Astrophys.J. 601 (2004) 778-797 We present an extensive synthetic observational analysis of numerically-
simulated radio galaxies designed to explore the effectiveness of conventional
observational ...analyses at recovering physical source properties. These are the
first numerical simulations with sufficient physical detail to allow such a
study. The present paper focuses on extraction of magnetic field properties
from nonthermal intensity information. Synchrotron and inverse-Compton
intensities provided meaningful information about distributions and strengths
of magnetic fields, although considerable care was called for. Correlations
between radio and X-ray surface brightness correctly revealed useful dynamical
relationships between particles and fields. Magnetic field strength estimates
derived from the ratio of X-ray to radio intensity were mostly within about a
factor of two of the RMS field strength along a given line of sight. When
emissions along a given line of sight were dominated by regions close to the
minimum energy/equipartition condition, the field strengths derived from the
standard power-law-spectrum minimum energy calculation were also reasonably
close to actual field strengths, except when spectral aging was evident.
Otherwise, biases in the minimum- energy magnetic field estimation mirrored
actual differences from equipartition. The ratio of the inverse-Compton
magnetic field to the minimum-energy magnetic field provided a rough measure of
the actual total energy in particles and fields in most instances, within an
order of magnitude. This may provide a practical limit to the accuracy with
which one may be able to establish the internal energy density or pressure of
optically thin synchrotron sources.
Astrophys.J.633:717-732,2005 We present a set of high-resolution 3D MHD simulations of steady light,
supersonic jets, exploring the influence of jet Mach number and the ambient
medium on jet ...propagation and energy deposition over long distances. The
results are compared to simple self-similar scaling relations for the
morphological evolution of jet-driven structures and to previously published 2D
simulations. For this study we simulated the propagation of light jets with
internal Mach numbers 3 and 12 to lengths exceeding 100 initial jet radii in
both uniform and stratified atmospheres.
The propagating jets asymptotically deposit approximately half of their
energy flux as thermal energy in the ambient atmosphere, almost independent of
jet Mach number or the external density gradient. Nearly one-quarter of the jet
total energy flux goes directly into dissipative heating of the ICM, supporting
arguments for effective feedback from AGNs to cluster media. The remaining
energy resides primarily in the jet and cocoon structures. Despite having
different shock distributions and magnetic field features, global trends in
energy flow are similar among the different models.
As expected the jets advance more rapidly through stratified atmospheres than
uniform environments. The asymptotic head velocity in King-type atmospheres
shows little or no deceleration. This contrasts with jets in uniform media with
heads that are slowed as they propagate. This suggests that the energy
deposited by jets of a given length and power depends strongly on the structure
of the ambient medium. While our low-Mach jets are more easily disrupted, their
cocoons obey evolutionary scaling relations similar to the high-Mach jets.
We present the first three-dimensional MHD radio galaxy simulations that
explicitly model transport of relativistic electrons, including diffusive
acceleration at shocks as well as radiative and ...adiabatic cooling in smooth
flows. We discuss three simulations of light Mach 8 jets, designed to explore
the effects of shock acceleration and radiative aging on the nonthermal
particle populations that give rise to synchrotron and inverse-Compton
radiations. We also conduct detailed synthetic radio observations of our
simulated objects. We have gained several key insights from this approach: 1.
The jet head in these multidimensional simulations is extremely complex. The
classical jet termination shock is often absent, but motions of the jet
terminus spin a ``shock-web complex'' within the backflowing jet material of
the head. 2. Understanding the spectral distribution of energetic electrons in
these simulations relies partly upon understanding the shock-web complex, for
it can give rise to distributions that confound interpretation in terms of the
standard model for radiative aging of radio galaxies. 3. The magnetic field
outside of the jet itself becomes very intermittent and filamentary in these
simulations, yet adiabatic expansion causes most of the cocoon volume to be
occupied by field strengths considerably diminished below the nominal jet
value. Thus population aging rates vary considerably from point to point.
We perform a series of so-called ``synthetic observations'' on a set of 3D
MHD jet simulations which explicitly include energy-dependent transport of
relativistic electrons, as described in the ...companion paper by Jones,
Tregillis, & Ryu. Analyzing them in light of the complex source dynamics and
energetic particle distributions described in that paper, we find that the
standard model for radiative aging in radio galaxies does not always adequately
reflect the detailed source structure.
