clear is whether these sources evolve into classical double-lobed FRI or
FRII sources. In particular it is unclear whether the population density of
CSOs is consistent with the predictions of the simplest such evolutionary
models in which all CSOs evolve gradually into classical double lobed
sources.
In more complex models periods of AGN activity may occur with very different
intrinsic luminosities and durations depending on the gas supply and feeding.
One possibility is that a large fraction of CSOs might be short-lived AGN which
do not have time to evolve into large scale sources before their activity
switches off. In addition observations which reveal some apparent CSOs embedded
inside classical double sources suggests that recurrent activity in AGN may be
common; adding an additional complication to evolutionary models. Such sources
might be explained by intermittent activity in the central engine.
Alternatively they could be due to 'smothering' by the deposition of dense gas
into the centres of the host galaxies.
Alison B. Peck (NRAO/NMIMT) & G. B. Taylor (NRAO)
Recent VLBI observations have identified several compact radio sources which
have symmetric structures on parsec scales, and exhibit HI absorption which
appears to be associated with the active nucleus. These sources are uniquely
well suited to investigations into the physics of the central engines, in
particular to studies of the kinematics of the gas within 100 pc of the core.
In these compact sources, it is reasonable to assume that this circumnuclear
material is accreting onto, and ``feeding'', the central engines.
We present results of HI imaging studies of 3 symmetric radio galaxies which
show evidence of a circumnuclear torus.
Shinji Horiuchi (National Astronomical Observatory Japan), S. Kameno, M. Inoue
(NAO) & H. Hirabayashi (ISAS)
We present 1.66 GHz VSOP (VLBI Space Observatory Programme) observations of a
GHz-peaked spectrum (GPS) source OQ 208. Two compact lobes with a 10 pc
separation in NE--SW direction are identified with those of ground VLBI
observations at higher frequencies. Brightness of the two lobes is highly
asymmetric in terms of a flux density ratio NE:SW ~60:1 at 1.66 GHz, larger
than at higher frequency. Both lobes show a steeply rising spectrum between
1.6 and 2.3 GHz, which implies free-free absorption by ambient plasma rather
than synchrotron self-absorption. We discuss how Narrow Line Region plasma
affects the evolution of radio galaxies.
Stefi Baum (STScI)
M. J. Ledlow (University of New Mexico), F. N. Owen & J. A. Eilek
We present an analysis of the optical/radio plane for FR I/II sources both in
and out of the rich cluster environment. We compare the radio power, size, and
optical luminosity distributions to look for effects related to the different
environments. We also present a detailed comparison between FR I and FR II
sources in the radio/optical/size plane.
Anton Koekemoer (GSFC/STScI)
I will discuss the overall emission-line properties of samples of different
types of radio galaxies, combining their excitation properties with kinematic
and luminosity data to investigate physical properties of the gas in the
immediate environments of the sources, and the extent to which this may affect
the propagation of the radio plasma. Specifically, emphasis will be placed on
extending this work to emission-line data obtained in recent years on samples
of CSS and GPS radio sources.
Geoffrey Bicknell (ANU Astrophysical Theory Centre, Australian National
University)
In one class of unified schemes, relativistic jets unify a number of apparently
different active galactic nuclei via the physics of aspect. The properties of
initially relativistic jets also play an important role in understanding the
connection between FR1 and FR2 radio galaxies. This involves a unique
relationship between the velocity and Mach number of a decelerating
relativistic jet. There are good arguments that jets in both FR1s and FR2s
consist of electrons and positrons.
Gigahertz Peak Spectrum (GPS) and Compact Steep Spectrum (CSS) sources are a
fascinating subclass of the radio galaxy population. Recent work indicates that
the properties of these sources may be understood through a model in which a
jet-inflated lobe ionizes the local ISM which absorbs low frequency radiation
through either free-free absorption or induced Compton scattering. The emission
lines from these sources are shock-excited on the basis of this model.
Extension of these ideas to Seyfert galaxies leads to the conclusion that there
are major differences between the composition of Seyfert and Radio Galaxy jets
and the processes by which the flows are initiated.
T. W. Jones, I. L. Tregillis & D. Ryu (University of Minnesota)
We have developed a simple, but effective numerical scheme for cosmic-ray
transport that is suitable for treatment of ~GeV electrons in radio galaxies.
It allows us to consider properly diffusive acceleration at shocks of any
strength, second order Fermi acceleration and radiative "aging" of the electron
population. The spectral form for the electrons is followed, so we can use it
to compute appropriate nonthermal emissions. We have now applied this method to
both 2D and 3D MHD simulations of jet flow and have begun to explore what can
be learned about the connection between jet dynamics and the properties of the
electron population in radio lobes. A companion paper will present and discuss
first examples of "synthetic observations" made using the results of these
simulations.
I. L. Tregillis, T. W. Jones & D. Ryu (University of Minnesota)
We have applied an effective numerical scheme for cosmic-ray transport to 3D
MHD simulations of jet flow in radio galaxies. The marriage of relativistic
particle and 3D magnetic field information allows us to construct a rich set of
"synthetic observations" of our simulated radio jets. The information
contained in these simulations is sufficient to calculate the "true"
synchrotron emissivity at a given frequency, enabling us to produce synchrotron
surface-brightness maps of our simulated sources, including polarization.
X-ray, inverse Compton, surface-brightness maps may also be produced. First
results from these synthetic observations used to explore the connection
between jet dynamics and electron transport in radio lobes will be discussed.
A companion paper will present and discuss the numerical scheme used for
capturing the cosmic-ray transport utilized in these simulations.
Philip Hardee (University of Alabama)
The appearance of wavelike helically twisted normal mode structures on steady
relativistic jets is presented. Wave speeds are a function of the wavelength,
and the highest wave speeds have a Lorentz factor about half that of the
underlying flow speed. A maximum pressure fluctuation criterion is used to find
the maximum jet distortions and velocity fluctuations as a function of Lorentz
factor. Jet distortion is reduced as the Lorentz factor increases and this
suggests a reduction in mass entrainment. Significant cyclic transverse
velocity fluctuation leads to variation in the flow direction on the order of
the relativistic beaming angle. Variation in the Doppler boost factor can lead
to significant brightness asymmetries as emission filaments twist around the
jet beam.
