arXiv subjects

Diego García Lambas

Publications and source records attributed to Diego García Lambas.

25 records · Page 2Linked to original sources

arXiv2014

AGN spiral galaxies in groups: effects of bars

We explore properties of barred active spiral galaxies in groups selected from the SDSS-DR7, with the aim of assessing the effects of bars on AGN and the role of the high density environment. We identified barred active galaxies that reside in groups from SDSS-DR7 group catalog. To provide a suitable quantification of the effects of bars, a reliable control sample of unbarred active galaxies in high density environments with similar redshift, magnitude, morphology, and bulge size distributions was constructed. We found that the fraction of barred AGN galaxies in groups (~ 38 %) is higher than those in the total barred AGN sample ( ~ 28 %), indicating that AGN spiral galaxies in groups are more likely to be barred than those in the field. We also found that barred AGN galaxies are more concentrated towards the group centers than the other unbarred AGN group members. In addition, barred AGN host galaxies show an excess of population dominated by red colors suggesting that bars produce an importanteffect on galaxy colors of AGN hosts. The host groups of the barred AGN exhibit a larger fraction of red colors than the host groups of the corresponding unbarred active galaxies. Color-magnitude relations of both host groups of AGN differ significantly: the host group colors of barred active galaxies display distributions spreading toward red populations, with respect to the host groups of the unbarred AGN objects. Barred active galaxies show an excess of nuclear activity compared to galaxies without bars. We found that barred active galaxies located farther from the group-center have stronger Lum[OIII]. Our findings suggest that the efficiency of bars to transport material towards the more central regions of the AGN galaxies in high density environments reveals an important dependence on the localization of objects within the group and on the host group colors.

astro-ph.GA↗

arXiv2013

Low X-Ray Luminosity Galaxy Clusters. II. Optical properties and morphological content at 0.18 < z < 0.70

This is the second of a series of papers on low X-ray luminosity galaxy clusters, in which we present the $r^\prime$, $g^\prime$ and $i^\prime$ photometry obtained with GMOS-IMAGE at Gemini North and South telescopes for seven systems in the redshift range of 0.18 to 0.70. Optical magnitudes, colours and morphological parameters, namely, concentration index, ellipticity and visual morphological classification, are also given. At lower redshifts, the presence of a well-defined red cluster sequence extending by more than 4 magnitudes showed that these intermediate-mass clusters had reached a relaxed stage. This was confirmed by the small fraction of blue galaxy members observed in the central regions of $\sim$ 0.75 Mpc. In contrast, galaxy clusters at higher redshifts had a less important red cluster sequence. We also found that the galaxy radial density profiles in these clusters were well fitted by a single power law. At 0.18 $<$ z $<$ 0.70, we observed an increasing fraction of blue galaxies and a decreasing fraction of lenticulars, with the early-type fraction remaining almost constant. Overall, the results of these intermediate-mass clusters are in agreement with those for high mass clusters.

astro-ph.CO↗

arXiv2013

Clues on void evolution II: Measuring density and velocity profiles on SDSS galaxy redshift space distortions

Using the redshift-space distortions of void-galaxy cross-correlation function we analyse the dynamics of voids embedded in different environments. We compute the void-galaxy cross-correlation function in the Sloan Digital Sky Survey (SDSS) in terms of distances taken along the line of sight and projected into the sky. We analyse the distortions on the cross-correlation isodensity levels and we find anisotropic isocontours consistent with expansion for large voids with smoothly rising density profiles and collapse for small voids with overdense shells surrounding them. Based on the linear approach of gravitational collapse theory we developed a parametric model of the void-galaxy redshift space cross-correlation function. We show that this model can be used to successfully recover the underlying velocity and density profiles of voids from redshift space samples. By applying this technique to real data, we confirm the twofold nature of void dynamics: large voids typically are in an expansion phase whereas small voids tend to be surrounded by overdense and collapsing regions. These results are obtained from the SDSS spectroscopic galaxy catalogue and also from semi-analytic mock galaxy catalogues, thus supporting the viability of the standard LCDM model to reproduce large scale structure and dynamics.

astro-ph.CO↗

arXiv2012

An improved method for the identification of galaxy systems: Measuring the gravitational redshift by Dark Matter Haloes

