11,567 research outputs found
Tidal Effects in Clusters of Galaxies
High-redshift clusters of galaxies show an over-abundance of spirals by a
factor of 2-3, and the corresponding under-abundance of S0 galaxies, relative
to the nearby clusters. This morphological evolution can be explained by tidal
interactions with neighboring galaxies and with the hierarchically growing
cluster halo. The efficiency of tidal interactions depends on the size and
structure of the cluster, as well as on the epoch of its formation. I simulate
the formation and evolution of Virgo-type clusters in three cosmologies: a
critical density model Omega_0=1, an open model Omega_0=0.4, and a flat model
Omega_0=0.4 with a cosmological constant. The orbits of identified halos are
traced with a high temporal resolution (~10^7 yr). Halos with low relative
velocities merge only shortly after entering the cluster; after virialization
mergers are suppressed. The dynamical evolution of galaxies is determined by
the tidal field along their trajectories. The maxima of the tidal force do not
always correspond to closest approach to the cluster center. They are produced
to a large extent by the local density structures, such as the massive galaxies
and the unvirialized remnants of infalling groups of galaxies. Collisions of
galaxies are intensified by the substructure, with about 10 encounters within
10 kpc per galaxy in the Hubble time. These very close encounters add an
important amount (10-50%) of the total heating rate. The integrated effect of
tidal interactions is insufficient to transform a spiral galaxy into an
elliptical, but can produce an S0 galaxy. Overall, tidal heating is stronger in
the low Omega_0 clusters
Improving Mechanical Ventilator Clinical Decision Support Systems with A Machine Learning Classifier for Determining Ventilator Mode
Clinical decision support systems (CDSS) will play an in-creasing role in
improving the quality of medical care for critically ill patients. However, due
to limitations in current informatics infrastructure, CDSS do not always have
com-plete information on state of supporting physiologic monitor-ing devices,
which can limit the input data available to CDSS. This is especially true in
the use case of mechanical ventilation (MV), where current CDSS have no
knowledge of critical ventilation settings, such as ventilation mode. To enable
MV CDSS to make accurate recommendations related to ventilator mode, we
developed a highly performant ma-chine learning model that is able to perform
per-breath clas-sification of 5 of the most widely used ventilation modes in
the USA with an average F1-score of 97.52%. We also show how our approach makes
methodologic improvements over previous work and that it is highly robust to
missing data caused by software/sensor error
Transformation of Morphology and Luminosity Classes of the SDSS Galaxies
We present a unified picture on the evolution of galaxy luminosity and
morphology. Galaxy morphology is found to depend critically on the local
environment set up by the nearest neighbor galaxy in addition to luminosity and
the large scale density. When a galaxy is located farther than the virial
radius from its closest neighbor, the probability for the galaxy to have an
early morphological type is an increasing function only of luminosity and the
local density due to the nearest neighbor (). The tide produced by the
nearest neighbor is thought to be responsible for the morphology transformation
toward the early type at these separations. When the separation is less than
the virial radius, i.e. when , its morphology
depends also on the neighbor's morphology and the large-scale background
density over a few Mpc scales () in addition to luminosity and
. The early type probability keeps increasing as increases if
its neighbor is an early type. But the probability decreases as
increases when the neighbor is a late type. The cold gas streaming from the
late type neighbor can be the reason for the morphology transformation toward
late type. The overall early-type fraction increases as increases
when . This can be attributed to the hot halo gas
of the neighbor which is confined by the pressure of the ambient medium held by
the background mass. We have also found that galaxy luminosity depends on
, and that the isolated bright galaxies are more likely to be recent
merger products. We propose a scenario that a series of morphology and
luminosity transformation occur through distant interactions and mergers, which
results in the morphology--luminosity--local density relation.Comment: 14 pages, 7 figures, for higher resolution figures download PDF file
at http://astro.kias.re.kr/docs/trans.pdf ; references added and typos in
section 3.2 corrected; Final version accepted for publication in Ap
Suppressed radio emission in supercluster galaxies: enhanced ram pressure in merging clusters?
The environmental influence on the 1.4 GHz continuum radio emission of
galaxies is analyzed in a 600 deg2 region of the local Universe containing the
Shapley Supercluster (SSC). Galaxies in the FLASH and 6dFGS redshift surveys
are cross-identified with NVSS radio sources, selected in a subsample doubly
complete in volume and luminosity. Environmental effects are studied through a
smoothed density field (normalized with random catalogs with the same survey
edges and redshift selection function) and the distance to the nearest cluster
(R/r200, where r200 is the virial radius, whose relation to the aperture
velocity dispersion is quantified). The fraction of high radio loudness
(R_K=L_radio/L_K) galaxies in the 10 Mpc Abell 3558 cluster complex at the core
of the SSC (SSC-CR) is half as large than elsewhere. In the SSC-CR, R_K is
anti-correlated with the density of the large-scale environment and correlated
with R/r200: central brightest cluster galaxies (BCGs) in the SSC-CR are 10x
less radio-loud than BCGs elsewhere, with signs of suppressed radio loudness in
the SSC-CR also present beyond the BCGs, out to at least 0.3 r200. This
correlation is nearly as strong as the tight correlation of L_K with R/r200
(K-luminosity segregation), inside the SSC-CR. The suppression of radio
loudness in SSC-CR BCGs can be attributed to cluster-cluster mergers that
destroy the cool core and thus the supply of gas to the central AGN. We
analytically demonstrate that the low radio loudness of non-BCG galaxies within
SSC-CR clusters cannot be explained by direct major galaxy mergers or rapid
galaxy flyby collisions, but by the loss of gas supply through the enhanced ram
pressure felt when these galaxies cross the shock front between the 2 merging
clusters and are later subjected to the stronger wind from the 2nd cluster.Comment: Version consolidated with Erratum A&A 499, 4
Shock-induced star formation in a model of the Mice
Star formation plays an important role in the fate of interacting galaxies.
To date, most galactic simulations including star formation have used a
density-dependent star formation rule designed to approximate a Schmidt law.
Here, I present a new star formation rule which is governed by the local rate
of energy dissipation in shocks. The new and old rules are compared using
self-consistent simulations of NGC 4676; shock-induced star formation provides
a better match to the observations of this system.Comment: Submitted to MNRAS. 12 pages, 5 B&W figures, 2 color figures. See
http://www.ifa.hawaii.edu/~barnes/sisfmm.html for a version with
high-resolution figures, and
http://www.ifa.hawaii.edu/~barnes/research/interaction_models/mice/index.html
for animations of the simulation
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