Paola Parma (Istituto di Radioastronomia del CNR, Bologna), M. Murgia (CNR and
Dip. di Astronomia, Università di Bologna), H. R. de Ruiter
(CNR and Osservatorio Astronomico di Bologna), R. Fanti (CNR and Dip.
di Fisica, Università di Bologna)
After a brief introduction to the morphological properties of FRI radio
sources, we describe a recent study of Laing et al. (1999), in which it is
shown that FRI jets are relativistic at their bases and decelerate quickly to
non-relativistic velocities.
From two-frequency data we determine spectral index distributions and
consequently the ages of FRI sources. We show that in the large majority of
cases synchrotron theory provides unambiguous and plausible answers; in a few
objects re-acceleration of electrons may be needed. The derived ages are of the
order 107-108 years, ~2-4× larger than the ages inferred
from dynamical arguments and a factor ~5-10 larger than the ages of FRII
sources. The linear sizes of FRI and FRII sources make it unlikely that many
FRII's evolve into FRI's.
A brief discussion is given about the possibility that radio sources go through
different cycles of activity.
Jean Eilek (New Mexico Tech)
The data now show that what we have called ``Type I'' radio galaxies divide
into two classes. This division is clear from their morphology. I suspect the
two classes are due to intrinsic, if yet unknown, differences in their basic
flow dynamics, possibly modified by local cluster weather. Understanding these
differences should lead us to a clearer picture of the ``life cycle'' of a
radio galaxy.
This division is apparent when one studies the 250 sources in the Owen-Ledlow
sample of radio galaxies in nearby clusters. Nearly all of these are Type I in
terms of their radio power and parent galaxy magnitude, but they clearly are
not all the same in their morphological properties. Study of these data
reveals that there are, indeed, two types of Type I galaxies. I will describe
the sample, present images, and discuss correlations with measured parameters
(radio power, galaxy magnitude, radio flux size, offset from X-ray peak, local
ambient gas density). Based on trends in the data, I will present dynamical
(toy?) models of these intriguing sources.
Eric S. Perlman, John A. Biretta, William B. Sparks & F. Duccio Macchetto
(STScI)
We present 1998 HST observations of M87 which yield the first single-epoch
spectrum of the jet from 0.3-2mm. The flattest
optical spectra (a
o~
0.6, where Fn
µ
n
-
a
; comparable to a
ro) are found in two inner jet knots which contain the fastest
superluminal components. Other knots have somewhat steeper optical
(a
o = 0.8 -
1.1) than radio-optical (a
ro ~ 0.65) spectra, but still show increasing power
n
Ln
. We do not find significant evidence of steepening for any component in the
near-IR to UV band, contrary to previous predictions.
Our data are combined with published X-ray and radio data to explore
synchrotron emission models, and re-examine hypotheses for the nature of the
jet's X-ray emission. If the X-ray emissions are co-spatial with lower-energy
emissions, we can strongly rule out ``continuous injection'' models, which
overpredict the X-ray emissions by factors 5-50. As a result, sites of in
situ particle acceleration must take up only a small fraction of the jet
volume. Models fit to other regions of the jet yield break frequencies
~ 1015-16 Hz. The highest break frequencies are in "strong
shock" regions, consistent with possible particle injection or
acceleration.
Everton Lüdke (Santa Maria Federal University, Brazil), Simon Garrington &
Sandro Coelho
In this paper, we present the first results of a study of the depolarization
asymmetry in radio galaxies and quasars with a single visible jet.
Polarization-sensitive images of the radio galaxy 3C352 and the quasar 3C275.1
have been produced with the Very Large Array at 5, 8 and 15 GHz and the
rotation measures and depolarization measures have been measured. At 330 mas
resolution, the depolarization values are greater than 0.92 and similar at the
jet and counter-jet sides. The peak rotation measures are around
-28 rad m-2 for the jet hotspot and -68 rad m-2 for the
counter-jet side of the radiogalaxy and are 17 rad m-2 smaller than
the quasar components. We interpret the results as there is little beam
depolarization minimal. These images are compared with Hubble Space Telescope
images at R band and show no suggestion that the radio components are spatially
coincident with the optical components and therefore the Faraday rotation and
depolarization can be due to an external invisible medium with central values
of Faraday depths of 1-3´
10-3 mG cm-3. This value
obtained from partially-resolved Rotation Measure analysis agree well with
depolarization values demanded by published radio source statistics at
substantially lower resolutions.
Joel Carvalho (Departamento de Fisica - UFRN - BRAZIL)
We present a theoretical model of the propagation of radio sources taking into
account the detailed expansion of the lobe surrounding the jet. Numerical
simulations of hydrodynamic supersonic jets have been carried out and different
features of the jet propagation not present in most analytical models are
incorporated into the model. In particular, we describe the pressure gradient
inside the lobes and point out the implications of it for the suggestions that
the lateral shock wave could be responsible for the optical emission and
trigger star formation in the neighborhood of compact radio sources. The
numerical simulations are also used to test the validity of the model and this
procedure is expected to improve our description of the jet propagation
phenomenon.
C. H. Ishwara-Chandra & D. J. Saikia (NCRA, TIFR)
In this paper we present multi-frequency radio observations of two new
giant quasars, 0437-244 and 1025-229 from the Molonglo 1 Jy
sample. These sources have well-defined double-lobed radio structure and
possible one-sided jets, no significant depolarization between 1.4
and 5 GHz and low rotation measure (RM < 20 rad m-2).
We have compiled a sample of about 50 known giant radio sources from the
literature, and have compared some of their properties with a complete
sample of 3CR radio sources of smaller sizes to investigate the evolution
of giant sources, and test their consistency with the unified scheme.
We find an inverse correlation between the
core prominence and the total radio luminosity, and show that
the giant radio sources have core strengths similar to those of
smaller sources of similar total luminosity. Hence their large sizes are
unlikely to be due to stronger nuclear activity. The degree of collinearity
and the arm-length ratio of the giant sources are also similar to that of
smaller sources. The luminosity-size diagram shows that the giant sources
are less luminous than smaller-sized sources, consistent
with evolutionary scenarios where the giants have evolved from the
smaller sources, losing energy as they expand. For the giant sources
the equipartition magnetic fields are smaller, and inverse Compton
losses with the microwave background radiation is the dominant process.
