79,220 research outputs found
Molecular gas in extreme star-forming environments: the starbursts Arp220 and NGC6240 as case studies
We report single-dish multi-transition measurements of the 12^CO, HCN, and
HCO^+ molecular line emission as well as HNC J=1-0 and HNCO in the two
ultraluminous infra-red galaxies Arp220 and NGC6240. Using this new molecular
line inventory, in conjunction with existing data in the literature, we
compiled the most extensive molecular line data sets to date for such galaxies.
The many rotational transitions, with their different excitation requirements,
allow the study of the molecular gas over a wide range of different densities
and temperatures with significant redundancy, and thus allow good constraints
on the properties of the dense gas in these two systems. The mass (~(1-2) x
10^10 Msun) of dense gas (>10^5-6 cm^-3) found accounts for the bulk of their
molecular gas mass, and is consistent with most of their IR luminosities
powered by intense star bursts while self-regulated by O,B star cluster
radiative pressure onto the star-forming dense molecular gas. The highly
excited HCN transitions trace a gas phase ~(10-100)x denser than that of the
sub-thermally excited HCO^+ lines (for both galaxies). These two phases are
consistent with an underlying density-size power law found for Galactic GMCs
(but with a steeper exponent), with HCN lines tracing denser and more compact
regions than HCO^+. Whether this is true in IR-luminous, star forming galaxies
in general remains to be seen, and underlines the need for observations of
molecular transitions with high critical densities for a sample of bright
(U)LIRGs in the local Universe -- a task for which the HI-FI instrument on
board Herschel is ideally suited to do.Comment: 38 pages (preprint ApJ style), 3 figures, accepted for Ap
Supersymmetric Kerr--anti-deSitter solutions
We prove the existence of one quarter supersymmetric type IIB configurations
that arise as non-trivial scaling solutions of the standard five dimensional
Kerr-AdS black holes by the explicit construction of its Killing spinors. This
neutral, spinning solution is asymptotic to the static anti-deSitter space-time
with cosmological constant , it has two finite
equal angular momenta , mass and a naked singularity.We also address the scaling limit
associated with one half supersymmetric solution with only one angular
momentum.Comment: 15 pages, no figure
Structure of polydisperse inverse ferrofluids: Theory and computer simulation
By using theoretical analysis and molecular dynamics simulations, we
investigate the structure of colloidal crystals formed by nonmagnetic
microparticles (or magnetic holes) suspended in ferrofluids (called inverse
ferrofluids), by taking into account the effect of polydispersity in size of
the nonmagnetic microparticles. Such polydispersity often exists in real
situations. We obtain an analytical expression for the interaction energy of
monodisperse, bidisperse, and polydisperse inverse ferrofluids. Body-centered
tetragonal (bct) lattices are shown to possess the lowest energy when compared
with other sorts of lattices and thus serve as the ground state of the systems.
Also, the effect of microparticle size distributions (namely, polydispersity in
size) plays an important role in the formation of various kinds of structural
configurations. Thus, it seems possible to fabricate colloidal crystals by
choosing appropriate polydispersity in size.Comment: 22 pages, 8 figure
Magnetophoresis of nonmagnetic particles in ferrofluids
Ferrofluids containing nonmagnetic particles are called inverse ferrofluids.
On the basis of the Ewald-Kornfeld formulation and the Maxwell-Garnett theory,
we theoretically investigate the magnetophoretic force exerting on the
nonmagnetic particles in inverse ferrofluids due to the presence of a
nonuniform magnetic field, by taking into account the structural transition and
long-range interaction. We numerically demonstrate that the force can be
adjusted by choosing appropriate lattices, volume fractions, geometric shapes,
and conductivities of the nonmagnetic particles, as well as frequencies of
external magnetic fields.Comment: 24 pages, 7 figure
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