5,739 research outputs found
The Radio Emission from the Ultra-Luminous Far-Infrared Galaxy NGC 6240
We present new radio observations of the ``prototypical'' ultra-luminous far-
infrared galaxy NGC~6240, obtained using the VLA at 20~cm in `B' configuration
and at 3.6~cm in `A' configuration. These data, along with those from four
previous VLA observations, are used to perform a comprehensive study of the
radio emission from NGC~6240. Approximately 70\% (~3 x 10 W~Hz)
of the total radio power at 20 cm originates from the nuclear region ( <~ 1.5
kpc), of which half is emitted by two unresolved (\alphaS_{\nu} \propto \nu^{-\alpha}). The
supernova rate required to power the diffuse component is consistent with that
predicted by the stellar evolution models of Rieke \etal (1985). If the radio
emission from the two compact cores is powered by supernova remnants, then
either the remnants overlap and form hot bubbles in the cores, or they are very
young ( <~ 100 yr). Nearly all of the other 30\% of the total radio power comes
from an ``arm-like'' region extending westward from the nuclear region. The
western arm emission has a steep spectrum (\alpha^{-14}$ erg/s/cm2 in the 2-10 keV band. No significant radio
emission is detected from or near the possible ultra-massive ``dark core''
hypothesized by Bland-Hawthorn, Wilson \& Tully (1991).Comment: 36 pages (text and tables) as an uuencoded compressed postscript file
(figures available upon request), accepted for the ApJ (20 Nov issue), STScI
preprint no. ?? -- May 199
Extended Gas in Seyfert Galaxies: Near-Infrared Observations of 15 Active Nuclei
Results from an analysis of low resolution (R~250) near-IR long-slit spectra
covering simultaneously the I, J, H, and K bands, for a sample of 15 Seyfert
galaxies and the N5253 starburst nucleus, are presented. The Seyfert galaxies
were selected as presenting `linear' or cone-like high excitation emission line
in the optical, most probably due to the collimation of the central source's
radiation by a dusty molecular torus. Our goal was to look for signatures of
this torus, and to investigate the gaseous distribution, excitation and
reddening. The IR emission lines are spatially extended in most cases, and we
have used the [FeII]/Pa(beta) ratio as a measure of the gaseous excitation in
Mrk573, N1386, and N7582. Values for this ratio between 1.5 and 6 are found,
suggesting excitation of [FeII] by X-rays or shock waves in some regions.
Nuclear Pa(beta) in N1365, and possibly nuclear Br(gama) in Mrk573, are broad.
From analysis of the spatial distribution of the continuum (J-H) and (H-K)
colours derived from our spectra, we find redder colours for the nucleus than
the nearby bulge in most of the Seyfert 2s observed. Comparison with models
including emission from dust and stars shows that hot (T~1000 K) dust emission
dominates the nuclear continuum in N1365, N2110, N3281, N7582, and ESO362-G18.
In N1386, N5643, and N5728 the main contributor is the underlying stellar
population, combined with some foreground reddening and/or cool dust emission.
In a few cases, the (J-H) colours on opposite sides of the nucleus differ by
0.3-0.8 mag, an effect that we interpret as partly due to differences in the
local stellar population, and possibly extinction gradients.Comment: 19 pages (LaTeX, mn.sty), 27 Postscript figures embedded. Accepted
for publication in the Monthly Notices of the R.A.
Accretion onto the Supermassive Black Hole in M87
Chandra X-ray observations of the giant elliptical galaxy M87 resolve the
thermal state of the hot interstellar medium into the accretion (Bondi) radius
of its central 3 10^9 Msun black hole. We measure the X-ray gas temperature and
density profiles and calculate the Bondi accretion rate, Mdot_Bondi \sim 0.1
Msun/yr. The X-ray luminosity of the active nucleus of M87 observed with
Chandra is L_{x, 0.5-7 \keV} \sim 7 \times 10^{40}erg/s. This value is much
less than the predicted nuclear luminosity, L_{Bondi} \sim 5 \times 10^{44}
erg/s, for accretion at the Bondi rate with a canonical accretion radiative
efficiency of 10%. If the black hole in M87 accretes at this rate it must do so
at a much lower radiative efficiency than the canonical value. The
multiwavelength spectrum of the nucleus is consistent with that predicted by an
advection-dominated flow. However, as is likely, the X-ray nucleus is dominated
by jet emission then the properties of flow must be modified, possibly by
outflows. We show that the overall energetics of the system are just consistent
with the predicted Bondi nuclear power. This suggests that either most of the
accretion energy is released in the relativistic jet or that the central engine
of M87 undergoes on-off activity cycles. We show that, at present, the energy
dumped into the ISM by the jet may reduce the accretion rate onto the black
hole by a factor \propto (v_j/c_s)^{-2}, where v_j is the jet velocity and c_s
the ISM sound speed, and that this is sufficient to account for the low nuclear
luminosity.Comment: emulateapj.sty, revised version, accepted by Ap
The Narrow-Line Region in the Seyfert 2 Galaxy NGC 3393