The radio properties of the giant radio galaxies and quasars are
consistent with the unified scheme.
Lucas Lara (Instituto de Astrofisica de Andalucia), G. Giovannini, et al.
We present radio observations of two radio galaxies, 3C338 and J1835+620, which
show evidence of distinct phases of activity during their lifetimes. The
emission from 3C338 at large scales could be relic emission from a first stage
of activity. The small-scale structure looks young, similar to the high-power
medium-sized symmetric objects (MSOs) found at high redshift. J1835+620, a
giant radio galaxy, presents two symmetric bright component within a typical FR
II structure. Radio maps and radio polarization properties are consistent with
a dense new ejection evolving through an older underlying jet. We suggest that
interaction with nearby galaxies could be the reason for restarting the
activity in these radio galaxies.
J. P. Leahy & Nectaria A. B. Gizani
We present ROSAT data on the cluster gas surrounding two powerful radio
galaxies, 3C 388 and Hercules A. Both clusters are well fitted by a
"beta-model" gas distribution, after allowing for a compact central
source. In both sources the cluster thermal pressure at the deprojected
distance of the radio lobes is about an order of magnitude larger than
the lob minimum pressure. Since the radio lobes of both objects are
sharply-bounded, we argue that the missing pressure is not simply entrained
intracluster gas. Thus the minimum energy in the lobes is indeed a severe
underestimate of the actual energy content by an order of magnitude or
more (on most theories the lobes would be overpressured and supersonically
expanding). We argue that the extra energy is mostly in the form of particles,
so that the magnetic field is below equipartition and so not a major
factor in the lobe dynamics. The large departure from minimum energy,
if typical, has far-reaching implications for the nature of AGN central
engines and the supply of mechanical energy to the ICM from radio jets.
Everton Lüdke (UFSM-CCNE-Physics Department, Santa Maria RS, Brazil) &
Debora Katz-Stone (U.S. Naval Academy)
An evolutionary scheme in which Gigahertz-Peaked Radio Sources (GPS) are young
sources progenitors of normal luminous FRII radio source has been recently
proposed. It is predicted that the so-called Compact Steep Spectrum Radio
Sources should be an intermediate stage in extragalactic radio source
evolution. In this paper, we present preliminary results of a spectral
analysis of the radio continuum between 1.4 GHz and 44 GHz for the most
luminous CSS radiogalaxies made with the MERLIN array and the Very Large Array.
We have derived spectral breaking frequencies for the double components
above 10 GHz resulting in an intervals of the duration of the CSS evolutionary
phase between 0.8-1.2 Myrs from standard spectral ageing theory. Further
implications of this project to understand the CSS evolution are also discussed.
Lawrence Rudnick (University of Minnesota)
I introduce a method for filtering structures on various spatial scales from
astronomical images. This technique, a modification of one used in other
contexts, produces a series of positive-definite images of different scale
features which when added back together, sum to the original image. It differs,
in this way, from Fourier-based filtering which creates sidelobes, or from
gradient-based filtering which does not preserve the original structures. This
multiresolution filtering can, with judicious application, be used for
brightness/photometry measurements and spectra on different spatial scales in a
single image. I present some results on radio galaxies, illustrating the
mixture of spectral indices found within lobes, a significant impediment to
aging analyses.
Andrew Young (University of Minnesota), Lawrence Rudnick, Debora Katz-Stone
& Aileen O'Donoghue
Color-color diagrams have been useful in studying the spectral shapes in radio
galaxies. In this poster, we present color-color diagrams for two
Wide-Angle-Tails, 1231+674 and 1433+553, and find that the standard aging
models do not adequately represent the observed data. Although the JP and KP
models can explain some of the observed points in the color-color diagram, they
do not account for those found near the power-law line. This difficulty may be
attributable to several causes. Spectral tomography has been previously used to
discern two separate electron populations in these sources. The combination
spectra from two such overlying components can easily resemble a power-law. In
addition, any non-uniformity in the magnetic field strength can also create a
power-law-like spectrum. We will discuss the implications our results may have
on current aging analyses.
Mark Lacy (Oxford University)
The lowest frequencies correspond to the longest synchrotron lifetimes, so
finding dead radio sources, i.e. objects whose jets and AGN have turned off, is
much more probable in flux-limited samples selected at low radio frequencies.
We have found one good candidate in a complete sample of 58 sources selected
at 38MHz. There is no sign of compact radio emission from hotspots, jets or the
nucleus, and the presumed host galaxy shows no sign of nuclear activity. A low
resolution VLA map clearly shows an edge-brightened structure consistent with
an FRII morphology, however. We discuss possible implications for radio source
lifetime estimates.
Megan Donahue & Jennifer Mack (STScI)
We will present near-infrared HST images of three central galaxies embedded in
clusters of galaxies with inferred massive cooling flows, Perseus/NGC1275,
Abell 2597, and PKS0745-191. Narrow-band imaging centered on molecular hydrogen
emission at 2 microns shows extended features of warm (~2000 K) molecular
hydrogen gas with nearly the same morphology as the ionized hydrogen features
that emit H-alpha in Abell 2597 and PKS0745-191. Molecular hydrogen in NGC1275
was detected only in the nucleus. We map significant dust features in these
galaxies at 1.6 microns. We compare the images to the radio morphologies at
similar scale. We discuss possible heating mechanisms.
Everton Lüdke (Universidade Federal de Santa Maria, Santa Maria, Brasil),
Thaisa S. Bergmann & Alcides G. R. Adornes (Universidade Federal do Rio
Grande do Sul, Porto Alegre, Brasil)
In this paper, we discuss our recent results regarding our neutral hydrogen
survey of a sample of 380 southern galaxies with the ATNF/Mopra Radio Telescope
and which are associated with bright radio sources at z<0.08. Neutral
hydrogen masses have been calculated for galaxies with AGN in order to stablish
statistical correlations between the radio, optical, IR and ultraviolet
observables. We found no significant trends between the environment masses of
these galaxies and the 5 GHz radio continuum emmission although a significant
relationship between the IRAS fluxes and radio has been verified. Further
correlations between the fluxes are also shown and the astrophysical
implications of this project in the understanding of the AGN phenomena are
briefly discussed.
