159 research outputs found
Velocity dispersion estimates of APM galaxy clusters
We present 83 new galaxy radial velocities in the field of 18 APM clusters
with redshifts between 0.06 and 0.13. The clusters have Abell identifications
and the galaxies were selected within 0.75 hMpc in projection from their
centers. We derive new cluster velocity dispersions for 13 clusters using our
data and published radial velocities.
We analyze correlations between cluster velocity dispersions and cluster
richness counts as defined in Abell and APM catalogs. The correlations show a
statistically significant trend although with a large scatter suggesting that
richness is a poor estimator of cluster mass irrespectively of cluster
selection criteria and richness definition. We find systematically lower
velocity dispersions in the sample of Abell clusters that do not fulfill APM
cluster selection criteria suggesting artificially higher Abell richness counts
due to contamination by projection effects in this subsample.Comment: Accepted for publication in MNRA
Galaxy Peculiar Velocities and Infall onto Groups
We perform statistical analyses to study the infall of galaxies onto groups
and clusters in the nearby Universe. The study is based on the UZC and SSRS2
group catalogs and peculiar velocity samples. We find a clear signature of
infall of galaxies onto groups over a wide range of scales 5 h^{-1} Mpc<r<30
h^{-1} Mpc, with an infall amplitude on the order of a few hundred kilometers
per second. We obtain a significant increase in the infall amplitude with group
virial mass (M_{V}) and luminosity of group member galaxies (L_{g}). Groups
with M_{V}<10^{13} M_{\odot} show infall velocities V_{infall} \simeq 150 km
s^{-1} whereas for M_{V}>10^{13} M_{\odot} a larger infall is observed,
V_{infall} \simeq 200 km s^{-1}. Similarly, we find that galaxies surrounding
groups with L_{g}<10^{15} L_{\odot} have V_{infall} \simeq 100 km s^{-1},
whereas for L_{g}>10^{15} L_{\odot} groups, the amplitude of the galaxy infall
can be as large as V_{infall} \simeq 250 km s^{-1}. The observational results
are compared with the results obtained from mock group and galaxy samples
constructed from numerical simulations, which include galaxy formation through
semianalytical models. We obtain a general agreement between the results from
the mock catalogs and the observations. The infall of galaxies onto groups is
suitably reproduced in the simulations and, as in the observations, larger
virial mass and luminosity groups exhibit the largest galaxy infall amplitudes.
We derive estimates of the integrated mass overdensities associated with groups
by applying linear theory to the infall velocities after correcting for the
effects of distance uncertainties obtained using the mock catalogs. The
resulting overdensities are consistent with a power law with \delta \sim 1 at r
\sim 10 h^{-1}Mpc.Comment: 25 pages, 10 figure
Cluster-Galaxy Correlations in CDM Models
We study the ability of COBE-normalized CDM models to reproduce observed
properties of the distribution of galaxies and clusters using N-body numerical
simulations. We analyze the galaxy-galaxy and cluster-galaxy two-point
correlation functions, and , in open (), and flat () CDM models which both reproduce the
observed abundances of rich clusters of galaxies. To compare models with
observations we compute projected cross-correlation functions and
to derive the corresponding and . We use
target galaxies selected from Las Campanas Redshift Survey, target clusters
selected from the APM Cluster Survey and tracer galaxies from the Edinburgh
Durham Sky Survey catalog.Comment: 13 pages, 6 figures, to appear in: The Astrophysical Journa
The faint-end of the galaxy luminosity function in groups
We compute the galaxy luminosity function in spectroscopically selected
nearby groups and clusters. Our sample comprises 728 systems extracted from the
third release of the Sloan Digital Sky Survey in the redshift range with virial mass range . In order to compute the galaxy luminosity function, we apply a
statistical background subtraction method following usually adopted techniques.
