Omar Lopez-Cruz

THE BRIGHTEST CLUSTER GALAXY IN A85: THE LARGEST CORE KNOWN SO FAR

We have found that the brightest cluster galaxy (BCG) in Abell 85, Holm 15A, displays the largest core so far known. Its cusp radius, r = 4.57 ± 0.06 kpc (4. ′′ 26±0.

Molecular gas and dust in the highly magnified z ~ 2.8 galaxy behind the Bullet Cluster

Context. The gravitational magnification provided by massive galaxy clusters makes it possible to probe the physical conditions in distant galaxies that are of lower luminosity than those in blank fields and likely more representative of the bulk of the high-redshift galaxy population. Aims. We aim to constrain the basic properties of molecular gas in a strongly magnified submm galaxy located behind the massive Bullet Cluster (1E 0657-56). This galaxy (SMM J0658) is split into three images, with a total magnification factor of almost 100. Methods. We used the Australia Telescope Compact Array (ATCA) to search for 12 CO(1–0) and 12 CO(3–2) line emission from SMM J0658. We also used the SABOCA bolometer camera on the Atacama Pathfinder EXperiment (APEX) telescope to measure the continuum emission at 350 μm. Results. CO(1–0) and CO(3–2) are detected at 6.8σ and 7.5σ significance when the spectra toward the two brightest images of the galaxy are combined. From the CO(1–0) luminosity we derive a mass of cold molecular gas of (1.8 ± 0.3) × 10 9 M� ,u sing the CO to H2 conversion factor commonly used for luminous infrared galaxies. This is 45 ± 25% of the stellar mass. From the width of the CO lines we derive a dynamical mass within the CO-emitting region L of (1.3 ± 0.4) × 10 10 (L/1 kpc) M� .W e ref ine the redshift determination of SMM J0658 to z = 2.7793 ± 0.0003. The CO(3–2) to CO(1–0) brightness temperature ratio is 0.56 +0.21 −0.15 ,w hich is similar to the values found in other star-forming galaxies. Continuum emission at 350 μm from SMM J0658 was detected with SABOCA at a signal-to-noise ratio of 3.6. The flux density is consistent with previous measurements at the same wavelength by the Herschel satellite and BLAST balloon-borne telescope. We study the spectral energy distribution of SMM J0658 and derive a dust temperature of 33 ± 5 K and a dust mass of 1.1 +0.8 −0.3 × 10 7 M � . Conclusions. SMM J0658 is one of the least massive submm galaxies discovered so far. As a likely representative of the bulk of the submm galaxy population, it is a prime target for future observations.

Improving neural-based classification of databases with overlapped classes: The case of star/galaxy segregation

There are many real-life classification problems where class overlapping severely limits the classification accuracy. In these situations is difficult to build automatic classifiers that obtain good generalization performance. An interesting case is found in the separation of stars and galaxies, which arises in galactic or extragalactic studies. There are many astronomical analysis packages which deal with this problem; for example, the very popular package SExtractor (Source Extractor) has incorporated a multi-layer perceptron (MLP) neural network classifier. We believe that SExtractor performance is suitable for improvement. In our way for building a better classifier, we analyzed the behavior of MLP-based classifiers for this kind of data. In this paper we present an experiment where, using WEKA, we have automatically selected the best characteristics to discriminate galaxies from stars and automatically selected the topology of a MLP that best defined the decision region. Our classifier obtained slightly better results than SExtractor when compared to classifications obtained by a human expert, using less computational resources that SExtractor. However, we conclude that more specific information about the problem needs to be used to build a better separator of star/galaxies.

Cluster Galaxy Morphologies: The Relationship among Structural Parameters, Activity and the Environment

We propose a new approach to estimate galaxy morphologies using a two‐dimensional approach based on an ellipticity (e) vs. Bulge‐to‐Total ratio (B/T) plane. We have calibrated this plane by comparing with Dressler’s classifications [5]. With the aid of our calibration, we have classified 635 galaxies in 18 Abell clusters (0.02<z<0.08). Our approach allowed us to recover the Kormendy relation [7]. We found that ellipticals and Spirals are slightly brighter than S0 in R band. As S0 bulges are brighter than spirals bulges, we believe that ram pressure is not the main mechanism to generate S0s. In our sample, cluster radio galaxy morphologies cover the range S0‐E‐cD and their bulges have absolutes magnitudes distributed within −21 mag<MR<−24.5 mag. If we believe Ferrarese & Merrit’s relation [6], these radio sources have 108–109 M⊙ black holes.