We report on an effort to study the connections between dynamics in simulated
radio galaxy plasma flows and the properties of nonthermal electron populations
carried in those flows. To do this we ...have introduced a new numerical scheme
for electron transport that allows a much more detailed look at this problem
than has been possible before. Especially when the dynamics is fully three
dimensional the flows are generally chaotic in the cocoon, and the jet itself
can flail about violently. The bending jet can pinch itself off and redirect
itself to enhance its penetration of the ambient medium. These behaviors often
eliminate the presence of a strong jet termination shock, which is assumed
present in all modern cartoon models of the RG phenomenon. Instead a much more
complex ``shock web'' forms near the end of the jet that leads to a far less
predictable pattern of particle acceleration. Similarly, the magnetic fields in
these flows are highly filamented, as well as spatially and temporally
intermittent. This leads to a very localized and complex pattern of synchrotron
aging for relativistic electron populations, which makes it difficult to use
properties of the electron spectrum to infer the local rate of aging.
New Astron.Rev. 46 (2002) 381-385 We have developed an economical, effective numerical scheme for cosmic-ray
transport suitable for treatment of electrons up to a few hundreds of GeV in
...multidimensional simulations of radio galaxies. The method follows the electron
population in sufficient detail to allow computation of synthetic radio and
X-ray observations of the simulated sources, including spectral properties (see
the companion paper by Tregillis et al. 1999). The cosmic-ray particle
simulations can follow the effects of shock acceleration, second-order Fermi
acceleration as well as radiative and adiabatic energy losses. We have applied
this scheme to 2-D and 3-D MHD simulations of jet-driven flows and have begun
to explore links between dynamics and the properties of high energy electron
populations in radio lobes. The key initial discovery is the great importance
to the high energy particle population of the very unsteady and inhomogeneous
flows, especially near the end of the jet. Because of this, in particular, our
simulations show that a large fraction of the particle population flowing from
the jet into the cocoon never passes through strong shocks. The shock strengths
encountered are not simply predicted by 1-D models, and are quite varied.
Consequently, the emergent electron spectra are highly heterogeneous. Rates of
synchrotron aging in "hot-spots" seem similarly to be very uneven, enhancing
complexity in the spectral properties of electrons as they emerge into the
lobes and making more difficult the task of comparing dynamical and radiative
ages.
New Astron.Rev. 46 (2002) 387-391 We have applied an effective numerical scheme for cosmic-ray transport to 3D
MHD simulations of jet flow in radio galaxies (see the companion paper by Jones
et al. ...1999). The marriage of relativistic particle and 3D magnetic field
information allows us to construct a rich set of ``synthetic observations'' of
our simulated objects. The information is sufficient to calculate the ``true''
synchrotron emissivity at a given frequency using explicit information about
the relativistic electrons. This enables us to produce synchrotron
surface-brightness maps, including polarization. Inverse-Compton X-ray
surface-brightness maps may also be produced. First results intended to explore
the connection between jet dynamics and electron transport in radio lobes are
discussed. We infer lobe magnetic field values by comparison of synthetically
observed X-ray and synchrotron fluxes, and find these ``inverse-Compton''
fields to be quite consistent with the actual RMS field averaged over the lobe.
The simplest minimum energy calculation from the synthetic observations also
seems to agree with the actual simulated source properties.
We present an extensive synthetic observational analysis of numerically- simulated radio galaxies designed to explore the effectiveness of conventional observational analyses at recovering physical ...source properties. These are the first numerical simulations with sufficient physical detail to allow such a study. The present paper focuses on extraction of magnetic field properties from nonthermal intensity information. Synchrotron and inverse-Compton intensities provided meaningful information about distributions and strengths of magnetic fields, although considerable care was called for. Correlations between radio and X-ray surface brightness correctly revealed useful dynamical relationships between particles and fields. Magnetic field strength estimates derived from the ratio of X-ray to radio intensity were mostly within about a factor of two of the RMS field strength along a given line of sight. When emissions along a given line of sight were dominated by regions close to the minimum energy/equipartition condition, the field strengths derived from the standard power-law-spectrum minimum energy calculation were also reasonably close to actual field strengths, except when spectral aging was evident. Otherwise, biases in the minimum- energy magnetic field estimation mirrored actual differences from equipartition. The ratio of the inverse-Compton magnetic field to the minimum-energy magnetic field provided a rough measure of the actual total energy in particles and fields in most instances, within an order of magnitude. This may provide a practical limit to the accuracy with which one may be able to establish the internal energy density or pressure of optically thin synchrotron sources.
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