We introduce a new method for the identification of galaxy systems in redshift surveys based on the halo model. This method is a modified version of the K-means identification algorithm developed by Yang et al (2005). We have calibrated and tested our algorithms using mock catalogs generated using the Millennium simulations (Springel et al. 2005) and applied them to the NYU-DR7 galaxy catalog (based on the SDSS datasets). Using this local sample of groups and clusters of galaxies we have measured the effect of gravitational redshift produced by their host dark matter haloes. Our results shows radial velocity decrements consistent with general relativity predictions and previous measurements by Wojtak et al (2011) in clusters of galaxies.

astro-ph.CO↗

arXiv2012

European Extremely Large Telescope Site Characterization II: High angular resolution parameters

This is the second article of a series devoted to European Extremely Large Telescope (E-ELT) site characterization. In this article we present the main properties of the parameters involved in high angular resolution observations from the data collected in the site testing campaign of the E-ELT during the Design Study (DS) phase. Observations were made in 2008 and 2009, in the four sites selected to shelter the future E-ELT (characterized under the ELT-DS contract): Aklim mountain in Morocco, Observatorio del Roque de los Muchachos (ORM) in Spain, Macón range in Argentina, and Cerro Ventarrones in Chile. The same techniques, instruments and acquisition procedures were taken on each site. A Multiple Aperture Scintillation Sensor (MASS) and a Differential Image Motion Monitor (DIMM) were installed at each site. Global statistics of the integrated seeing, the free atmosphere seeing, the boundary layer seeing and the isoplanatic angle were studied for each site, and the results are presented here. In order to estimate other important parameters such as the coherence time of the wavefront and the overall parameter "coherence étendue" additional information of vertical profiles of the wind speed was needed. Data were retrieved from the National Oceanic and Atmospheric Administration (NOAA) archive. Ground wind speed was measured by Automatic Weather Stations (AWS). More aspects of the turbulence parameters such as their seasonal trend, their nightly evolution and their temporal stability were also obtained and analyzed.

astro-ph.IM↗

arXiv2011

Galaxy triplets in SDSS-DR7: I. Catalogue

We present a new catalogue of galaxy triplets derived from the Sloan Digital Sky Survey Data Release 7. The identification of systems was performed considering galaxies brighter than M_r=-20.5 and imposing constraints over the projected distances, radial velocity differences of neighbouring galaxies and isolation. To improve the identification of triplets we employed a data pixelization scheme, which allows to handle large amounts of data as in the SDSS photometric survey. Using spectroscopic and photometric data in the redshift range 0.01<z<0.40 we obtain 5901 triplet candidates. We have used a mock catalogue to analyse the completeness and contamination of our methods. The results show a high level of completeness (~80%) and low contamination (~5%). By using photometric and spectroscopic data we have also addressed the effects of fiber collisions in the spectroscopic sample. We have defined an isolation criterion considering the distance of the triplet brightest galaxy to closest neighbour cluster, to describe a global environment, as well as the galaxies within a fixed aperture, around the triplet brightest galaxy, to measure the local environment. The final catalogue comprises 1092 isolated triplets of galaxies in the redshift range 0.01<z<0.40. Our results show that photometric redshifts provide very useful information, allowing to complete the sample of nearby systems whose detection is affected by fiber collisions, as well as extending the detection of triplets to large distances, where spectroscopic redshifts are not available.

astro-ph.CO↗

arXiv2010

Photometric redshifts and K-corrections for Sloan Digital Sky Survey Seven Data Release

We present a catalogue of galaxy photometric redshifts and k-corrections for the Sloan Digital Sky Survey Seven Data Release (SDSS-DR7), available on the World Wide Web. The photometric redshifts were estimated with an artificial neural network using five ugriz bands, concentration indices and Petrosian radii in the g and r bands. We have explored our redshift estimates with different training set concluding that the best choice to improve redshift accuracy comprises the Main Galaxies Sample (MGS), the Luminous Red Galaxies, and galaxies of active galactic nuclei covering the redshift range 0<z<0.3. For the MGS, the photometric redshift estimates agree with the spectroscopic values within rms=0.0227. The derived distribution of photometric redshifts in the range 0<zphot<0.6 agrees well with the model predictions. k-corrections were derived by calibration of the k-correct-v4.2 code results for the MGS with the reference frame (z=0.1) (g-r) colours. We adopt a linear dependence of k corrections on redshift and (g-r) colours that provide suitable distributions of luminosity and colours for galaxies up to redshift zphot=0.6 comparable to the results in the literature. Thus, our k-correction estimate procedure is a powerful, low computational time algorithm capable of reproducing suitable results that can be used for testing galaxy properties at intermediate redshifts using the large SDSS database.

astro-ph.CO↗