13 research outputs found
The brightest group galaxies and their large-scale environment
We use a sample of galaxy groups in SDSS data to study their brightestgalaxies (BGG), separating groups according to their large scale environment. The statistical properties of the BGG depend on the surrounding environment on large scales, characterized by the high density peaks within Future Virialized Structures (FVS). We also find that the luminosity, colour, stellar masses and concentration index of the BGG hosted by groups in superstructures are different, with statistical significance, from the corresponding properties of BGG hosted by groups elsewhere. Moreover, this signal is strongly dominated by disk-type galaxies.The results reveal connections between the large scale environment and the accretion process onto the brightest group galaxies.Estudiamos las galaxias más luminosas (del inglés Brightest Group Galaxy, BGG) de una muestra de grupos de galaxias en el SDSS, discriminando submuestras de grupos según su estructura circundante en gran escala. Encontramos que las propiedades de las BGG dependen del ambiente en gran escala, caracterizado por su pertenencia a los picos de densidad dentro de estructuras virializadas en el futuro (del inglés Future Virialized Structures, FVS). Los valores de luminosidad, índice de color, masa estelar e índice de concentración de las BGG alojadas en grupos en FVS difieren con significancia estadística de aquellas que no se encuentran en superestructuras. Esta señal está dominada por galaxias tipo disco. Estos resultados revelan conexiones entre la estructura en gran escala y los procesos de aglomeración de masa en grupos de galaxias.http://adsabs.harvard.edu/abs/2015BAAA...57...67LpublishedVersionFil: Luparello, Heliana E. Conicet. Instituto de Astronomía Teórica y Experimental; Argentina.Fil: Lares Harbin Latorre, Marcelo. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina.Fil: Luparello, Heliana E. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina.Fil: Lares Harbin Latorre, Marcelo. Conicet. Instituto de Astronomía Teórica y Experimental; Argentina.Fil: Paz, Dante Javier. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina.Fil: Paz, Dante Javier. Conicet. Instituto de Astronomía Teórica y Experimental; Argentina.Fil: Yaryura, Claudia Yamila. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina.Fil: Yaryura, Claudia Yamila. Conicet. Instituto de Astronomía Teórica y Experimental; Argentina.Fil: Lambas, Diego García. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina.Fil: Lambas, Diego García. Conicet. Instituto de Astronomía Teórica y Experimental; Argentina.Astronomía (incluye Astrofísica y Ciencias del Espacio
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 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
Environmental effects on associations of dwarf galaxies
We study the properties of associations of dwarf galaxies and their
dependence on the environment. Associations of dwarf galaxies are extended
systems composed exclusively of dwarf galaxies, considering as dwarf galaxies
those galaxies less massive than . We identify these particular systems using a
semi-analytical model of galaxy formation coupled to a dark matter only
simulation in the Cold Dark Matter cosmological model. To classify
the environment, we estimate eigenvalues from the tidal field of the dark
matter particle distribution of the simulation. We find that the majority, two
thirds, of associations are located in filaments ( per cent),
followed by walls ( per cent), while only a small fraction of them
are in knots ( per cent) and voids ( per cent).
Associations located in more dense environments present significantly higher
velocity dispersion than those located in less dense environments, evidencing
that the environment plays a fundamental role in their dynamical properties.
