arXiv subjects

Laerte Sodré Jr.

Publications and source records attributed to Laerte Sodré Jr..

40 records · Page 3Linked to original sources

arXiv2007

Bayesian analysis of joint strong gravitational lensing and dynamic galactic mass in SLACS: evidence of line-of-sight contamination

We readdress the calculation of the mass of early-type galaxies using strong gravitational lensing and stellar dynamics. Our sample comprises 27 galaxies in the Sloan Lens ACS (SLACS) Survey. Comparing the mass estimates from these two independent methods in a Bayesian framework, we find evidence of significant line-of-sight mass contamination. Assuming a power-law mass distribution, the best fit density profile is given by $ρ\propto r^{-1.69\pm0.05}$. We show that neglecting the line-of-sight mass contamination produces an overestimate of the mass attributed to the lens-galaxy by the lensing method, which introduces a bias in favor of a SIS profile when using the joint lensing and dynamic analysis to determine the slope of the density profile. We suggest that the line-of-sight contamination could also be important for other astrophysical and cosmological uses of joint lensing and dynamical measurements.

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arXiv2006

Shrinking of Cluster Ellipticals: a Tidal Stripping explanation and Implications for the Intra-Cluster Light

We look for evidence of tidal stripping in elliptical galaxies through the analysis of homogeneous CCD data corresponding to a sample of 228 elliptical galaxies belonging to 24 clusters of galaxies at $0.015<z<0.080$. We investigate departures from the standard magnitude-isophotal size relation, as a function of environmental (cluster-centric distance, local galaxy density) and structural (cluster velocity dispersion, Bautz-Morgan type) properties. We find that, for any particular galaxy luminosity, the ellipticals in the inner and denser regions of the clusters are about 5% smaller than those in the outer regions, which is in good agreement with the finding of Strom & Strom (1978) based on photographic photometry. The null hypothesis (ie., galaxy sizes are independent of the cluster-centric distance or density) is rejected at a significance level of better than 99.7%. Numericals models of Aguilar & White (1986) predict that tidal stripping can lead to changes in the whole structure of ellipticals producing shrinkage and brightening of the galaxy, qualitatively consistent with our measurements and also with the findings of Trujillo et al. (2002), that more centrally concentrated ellipticals populate denser regions. Our observational results can be interpreted as evidence for stripping of stars from ellipticals in the central/denser regions of clusters, contributing to the intra-cluster light observed in these structures.

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arXiv2003

Weak lensing mass distributions for 24 X-Ray Abell Clusters

We use the weak gravitational lensing effect to study the mass distribution and dynamical state of a sample of 24 X-ray luminous clusters of galaxies ($0.05<z<0.31$) observed with the VLT-FORS1 under homogeneous sky conditions and subarsecond image quality. The galaxy shapes were measured after deconvolution with a locally determined point-spread-function, while the two-dimensional mass distributions of the clusters were computed using an algorithm based on the maximum entropy method. By comparing the mass and light distributions of the clusters in our sample, we find that their mass centers, for the majority of the clusters, is consistent with the positions of optical centers. We find that some clusters present significant mass substructures which generally have optical counterparts. At least in one cluster (Abell 1451), we detect a mass substructure without an obvious luminous counterpart. The radial profile of the shear of the clusters was fitted using circular and elliptical isothermal elliptical distributions, which allowed the finding of a strong correlation between the orientation of the major-axis of the matter distribution and the corresponding major-axes of the brightest cluster galaxy light-profiles. Estimates of how close to dynamical relaxation are these clusters were obtained through comparison of our weak-lensing mass measurements with the x-ray and velocity dispersion determinations available in the literature. We find that clusters with intra-cluster gas colder than 8 keV show a good agreement between the different mass determinations, but clusters with gas hotter than 8 keV present discrepant mass values.

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arXiv1996

Regularities in galaxy spectra and the nature of the Hubble sequence

We have investigated some statistical properties of integrated spectra of galaxies with principal component analysis. The projection of the spectra onto the plane defined by the first two principal components shows that normal galaxies are in a quasi-linear sequence that we call spectral sequence and is closely related to the Hubble morphological sequence. We verify that the spectral sequence is also an evolutive sequence, with galaxy spectra evolving from later to earlier spectral types. Considering the close correspondence between the spectral and morphological sequences, we speculate that galaxies may evolve morphologically along the Hubble sequence, from Sm/Im to E. If this is the case, the first galaxies were mainly gas rich irregular objects, which evolved later along the morphological sequence as long as mergers and interactions increased their masses and developed their spheroidal components.

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