242 research outputs found
Very Extended X-ray and H-alpha Emission in M82: Implications for the Superwind Phenomenon
We discuss the properties and implications of a 3.7x0.9 kpc region of
spatially-coincident X-ray and H-alpha emission about 11.6 kpc to the north of
the galaxy M82 previously discussed by Devine and Bally (1999). The PSPC X-ray
spectrum is fit by thermal plasma (kT=0.80+-0.17 keV) absorbed by only the
Galactic foreground column density. We evaluate the relationship of the
X-ray/H-alpha ridge to the M82 superwind. The main properties of the X-ray
emission can all be explained as being due to shock-heating driven as the
superwind encounters a massive ionized cloud in the halo of M82. This encounter
drives a slow shock into the cloud, which contributes to the excitation of the
observed H-alpha emission. At the same time, a fast bow-shock develops in the
superwind just upstream of the cloud, and this produces the observed X-ray
emission. This interpretation would imply that the superwind has an outflow
speed of roughly 800 km/s, consistent with indirect estimates based on its
general X-ray properties and the kinematics of the inner kpc-scale region of
H-alpha filaments. The gas in the M82 ridge is roughly two orders-of-magnitude
hotter than the minimum "escape temperature" at this radius, so this gas will
not be retained by M82.
(abridged)Comment: 24 pages (latex), 3 figures (2 gif files and one postscript),
accepted for publication in Part 1 of The Astrophysical Journa
The Twin-Jet of NGC1052 at Radio, Optical, and X-ray Frequencies
We present results from a combined radio, optical, and X-ray study of the
jet-associated emission features in NGC1052. We analyse the radio-optical
morphology and find a good positional correlation between the radio jet and the
optical emission cone. Two optical emission knots are directly associated with
radio counterparts exhibiting a radio to X-ray broadband spectrum not
compatible with synchrotron emission. We discuss the possibility that the
thermal soft spectrum of the extended X-ray emission originates from jet driven
shocks produced in the interaction between the jet-plasma and its surrounding
medium.Comment: 4 pages, 1 figure, needs elsart.cls, to be published in ''The Physics
of Relativistic Jets in the CHANDRA and XMM Era'', G. Brunetti, D.E. Harris,
R.M. Sambruna, G. Setti (eds.
Simulations of Supernova Remnants in Diffuse Media III. The Population of Buoyant Remnants Above the Milky Way's Disk
We model SNRs at a variety of heights above the disk. Our detailed numerical
simulations include non-equilibrium ionization and recombination and follow the
remnants' evolution until their hot bubbles have cooled. We analytically
calculate the bubbles' buoyant acceleration. From the results, we estimate the
time and space average O VI, N V, and C IV column densities and emission
intensities, 1/4 keV soft X-ray surface brightness, area coverage, and volume
occupation of the population of isolated SNRs above the Galaxy's HI layer.
Irrespective of assumed supernova explosion energy, ambient nonthermal
pressure, or frictional drag coefficient, the predicted O VI column density
matches the observed distribution between 130 pc and 2000 pc. The SNRs' O VI
intensity is a significant fraction of the average observed intensity. Within
the range of uncertainty in the SN rate, such SNRs can explain all of the
observed 1/4 keV surface brightness attributed to the extraplanar gas beyond
the H I layer in the southern hemisphere (~400 x 10^-6 counts/s/arcmin^2).
Thus, extraplanar SNRs could be the most important source of hot gas between
the Local Bubble and z ~ 2000 pc in the relatively quiescent southern
hemisphere. These results stand whether the remnants are assumed to be buoyant
or not. The population of old extraplanar SNRs should cover most of the high
latitude sky, but bright young extraplanar SNRs should cover less than 1% of
the sky. Perhaps the l=247, b=-64 crescent in the 1/4 keV X-ray maps could be a
young remnant.Comment: Accepted by ApJ for publication on February 10, 2006 (Volume 638). 44
pages, including 6 figures, 10 tables (and 1 blank page
Jet emission in NGC1052 at radio, optical, and X-ray frequencies
We present a combined radio, optical, and X-ray study of the nearby LINER
galaxy NGC 1052. Data from a short (2.3 ksec) {\it CHANDRA} observation of NGC
1052 reveal the presence of various jet-related X-ray emitting regions, a
bright compact core and unresolved knots in the jet structure as well as an
extended emitting region inside the galaxy well aligned with the radio
synchrotron jet-emission. The spectrum of the extended X-ray emission can best
be fitted with a thermal model with keV, while the compact
core exhibits a very flat spectrum, best approximated by an absorbed power-law
with . We compare the radio
structure to an optical ``structure map'' from a {\it Hubble Space Telescope}
({\it HST}) observation and find a good positional correlation between the
radio jet and the optical emission cone. Bright, compact knots in the jet
structure are visible in all three frequency bands whose spectrum is
inconsistent with synchrotron emission.Comment: 8 pages, 5 figures (figure 2 in color), image resolution degraded wrt
journal version, needs aa.cls. Accepted for publication in A&
Magnetic Reconnection Triggered by the Parker Instability in the Galaxy: Two-Dimensional Numerical Magnetohydrodynamic Simulations and Application to the Origin of X-Ray Gas in the Galactic Halo
We propose the Galactic flare model for the origin of the X-ray gas in the