Everton Lüdke (Universidade Federal de Santa Maria, Santa Maria RS,
Brazil), William Cotton (NRAO Charlottesville), Daniele Dallacasa (Istituto di
Radioastronomia del CNR, Bologna, Italy) & Hardip Sanghera (Institute of
Astronomy, Cambridge, UK)
Millisecond-resolution, polarization-sensitive observations with Very Long
Baseline Interferometry are useful to study magnetic fields towards the core
component of radio quasars. In this paper, we report our results of a two-epoch
polarization observations of a sample of luminous quasars belonging to the
Compact Steep Spectrum (CSS) group of radio sources according to Fanti &
Fanti classification at multiple frequencies. We obtain average rotation
measures in the range 1000-1400 rad m-2 in very distorted radio
sources, suggesting that the overall distortion in the radio components which
some sources do exhibit cannot be explained with simple jet-could arguments and
therefore internal instabilities may play a significant role in relativistic
jet dynamics. The relevance of this project to the age determination of CSS
quasars are briefly discussed.
Everton Lüdke (UFSM-CCNE-Physics Department, Santa Maria RS, Brazil) &
Simon Garrington (University of Manchester)
In this poster we present preliminary results of an ongoing project to look
for clues on the evolution of the Laing-Garrington effect and depolarization
asymmetries in extragalactic radio quasars and galaxies with a single visible
jet, accordingly with Fanaroff and Riley morphological classification of radio
sources. By comparing the polarization properties of CSSs, GPS and extended
luminous FRII sources, we conclude that (a) galactic-size sources belonging to
the CSS group show similar spectral index distribution on the lobes but
spectral index asymmetries are common for sources with projected angular
sizes larger than 20 kpc, (b) the depolarization asymmetry is the strongest
among the CSS sources and it decreases with source projected linear sizes,
(c) Faraday rotation asymmetry arises mostly from the hotspots rather than
diffuse lobe components. We also present observational arguments which
suggest that radio observations of Faraday effects are not accurate tools as
diagnostics for ages in extragalactic radio sources and that aberration of
light may be an important source of error in age determination of the lobes
of extragalactic radio sources.
Mark Allen (STScI)
Classical equipartition calculations for Seyfert jets suggest that the pressure
in the relativistic plasma is inadequate to drive shocks into the interstellar
medium and produce the observed emission line flux. We argue that the radio
plasma may only trace a fraction of the available energy which may exist in an
entrained thermal phase. Using the optical, radio and X-ray properties of the
Seyfert galaxy NGC 2992 we find that the energy associated with the radio lobe
may provide a larger fraction of the energy required to power the narrow line
region than previously anticipated.
Paola Grandi (IAS/CNR), C. M. Urry (STScI) & L. Maraschi
We review BeppoSAX observations of radio-loud AGN, with particular attention to
radio galaxies. Our picture of radio galaxies has been changed by the BeppoSAX
results: their X-ray spectra are quite varied, and perhaps surprisingly, any
similarity between radio-loud AGN and Seyfert galaxies is the exception rather
than the rule.
It is possible that beamed radiation from the jet contributes substantially to
the X-ray emission from radio galaxies, and hot/ionized material, rather than
a cold geometrically thin accretion disk, dominates the X-ray emission from the
inner nuclear regions.
Neil M. Nagar (University of Maryland), Heino Falcke, Andrew S. Wilson &
Luis C. Ho
About a third of all nearby low-luminosity (L(Ha
) < 1040 ergs/s) AGN (LLAGN), appear more closely related to
radio galaxies than to "classical" Seyferts, even though their radio and
optical luminosities are lower than those of FR I's and FR II's by ~2-3 orders
of magnitude - e.g., on a plot of radio core power versus emission line
luminosity these objects lie along the low luminosity extrapolation of
radio-loud galaxies. Interestingly, on the same plot, low luminosity Seyferts
lie in the same general area as "radio-loud" LLAGN, but closely follow the low
luminosity extrapolation of "classical" Seyferts. These "radio-loud" LLAGN
(which predominantly occur in LINER nuclei) and low-luminosity Seyferts
therefore provide important clues into the fundamental reasons for the
radio-loud radio-quiet division. Their low luminosity and relative abundance
in the local universe raise interesting questions about the origin and lifetime
of nuclear activity.
Henrique R. Schmitt (STScI)
We have recently shown that there is no correlation between the orientation of
the accretion disk, traced by the position angle of radio jets, and the host
galaxy disk in Seyfert galaxies. This result is counter to intuition, since
most of the gas in a spiral is in the plane of the galaxy, and one would
naively expect the central accretion disk angular momentum vector to be aligned
with that of the galaxy. We will review what is known about the subject and
present our new results, obtained using a well defined sample selected by a
mostly isotropicproperty. We will also discuss possible causes for this
misalignment, which may have implications on the mechanisms to feed the
nucleus.
Ann E. Wehrle, Dayton L. Jones, B. Glenn Piner & David L. Meier
We derive the physical characteristics of the accretion disk within one parsec
of the central supermassive black hole in the nearby FR-1 galaxy NGC 4261. The
disk absorbs synchrotron radiation from the base of relativistic jets through
free-free absorption. Multifrequency VLBA data yield the accretion disk
thickness, diameter, electron density, and magnetic field.
Johan P. U. Fynbo (ESO), B. Ingunn & P. Moller
We report the detection of the host Galaxy of the radio quiet QSO Q0151+048A at
z=1.92. Deep U, B and I imaging of the QSO pair Q0151+048A+B obtained at the
Nordic Optical Telescope in good seeing has revealed a very luminous host
(Mobs » -24 in all three bands
assuming W=1) centred on the position of
Q0151+048A. The colours and extreme brightness of this host galaxy resembles
the colours and brightnesses of high redshift radio galaxies.
The host galaxy of the 3.4 magnitudes fainter Q0151+048B is marginally detected
in our deepest image, which is in the B-band. This host galaxy is about 3
magnitudes fainter than the host galaxy of Q0151+048A indicating a strong
correlation between QSO and host galaxy brightness.
