17,665 research outputs found
The effect of ram pressure on the star formation, mass distribution and morphology of galaxies
We investigate the dependence of star formation and the distribution of the
components of galaxies on the strength of ram pressure. Several mock
observations in X-ray, H and HI wavelength for different ram-pressure
scenarios are presented. By applying a combined N-body/hydrodynamic description
(GADGET-2) with radiative cooling and a recipe for star formation and stellar
feedback 12 different ram-pressure stripping scenarios for disc galaxies were
calculated. Special emphasis was put on the gas within the disc and in the
surroundings. All gas particles within the computational domain having the same
mass resolution. The relative velocity was varied from 100 km/s to 1000 km/s in
different surrounding gas densities in the range from to
g/cm. The temperature of the surrounding gas was
initially K. The star formation of a galaxy is enhanced by more
than a magnitude in the simulation with a high ram-pressure (
dyn/cm) in comparison to the same system evolving in isolation. The
enhancement of the star formation depends more on the surrounding gas density
than on the relative velocity. Up to 95% of all newly formed stars can be found
in the wake of the galaxy out to distances of more than 350 kpc behind the
stellar disc. Continuously stars fall back to the old stellar disc, building up
a bulge-like structure. Young stars can be found throughout the stripped wake
with surface densities locally comparable to values in the inner stellar disc.
Ram-pressure stripping can shift the location of star formation from the disc
into the wake on very short timescales. (Abridged)Comment: 19 pages, 25 figures, A&A accepted, high resolution version can be
found at http://astro.uibk.ac.at/~wolfgang/kapferer_rps_galaxies.pd
ATCA observations of the galaxy cluster Abell 3921 - I. Radio emission from the central merging sub-clusters
We present the analysis of our 13 and 22 cm ATCA observations of the central
region of the merging galaxy cluster A3921 (z=0.094). We investigated the
effects of the major merger between two sub-clusters on the star formation (SF)
and radio emission properties of the confirmed cluster members. The origin of
SF and the nature of radio emission in cluster galaxies was investigated by
comparing their radio, optical and X-ray properties. We also compared the radio
source counts and the percentage of detected radio galaxies with literature
data. We detected 17 radio sources above the flux density limit of 0.25
mJy/beam in the central field of A3921, among which 7 are cluster members. 9
galaxies with star-forming optical spectra were observed in the collision
region of the merging sub-clusters. They were not detected at radio
wavelengths, giving upper limits for their star formation rate significantly
lower than those typically found in late-type, field galaxies. Most of these
star-forming objects are therefore really located in the high density part of
the cluster, and they are not infalling field objects seen in projection at the
cluster centre. Their SF episode is probably related to the cluster collision
that we observe in its very central phase. None of the galaxies with
post-starburst optical spectra was detected down our 2 flux density
limit, confirming that they are post-starburst and not dusty star-forming
objects. We finally detected a narrow-angle tail (NAT) source associated with
the second brightest cluster galaxy (BG2), whose diffuse component is a partly
detached pair of tails from an earlier period of activity of the BG2 galaxy.Comment: 17 pages, 9 figures, accepted for publication in A&A, date of
acceptance 29/06/2006. A version of the paper with higher resolution images
can be downloaded at:
http://astro.uibk.ac.at/~c.ferrari/ATCA_Paper/A3921_ATCA.pd
Bosonic Field Propagators on Algebraic Curves
In this paper we investigate massless scalar field theory on non-degenerate
algebraic curves. The propagator is written in terms of the parameters
appearing in the polynomial defining the curve. This provides an alternative to
the language of theta functions. The main result is a derivation of the third
kind differential normalized in such a way that its periods around the homology
cycles are purely imaginary. All the physical correlation functions of the
scalar fields can be expressed in terms of this object. This paper contains a
detailed analysis of the techniques necessary to study field theories on
algebraic curves. A simple expression of the scalar field propagator is found
in a particular case in which the algebraic curves have internal symmetry
and one of the fields is located at a branch point.Comment: 26 pages, TeX + harvma
Update On The Code Intercomparison and Benchmark For Muon Fluence and Absorbed Dose Induced By An 18-GeV Electron Beam After Massive Iron Shielding
In 1974, Nelson, Kase and Svensson published an experimental investigation on
muon shielding around SLAC high-energy electron accelerators. They measured
muon fluence and absorbed dose induced by 14 and 18 GeV electron beams hitting
a copper/water beamdump and attenuated in a thick steel shielding. In their
paper, they compared the results with the theoretical models available at that
time.