Galactic halo. For this purpose, we examine the magnetic reconnection triggered
by Parker instability (magnetic buoyancy instability), by performing the
two-dimensional resistive numerical magnetohydrodynamic simulations. As a
result of numerical simulations, the system evolves as following phases: Parker
instability occurs in the Galactic disk. In the nonlinear phase of Parker
instability, the magnetic loop inflates from the Galactic disk into the
Galactic halo, and collides with the anti-parallel magnetic field, so that the
current sheets are created in the Galactic halo. The tearing instability
occurs, and creates the plasmoids (magnetic islands). Just after the plasmoid
ejection, further current-sheet thinning occurs in the sheet, and the anomalous
resistivity sets in. Petschek reconnection starts, and heats the gas quickly in
the Galactic halo. It also creates the slow and fast shock regions in the
Galactic halo. The magnetic field (G), for example, can heat the
gas ( cm) to temperature of K via the
reconnection in the Galactic halo. The gas is accelerated to Alfv\'en velocity
( km s). Such high velocity jets are the evidence of the
Galactic flare model we present in this paper, if the Doppler shift of the
bipolar jet is detected in the Galactic halo. Full size figures are available
at http://www.kwasan.kyoto-u.ac.jp/~tanuma/study/ApJ2002/ApJ2002.htmlComment: 13 pages, 12 figures, uses emulateapj.sty, accepted by Ap
First Permian occurrence of the shark egg capsule morphotype Palaeoxyris Brongniart, 1828
© 2016, © by the Society of Vertebrate Paleontology.Citation for this article: Abu Hamad, A., J. Fischer, S. Voigt, H. Kerp, J. W. Schneider, and F. Scholze. 2016. First Permian occurrence of the shark egg capsule morphotype Palaeoxyris Brongniart, 1828. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1112290
Hard X-ray emission from a young massive star-forming cluster
We report the detection of hard X-ray emission (>2 keV) from a number of
point sources associated with the very young massive star-forming region IRAS
19410+2336. The X-ray emission is detected from several sources located around
the central and most deeply embedded mm continuum source, which remains
undetected in the X-ray regime. All X-ray sources have K-band counterparts, and
those likely belonging to the evolving massive cluster show near-infrared
colors in the 2MASS data indicative of pre-main-sequence stages. The X-ray
luminosities around 10^{31} erg/s are at the upper end of luminosities known
for low-mass pre-main-sequence sources, and mass estimates based on the
infrared data indicate that at least some of the X-ray detected sources are
intermediate-mass objects. Therefore, we conclude that the X-ray emission is
due to intermediate-mass pre-main-sequence Herbig Ae/Be stars or their
precursors. The emission process is possibly due to magnetic star-disk
interaction as proposed for their low-mass counterparts.Comment: 10 pages, 5 figures, A&A accepte
From the transantarctic basin to the ferrar large igneous province-new palynostratigraphic age constraints for triassic-jurassic sedimentation and magmatism in East Antarctica
We present new palynological data from the Transantarctic Mountains that clarify the timing of sedimentary and magmatic processes in the transition from continental deposition of the Beacon Supergroup to emplacement of the Ferrar Large Igneous Province. Samples were collected from twenty-three Triassic and Jurassic sections in the southern area of north Victoria Land (NVL), East Antarctica. Recovered palynomorph assemblages are correlated with the widely used, although informal palynostratigraphic framework established for eastern Australia by Price. The associated Late Triassic-earliest Jurassic zone, APT5, is modified here with a proposed new subdivision: Lower APT5 ("APT5L"; middle-late Norian), Middle APT5 ("APT5M"; Rhaetian), and Upper APT5 ("APT5U"; Hettangian-earliest Sinemurian). We further propose a modification unifying the relevant formal eastern Australian and New Zealand palynostratigraphic zones, with a new Polycingulatisporites crenulatus Association Zone (new zonal status) that includes the P. crenulatus Association Subzone (new subzone; equivalent to APT5L) and the following Foveosporites moretonensis Association Subzone (new subzonal status; equivalent to APT5M). Our palynostratigraphic dating of the NVL assemblages demonstrates that the onset of sedimentation was diachronous in this part of the Transantarctic Basin, ranging from at least the Rhaetian to, in places, early Sinemurian. By lack of evidence for rocks containing APT5U assemblages and by analogy with the few coeval sections in Australia, we infer that the Hettangian interval in NVL is probably consumed by unconformity. Deposition of ashes from distal silicic volcanism commenced in the early Sinemurian and reached a peak phase beginning in middle Pliensbachian (ca 187. Ma), coinciding with the first major magmatic interval of the silicic Chon Aike Province in Patagonia and West Antarctica. Two major episodes of phreatomagmatic activity, driven by shallow-level sill intrusion into sandstone aquifers, occurred during the middle Pliensbachian and during the late Pliensbachian-early Toarcian. The latter episode was closely followed by the first pillow extrusion and local lava effusion. Contrary to some previous studies, we further conclude that all available palynological evidence is compatible with a short-lived emplacement of the plateau-forming Kirkpatrick Basalt at around 180. Ma during the early Toarcian. © 2014 Elsevier B.V
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