4,707 research outputs found
High Excitation Molecular Gas in the Magellanic Clouds
We present the first survey of submillimeter CO 4-3 emission in the
Magellanic Clouds. The survey is comprised of 15 6'x6' maps obtained using the
AST/RO telescope toward the molecular peaks of the Large and Small Magellanic
Clouds. We have used these data to constrain the physical conditions in these
objects, in particular their molecular gas density and temperature. We find
that there are significant amounts of molecular gas associated with most of
these molecular peaks, and that high molecular gas temperatures are pervasive
throughout our sample. We discuss whether this may be due to the low
metallicities and the associated dearth of gas coolants in the Clouds, and
conclude that the present sample is insufficient to assert this effect.Comment: 18 pages, 3 figures, 5 tables. To appear in Ap
On the dual interpretation of zero-curvature Friedmann-Robertson-Walker models
Two possible interpretations of FRW cosmologies (perfect fluid or dissipative
fluid)are considered as consecutive phases of the system. Necessary conditions
are found, for the transition from perfect fluid to dissipative regime to
occur, bringing out the conspicuous role played by a particular state of the
system (the ''critical point '').Comment: 13 pages Latex, to appear in Class.Quantum Gra
Weyl-Conformally-Invariant Lightlike p-Brane Theories: New Aspects in Black Hole Physics and Kaluza-Klein Dynamics
We introduce and study in some detail the properties of a novel class of
Weyl-conformally invariant p-brane theories which describe intrinsically
lightlike branes for any odd world-volume dimension. Their dynamics
significantly differs from that of the ordinary (conformally non-invariant)
Nambu-Goto p-branes. We present explicit solutions of the Weyl-invariant
lightlike brane- (WILL-brane) equations of motion in various gravitational
models of physical relevance exhibiting various new phenomena. In D=4 the
WILL-membrane serves as a material and charged source for gravity and
electromagnetism in the coupled Einstein-Maxwell-WILL-membrane system; it
automatically positions itself on (``straddles'') the common event horizon of
the corresponding matching black hole solutions, thus providing an explicit
dynamical realization of the membrane paradigm in black hole physics. In
product spaces of interest in Kaluza-Klein theories the WILL-brane wraps
non-trivially around the compact (internal)dimensions and still describes
massless mode dynamics in the non-compact (space-time) dimensions. Due to
nontrivial variable size of the internal compact dimensions we find new types
of physically interesting solutions describing massless brane modes trapped on
bounded planar circular orbits with non-trivial angular momentum, and with
linear dependence between energy and angular momentum.Comment: 28 pages, published versio
Results of the ESO-SEST Key Programme on CO in the Magellanic Clouds. IX. The giant LMC HII region complex N11
We present maps and a catalogue containing the J=1-0 12CO parameters of 29
individual molecular clouds in the second-brightest LMC star formation complex,
N11. In the southwestern part of N11, molecular clouds occur in a ring or shell
surrounding the major OB star association LH9. In the northeastern part, a
chain of molecular clouds delineates the rim of one of the so-called supergiant
shells in the LMC. The well-defined clouds have dimensions close to those of
the survey beam (diameters of 25 pc or less). Some of the clouds were also
observed in J=2-1 12CO, and in the lower two transitions of 13CO. Clouds mapped
with a twice higher angular resolution in J=2-1 12CO show substructure with
dimensions once again comparable to those of the mapping beam. The few clouds
for which we could model physical parameters have fairly warm (T(kin) = 60 -
150 K) and moderately dense (n(H2) = 3000 cm-3) gas. The northeastern chain of
CO clouds, although lacking in diffuse intercloud emission, is characteristic
of the more quiescent regions of the LMC and appears to have been subject to
relatively little photo-processing. The clouds forming part of the southwestern
shell or ring, however, are almost devoid of diffuse intercloud emission and
also exhibit other characteristics of an extreme photon-dominated region (PDR).Comment: 14 pages; accepted for publication in A&
Reply to "On scaling solutions with a dissipative fluid"
In this paper we show that the claims in [Class. Quantum Grav. 19 (2002)
3067, gr-qc/0203081] related to our analysis in [Phys. Rev. D 62, 063508
(2000), astro-ph/0005070] are wrong.Comment: 4 pages, uses RevTeX. v2: To appear in Class. Quantum Gra
CO Emission in Low Luminosity, HI Rich Galaxies
We present 12CO 1-0 observations of eleven low luminosity M_B > -18),
HI--rich dwarf galaxies. Only the three most metal-rich galaxies, with
12+log(O/H) ~ 8.2, are detected. Very deep CO spectra of six extremely
metal-poor systems (12+log(O/H) < 7.5) yield only low upper limits on the CO
surface brightness, I_CO < 0.1 K km/s. Three of these six have never before
been observed in a CO line, while the others now have much more stringent upper
limits. For the very low metallicity galaxy Leo A, we do not confirm a
previously reported detection in CO, and the limits are consistent with another
recent nondetection. We combine these new observations with data from the
literature to form a sample of dwarf galaxies which all have CO observations
and measured oxygen abundances. No known galaxies with 12+log(O/H) < 7.9 (Z <
0.1 solar) have been detected in CO. Most of the star-forming galaxies with
higher (12+log(O/H) > 8.1) metallicities are detected at similar or higher I_CO
surface brightnesses. The data are consistent with a strong dependence of the
I_CO/M_H_2 = X_CO conversion factor on ambient metallicity. The strikingly low
upper limits on some metal-poor galaxies lead us to predict that the conversion
factor is non-linear, increasing sharply below approximately 1/10 of the solar
metallicity (12+log(O/H) < 7.9).Comment: 25 pages, 4 figures, 3 tables. Accepted for publication in AJ Tables
replaced -- now formated for landscape orientatio
Thermal Conduction in Systems out of Hydrostatic Equilibrium
We analyse the effects of thermal conduction in a relativistic fluid, just
after its departure from hydrostatic equilibrium, on a time scale of the order
of thermal relaxation time. It is obtained that the resulting evolution will
critically depend on a parameter defined in terms of thermodynamic variables,
which is constrained by causality requirements.Comment: 16 pages, emTex (LaTex 2.09). To appear in Classical and Quantum
Gravit
Dynamics of a self-gravitating thin cosmic string
We assume that a self-gravitating thin string can be locally described by
what we shall call a smoothed cone. If we impose a specific constraint on the
model of the string, then its central line obeys the Nambu-Goto equations. If
no constraint is added, then the worldsheet of the central line is a totally
geodesic surface.Comment: 20 pages, latex, 1 figure, final versio
Constraints on Embeddings
We show that the embedding of either a static or a time dependent maximally
3-symmetric brane with non-zero spatial curvature into a non-compactified
bulk does not yield exponential suppression of the geometry away from
the brane. Implications of this result for brane-localized gravity are
discussed.Comment: RevTeX, 9 pages (updated version v2, conclusions unchanged after
extension to the non-static case
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