Anton M. Koekemoer & G. V. Bicknell
The FR II radio galaxy PKS 0349-27 contains a luminous emission-line nebula,
extending over several tens of kpc around its host galaxy. We investigate the
spatial distribution of the kinematics, line ratios and total emission-line
flux of the gas by means of a detailed series of long-slit spectra that cover
its entire extent. We show that the physical properties of the line-emitting
gas, in particular its ionization properties, excitation state, dynamics and
energy budget, suggest a scenario involving auto-ionizing shocks as the
dominant ionization mechanism. We discuss ways in which shocks with the
required characteristics can be formed.
Anton M. Koekemoer, C. P. O'Dea, S. A. Baum, M. Donahue, M. Voit (STScI),
J. F. Gallimore (NRAO), B. McNamara (CfA) & C. Sarazin (Univ. Virginia)
We present results from detailed HST/WFPC2 imaging of the centrally dominant
radio elliptical galaxy in the cooling flow cluster Abell 2597. This object
is an archetypal `blue-lobed' cooling flow radio galaxy and contains a
luminous emission-line nebula, a compact radio source, and substantial
dust and molecular gas in its center. We show that the emission-line filaments
directly trace interactions between the radio lobe and ambient cold gas. We
resolve the blue continuum emission into a series of knots and clumps, most
likely due to regions of recent star formation. We investigate several possible
triggering mechanisms for the star formation, including direct interactions
with the radio source, filaments condensing from the cooling flow, or the
result of an interaction with a gas-rich galaxy, which may also have been
responsible for fueling the active nucleus. We propose that the properties
of the source are plausibly explained in terms of accretion of gas by the cD
during an interaction with a gas-rich galaxy, which combined with the fact that
this object is located at the center of a dense, high-pressure ICM can account
for the high rates of star formation and the strong confinement of the radio
source.
Mark Lacy (Oxford University)
We have imaged 8C 1435+635 (z=4.25) and 6C 0140+326 (z=4.41) in continuum and
line plus continuum bands with the HST. Our images show patchy distributions of
continuum and line emission with a tendency for the two types of emission to
anticorrelate. When compared to Keck K-band images, it seems likely that the
presence of dusty neutral gas is strongly influencing the UV continuum and line
emission. It is suggested that the observed radio-optical alignment is
produced as dust is cleared from the radio lobes by shocks associated by the
radio source. 8C1435+635 could therefore be hosting a luminous, galaxy-scale
starburst, as suggested by submm observations.
André R. Martel, S. A. Baum, W. B. Sparks, J. A. Biretta, G. Verdoes
(STScI) & N. J. Turner (U. of Maryland, College Park)
We present broad- and narrow-band WFPC2 images of the nuclear dust
disks and rings of five low-$z$ elliptical galaxies hosting 3C radio
sources : NGC 383 (3C 31)/NGC 382, NGC 3862 (3C 264), NGC 4261 (3C
270), UGC 12064 (3C 449), and NGC 7720 (3C 465)/NGC 7720A. We detect
resolved line emission in the core of the disks of NGC 3862 and UGC
12064, and possibly in NGC 383 and NGC 7720. In NGC 383, NGC 7720, and
UGC 12064, the emission is extended along the major axis of the disks,
suggesting a true physical association between the ionized material
and the dust. The color maps clearly reveal that the disks of NGC
383, NGC 4261, NGC 7720, and possibly NGC 3862 are inclined. The disk
of NGC 383 is the most disturbed and filamentary and appears to
consist of an inner (~ 0.5 kpc) and outer disk (~ 2.5 kpc).
We suggest that the colors of the unresolved nuclei of NGC
383 and NGC 3862 may be partially accounted for by optical synchrotron
emission (and may in fact dominate in NGC 3862) while in NGC 4261, the
nuclear emission is completely dominated by line emission. The disk
colors are generally redder than predicted by a simple "sandwich"
model, implying that the disks can not be simply treated as uniform,
thin sheets of dust. Preliminary results from a radiative transfer
code which incorporates backscattering and varying dust composition
and distributions appear more promising.
Emmanuel Moy & Brigitte Rocca-Volmerange (IAP)
One of the remaining open questions about radiogalaxies is the connection
between phenomena associated with the central object and the environment of the
radiogalaxies. This connection manifests itself in the radio-optical alignment
phenomenon: continuum and emission line morphologies are aligned with the radio
jet or coincident with the radio lobes. Different hypothesis have been
suggested to explain this association: photoionizing shocks due to the
propagation of the radio jet, emission from gas cloud embedded in the
ionisation cone of the AGN, or jet-induced star formation.
To disentangle these process requires, on the one hand, high spatial resolution
onservations. On the other hand, a multi-component model including
photoionization by shocks, AGN radiation and massive stars has to be achieved.
We present observations conducted with the Integral Field Units TIGER and OASIS
at CFHT, and the current status of our model.
Susan M. Simkin & B. I Grimberg (Michigan State University)
High resolution studies of the inner regions of nearby radio galaxies
may allow us to identify those processes which arise from the
interaction between the galaxy's ISM and the ejected radio plasma close
to the nucleus, before the radio jet plasma has been modified by aging
and interaction with multiple clouds of gas. We examine the emission
line ratios of [NII] : H$\alpha$, [OI] : H$\alpha$,
[SII] : H$\alpha$, and [OIII] : H$\beta$ for three nearby objects,
Minkowski's Object, NGC 7385, and Pictor A. All of these objects have
published radio images which show detailed correspondence between the
disrupted morphology of the ionized gas clouds and the radio features
at a spatial resolution of $\le$1 kpc $h.^{-1}$. In all of these
cases the clouds have measured velocities which indicate motion which
differs from that of the ambient medium and is directed away from the
impingeing radio plasma. We find that that the values for
[NII] : H$\alpha$ are lower than those usually found for active
galaxy nuclei with similar values of [OI] : H$\alpha$, Although there
are several competing models for calculating the expected emission line
ratios from shock heating and/or UV continuum excitation and ionization
for the EELR in galaxies as well as the nuclear regions of AGNs, none
of these models reproduce the extreme values of the [OI] and [NII] :
H$\alpha$ ratios which we find here. We postulate that he extremely
low emisivity for [NII] which we see in the case of Pictor A (and to a
lesser extent NGC \,7385) may arise from the way in which the radio jet
energized the interstellar gas in the galaxy.
