365 research outputs found
Dissecting the spiral galaxy M83: mid-infrared emission and comparison with other tracers of star formation
We present a detailed mid-infrared study of the nearby, face-on spiral galaxy
M83 based on ISOCAM data. M83 is a unique case study, since a wide variety of
MIR broad-band filters as well as spectra, covering the wavelength range of 4
to 18\mu m, were observed and are presented here. Emission maxima trace the
nuclear and bulge area, star-formation regions at the end of the bar, as well
as the inner spiral arms. The fainter outer spiral arms and interarm regions
are also evident in the MIR map. Spectral imaging of the central 3'x3' (4 kpc x
4 kpc) field allows us to investigate five regions of different environments.
The various MIR components (very small grains, polycyclic aromatic hydrocarbon
(PAH) molecules, ionic lines) are analyzed for different regions throughout the
galaxy. In the total 4\mu m to 18\mu m wavelength range, the PAHs dominate the
luminosity, contributing between 60% in the nuclear and bulge regions and 90%
in the less active, interarm regions. Throughout the galaxy, the underlying
continuum emission from the small grains is always a smaller contribution in
the total MIR wavelength regime, peaking in the nuclear and bulge components.
The implications of using broad-band filters only to characterize the
mid-infrared emission of galaxies, a commonly used ISOCAM observation mode, are
discussed. We present the first quantitative analysis of new H-alpha and 6cm
VLA+Effelsberg radio continuum maps of M83. The distribution of the MIR
emission is compared with that of the CO, HI, R band, H-alpha and 6cm radio. A
striking correlation is found between the intensities in the two mid-infrared
filter bands and the 6cm radio continuum. To explain the tight
mid-infrared-radio correlation we propose the anchoring of magnetic field lines
in the photoionized shells of gas clouds.Comment: 22 pages, 15 figures. Accepted for publication in A&
Chandra Observations of the Disruption of the Cool Core in Abell 133
We present the analysis of a Chandra observation of the galaxy cluster Abell
133, which has a cooling flow core, a central radio source, and a diffuse,
filamentary radio source which has been classified as a radio relic.
The X-ray image shows that the core has a complex structure. The most
prominent feature is a "tongue" of emission which extends from the central cD
galaxy to the northwest and partly overlaps the radio relic. One possibility is
that this tongue is produced by Kelvin-Helmholtz (KH) instabilities through the
interaction between the cold gas around the cD galaxy and hot intracluster
medium. We estimate the critical velocity and time scale for the KH instability
to be effective for the cold core around the cD galaxy. We find that the KH
instability can disrupt the cold core if the relative velocity is >~400 km
s^-1. We compare the results with those of clusters in which sharp, undisrupted
cold fronts have been observed; in these clusters, the low temperature gas in
their central regions has a more regular distribution. In contrast to Abell
133, these cluster cores have longer timescales for the disruption of the core
by the KH instability when they are normalized to the timescale of the cD
galaxy motion. Thus, the other cores are less vulnerable to KH instability.
Another possible origin of the tongue is that it is gas which has been uplifted
by a buoyant bubble of nonthermal plasma that we identify with the observed
radio relic. From the position of the bubble and the radio estimate of the age
of the relic source, we estimate avelocity of ~700 km s^-1 for the bubble. The
structure of the bubble and this velocity are consistent with numerical models
for such buoyant bubbles. (abridged)Comment: 38 pages, 15 figures, accepted for publication in Ap
The dust-scattering X-ray rings of the anomalous X-ray pulsar 1E 1547.0-5408
On 2009 January 22 numerous strong bursts were detected from the anomalous
X-ray pulsar 1E 1547.0-5408. Swift/XRT and XMM-Newton/EPIC observations carried
out in the following two weeks led to the discovery of three X-ray rings
centered on this source. The ring radii increased with time following the
expansion law expected for a short impulse of X-rays scattered by three dust
clouds. Assuming different models for the dust composition and grain size
distribution, we fit the intensity decay of each ring as a function of time at
different energies, obtaining tight constrains on the distance of the X-ray
source. Although the distance strongly depends on the adopted dust model, we
find that some models are incompatible with our X-ray data, restricting to 4-8
kpc the range of possible distances for 1E 1547.0-5408. The best-fitting dust
model provides a source distance of 3.91 +/- 0.07 kpc, which is compatible with
the proposed association with the supernova remnant G 327.24-0.13, and implies
distances of 2.2 kpc, 2.6 kpc and 3.4 kpc for the dust clouds, in good
agreement with the dust distribution inferred by CO line observations towards
1E 1547.0-5408. However, dust distances in agreement with CO data are also
obtained for a set of similarly well-fitting models that imply a source
distance of about 5 kpc. A distance of about 4-5 kpc is also favored by the
fact that these dust models are already known to provide good fits to the
dust-scattering halos of bright X-ray binaries.Comment: Accepted for publication in The Astrophysical Journal; 10 pages in
emulate-apj style, 3 tables, 5 color figures. Note: abstract truncated; full
abstract in the pape
One step multiderivative methods for first order ordinary differential equations
A family of one-step multiderivative methods based on Padé approximants to the exponential function is developed.
