34 research outputs found
Ariel - Volume 8 Number 4
Executive Editor
James W. Lockard Jr.
Issues Editor
Neeraj K. Kanwal
Business Manager
Neeraj K. Kanwal
University News
Martin Trichtinger
World News
Doug Hiller
Opinions
Elizabeth A. McGuire
Features
Patrick P. Sokas
Sports Desk
Shahab S. Minassian
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Edward H. Jasper
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Brenda Peterson
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Robert D. Lehman, Jr.
Graphics
Christine M. Kuhnl
AGN-Induced Cavities in NGC 1399 and NGC 4649
ABSTRACT We present an analysis of archival Chandra and VLA observations of the E0 galaxy NGC 1399 and the E2 galaxy NGC 4649 in which we investigate cavities in the surrounding X-ray emitting medium caused by the central AGN. We calculate the jet power required for the AGN to evacuate these cavities and find values of ∼ 8 × 10 41 erg s −1 and ∼ 14 × 10 41 erg s −1 for the lobes of NGC 1399 and ∼ 7 × 10 41 erg s −1 and ∼ 6 × 10 41 erg s −1 for those of NGC 4649. We also calculate the k/f values for each cavity, where k is the ratio of the total particle energy to that of electrons radiating in the range of 10 MHz to 10 GHz, and f is the volume filling factor of the plasma in the cavity. We find that the values of k/f for the lobes of NGC 1399 are ∼ 93 and ∼ 190, and those of the lobes of NGC 4649 are ∼ 15000 and ∼ 12000. We conclude that the assumed spectrum describes the electron distribution in the lobes of NGC 1399 reasonably well, and that there are few entrained particles. For NGC 4649, either there are many entrained particles or the model spectrum does not accurately describe the population of electrons
AGN-Induced Cavities in NGC 1399 and NGC 4649
We present an analysis of archival Chandra and VLA observations of the E0
galaxy NGC 1399 and the E2 galaxy NGC 4649 in which we investigate cavities in
the surrounding X-ray emitting medium caused by the central AGN. We calculate
the jet power required for the AGN to evacuate these cavities and find values
of ~8x10^{41} erg/s and ~14x10^{41} erg/s for the lobes of NGC 1399 and
~7x10^{41} erg/s and ~6x10^{41} erg/s for those of NGC 4649. We also calculate
the k/f values for each cavity, where k is the ratio of the total particle
energy to that of electrons radiating in the range of 10 MHz to 10 GHz, and f
is the volume filling factor of the plasma in the cavity. We find that the
values of k/f for the lobes of NGC 1399 are ~93 and ~190, and those of the
lobes of NGC 4649 are ~15000 and ~12000. We conclude that the assumed spectrum
describes the electron distribution in the lobes of NGC 1399 reasonably well,
and that there are few entrained particles. For NGC 4649, either there are many
entrained particles or the model spectrum does not accurately describe the
population of electrons.Comment: 8 pages, 2 figures, accepted for publication in MNRA
The radio properties of a complete, X-ray selected sample of nearby, massive elliptical galaxies
We investigate the radio properties of a complete sample of nearby, massive,
X-ray bright elliptical and S0 galaxies. Our sample contains 18 galaxies with
ROSAT All-Sky Survey X-ray fluxes Fx_(0.1-2.4 keV) > 3 x 10^(-12) erg/s/cm^2,
within a distance of 100 Mpc. For these galaxies, we have complete (18/18) VLA
radio and Chandra X-ray coverage. Nuclear radio emission is detected from 17/18
of the galaxies. Ten of the galaxies exhibit extended radio emission; of these
ten, all but one also exhibit clear evidence of interaction of the radio source
with the surrounding, X-ray emitting gas. Among the seven galaxies with
unresolved radio sources, one has clear, and one has small, cavity-like
features in the Chandra X-ray images; a third has a disturbed X-ray morphology.