D. Dallacasa, C. Stanghellini, R. Fanti & M. Centonza
Two samples of radio sources with peaked radio spectra, and peaking at high
(> a few GHz) frequencies (High Frequency Peakers or HFP) have been selected
by a comparison between the Green Bank 6 cm survey and the 20 cm NRAO VLA Sky
Survey (NVSS). In the framework in which GPS radio sources are the progenitors
of FRI and FRII radio sources, HFP should represent an even earlier stage. We
present here the 2 sample and the first simultaneous multifrequency VLA
observations of these objects.
E. J. Guerra, Shawn Newlander (Rowan University), Deborah B. Haarsma &
R. Bruce Partridge (Haverford College)
Until surveys at higher frequencies are performed, selecting sources with
inverted-spectra between 1.4 GHz and 4.8 GHz is the most promising method of
detecting Gigahertz Peaked Spectrum (GPS) sources that peak above 4.8 GHz.
Models of radio source evolution predict the existence of such sources. These
sources can be a significant foreground for cosmic microwave background
anisotropy satellites (such as MAP and Planck).
A sample of 308 inverted-spectrum radio sources was selected from the
cross-correlation of the VLA FIRST and GB6 surveys. These sources have 1.4-4.8
GHz spectral indices greater than +0.4, where
Sn
∝
n
+a
. Results from 20 GHz observations taken at the NRAO 140-foot are
presented for this sample.
M. Murgia, C. Fanti, R. Fanti, L. Gregorini, U. Klein, K.-H. Mack & M. Vigotti
The high-frequency integrated spectra of Compact Steep Spectrum (CSS) sources
show breaks with a moderate spectral steepening well fitted by continuous
injection synchrotron spectra. In lobe-dominated CSS sources the radiative ages
deduced by the synchrotron theory are in the range of up to 105
years, if equipartition magnetic fields are assumed. These radiative ages are
well correlated with the source size indicating that "the CSS sources are
young". In order to maintain the "frustration scenario", in which the sources'
lifetimes are 107 years, their equipartition magnetic field would be
systematically decreased by a factor ~20.
A. B. Peck (NRAO/NMIMT) & G. B. Taylor (NRAO)
The class of radio sources known as Compact Symmetric Objects (CSOs) is of
particular interest in the study of the evolution of radio galaxies. CSOs are
thought to be young (probably ~104 years), and a very high fraction
of them exhibit HI absorption toward the central parsecs. The HI, which is
thought to be part of a circumnuclear torus of accreting gas, can be observed
using the VLBA with high enough angular resolution to map the velocity field of
the gas. This velocity field provides new information on the accretion process
in the central engines of these young sources.
We have identified 9 new CSOs from radio continuum observations for the VLBA
Calibrator Survey, increasing the number of known CSOs by almost 50%.
Eric Perlman (STScI), John Stocke (Colorado), John Conway (Onsala), Chris
Reynolds (Colorado) & Mitch Begelman (Colorado)
We present 3-band HST imaging of three nearby (z<0.1) CSOs: 4C31.04,
1946+708 and 1146+596 (=NGC3894). These objects were chosen for HST
observation on the basis of detected HI and molecular line absorption. The
images show large amounts of obscuration in each source, well distributed
throughout the host galaxies, but somewhat concentrated in the nuclear regions.
All three also show evidence of nuclear structures which resemble disks or
tori. We discuss the possible association of the nuclear structures and
obscuration with their radio structure, and compare with other HST observations
of GPS, CSS and large-scale radio galaxies.
Satoko Satoh (National Astronomical Observatory of Japan), Seiji Kameno,
Kiyoaki Wajima, Masafumi Imai & Makoto Inoue
We present results of multi-frequency observations towards GHz-Peaked Spectrum
(GPS) sources with VLBA. Recent VSOP observations of a GPS source OQ208 have
shown that its convex spectrum is caused by free-free absorption (FFA) due to
external ionized gas surrounding the source. The keys are (1) sharp cut-off at
low frequency in the spectrum and (2) asymmetric peak frequency in double lobe.
In order to investigate how common is FFA in GPS sources, we observed 9 samples
(5 QSOs, 2 RGs, 2 Sy2s) selected from the GPS catalog. We tried spectral
fitting using FFA model for each sources. All QSOs show asymmetric FFA opacity
like OQ208 does, while the opacity of RGs and Sy2s are symmetric. It supports
that the Unification model between RGs and QSOs.
Carlo Stanghellini (Istituto di Radioastronomia del CNR, Noto SR, Italy),
D. Dallacasa, C. P. O'Dea, S. A. Baum, R. Fanti & C. Fanti
We present a complete sample of Compact Symmetric Objects (CSO) which are
currently thought to be the progenitors of the extended powerful extragalactic
radio sources (O'Dea & Baum 1997, AJ 113, 148, Fanti et al 1995, A&A
302, 317), and briefly discuss their properties. The objects presented here
are a subsample of the complete sample of bright GHz-Peaked-Spectrum radio
sources selected by Stanghellini et al. (1998, A&AS 131, 303).
C. Stanghellini, X. Liu, D. Dallacasa & M. Bondi
We report on an ongoing work aimed to detect the separation speed of the two
hot-spots of the Compact Symmetric Object OQ208. Comparing images at 8.4 GHz
taken between 1994 and 1997 we obtain a tentative estimate of a relative
motions between two components of the radio source. This research has made use
of the United States Naval Observatory (USNO) Radio Reference Frame Image
Database (RRFID).
Wolfgang Tschager (Leiden Observatory), R. T. Schilizzi, I. A. G. Snellen,
H. J. A. Rottgering & G. K. Miley
There is growing evidence that compact radio sources with peaked radio spectra
- GHz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sources - are
young objects and as such are the precursors of the large, extended, double
lobed radio galaxies. We are conducting a population study of faint CSS sources
in the radio and the optical. Results will be compared with those obtained on
samples of bright GPS and CSS sources and faint GPS sources. In this
presentation, an overview of the data obtained so far and the first, very
preliminary results, are given. In addition, Space-VLBI observations at 5 GHz
and ground-based matched-beam images at 15 GHz of the GPS radio source 2021+614
are presented. From comparison with observations at earlier epochs we deduce an
age of about 450 yr for 2021+614. This provides additional support for the
contention that peaked spectrum radio sources are young.
