Galaxy Morphological Segregation in Clusters: Local vs. Global Conditions

We study the relative fraction of galaxy morphological types in clusters, as a function of the projected local galaxy density and different global parameters: cluster projected gas density, cluster projected total mass density , and reduced clustercentric distance. Since local and global densities are correlated, we have considered different tests to search for the parameters to which segregation show the strongest dependence. Also, we have explored the results of our analysis applied to the central regions of the clusters and their outskirts. We consider a sample of clusters of galaxies with temperature estimates to derive the projected mass density profile and the 500 density contrast radius ($r_{500}$) using the NFW model and the scaling relation respectively. The X-ray surface brightness profiles are used to obtain the projected gas density assuming the hydrostatic equilibrium model. Our results suggest that the morphological segregation in clusters is controlled by the local galaxy density in the outskirts. On the other hand, the global projected mass density, shows the strongest correlation with the fraction of morphological types in the central high density region, with a marginal dependence on the local galaxy density.Comment: 10 pages, 8 figures, Accepted AJ (February 2001 issue

Low X-ray Luminosity Galaxy Clusters. III: Weak Lensing Mass Determination at 0.18 << z << 0.70

This is the third of a series of papers of low X-ray luminosity galaxy clusters. In this work we present the weak lensing analysis of eight clusters, based on observations obtained with the Gemini Multi-Object Spectrograph in the $g'$, $r'$ and $i'$ passbands. For this purpose, we have developed a pipeline for the lensing analysis of ground-based images and we have performed tests applied to simulated data. We have determined the masses of seven galaxy clusters, six of them measured for the first time. For the four clusters with availably spectroscopic data, we find a general agreement between the velocity dispersions obtained via weak lensing assuming a Singular Isothermal Sphere profile, and those obtained from the redshift distribution of member galaxies. The correlation between our weak lensing mass determinations and the X-ray luminosities are suitably fitted by other observations of the $M-L_{X}$ relation and models

Calibration of semi-analytic models of galaxy formation using Particle Swarm Optimization

We present a fast and accurate method to select an optimal set of parameters in semi-analytic models of galaxy formation and evolution (SAMs). Our approach compares the results of a model against a set of observables applying a stochastic technique called Particle Swarm Optimization (PSO), a self-learning algorithm for localizing regions of maximum likelihood in multidimensional spaces that outperforms traditional sampling methods in terms of computational cost. We apply the PSO technique to the SAG semi-analytic model combined with merger trees extracted from a standard $\Lambda$CDM N-body simulation. The calibration is performed using a combination of observed galaxy properties as constraints, including the local stellar mass function and the black hole to bulge mass relation. We test the ability of the PSO algorithm to find the best set of free parameters of the model by comparing the results with those obtained using a MCMC exploration. Both methods find the same maximum likelihood region, however the PSO method requires one order of magnitude less evaluations. This new approach allows a fast estimation of the best-fitting parameter set in multidimensional spaces, providing a practical tool to test the consequences of including other astrophysical processes in SAMs.Comment: 11 pages, 4 figures, 1 table. Accepted for publication in ApJ. Comments are welcom

How accurate is it to update the cosmology of your halo catalogues?

We test and present the application of the full rescaling method by Angulo & White to change the cosmology of halo catalogues in numerical simulations for cosmological parameter search using semi-analytic galaxy properties. We show that a reduced form of the method can be applied to small simulations with box side of ~50h-1Mpc or smaller without loss of accuracy. We perform statistical tests on the accuracy of the properties of rescaled individual haloes, and also on the rescaled population as a whole. We find that individual positions and velocities are recovered with almost no detectable biases, but with a scatter that increases slightly with the size of the simulation box when using the full method. The dispersion in the recovered halo mass does not seem to depend on the resolution of the simulation. Regardless of the halo mass, the individual accretion histories, spin parameter evolution and fraction of mass in substructures are remarkably well recovered. In particular, in order to obtain a more accurate estimate of the halo virial mass, it was necessary to apply an additional correction due to the change in the virial overdensity and the estimate of its effect on a Navarro, Frenk & White (NFW) virial mass. The mass of rescaled haloes can be underestimated (overestimated) for negative (positive) variations of either σ8 or in a way that does not depend on the halo mass. Statistics of abundances and correlation functions of haloes also show small biases of <10 per cent when moving away from the base simulation by up to two times the uncertainty in the WMAP7 cosmological parameters. The merger tree properties related to the final galaxy population in haloes also show small biases; the time since the last major merger, the assembly time-scale, and a time-scale related to the stellar ages show correlated biases which indicate that the spectral shapes of galaxies would only be affected by global age changes of ~150Myr, i.e. relatively small shifts in their broad-band colours. We show some of these biases for different separations in the cosmological parameters with respect to the desired cosmology so that these can be used to estimate the expected accuracy of the resulting halo population. We also present a way to construct grids of simulations to provide a stable accuracy across the versus σ8 parameter space.Instituto de Astrofísica de La Plat

