117,786 research outputs found
Galaxy Ecosystems: gas contents, inflows and outflows
We use a set of observational data for galaxy cold gas mass fraction and gas
phase metallicity to constrain the content, inflow and outflow of gas in
central galaxies hosted by halos with masses between to
. The gas contents in high redshift galaxies are obtained by
combining the empirical star formation histories of Lu et al. (2014) and star
formation models that relate star formation rate with the cold gas mass in
galaxies. We find that the total baryon mass in low-mass galaxies is always
much less than the universal baryon mass fraction since , regardless of
star formation model adopted. The data for the evolution of the gas phase
metallicity require net metal outflow at , and the metal loading
factor is constrained to be about , or about of the metal yield.
Based on the assumption that galactic outflow is more enriched in metal than
both the interstellar medium and the material ejected at earlier epochs, we are
able to put stringent constraints on the upper limits for both the net
accretion rate and the net mass outflow rate. The upper limits strongly suggest
that the evolution of the gas phase metallicity and gas mass fraction for
low-mass galaxies at is not compatible with strong outflow. We
speculate that the low star formation efficiency of low-mass galaxies is owing
to some preventative processes that prevent gas from accreting into galaxies in
the first place.Comment: 15 pages, 10 figures, submitted to MNRA
A Note on N=2 Superstrings
In this note we investigate the generalised critical superstrings in
spacetime signature. We calculate the four-point functions for the
tachyon operators of these theories. In contrast to the usual superstring
in spacetime, the four-point functions do not vanish. The exchanged
particles of the four-point function are included in the physical spectrum of
the corresponding theory and have vanishing fermion charge.Comment: 8 pages, CTP TAMU-57/92, EFI-92-3
Quantum theory of the real and the complexified projective line
Quantum deformations of sets of points of the real and the complexified
projective line are constructed. These deformations depend on the deformation
parameter q and certain further parameters \lambda_{ij}. The deformations for
which the subspace of polynomials of degree three has a basis of ordered
monomials are selected. We show that the corresponding algebras of three points
have "polynomiality". Invariant elements which turn out to be cross ratios in
the classical limit are defined. For the special case |\lambda_{ij}| = 1 a
quantum cross ratio with properties similar to the classical case is presented.
As an application a quantum version of the real Euclidean distance is given.Comment: 25 page
The Accretion and Cooling of Preheated Gas in Dark Matter Halos
(abridged) We use a one-dimensional hydrodynamical code to investigate the
effects of preheating on gas accretion and cooling in cold dark matter halos.
In the absence of radiative cooling, preheating reduces the amount of gas that
can be accreted into a halo, and the accreted gas fraction is determined by the
ratio of the initial specific entropy of the gas to the virial entropy of the
halo. In the presence of radiative cooling, preheating affects the gas fraction
that can cool in two different ways. For small halos with masses <10^12Msun,
preheating suppresses gas accretion, but most of the accreted gas can cool. For
more massive halos, preheating not only reduces the amount of accreted gas, but
also reduces the cooling efficiency. For both small and massive halos, gas
cooling is delayed by preheating and in an inside-out fashion if the halo gas
is assumed to be a single-phase medium. However, cooling can occur over a wider
range of redshifts and radii, if we assume a multi-phase medium. As examples,
two specific preheating cases are investigated. In the first case, the
preheating entropy is assumed to be proportional to the virial entropy of the
halo, as expected from AGN feedback. Such preheating effectively suppresses
radiative cooling in halos with M>10^13Msun. We suggest that this may be the
reason why the stellar mass function of galaxies breaks sharply at the massive
end. Such preheating also helps create the hot diffused halos within which the
"radio mode" feedback of AGNs can act effectively. In the second case, we
assume the intergalactic medium is warm. Here the total amount of gas that can
cool in a halo scales with halo mass as ~M^2, as would be required to match the
observed stellar- and HI-mass functions in the current CDM model at the small
mass end.Comment: 14 pages, 13 figures, submitted to MNRA
Penrose Limits of Non-standard Brane Intersections
The non-standard intersection of two 5-branes and a string can give rise to
AdS_3\times S^3\times S^3\times S^1. We consider the Penrose limit of this
geometry and study the supersymmetry of the resulting pp-wave solution. There
is a one-parameter family of Penrose limits associated with the orthogonal
rotation of the two foliating circles within the two 3-spheres. Supernumerary
Killing spinors arise only when the rotation angle is 45 degrees, for which
case we obtain the corresponding light-cone string action that has
linearly-realised supersymmetry. We also obtain Penrose limits of other
non-standard intersections that give rise to the product of AdS_3 or AdS_2 and
two spheres. The resulting pp-waves are supported by multiple constant field
strengths.Comment: Latex, 15 pages, references adde
Density oscillations in trapped dipolar condensates
We investigated the ground state wave function and free expansion of a
trapped dipolar condensate. We find that dipolar interaction may induce both
biconcave and dumbbell density profiles in, respectively, the pancake- and
cigar-shaped traps. On the parameter plane of the interaction strengths, the
density oscillation occurs only when the interaction parameters fall into
certain isolated areas. The relation between the positions of these areas and
the trap geometry is explored. By studying the free expansion of the condensate
with density oscillation, we show that the density oscillation is detectable
from the time-of-flight image.Comment: 7 pages, 9 figure
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