14,206 research outputs found
The roles of ram-pressure stripping and minor mergers in evolution of galaxies
We investigate environmental effects on evolution of bright cluster galaxies
in a Lambda-dominated cold dark matter universe using a combination of
dissipationless N-body simulations and a semi-analytic galaxy formation model.
We incorporate effects of ram-pressure stripping (RPS) and minor merger-induced
small starburst (minor burst) into our model. By considering minor burst,
observed morphology-radius relation is successfully reproduced. When we do not
consider minor burst, the RPS hardly increases the intermediate B/T population.
In addition, the RPS and minor burst are not important for colours or star
formation rates of galaxies in the cluster core if star formation time-scale is
properly chosen, because the star formation is sufficiently suppressed by
consumption of the cold gas. We also find that SF in bulge-dominated galaxies
is mainly terminated by starburst induced by major mergers in all environments.Comment: To appear in the proceedings of IAU colloq. No. 195, "Outskirts of
Galaxy Clusters: intense life in the suburbs", Torino, 12-16 March 2004, 5
pages, 2 figures, uses IAU macr
The Effect of Spatial Correlations on Merger Trees of Dark Matter Haloes
The effects of spatial correlations of density fluctuations on merger
histories of dark matter haloes (so-called `{\it merger trees}') are analysed.
We compare the mass functions of dark haloes derived by a new method for
calculating merger trees, that proposed by Rodrigues \& Thomas (RT), with those
given by other methods such as the Block model, the Press-Schechter formula and
our own formula in which the mass functions are analytically expressed in a way
that takes into consideration the spatial correlations. It is found that the
mass functions given by the new method are well fit by those given by our
formula. We believe that new method (RT) {\it naturally} and correctly takes
into account the spatial correlations of the density fluctuations due to a
calculated, grid-based realisation of the density fluctuations and so is very
useful for estimating the merger tree accurately in a way that takes into
consideration spatial correlations.
Moreover, by applying our formula, we present an analytic expression which
reproduces the mass function derived by the Block model. We therefore show
clearly why and how the mass functions given by the new method and the Block
model are different from each other. Furthermore, we note that the construction
of merger trees is sensitive to the criterion of collapse and merging of
overlapped haloes in cases in which two or more haloes happen to overlap. In
fact, it is shown that the mass function is very much affected when the
criterion of overlapping is changed.Comment: Submitted to MNRAS; 10 pages MN latex file, including 5 figures
(epsf
Gamma-Rays from Large Scale Structure Formation and the Warm-Hot Intergalactic Medium: Cosmic Baryometry with Gamma-Rays
It is shown that inverse Compton gamma-rays from electrons accelerated in
large scale structure formation shocks can be crucially affected by
non-gravitational effects such as radiative cooling and galaxy formation, with
corresponding uncertainties by an order of magnitude in either the gamma-ray
source counts or the extragalactic background contribution. However, this also
implies that such gamma-rays may in the near future provide us with valuable
information about the fraction of cosmic baryons in different forms,
particularly the warm-hot intergalactic medium where the majority of the
baryons in the universe are believed to reside. We address this problem in a
simple way through semi-analytic modeling of structure formation shocks which
self-consistently treats merger and accretion shocks.Comment: 7 pages, 2 figures; slightly modified version of article to appear in
Proc. of the "International Symposium on High Energy Gamma-Ray Astronomy"
Heidelberg (2004), eds. F.A. Aharonian, H.J. Voelk and D. Horns (AIP, NY
Analytic Approach to the Cloud-in-cloud Problem for Non-Gaussian Density Fluctuations
We revisit the cloud-in-cloud problem for non-Gaussian density fluctuations.
We show that the extended Press-Schechter (EPS) formalism for non-Gaussian
fluctuations has a flaw in describing mass functions regardless of type of
filtering. As an example, we consider non-Gaussian models in which density
fluctuations at a point obeys a \chi^2 distribution with \nu degrees of
freedom. We find that mass functions predicted by using an integral formula
proposed by Jedamzik, and Yano, Nagashima and Gouda, properly taking into
account correlation between objects at different scales, deviate from those
predicted by using the EPS formalism, especially for strongly non-Gaussian
fluctuations. Our results for the mass function at large mass scales are
consistent with those by Avelino and Viana obtained from numerical simulations.Comment: 10 pages, 7 EPS files, submitted to Ap
Dynamical response to supernova-induced gas removal in two-component spherical galaxies
We investigate dynamical response on size and velocity dispersion to mass
loss by supernovae in formation of two-component spherical galaxies composed of
baryon and dark matter. Three-dimensional deprojected de Vaucouleurs-like and
exponential-like profiles for baryon, embedded in truncated singular isothermal
and homogeneous profiles for dark matter, are considered. As a more realistic
case, we also consider a dark matter profile proposed by Navarro, Frenk &
White. For simplicity we assume that dark matter distribution is not affected
by mass loss and that the change of baryonic matter distribution is homologous.
We found that the degree of the response depends on the fraction of dark matter
in the region where baryon is distributed, so that dwarf spheroidal galaxies
would be affected even in a dark halo if they are formed by galaxy mergers in
the envelope of the dark halo. Our results suggest that this scenario, combined
with dynamical response, would make not only the observed trends but the
dispersed characteristics of dwarf spheroidals.Comment: 13 pages, 4 figures, to appear in MNRA
Effect of Supersymmetric Right-handed Flavor Mixing on decays
Motivated by the possibility of , we study the
implications for meson system. In a specific model that realizes with large - mixing, right-handed dynamics and a new CP
phase, we present predictions for CP asymmetries in ,
and decays. Even if the measurement of time-dependent CP
asymmetry becomes hampered by very fast oscillation, a finite difference
between the decay rates of mass eigenstates may enable the studies of CP
violations with untagged data samples. Thus, studies of CP violation in the
system would remain useful for the extraction of new physics information.Comment: 7 pages, 15 figure
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