Simultaneous multi-frequency observation of the unknown redshift blazar PG1553+113 in March-April 2008

5 páginas, 2 figuras, 3 tablas.-- El Pdf del artículo es la versión pre-print: arXiv: arXiv:0911.1088.-- MAGIC Collaboration: et al.The blazar PG 1553+113 is a well known TeV γ-ray emitter. In this paper we determine its spectral energy distribution through simultaneous multi-frequency data to study its emission processes. An extensive campaign was carried out between March and April 2008, where optical, X-ray, high-energy (HE) γ-ray, and very-high-energy (VHE) γ-ray data were obtained with the KVA, Abastumani, REM, RossiXTE/ASM, AGILE and MAGIC telescopes, respectively. We combine the data to derive the source's spectral energy distribution and interpret its double-peaked shape within the framework of a synchrotron self-Compton model.Major support from Germany’s Bundesministerium f¨ur Bildung, Wissenschaft, Forschung und Technologie and Max-Planck-Gesellschaft, Italy’s Istituto Nazionale di Fisica Nucleare (INFN) and Istituto Nazionale di Astrofisica (INAF), and Spain’s Ministerio de Ciencia e Innovacion is gratefully acknowledged. The work was also supported by Switzerland’s ETH Research grant TH34/043, Poland’s Ministertwo Nauki i Szkolnictwa Wy˙zszego grant N N203 390834, and Germany’s Young Investigator Program of the Helmholtz Gemeinschaft. This work was also supported by Georgian National Science Foundation grant GNSF/ST07/4-180. EP acknowledges support from the Italian Space Agency through grants ASI-INAF I/023/05/0 and ASI I/088/06/0.Peer reviewe

How accurate is it to update the cosmology of your halo catalogues?

We test and present the application of the full rescaling method by Angulo & White (2010) to change the cosmology of halo catalogues in numerical simulations for cosmological parameter search using semi-analytic galaxy properties. We show that a reduced form of the method can be applied in small simulations with box side of ~50/h Mpc. We perform statistical tests on the accuracy of the properties of rescaled individual haloes, and also on the rescaled population as a whole. We find that individual positions and velocities are recovered with almost no detectable biases. The dispersion in the recovered halo mass does not seem to depend on the resolution of the simulation. Regardless of the halo mass, the individual accretion histories, spin parameter evolution and fraction of mass in substructures are well recovered. The mass of rescaled haloes can be underestimated (overestimated) for negative (positive) variations of either sigma_8 or Omega_m, in a way that does not depend on the halo mass. Statistics of abundances and correlation functions of haloes show also small biases of <10 percent when moving away from the base simulation by up to 2 times the uncertainty in the WMAP7 cosmological parameters. The merger tree properties related to the final galaxy population in haloes also show small biases; the time since the last major merger, the assembly time-scale, and a time-scale related to the stellar ages show correlated biases which indicate that the spectral shapes of galaxies would only be affected by global age changes of ~150 Myr. We show some of these biases for different separations in the cosmological parameters with respect to the desired cosmology so that these can be used to estimate the expected accuracy of the resulting halo population. We also present a way to construct grids of simulations to provide stable accuracy across the Omega_m vs sigma_8 parameter space.Comment: 14 pages, 2 tables, 10 figures. Accepted for publication in MNRA