Gopal-Krishna (NCRA) & Paul J. Wiita (GSU)
A brief observational and theoretical perspective is provided on
the issue of Fanaroff-Riley (FR) morphological
dichotomy of extragalactic radio sources. In this context we highlight
the existence of double radio sources where the two lobes exhibit
different FR morphologies. It is pointed out that, although rare,
such `hybrid morphology radio sources', or HYMORS, could be an
effective probe of the origin of the FR dichotomy. Their existence
supports explanations based upon jet interactions with external
media and appears difficult to reconcile with explanations assuming
fundamental differences in the nature of the jets or the central engine.
J. E. Pesce (Eureka Scientific), C. M. Urry, M. O'Dowd, R. Scarpa (STScI),
R. Falomo (Padua Observatory) & A. Treves (University of Milan)
We analyze images of BL Lacertae objects obtained with the HST.
The nine objects cover a redshift range of 0.19 to 0.997. The relatively
deep images are sufficient to detect galaxies at least one magnitude
below MI*(-21.4) and in most cases to three magnitudes
below M*. Galaxy enhancement over the average background is found
around four out of the nine objects. Results for some cases are confirmed by
ground-based imaging. In the other cases, the redshifts of the target
BL Lac objects may be incorrect or they are truly isolated. These findings
reinforce the idea that on average, BL Lac objects are found in regions
of above average galaxy density. However, isolated objects apparently can host
BL Lac nuclei too, a result that has implications for the processes
that trigger/fuel the nuclear activity.
M. Sandell (NRAL Jodrell Bank) & J. P. Leahy
Using data from the Atlas of DRAGNs a selection of mainly FR-II
sources are subjected to a correlation analysis. Parameters include source
power, compactness, and axial ratio. The previous result of Jenkins & McEllin
(1977) between compactness and power is shown not to hold for these close
(z<0.5) sources. The previous result of Leahy & Williams (1984), betweem
axial ratio and power, is shown to hold if the 10% peak width is used instead
of the half maximum width in calculating the axial ratio.
Riccardo Scarpa (Space Telescope Science Institute), Federica Govoni, Renato
Falomo & Gianni Fasano (Padua Observatory)
Photometric and morphological (re, ellipticity, PA, c4)
properties of 79 low redshift (z</~0.1) radio galaxies are discussed.
It is found that most of host galaxies are luminous bulge dominated systems
similar to normal non radio giant ellipticals. Besides for objects clearly in
interaction, radio galaxies follow the same m
e - re relation, and have ellipticity, amount of
twisting, and isophotes shape (boxy , disky) indistinguishable from those of
other ellipticals. Some cases of additional disc components are found with
spheroid-to-disk luminosity ratio similar to that found in many ellipticals.
The average Cousins R total absolute magnitude is
<MR> = -23.99 with a clear trend for FR I sources to be
~0.5 mag brighter than FR II galaxies. In about 40% of the objects we find an
excess of light in the nucleus attributable to the presence of a nuclear point
source, which contributes on average for ~1-2% of the total flux from the host
galaxy. These results support a scenario where radio emission is little related
with the overall properties and/or the activity have negligible effects on the
global characteristics of the host galaxy.
C. M. Urry, R. Scarpa, M. O'Dowd, R. Falomo, M. Giavalisco, J. Pesce &
A. Treves
Our HST WFPC2 survey of 109 BL~Lac objects, from six complete
radio-, X-ray-, and optically-selected catalogs, probes the host
galaxies of low-luminosity radio sources in the redshift range 0<z<1.35
The host galaxies are luminous ellipticals, well matched in radio power
and galaxy magnitude to FRI radio galaxies. Similarly, the host galaxies
of high luminosity quasars from the literature occupy the same region of
this plane as FRII radio galaxies (matched in redshift). This strongly
supports the unification of radio-loud AGN, and suggests that studying
blazars at high redshift is a proxy for investigating less luminous (to us)
but intrinsically identical radio galaxies, which are harder to find
at high z. Accordingly, the difference between low-power jets in BL Lac
objects and high-power jets in quasars can then be related to the FRI/FRII
dichotomy; and the evolution of blazar host galaxies or their nuclei (jets)
should correspond to the evolution of radio galaxies.
John Biretta (STScI), W. Junor (UNM) & M. Livio (STScI)
The elliptical galaxy M87 contains the nearest AGN
with a bright radio core. We present new VLBI
observations of its nucleus obtained with both global
VLBI at 7mm, and with space-based VLBI
using HALCA at 6 cm wavelength. The 7mm observations
are the highest linear resolution observations yet
obtained on a powerful radio galaxy nucleus. Both
data sets show the jet is strongly limb-brightened
on these scales and with evidence for sinusoidal
structures within the jet. The opening angle
of the jet increases dramatically near the radio core,
indicating we are directly observing the jet's initial
formation and collimation on a scale 10s of
Schwartzschild radii from the central black hole. These results
are consistent with collimation by poloidal B fields achored
in an orbiting accretion disk.
John Biretta, E. Perlman, W. Sparks & F. D. Macchetto (STScI)
We present highlights from our four-year monitoring campaign
on the M87 jet using the FOC and WFPC2 cameras on-board HST.
Numerous optical features within the first arcseconds
of the jet display apparent superluminal motion at speeds of
4c - 6c. These speeds indicate bulk flow with a Lorentz factor of
6 or greater, and strongly support unified models for this FR-I
radio source. These speeds also constrain the velocity vector to be
oriented within 19 degrees of the line of sight, indicating
the jet is misaligned with the circumnuclear gas disk,
or possibly that jet material moves on a helical path about the
jet axis. The brightness evolution of the superluminal
components is also discussed.
Mark Birkinshaw (University of Bristol)
We now have good measurements of the gas densities and pressures of the
atmospheres near radio galaxies, and so can re-examine the question of the
stability of radio jets. The issue of how the Kelvin-Helmholtz instability of
radio jets is tamed remains important, and I will describe a number of ways
that the short-wavelength instabilities that can cause jet disruption can be
suppressed, while the long-wavelength instabilities that are popular as causes
of distorted jet structures can be preserved.