The narrow-line region (NLR) of the Seyfert 2 galaxy NGC 3393 is dominated by a symmetric structure which appears as S-shaped arms in Hubble Space Telescope (HST) images. These arms, which occupy the central few arcseconds of the nucleus, border a linear, triple-lobed radio source. We use HST imaging and spectra, ground-based optical images, long-slit spectra, Fabry-Perot imaging spectroscopy, and VLA radio data to perform a detailed investigation of the kinematics and ionization of the line-emitting gas in NGC 3393 and of its relationship with the relativistic gas responsible for the radio emission. The excitation map [O III] λ5007/(Hα + [N II] λλ6548, 6584) shows a biconical structure, consistent with the anisotropic nuclear ionizing radiation expected in the unified scheme. Extrapolation to ionizing frequencies of our upper limit to the 2100 Å flux of the nuclear source provides a factor ≥3 × 104 too few ionizing photons to account for the recombination line emission, which also suggests that the nuclear ionizing source radiates anisotropically. However, the kinetic energy of the outflow is sufficient to power the line emission via photoionizing shocks, and a tentative detection of extended UV emission is consistent with this model. Furthermore, the broad component of the emission lines has a similar orientation and spatial extent as the triple radio source. Nevertheless, other tests are inconsistent with the photoionizing shock model—there is no correlation between local velocity dispersion, surface brightness, and excitation, and the gaseous abundances of [Ca II], Al II], and Mg II are much lower than expected if these species have been liberated into the gas phase through grain destruction by shocks. We conclude that the radio lobes appear to have created denser regions of gas on their leading edges, thus forming the S-shaped arms, but that the ionization is most likely due to photoionization by an obscured central source
Dynamical instabilities of Bose-Einstein condensates at the band-edge in one-dimensional optical lattices
We report on experiments that demonstrate dynamical instability in a
Bose-Einstein condensate at the band-edge of a one-dimensional optical lattice.
The instability manifests as rapid depletion of the condensate and conversion
to a thermal cloud. We consider the collisional processes that can occur in
such a system, and perform numerical modeling of the experiments using both a
mean-field and beyond mean-field approach. We compare our numerical results to
the experimental data, and find that the Gross-Pitaevskii equation is not able
to describe this experiment. Our beyond mean-field approach, known as the
truncated Wigner method, allows us to make quantitative predictions for the
processes of parametric growth and thermalization that are observed in the
laboratory, and we find good agreement with the experimental results.Comment: v2: Added several reference
The X-ray Emissions from the M87 Jet: Diagnostics and Physical Interpretation
We reanalyze the deep Chandra observations of the M87 jet, first examined by
Wilson & Yang (2002). By employing an analysis chain that includes image
deconvolution, knots HST-1 and I are fully separated from adjacent emission. We
find slight but significant variations in the spectral shape, with values of
ranging from . We use VLA radio observations, as well
as HST imaging and polarimetry data, to examine the jet's broad-band spectrum
and inquire as to the nature of particle acceleration in the jet. As shown in
previous papers, a simple continuous injection model for synchrotron-emitting
knots, in which both the filling factor, , of regions within which
particles are accelerated and the energy spectrum of the injected particles are
constant, cannot account for the X-ray flux or spectrum. Instead, we propose
that is a function of position and energy and find that in the inner
jet, , and
in knots A and B, , where is the emitted photon energy and and is the
emitting electron energy. In this model, the index of the injected electron
energy spectrum () is at all locations in
the jet, as predicted by models of cosmic ray acceleration by ultrarelativistic
shocks. There is a strong correlation between the peaks of X-ray emission and
minima of optical percentage polarization, i.e., regions where the jet magnetic
field is not ordered. We suggest that the X-ray peaks coincide with shock waves
which accelerate the X-ray emitting electrons and cause changes in the
direction of the magnetic field; the polarization is thus small because of beam
averaging.Comment: Accepted for publication in ApJ; 21 pages, 9 figures, 2 tables;
abstract shortened for astro-ph; Figures 1, 7 and 8 at reduced resolutio
Advantages and Disadvantages of Health Care Accreditation Models
Background: This systematic review seeks to define the general advantages and disadvantagesof accreditation programs to assist in choosing the most appropriate approach.Method: Systematic search of SID, Ovid Medline & PubMed databases was conducted by thekeywords of accreditation, hospital, medical practice, clinic, accreditation models, health careand Persian meanings. From 2379 initial articles, 83 articles met the full inclusion criteria.From initial analysis, 23 attributes were identified which appeared to define advantages anddisadvantages of different accreditation approaches and the available systems were comparedon these.Results: Six systems were identified in the international literature including the JCAHO fromUSA, the Canadian program of CCHSA, and the accreditation programs of UK, Australia,New Zealand and France. The main distinguishing attributes among them were: qualityimprovement, patient and staff safety, improving health services integration, public’s confidence,effectiveness and efficiency of health services, innovation, influence global standards,information management, breadth of activity, history, effective relationship with stakeholders,agreement with AGIL attributes and independence from government.Conclusion: Based on 23 attributes of comprehensive accreditation systems we have definedfrom a systematic review, the JCAHO accreditation program of USA and then CCHSA ofCanada offered the most comprehensive systems with the least disadvantages. Other programssuch as the ACHS of Australia, ANAES of France, QHNZ of New Zealand and UK accreditationprograms were fairly comparable according to these criteria. However the decision forany country or health system should be based on an assessment weighing up their specificobjectives and needs
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