2,399 research outputs found
Chandra Observations of ULIRGs: Extended Hot Gas Halos in Merging Galaxies
We study the properties of hot gaseous halos in 10 nearby ultraluminous IRAS
galaxies observed with the ACIS instrument on board Chandra. For all sample
galaxies, diffuse soft X-ray emissions are found within ~10 kpc of the central
region; their spectra are well fitted by a MEKAL model plus emission lines from
alpha-elements and other ions. The temperature of the hot gas is about 0.7 keV
and metallicity is about 1 solar. Outside the central region, extended hot
gaseous halos are found for nine out of the ten ULIRGs. Most spectra of these
extended halos can be fitted with a MEKAL model with a temperature of about 0.6
keV and a low metallicity (~ 0.1 solar). We discuss the implications of our
results on the origin of X-ray halos in elliptical galaxies and the feedback
processes associated with starbursts.Comment: 31 pages, 6 figuers, ApJ in press, accepted versio
The Exceptionally Soft X-ray Spectrum of the Low-mass Starburst Galaxy NGC 1705
NGC 1705 is one of the optically brightest and best studied dwarf galaxies.
It appears to be in the late stage of a major starburst and contains a young
super star cluster. Type II supernovae are therefore likely to have been a
major effect in the recent evolution of this galaxy and are likely to have
produced a superbubble whose affects on the low-density ambient interstellar
medium can be ideally studied. ROSAT PSPC observations of this galaxy reveal
two striking blobs of X-ray emission embedded in \Ha loops which can be
interpreted as both sides of the upper plumes of the same superbubble. These
sources are a surprise. They are much softer than those observed from other
starburst dwarf galaxies, and are so soft that they should have been blocked if
the observed Galactic HI column density were uniformly distributed across NGC
1705 or if the sources were embedded in the HI disk of NGC 1705. In addition,
the total X-ray luminosity in the ROSAT energy band of 1.2x10^{38} erg s^{-1}
is low in comparison to similar objects. We discuss possible models for the two
X-ray peaks in NGC 1705 and find that the sources most likely originate from
relatively cool gas of one single superbubble in NGC 1705. The implications of
the exceptional softness of these sources are addressed in terms of intrinsic
properties of NGC 1705 and the nature of the foreground Galactic absorption.Comment: 7 pages, 2 ps-figures, LATEX-file; accepted for publication in
ApJ.Letter
SWAS observations of comet 9P/Tempel 1 and Deep Impact
On 4 July 2005 at 1:52 UT the Deep Impact mission successfully completed its
goal to hit the nucleus of 9P/Tempel 1 with an impactor, forming a crater on
the nucleus and ejecting material into the coma of the comet. The 370 kg
impactor collided with the sunlit side of the nucleus with a relative velocity
of 10.2 km/s. NASA's Submillimeter Wave Astronomy Satellite (SWAS) observed the
1(10)-1(01) ortho-water ground-state rotational transition in comet 9P/Tempel 1
before, during, and after the impact. No excess emission from the impact was
detected by SWAS. However, the water production rate of the comet showed large
natural variations of more than a factor of three during the weeks before the
impact.Comment: to appear in the proceedings of the IAU Symposium No. 231:
"Astrochemistry - Recent Successes and Current Callenges". Typo corrected in
author affiliation lis
Spitzer spectral line mapping of supernova remnants: I. Basic data and principal component analysis
We report the results of spectroscopic mapping observations carried out
toward small (1 x 1 arcmin) regions within the supernova remnants W44, W28,
IC443, and 3C391 using the Infrared Spectrograph of the Spitzer Space
Telescope. These observations, covering the 5.2 - 37 micron spectral region,
have led to the detection of a total of 15 fine structure transitions of Ne+,
Ne++, Si+, P+, S, S++, Cl+, Fe+, and Fe++; the S(0) - S(7) pure rotational
lines of molecular hydrogen; and the R(3) and R(4) transitions of hydrogen
deuteride. In addition to these 25 spectral lines, the 6.2, 7.7, 8.6, 11.3 and
12.6 micron PAH emission bands were also observed. Most of the detected line
transitions have proven strong enough to map in several sources, providing a
comprehensive picture of the relative distribution of the various line
emissions observable in the Spitzer/IRS bandpass. A principal component
analysis of the spectral line maps reveals that the observed emission lines
fall into five distinct groups, each of which may exhibit a distinct spatial
distribution: (1) lines of S and H2 (J > 2); (2) the H2 S(0) line; (3) lines of
ions with appearance potentials less than 13.6 eV; (4) lines of ions with
appearance potentials greater than 13.6 eV, not including S++; (5) lines of
S++. Lines of group (1) likely originate in molecular material subject to a
slow, nondissociative shock that is driven by the overpressure within the
supernova remnant, and lines in groups (3) - (5) are associated primarily with
dissociative shock fronts with a range of (larger) shock velocities. The H2
S(0) line shows a low-density diffuse emission component, and - in some sources
- a shock-excited component.Comment: 43 pages, including 21 figures. Accepted for publication in Ap
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