In the band, the composite galaxy luminosity function shows a slope
in the bright--end, and an upturn of the slope in the faint--end,
M_r\ga -18+5log(h), to slopes . We find that this feature
is present also in the and bands, and for all explored group
subsamples, irrespective of the group mass, number of members, integrated color
or the presence of a hot intra-cluster gas associated to X-ray emission.Comment: 8 pages, 10 figures, Submitted to Astronomy and Astrophysic
Leiomyosarcoma of the Larynx: A Complex Diagnosis
An 84-year-old man was referred to our institution for dysphonia present for 2 months. Fiberoptic laryngoscopy demonstrated a polypoid lesion of the right true vocal fold with normal motility. Excisional biopsy of a submucosal thickening of the right vocal fold with vocal ligament calcification was performed. Histology revealed squamous cell epithelium without malignancy. Postoperative endoscopic follow-up was regular. Six months after surgery, dysphonia and dyspnea occurred. Flexible laryngoscopy demonstrated right hemilaryngeal paralysis, edema, and partial airway obstruction. Necrotic tissue and purulent secretions were visible at the anterior commissure, right vocal fold, and ipsilateral vestibule. A second microlaryngoscopic surgery included multiple biopsies and debridement of the necrotic tissue. Histological report was negative for malignancy, and purulent chondritis was diagnosed. Intravenous antibiotic therapy was administered with improvement of infection, inflammation, dysphonia, and dyspnea. The patient was discharged
Quasar-galaxy and AGN-galaxy cross-correlations
We compute quasar-galaxy and AGN-galaxy cross-correlation functions for
samples taken from the \cite{VCV98} catalog of quasars and active galaxies,
using tracer galaxies taken from the Edinburgh/Durham Southern Catalog. The
sample of active galaxy targets shows positive correlation at projected
separations consistent with the usual power-law. On the
other hand, we do not find a statistically significant positive quasar-galaxy
correlation signal except in the range
where we find similar AGN-galaxy and quasar-galaxy correlation amplitudes. At
separations a strong decline of quasar-galaxy correlations
is observed, suggesting a significant local influence of quasars in galaxy
formation. In an attempt to reproduce the observed cross-correlation between
quasars and galaxies, we have performed CDM cosmological hydrodynamical
simulations and tested the viability of a scenario based on the model developed
by \cite{silkrees98}. In this scheme a fraction of the energy released by
quasars is considered to be transferred into the baryonic component of the
intergalactic medium in the form of winds. The results of the simulations
suggest that the shape of the observed quasar-galaxy cross-correlation function
could be understood in a scenario where a substantial amount of energy is
transferred to the medium at the redshift of maximum quasar activity.Comment: 11 pages, 9 figures. Accepted for publication in Ap
Archaeology, heritage and identity : the creation and development of a national museum in Wales
This thesis examines selected issues, events, episodes and timeframes in the early life of the National Museum of Wales in order to analyse influential and defining aspects in its complex past. It provides a critical perspective on the cultural processes surrounding the foundation and development of the Museum, as well as the array of identities, archaeologies and representations produced. A further aim is to identify and deconstruct the trajectories of research and thought within the Museum's Archaeological department during the early 20th century. The thesis seeks to demonstrate the complexities of the museum experience and to highlight the nuances and subtleties within the national context. It provides a contextual view of the initial movement to establish a national museum and antiquities collection, and subsequently focuses mainly on critical aspects in the development, research and interpretive practices of the Archaeological department. While some awareness exists across the archaeological and museum spectrum that figures such as Sir R.E. Mortimer Wheeler and Sir Cyril Fox spent part of their archaeological careers at the National Museum of Wales, there has to date been no focused, critical analysis of their active roles in shaping, and contributing to, archaeological practice within the Museum itself and within the wider contexts of Welsh and British archaeology. Closer examination of the curatorial and personnel structures in the Museum raises important questions regarding research agendas, the ways in which the material culture collections were augmented, interpreted and displayed, and conflicting political ideologies. Additionally, it draws attention to the dynamics of curatorial practice and representation in a national institutional context. Studying the period of time between the initial move to establish a national museum in the 1890s and the development of a national archaeological collection in the 1920s/30s, reveals the shifts and transformations in cultural politics, institutional practices and museological philosophies.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
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