S. Jeyakumar & D. J. Saikia (NCRA, TIFR)
We study the collimation of radio jets in the high luminosity Fanaroff-Riley
class II sources by examining the dependence of the sizes of hotspots and knots
in the radio jets on the overall size of the objects for a sample of compact
steep-spectrum or CSS and larger-sized objects. The objects span a wide range
in overall size from about 50 pc to 1 Mpc. The mean size of the hotspots
increases with the source size during the CSS phase, which is typically taken
to be about 20 kpc, and the relationship flattens for the larger sources.
The sizes of the knots in the compact as well as the larger sources are
consistent with this trend. We discuss possible implications of these trends.
We find that the hotspot closer to the nucleus or core component tends to be
more compact for the most asymmetric objects where the ratio of separations of
the hotspots from the nucleus, rd > 2. These highly asymmetric
sources are invariably CSS objects, and their location in the hotspot size
ratio - separation ratio diagram is possibly due to their evolution in an
asymmetric environment. We also suggest that some sources, especially of lower
luminosity, exhibit an asymmetry in the collimation of the oppositely-directed
radio jets. We also present 3-Dimensional numerical simulations of propagation
of jets to understand their collimation for realistic ambient environments.
A. Rosen & P. Hardee (University of Alabama)
We have investigated with a 3D MHD code the spatial development of three sets
of jet flows: trans-Alfvénic expanding jets, supermagnetosonic
cylindrical jets, and supermagnetosonic expanding jets. In the first two sets,
we have also simulated jets with primarily poloidal and primarily toroidal
magnetic field configurations. The entrained mass increases at differing rates
with axial position, from slow to fast and occasionally to nearly zero. These
different entraining rates appear correlated with the growth of the
Kelvin-Helmholtz instability from linear to nonlinear stages and occasionally
to a saturation stage. In general, jets that have a primarily toroidal
magnetic field, that are sub-Alfvénic, or that are expanding remain more
stable than jets that have a primarily poloidal field, that are slightly
super-Alfvénic, or that are initially cylindrical, respectively.
Riccardo Scarpa & C. Megan Urry (Space Telescope Science Institute)
The kinetic energy budget of all known optical jets is discussed,
investigating its dependence on the free parameters, mainly plasma bulk speed
and jet inclination q to respect with the line
of sight. It is found that in order to power the extended radio lobes of radio
galaxies, the bulk motion of the plasma on kiloparsec scales must be
relativistic Gbulk >/~ 2).
Based on various constraints, a "most probable" region in the parameter space
is found. This is located around G
bulk~ 5 and q
~ 25°
.
Renouncing to equipartition, it is also shown that observations and theoretical
expectation agree in a larger and less extreme range of values of the relevant
parameters. As a whole, we found evidences that optical jets are relativistic
at kpc scales, and may be well out of equipartition, with average magnetic
field intensity ~ 10% of the equipartition value. The field is weak enough that
electron reacceleration is no longer necessary (at least) as the
major mechanism to explain optical emission at kiloparsecs scales. In this
condition, relativistic particles carry most of the energy, roughly
102 times the energy density of the magnetic field.
Paul J. Wiita (GSU), Z. Wang (GSU & MIT) & Jagbir S. Hooda (GSU & IPST)
Three-dimensional hydrodynamical simulations of light, supersonic jets striking
dense clouds have been performed. For high Mach numbers, the jets eventually
destroy the clouds, but instabilities are induced which disrupt the jets sooner
than they would otherwise become unstable. For low jet thrusts, the jets
splash off the clouds and essentially stall for extended periods. Only for a
small area in parameter space, where relatively dense jets with marginally
supersonic internal Mach numbers interact with very dense clouds, does it
appear that jets can be stably bent and continue to propagate substantial
distances. Such interactions are relevant for Compact Steep Spectrum radio
galaxies and "dog-leg" radio sources, as well as some Wide-Angle Tail
morphologies.
J. Wiseman (JHU) & J. Biretta (STScI)
Besides extragalactic radio sources, jets are also seen in young stellar
objects and x-ray binaries within our own galaxy. These occupy a very
different parameter space from the extragalactic jets, and yet many are
similar in appearance and nature to their powerful extragalactic cousins.
In many cases far more information is available for the galactic jets, due
to, e.g., rapid evolution and emission line ratios and velocities.
We review properties of galactic jets and speculate at implications
they have for extragalactic ones. Specifically we consider central
engine mass, jet opening angle and Mach number, the nature of the emission
knots, the symmetry of the ejection process, and the long-term source history.
A. Capetti (Osservatorio Astronomico di Torino, Italy), A. Celotti (SISSA di
Trieste, Italy), L. Feretti (Istituto di radioastronomia del CNR di Bologna,
Italy) & E. Trussoni (Osservatorio Astronomico di Torino, Italy)
In the unified model for Active Galactic Nuclei, FR I radio galaxies are
interpreted as BL Lac objects with relativistic jets misaligned from the line
of sight, with possible obscured nuclei by thick inner tori. In the framework
of this problem, we present the results of multiwavelength observations of the
five radio galaxies 3C 31, 3C 264, 3C 270, 3C 465 and NGC 7052. The radio data
have been obtained with the VLA/VLBI, HST observations in the IR (NICMOS) and
optical bands (WFPC2) are available, while the X-ray data come from ROSAT
archive observations. The first main conclusion from this analysis is that no
heavy obscuration of the inner AGN seems to be present. Furthermore, it turns
out apparently that the different features between the SED of these radio
galaxies and the typical SED of BL Lac objects cannot be understood in terms of
beaming effects only.
M. Chiaberge, A. Capetti & A. Celotti
Emission from an unresolved Central Compact Core (CCC)
is detected by the Hubble Space Telescope in the great majority of a
complete sample of 33 FR I radio galaxies.
CCC optical emission shows a striking correlation with
the radio core fluxes, which extends over four decades with a slope
consistent with unity. This strongly argues for a non-thermal synchrotron origin
of the CCCs, which would then dominate the nuclear emission both in
the radio and in the optical bands.
The high rate detection of CCCs sets strong
constraints on the existence/geometry of any obscuring, optically
thick structure (torus) in FR I.