11,905 research outputs found
SPIDER X - Environmental effects in central and satellite early-type galaxies through the stellar fossil record
A detailed analysis of how environment affects the star formation history of
early-type galaxies (ETGs) is undertaken via high signal to noise ratio stacked
spectra obtained from a sample of 20,977 ETGs (morphologically selected) from
the SDSS-based SPIDER survey. Two major parameters are considered for the
study: the central velocity dispersion (sigma), which relates to local drivers
of star formation, and the mass of the host halo, which relates to
environment-related effects. In addition, we separate the sample between
centrals (the most massive galaxy in a halo) and satellites. We derive trends
of age, metallicity, and [alpha/Fe] enhancement, with sigma. We confirm that
the major driver of stellar population properties in ETGs is velocity
dispersion, with a second-order effect associated to the central/satellite
nature of the galaxy. No environmental dependence is detected for satellite
ETGs, except at low sigma - where satellites in groups or in the outskirts of
clusters tend to be younger than those in the central regions of clusters. In
contrast, the trends for centrals show a significant dependence on halo mass.
Central ETGs in groups (i.e. with a halo mass >10^12.5 M_Sun) have younger
ages, lower [alpha/Fe], and higher internal reddening, than "isolated" systems
(i.e. centrals residing in low-mass, <10^12.5 M_Sun, halos). Our findings imply
that central ETGs in groups formed their stellar component over longer time
scales than "isolated" centrals, mainly because of gas-rich interactions with
their companion galaxies.Comment: 22 pages, 19 figures, accepted for publication in MNRA
A Comparative Study of Some Markov Random Fields and Different Criteria Optimization in Image Restoration
The present chapter illustrates the use of some recent alternative methods to deal with digital image filtering and restoration. This collection of methods is inspired on the use of Markov Random Fields (MRF), which introduces prior knowledge of information that will allow, more efficiently, modeling the image acquisition process. The methods based on the MRF are analyzed and proposed into a Bayesian framework and their principal objective is to eliminate noise and some effects caused by excessive smoothness on the reconstruction process of images which are rich in contours or edges. In order to preserve object edges into the image, the use of certain convexity criteria into the MRF is proposed obtaining adequate weighting of cost functions in cases where discontinuities are remarked and, even better, for cases where such discontinuities are very smooth
Spatial interpolation techniques for near real-time mapping of Pressure and Temperature data
Among the different techniques for atmosphere monitoring, the GNSS (Global Navigation Satellite
System) can provide an innovative contribution (Bevis et al., 1992; Crespi et al., 2004; Sguerso et al.,
2013, 2015). The Laboratory of Geomatics, Geodesy and GIS of the University of Genoa has identified a
GIS procedure and a simplified physical model to monitor the Precipitable Water Vapour (PWV) content,
using data measured by existing infrastructures. The starting points are local estimations of Zenith Total
Delay (ZTD) from a GNSS Permanent Stations (PSs) network, a Digital Terrain Model (DTM) and local
Pressure (P) and Temperature (T) measurements (Sguerso et al., 2014; Ferrando et al., 2016). The
present paper shows the study of the most appropriate interpolation technique for P and T data to create
PWV maps in a quick, stable and automatic way, to support the monitoring of intense meteorological
events for both a posteriori and near real-time applications. The resulting P and T maps were compared
to meteorological re-analysis, to check the reliability of the simplified physical model. Additionally, the
Regression Kriging (RK) was employed to evaluate the data correlation with elevation and to study the
applicability of the technique
Alimentació, model estètic femenà i mitjans de comunicació entre els adolescents
La preocupació pel cos i l'estètica i els mals hà bits en l'alimentació comporten trastorns en la conducta alimentà ria cada cop més freqüents i persistensts en nens i adolescents. Investigadors de la UAB han dissenyat un original programa de prevenció de trastorns alimentaris a les escoles que combina una acció directa sobre els hà bits alimentaris dels adolescents -corregint falses creences sobre nutrició i alimentació, proporcionant coneixements sobre una alimentació equilibrada i promovent l'anà lisi participatiu dels menús- amb una alfabetització medià tica que els permeti generar una anà lisi crÃtica del model estètic imperant i dels anuncis publicitaris. El programa ha demostrat ser eficaç en prevenir tant l'aparició d'actituds alterades cap al menjar com en reduir la influència dels ideals estètics corporals en una mostra mixta d'adolescents escolaritzats.La preocupación por el cuerpo y la estética y los malos hábitos en la alimentación conllevan trastornos en la conducta alimentaria cada vez más frecuentes y persistentes en niños y adolescentes. Investigadores de la UAB han diseñado un original programa de prevención de trastornos alimentarios en las escuelas que combina una acción directa sobre los hábitos alimentarios de los adolescentes -corrigiendo falsas creencias sobre nutrición y alimentación, proporcionando conocimientos sobre una alimentación equilibrada y promoviendo el análisis participativo de los menús- con una alfabetización mediática que les permita generar un análisis crÃtico del modelo estético imperante y los anuncios publicitarios. El programa ha demostrado ser eficaz en prevenir tanto la aparición de actitudes alteradas hacia la comida como en reducir la influencia de los ideales estéticos corporales en una muestra mixta de adolescentes escolarizados
A Principal Component Analysis approach to the Star Formation History of elliptical galaxies in Compact Groups
(Abridged) Environmental differences in the stellar populations of early-type
galaxies are explored using principal component analysis (PCA), focusing on
differences between elliptical galaxies in Hickson Compact Groups (HCGs) and in
the field. The method is model-independent and relies on variations between the
observed spectra. The projections (PC1,PC2) reveal a difference with respect to
environment, with a wider range in PC1 and PC2 in the group sample. We define a
spectral parameter (zeta=0.36PC1-PC2) which simplifies this result to a single
number: field galaxies have a very similar value of zeta, whereas HCG galaxies
span a wide range in this parameter. We obtain a strong correlation between the
values of zeta and the mass fraction in younger stars, so that some group
galaxies present a higher fraction of them. PCA is more sensitive than other
methods based on a direct analysis of observables such as the structure of the
surface brightness profile or the equivalent width of absorption lines. The
latter do not reveal any significant variation between field and compact group
galaxies. Our results imply that the presence of young stars only amounts to a
fraction of a percent in its contribution to the total variance.Comment: 9 pages, 8 figures. Accepted for publication in MNRA
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