131 research outputs found
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
Estudio sobre los efectos del medio sobre propiedades de galaxias
Hemos realizado un estudio estadÃstico en los catálogos CfA y SRC 2 sobre la dependencia de la morfologÃa de las galaxias y sus velocidades circulares con el medio. El Ãndice morfológico resulta una función decreciente de la densidad numérica de galaxias. Para un determinado valor de la densidad en una capa interna encontramos que el Ãndice morfológico del objeto central es más negativo cuando la densidad de galaxias en capas externas es mayor. Este efecto está presente sólo cuando los tip tempranos y tardÃos están simultáneamente presentes en la estadÃstica y no cuando los tipos tempranos y los tipos tardÃos son considerados por separado. Este resultado puede ser explicado en términos de una mayor tasa de "mergers" de galaxias espirales que dan origen a objetos tempranos en regiones 'globalmente densas (cúmulos). Por otro lado, tanto la relación disk-bulge de tipos tardÃos como las elipticidades de tipos tempranos dependen sólo localmente de la densidad. Encontramos que la velocidad circular media de las galaxias tiene aproximadamente un incremento lineal con la densidad como es esperado en el régimen lineal de un escenario de agregación jerárquica como el modelo CDM. Mediante una técnica de análisis similar a la utilizada con los tipos morfológicos se encuentra que las velocidades circulares son un 10% menores para aquellas galaxias en regiones globalmente densas (cúmulos). Este resultado es evidencia estadÃstica del "stripping" del material de los halos causado por encuentros.Asociación Argentina de AstronomÃ
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
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
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
The VVV near-IR galaxy catalogue in a Northern part of the Galactic disc
The automated identification of extragalactic objects in large surveys
provides reliable and reproducible samples of galaxies in less time than
procedures involving human interaction. However, regions near the Galactic disc
are more challenging due to the dust extinction. We present the methodology for
the automatic classification of galaxies and non-galaxies at low Galactic
latitude regions using both images and, photometric and morphological near-IR
data from the VVVX survey. Using the VVV-NIRGC, we analyse by statistical
methods the most relevant features for galaxy identification. This catalogue
was used to train a CNN with image data and an XGBoost model with both
photometric and morphological data and then to generate a dataset of
extragalactic candidates. This allows us to derive probability catalogues used
to analyse the completeness and purity as a function of the configuration
parameters and to explore the best combinations of the models. As a test case,
we apply this methodology to the Northern disc region of the VVVX survey,
obtaining 172,396 extragalatic candidates with probabilities of being galaxies.
We analyse the performance of our methodology in the VVV disc, reaching an
F1-score of 0.67, a 65 per cent purity and a 69 per cent completeness. We
present the VVV-NIR Galaxy Catalogue: Northern part of the Galactic disc
comprising 1,003 new galaxies, with probabilities greater than 0.6 for either
model, with visual inspection and with only 2 previously identified galaxies.
In the future, we intend to apply this methodology to other areas of the VVVX
survey.Comment: 12 pages, 14 figures, accepted in MNRA
The V-band luminosity function of galaxies in A2151
We present a wide field -band imaging survey of approximately 1 deg
( Mpc) in the direction of the nearby cluster of
galaxies Abell 2151 (the Hercules Cluster). The data are used to construct the
luminosity function (LF) down to , thus allowing us to
study the dwarf galaxy population in A2151 for the first time. The obtained
global LF is well described by a Schechter function with best-fit parameters
and . The
radial dependence of the LF was investigated, with the faint-end slope tending
to be slightly steeper in the outermost regions and farther away than the
virial radius. Given the presence of significant substructure within the
cluster, we also analysed the LFs in three different regions. We find that the
dwarf to giant ratio increases from the northern to the southern subcluster,
and from low to high local density environments, although these variations are
marginally significant (less than 2).Comment: Accepted for publication in A&
LLAMA Millimeter and Submillimeter Observatory. Update on its Science Opportunities
The Large Latin American Millimeter Array (LLAMA for short) is a joint
scientific and technological undertaking of Argentina and Brazil whose goal is
to install and to operate an observing facility capable of performing
observations of the Universe at millimeter and sub-millimeter wavelengths. It
will consist of a 12m ALMA-like antenna with the addition of two Nasmyth
cabins. LLAMA is located at 4850m above sea level in the Puna Saltenia, in the
northwest region of Argentina. When completed, LLAMA will be equipped with six
ALMA receivers covering Bands 1, 2+3, 5, 6, 7, and 9, which will populate the
two Nasmyth cabins. We summarize here the main ideas related with the Science
that LLAMA could accomplish on different astronomical topics, gathered from the
experience of a group of international experts on each field.Comment: 11 pages, contributed paper to the workshop "Prospects for
low-frequency radio astronomy in South America", held in Buenos Aires, Nov
2022; to appear in the RevMexAA-S
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