In order to compare their experimental results with present model
calculations, we use the modern transport Monte Carlo codes MARS15, FLUKA2011
and GEANT4 to model the experimental setup and run simulations. The results are
then compared between the codes, and with the SLAC data.Comment: 14 pp. Presented paper at the 13th Meeting of the task-force on
Shielding aspects of Accelerators, Targets and Irradiation Facilities
(SATIF-13), HZDR, October 10-12, 2016, Dresden, Germany. arXiv admin note:
substantial text overlap with arXiv:1502.0168
Specific heat of the ideal gas obeying the generalized exclusion statistics
We calculate the specific heat of the ideal gas obeying the generalized
exclusion statistics (GES) in the continuum model and the tight binding model
numerically. In the continuum model of 3-d space, the specific heat increases
with statistical parameter at low temperature whereas it decreases with
statistical parameter at high temperature. We find that the critical
temperature normalized by (Fermi energy) is 0.290. The specific heat of
2-d space was known to be independent of in the continuum model, but it
varies with drastically in the tight-binding model. From its unique
behavior, identification of GES particles will be possible from the specific
heat.Comment: 14 pages, 9 figures, to be published in Eur. Phys. J. B, References
and figures added, typos corrected, one section removed and two sections
merge
Distinguishing double neutron star from neutron star-black hole binary populations with gravitational wave observations
Gravitational waves from the merger of two neutron stars cannot be easily
distinguished from those produced by a comparable-mass mixed binary in which
one of the companions is a black hole. Low-mass black holes are interesting
because they could form in the aftermath of the coalescence of two neutron
stars, from the collapse of massive stars, from matter overdensities in the
primordial Universe, or as the outcome of the interaction between neutron stars
and dark matter. Gravitational waves carry the imprint of the internal
composition of neutron stars via the so-called tidal deformability parameter,
which depends on the stellar equation of state and is equal to zero for black
holes. We present a new data analysis strategy powered by Bayesian inference
and machine learning to identify mixed binaries, hence low-mass black holes,
using the distribution of the tidal deformability parameter inferred from
gravitational-wave observations.Comment: 13 pages, 6 figures - v2: matches the published version in Phys. Rev.
D 102, 02302
On the development of thermohaline correlations as a result of nonlinear diffusive parameterizations
Some oceanographic mixing parameterizations assume that transports depend nonlinearly on the buoyancy gradient; e.g., diffusivities are proportional to some power of the buoyancy gradient. In this paper we examine the consequences of these nonlinear-diffusion parameterizations by solving an initial value problem in which the t = 0 thermohaline fields are prepared as random and uncorrelated distributions of temperature and salinity. Solutions of the nonlinear diffusion equation as a ârundownâ problem show that correlations develop between the temperature and salinity. These correlations are such that the evolving thermohaline gradients tend to be strongly compensating in their joint effect on buoyancy
On Abelian Multi-Chern-Simons Field Theories
In this paper a class of multi-Chern-Simons field theories which is relevant
to the statistical mechanics of polymer systems is investigated. Motivated by
the problems which one encounters in the treatment of these theories, a general
procedure is presented to eliminate the Chern-Simons fields from their action.
In this way it has been possible to derive an expression of the partition
function of topologically linked polymers which depends explicitly on the
topological numbers and does not have intractable nonlocal terms as it happened
in previous approaches. The new formulation of multi-Chern-Simons field
theories is then used to remove and clarify some inconsistencies and
ambiguities which apparently affect field theoretical models of topologically
linked polymers. Finally, the limit of disentangled polymers is discussed.Comment: 18 pages, plain LaTe
Of Higgs, Unitarity and other Questions
On the verge of conclusive checks on the Standard Model by the LHC, we
discuss some of the basic assumptions. The reason for this analysis stems from
a recent proposal of an Electroweak Model based on a nonlinearly realized gauge
group SU(2) X U(1), where, in the perturbative approximation, there is no Higgs
boson. The model enjoys the Slavnov-Taylor identities and therefore the
perturbative unitarity. On the other hand, it is commonly believed that the
existence of the Higgs boson is entangled with the property of unitarity, when
high energy processes are considered. The argument is based mostly on the
Froissart bound and on the Equivalence Theorem. In this talk we briefly review
some of our objections on the validity of such arguments. Some open questions
are pointed out, in particular on the limit of zero mass for the vector mesons
and on the fate of the longitudinal polarizations.Comment: 23 pages, 1 figure, presented by Ruggero Ferrari at the International
Conference "Gauge Fields. Yesterday, Today, Tomorrow" in honor of A.A.
Slavnov. Moscow, January 19-24 201
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