The methods are extrapolated and analysed for use in PECE mode.
Error constants and stability intervals are calculated and the combinations compared with well known linear multi-step combinations and combinations using high accuracy Newton-Cotes quadrature formulas as correctors.
w926020
A Chandra Observation of Abell 13: Investigating the Origin of the Radio Relic
We present results from the Chandra X-ray observation of Abell 13, a galaxy
cluster that contains an unusual noncentral radio source, also known as a radio
relic. This is the first pointed X-ray observation of Abell 13, providing a
more sensitive study of the properties of the X-ray gas. The X-ray emission
from Abell 13 is extended to the northwest of the X-ray peak and shows
substructure indicative of a recent merger event. The cluster X-ray emission is
centered on the bright galaxy H of Slee et al. 2001. We find no evidence for a
cooling flow in the cluster. A knot of excess X-ray emission is coincident with
the other bright elliptical galaxy F. This knot of emission has properties
similar to the enhanced emission associated with the large galaxies in the Coma
cluster.
With these Chandra data we are able to compare the properties of the hot
X-ray gas with those of the radio relic from VLA data, to study the interaction
of the X-ray gas with the radio emitting electrons. Our results suggest that
the radio relic is associated with cooler gas in the cluster. We suggest two
explanations for the coincidence of the cooler gas and radio source. First, the
gas may have been uplifted by the radio relic from the cluster core.
Alternatively, the relic and cool gas may have been displaced from the central
galaxy during the cluster merger event.Comment: 11 pages, 9 figures, Accepted for Publication in the Astrophysical
Journal, higher-resolution figures can be found at
http://www.astro.virginia.edu/~amj3r/Abell13
Multi-frequency study of a new Fe-rich supernova remnant in the Large Magellanic Cloud, MCSNR J0508-6902
We present a detailed radio, X-ray and optical study of a newly discovered
Large Magellanic Cloud (LMC) supernova remnant (SNR) which we denote MCSNR
J0508-6902. Observations from the Australian Telescope Compact Array (ATCA) and
the X-ray observatory are complemented by deep H
images and Anglo Australian Telescope AAOmega spectroscopic data to study the
SNR shell and its shock-ionisation. Archival data at other wavelengths are also
examined. The remnant follows a filled-in shell type morphology in the
radio-continuum and has a size of 74 pc 57 pc at the LMC
distance. The X-ray emission exhibits a faint soft shell morphology with
Fe-rich gas in its interior indicative of a Type Ia origin. The remnant
appears to be mostly dissipated at higher radio-continuum frequencies leaving
only the south-eastern limb fully detectable while in the optical it is the
western side of the SNR shell that is clearly detected. The best-fit
temperature to the shell X-ray emission ( keV) is
consistent with other large LMC SNRs. We determined an O/Fe ratio of and
an Fe mass of 0.5-1.8 in the interior of the remnant, both of which
are consistent with the Type Ia scenario. We find an equipartition magnetic
field for the remnant of 28 G, a value typical of older SNRs and
consistent with other analyses which also infer an older remnant
XMM-Newton Observations of A133: A Weak Shock Passing through the Cool Core
We use XMM-Newton observations of the cluster of galaxies A133 to study the
X-ray spectrum of the intracluster medium (ICM). We find a cold front to the
southeast of the cluster core. From the pressure profile near the cold front,
we derive an upper limit to the velocity of the core relative to the rest of
the cluster of <230 km s^-1. Our previous Chandra image of A133 showed a
complex, bird-like morphology in the cluster core. Based on the XMM-Newton
spectra and hardness ratio maps, we argue that the wings of this structure are
a weak shock front. The shock was probably formed outside the core of the
cluster, and may be heating the cluster core. Our Chandra image also showed a
``tongue'' of relatively cool gas extending from the center of the cD to the
center of the radio relic. The XMM-Newton results are consistent with the idea
that the tongue is the gas which has been uplifted by a buoyant radio bubble
including the radio relic to the northwest of the core. Alternatively, the
tongue might result from a cluster merger. The small velocity of the core
suggests that the bubble including the relic has moved by buoyancy, rather than
by motions of the core or the ICM. We do not find clear evidence for nonthermal
X-ray emission from the radio relic. Based on the upper limit on the inverse
Compton emission, we derive a lower limit on the magnetic field in the relic of
B>~1.5\mu G.Comment: 29 pages, ApJ in pres
The XMM-Newton survey of the Small Magellanic Cloud: XMMUJ005011.2-730026 = SXP214, a Be/X-ray binary pulsar
In the course of the XMM-Newton survey of the Small Magellanic Cloud (SMC), a
region to the east of the emission nebula N19 was observed in November 2009. To
search for new candidates for high mass X-ray binaries the EPIC PN and MOS data
of the detected point sources were investigated and their spectral and temporal
characteristics identified. A new transient (XMMUJ005011.2-730026= SXP214) with
a pulse period of 214.05 s was discovered; the source had a hard X-ray spectrum
with power-law index of ~0.65. The accurate X-ray source location permits the
identification of the X-ray source with a ~15th magnitude Be star, thereby
confirming this system as a new Be/X-ray binary.Comment: 8 pages 11 figures. Accepted for publication in MNRA
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