Using a radio luminosity limit equivalent to L_(1.4 Ghz) > 10^(23) W/Hz to
calculate the radio-loud fraction, we find that this misses the majority of the
radio detected galaxies in the sample. We determine integrated radio-to-X-ray
flux ratios for the galaxies, GRx, which are shown to span a large range
(factor of 100). We calculate the mass-weighted cooling times within 1 kpc, and
find hints for an anticorrelation with the radio luminosity. We also calculate
limits on k/f, where k is the ratio of the total particle energy to that of
relativistic electrons radiating in the range 10 MHz-10 GHz and f is the volume
filling factor of the plasma in the cavity. The k/f distribution is also broad,
reflecting previous results for larger galaxy clusters. Lowering the X-ray flux
limit, at the expense of less complete VLA and Chandra coverage, increases the
size of our sample to 42 galaxies. Nuclear radio activity is detected in at
least 34/42 of this extended sample.Comment: Accepted for publication in MNRAS, 19 pages, 11 Figures and 7 Table
Recommended from our members
AGN-Induced Cavities in NGC 1399 And NGC 4649
We present an analysis of archival Chandra and VLA observations of the E0 galaxy NGC1399 and the E2 galaxy NGC4649 in which we investigate cavities in the surrounding X-ray emitting medium caused by the central AGN. We calculate the jet power required for the AGN to evacuate these cavities and find values of {approx} 8x10{sup 41} erg s-1 and {approx} 14x10{sup 41} erg s{sup -1} for the lobes of NGC1399 and {approx} 7x10{sup 41} erg s{sup -1} and {approx} 6x1041 erg s{sup -1} for those of NGC4649. We also calculate the k/f values for each cavity, where k is the ratio of the total particle energy to that of electrons radiating in the range of 10 MHz to 10 GHz, and f is the volume filling factor of the plasma in the cavity. We find that the values of k/f for the lobes of NGC1399 are {approx} 93 and {approx} 190, and those of the lobes of NGC4649 are {approx} 15000 and {approx} 12000. We conclude that the assumed spectrum describes the electron distribution in the lobes of NGC1399 reasonably well, and that there are few entrained particles. For NGC4649, either there are many entrained particles or the model spectrum does not accurately describe the population of electrons
Constraints on turbulent pressure in the X-ray halos of giant elliptical galaxies from resonant scattering
The dense cores of X-ray emitting gaseous halos of large elliptical galaxies
with temperatures below about 0.8 keV show two prominent Fe XVII emission
features, which provide a sensitive diagnostic tool to measure the effects of
resonant scattering. We present here high-resolution spectra of five bright
nearby elliptical galaxies, obtained with the Reflection Grating Spectrometers
(RGS) on the XMM-Newton satellite. The spectra for the cores of four of the
galaxies show the Fe XVII line at 15.01 Angstrom being suppressed by resonant
scattering. The data for NGC 4636 in particular allow the effects of resonant
scattering to be studied in detail and to prove that the 15.01 Angstrom line is
suppressed only in the dense core and not in the surrounding regions. Using
deprojected density and temperature profiles for this galaxy obtained with the
Chandra satellite, we model the radial intensity profiles of the strongest
resonance lines, accounting for the effects of resonant scattering, for
different values of the characteristic turbulent velocity. Comparing the model
to the data, we find that the isotropic turbulent velocities on spatial scales
smaller than about 1 kpc are less than 100 km/s and the turbulent pressure
support in the galaxy core is smaller than 5% of the thermal pressure at the
90% confidence level, and less than 20% at 95% confidence. Neglecting the
effects of resonant scattering in spectral fitting of the inner 2 kpc core of
NGC 4636 will lead to underestimates of the chemical abundances of Fe and O by
~10-20%.Comment: Accepted for publication in MNRAS, in v2 typo in eq. 6, 7, 8
correcte
Reconciling stellar dynamical and hydrostatic X-ray mass measurements of an elliptical galaxy with gas rotation, turbulence and magnetic fields
Recent hydrostatic X-ray studies of the hot interstellar medium (ISM) in
early-type galaxies underestimate the gravitating mass as compared to stellar
dynamics, implying modest, but significant deviations from exact hydrostatic
equilibrium. We present a method for combining X-ray measurements and stellar
dynamical constraints in the context of Bayesian statistics that allows the
radial distribution of the implied nonthermal pressure or bulk motions in the
hot ISM to be constrained. We demonstrate the accuracy of the method with
hydrodynamical simulations tailored to produce a realistic galaxy model.
Applying the method to the nearby elliptical galaxy NGC4649, we find a
significant but subdominant nonthermal pressure fraction (0.27+/-0.06) in the
central (<5 kpc) part of the galaxy, similar to the level of deviations from
hydrostatic equilibrium expected in galaxy clusters. Plausible sources of
systematic error, if important, may reduce this fraction. This would imply >360
km/s random turbulence or a magnetic field B=(39+/-6)(n_e/0.1
cm^{-3})^{0.59+/-0.09} muG, whereas gas rotation alone is unlikely to explain
the detailed nonthermal profile. Future observations with Astro-H will allow
turbulence or gas rotation at this level to be detected.Comment: 14 pages, 8 figures, 1 table. Accepted by Monthly Notices of the
Royal Astronomical Society. Minor changes to match accepted versio