MAGIC observation of the GRB 080430 afterglow

6 páginas, 1 figura.-- El Pdf del artículo es la versión pre-print: arXiv:1004.3665v2.-- MAGIC Collaboration: et al.[Context]: Gamma-ray bursts are cosmological sources emitting radiation from the gamma-rays to the radio band. Substantial observational efforts have been devoted to the study of gamma-ray bursts during the prompt phase, i.e. the initial burst of high-energy radiation, and during the long-lasting afterglows. In spite of many successes in interpreting these phenomena, there are still several open key questions about the fundamental emission processes, their energetics and the environment. [Aims]: Independently of specific gamma-ray burst theoretical recipes, spectra in the GeV/TeV range are predicted to be remarkably simple, being satisfactorily modeled with power-laws, and therefore offer a very valuable tool to probe the extragalactic background light distribution. Furthermore, the simple detection of a component at very-high energies, i.e. at ~100 GeV, would solve the ambiguity about the importance of various possible emission processes, which provide barely distinguishable scenarios at lower energies. [Methods]: We used the results of the MAGIC telescope observation of the moderate resdhift (z ~ 0.76) GRB 080430 at energies above about 80 GeV, to evaluate the perspective for late-afterglow observations with ground based GeV/TeV telescopes. [Results]: We obtained an upper limit of F95% CL = 5.5 × 10-11 erg cm-2 s-1 for the very-high energy emission of GRB 080430, which cannot set further constraints on the theoretical scenarios proposed for this object also due to the difficulties in modeling the low-energy afterglow. Nonetheless, our observations show that Cherenkov telescopes have already reached the required sensitivity to detect the GeV/TeV emission of GRBs at moderate redshift (z ≲ 0.8), provided the observations are carried out at early times, close to the onset of their afterglow phase.The support of the German BMBF and MPG, the Italian INFN and Spanish MICINN is gratefully acknowledged. This work was also supported by ETH Research Grant TH 34/043, by the Polish MNiSzW Grant N N203 390834, and by the YIP of the Helmholtz Gemeinschaft.Peer reviewe

An Indigenous Measure of Social Desirability Across Non-Western Countries

Cross-cultural differences in Social Desirability (SD) could be partly due to the nonequivalence of constructs, items, or other challenges of cross-cultural research. We tested to what extent a Mexican, indigenous scale of SD, capturing both positive and negative features of SD, would be useful in other countries. Data were collected in convenience samples in eight countries (Argentina, China, Colombia, Costa Rica, Lebanon, Mexico, Nicaragua, and Spain) in order to test the psychometric accuracy and invariance of the factor structure. Values of Tucker’s factor congruence coefficients (gauging invariance) and tests of the similarity of the cross-country similarity of Cronbach’s alpha (gauging internal consistency) revealed that SD, as measured by this indigenous list, is stable and comparable across cultures. The results are interpreted in a conceptual framework in which SD is viewed as a culturally embedded communication style that people use to integrate successfully into their groups

GW150914: First search for the electromagnetic counterpart of a gravitational-wave event by the TOROS collaboration

We present the results of the optical follow-up conducted by the TOROS collaboration of the first gravitational-wave event GW150914. We conducted unfiltered CCD observations (0.35-1 micron) with the 1.5-m telescope at Bosque Alegre starting ~2.5 days after the alarm. Given our limited field of view (~100 square arcmin), we targeted 14 nearby galaxies that were observable from the site and were located within the area of higher localization probability. We analyzed the observations using two independent implementations of difference-imaging algorithms, followed by a Random-Forest-based algorithm to discriminate between real and bogus transients. We did not find any bona fide transient event in the surveyed area down to a 5-sigma limiting magnitude of r=21.7 mag (AB). Our result is consistent with the LIGO detection of a binary black hole merger, for which no electromagnetic counterparts are expected, and with the expected rates of other astrophysical transients.Comment: ApJ Letters, in pres

The functioning of the Cuban home hospitalization programme: a descriptive analysis

BACKGROUND: Over the last decades hospital at home (HaH) programmes have been set up in many, mainly European, countries. The Cuban HaH programme is not hospital driven, but the responsibility of the first line health services, and family doctors play a pivotal role. METHODS: We analyse the structure and functioning of the Cuban programme. In this descriptive study, information was prospectively collected on HaH patients admitted between July 1st 2001 and June 30th 2002. RESULTS: Admission rates varied between areas from 0.014 to 0.035 per person per year (ppy). The < 1 y and 1-4 y age groups had the highest admission rates. In one area the follow-up of pregnancy problems led to high 15-24 y and 25-49 y female admission rates (0,070 and 0,058 respectively). Respiratory affections were the most frequent reason for admission (32,6%), followed by early hospital discharge (16,0%) and gynaeco-obstetrical problems (10.8%). The median length of stay varied from 5 to 7 days between regions and from 5 days (early discharge) to 7 days (gynaeco-obstetrical problems) in function of the reason for admission. On average an HaH episode entailed 1.4 and 1.6 contacts per patient-day with the family doctor and nurse respectively. CONCLUSION: Difference in admission criteria in function of geography, distance to the hospital, transport facilities, and staff factors, as well as differences in hospital policy on early discharge explain the observed variability. The programme plays an important role in the integrated approach to quality care in the Cuban health system, but could benefit from more uniform admission criteria