90 research outputs found
The fraction of BL Lac objects in groups of galaxies
Context: BL Lac objects are a rare class of active galactic nuclei that
typically show featureless optical spectra that make it difficult to estimate
the redshift. A novel method for estimating the redshift of BL Lac objects has
recently been proposed which assumes that these objects typically reside in
groups of galaxies.
Aims: The aim of this work is to estimate the fraction of BL Lac objects that
reside in groups of galaxies.
Methods: We use a sample of groups (M12 catalogue) selected by applying a
friends-of-friends algorithm in the SDSS DR12. Galaxies in the M12 sample were
cross-correlated with the sample of blazars in the BZCAT.
Results: We found that 121 galaxies in the M12 catalogue are blazars in the
BZCAT sample, all but one are BL Lac objects, and a large fraction are
classified as BL Lac-galaxy dominated. Analysing the fraction of galaxies in
groups as a function of redshift we have estimated a correction factor that
takes into account the typical incompleteness of the catalogues based on the
friends-of-friends algorithm. Once this factor was applied to the sample of BL
Lac objects with a counterpart in the M12 catalogue, we found that the
percentage of BL Lac objects in groups is .
Conclusions: The high rate of BL Lac objects in groups found in this work
strongly supports a recent method that has successfully estimated the redshift
of BL Lac objects with featureless spectra.Comment: Accepted for publication in Astronomy and Astrophysics (Letter
Comparing galaxy populations in compact and loose groups of galaxies II: brightest group galaxies
The properties of the brightest galaxies (BCGs) are studied in both compact
and loose groups of galaxies in order to better understand the physical
mechanisms influencing galaxy evolution in different environments. Samples of
BCGs are selected in the compact groups identified by McConnachie et al.
(2009), and in loose groups taken from Zandivarez & Mart\'inez (2011). The
following physical properties of the BCGs in compact groups and in subsamples
of loose groups are compared, defined by their mass and total luminosity. The
fraction of BCGs classified as red and/or early-type as a function of galaxy
luminosity are studied. The fraction of the group's total luminosity contained
in the BCG and the difference in luminosity between the BCG and the
second-ranked galaxy, are also analysed. Some properties of BCGs in compact and
loose groups are comparable. However, BCGs in compact groups are systematically
more concentrated and have larger surface brightness than their counterparts in
both, high- and low-mass loose groups. The fractions of red and early-type BCGs
in compact groups are consistent with those of high-mass loose groups.
Comparing BCGs in subsamples of compact and loose groups selected for their
similar luminosities, BCGs in compact groups are found to be, on average,
brighter, more massive, larger, redder and more frequently classified as
elliptical. In compact groups, the BCG contains a larger fraction of the
system's total luminosity and differs more in absolute magnitude from the
second-ranked galaxy. BCGs in compact and loose groups are found to be
different. Some mechanisms responsible for transforming late-type galaxies into
early types, such as mergers, may be more effective within compact groups due
to their high densities and small velocity dispersion, which would lead their
BCGs along somewhat different evolutionary paths.Comment: Accepted for publication in Astronomy & Astrophysics (A&A
Tidal stripping of globular clusters in a simulated galaxy cluster
Using a cosmological N-body numerical simulation of the formation of a galaxy
cluster- sized halo, we analyze the temporal evolution of its globular cluster
population. We follow the dynamical evolution of 38 galactic dark matter halos
orbiting in a galaxy cluster that at redshift z=0 has a virial mass of 1.71 *
10 ^14 Msol h^-1. In order to mimic both "blue" and "red" populations of
globular clusters, for each galactic halo we select two different sets of
particles at high redshift (z ~ 1), constrained by the condition that, at
redshift z=0, their average radial density profiles are similar to the observed
profiles. As expected, the general galaxy cluster tidal field removes a
significant fraction of the globular cluster populations to feed the
intracluster population. On average, halos lost approximately 16% and 29% of
their initial red and blue globular cluster populations, respectively. Our
results suggest that these fractions strongly depend on the orbital trajectory
of the galactic halo, specifically on the number of orbits and on the minimum
pericentric distance to the galaxy cluster center that the halo has had. At a
given time, these fractions also depend on the current clustercentric distance,
just as observations show that the specific frequencyof globular clusters S_N
depends on their clustercentric distance.Comment: 11 pages, 8 figures. Accepted for publication in Ap
Backsplash Galaxies
Abstract. We explore the properties of galaxies on the outskirts of clusters and their dependence on recent dynamical history in order to understand the real impact that the cluster core has on the evolution of galaxies.publishedVersionFil: Muriel, Hernán. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina.Fil: Muriel, Hernán. Conicet, Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Argentina.Fil: Coenda, Valeria. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina.Fil: Coenda, Valeria. Conicet, Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Argentina.Astronomía (incluye Astrofísica y Ciencias del Espacio
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.Comment: Accepted for Publication in MNRAS Letters, 2 figures. arXiv admin
note: text overlap with arXiv:astro-ph/0405234, arXiv:astro-ph/0406593 by
other author
Comparing galaxy populations in compact and loose groups of galaxies
Abstract.We compare the properties of galaxies in compact groups, loose groups, and the eld to deepen our understanding of the physical mechanisms acting upon galaxy evolution in dierent environments. This contribution is detailed in Coenda et al. (2012) and Martínez et al. (2013).Fil: Martínez, Héctor Julián Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; ArgentinaFil: Martínez, Héctor Julián Conicet. Instituto de Astronomía Teórica y Experimental; Argentina.Fil: Coenda, Valeria Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina.Fil:Coenda, Valeria Conicet. Instituto de Astronomía Teórica y Experimental; Argentina.Fil: Muriel, Hernán Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina.Fil: Muriel, Hernán Conicet. Instituto de Astronomía Teórica y Experimental; Argentina.http://adsabs.harvard.edu/abs/2014RMxAC..44...81MpublishedVersionAstronomía (incluye Astrofísica y Ciencias del Espacio
- …