However, this connection between velocity dispersion and the environment
depends exclusively on whether the systems are gravitational bound or unbound,
given that it disappears when we consider associations of dwarf galaxies that
are gravitationally bound. Although less than a dozen observationally detected
associations of dwarf galaxies are currently known, our results are predictions
on the eve of forthcoming large surveys of galaxies, which will enable these
very particular systems to be identified and studied.Comment: 13 pages, 9 figures. Accepted for publication in MNRA
Associations of dwarf galaxies in a λCDM Universe
Associations of dwarf galaxies are loose systems composed exclusively of dwarf galaxies. These systems were identified in the Local Volume for the first time more than 30 yr ago. We study these systems in the cosmological framework of the λ cold dark matter (λCDM) model.We consider the Small MultiDark Planck simulation and populate its dark matter haloes by applying the semi-analytic model of galaxy formation SAG. We identify galaxy systems using a friends-of-friends algorithm with a linking length equal to b = 0.4Mpc h-1to reproduce the size of dwarf galaxy associations detected in the Local Volume. Our samples of dwarf systems are built up removing those systems that have one or more galaxies with stellar mass larger than a maximum thresholdMmax.We analyse three different samples defined by log10(Mmax[M⊙ h-1]) = 8.5, 9.0, and 9.5. On average, our systems have typical sizes of ∼ 0.2Mpc h-1, velocity dispersion of ∼ 30km s-1, and estimated total mass of ∼ 1011M⊙ h-1. Such large typical sizes suggest that individual members of a given dwarf association reside in different dark matter haloes and are generally not substructures of any other halo. Indeed, in more than 90 per cent of our dwarf systems their individual members inhabit different dark matter haloes, while only in the remaining 10 per cent members do reside in the same halo. Our results indicate that the λCDM model can naturally reproduce the existence and properties of dwarf galaxies' associations without much difficulty.Fil: Yaryura, Claudia Yamila. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Abadi, Mario Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Gottlöber, Stefan. Leibniz Universitat Hannover; AlemaniaFil: Libeskind, Noam I.. Leibniz Universitat Hannover; AlemaniaFil: Cora, Sofia Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Ruiz, Andrés Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentina. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; ArgentinaFil: Vega Martínez, Cristian Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad de La Serena; ChileFil: Yepes, Gustavo. Universidad Autónoma de Madrid; EspañaFil: Behroozi, Peter. George Mason University. School Of Physics. Astronomy And Computational Sciences; Estados Unido
Extreme value statistics of smooth random Gaussian fields
We consider the Gumbel or extreme value statistics describing the
distribution function p_G(x_max) of the maximum values of a random field x
within patches of fixed size. We present, for smooth Gaussian random fields in
two and three dimensions, an analytical estimate of p_G which is expected to
hold in a regime where local maxima of the field are moderately high and weakly
clustered. When the patch size becomes sufficiently large, the negative of the
logarithm of the cumulative extreme value distribution is simply equal to the
average of the Euler Characteristic of the field in the excursion x > x_max
inside the patches. The Gumbel statistics therefore represents an interesting
alternative probe of the genus as a test of non Gaussianity, e.g. in cosmic
microwave background temperature maps or in three-dimensional galaxy catalogs.
It can be approximated, except in the remote positive tail, by a negative
Weibull type form, converging slowly to the expected Gumbel type form for
infinitely large patch size. Convergence is facilitated when large scale
correlations are weaker. We compare the analytic predictions to numerical
experiments for the case of a scale-free Gaussian field in two dimensions,
achieving impressive agreement between approximate theory and measurements. We
also discuss the generalization of our formalism to non-Gaussian fields.Comment: 10 pages, 2 figures, accepted for publication in MNRA
Associations of dwarf galaxies in a ΛCDM Universe
Associations of dwarf galaxies are loose systems composed exclusively of dwarf galaxies. These systems were identified in the Local Volume for the first time more than 30 yr ago. We study these systems in the cosmological framework of the Λ cold dark matter (ΛCDM) model. We consider the Small MultiDark Planck simulation and populate its dark matter haloes by applying the semi-analytic model of galaxy formation SAG. We identify galaxy systems using a friends-of-friends algorithm with a linking length equal to b=0.4Mpch−1 to reproduce the size of dwarf galaxy associations detected in the Local Volume. Our samples of dwarf systems are built up removing those systems that have one or more galaxies with stellar mass larger than a maximum threshold Mmax. We analyse three different samples defined by log10(Mmax[M⊙h−1])=8.5,9.0, and 9.5. On average, our systems have typical sizes of ∼0.2Mpch−1, velocity dispersion of ∼30kms−1, and estimated total mass of ∼1011M⊙h−1. Such large typical sizes suggest that individual members of a given dwarf association reside in different dark matter haloes and are generally not substructures of any other halo. Indeed, in more than 90 per cent of our dwarf systems their individual members inhabit different dark matter haloes, while only in the remaining 10 per cent members do reside in the same halo. Our results indicate that the ΛCDM model can naturally reproduce the existence and properties of dwarf galaxies’ associations without much difficulty.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica
The Sloan Great Wall. Morphology and galaxy content
We present the results of the study of the morphology and galaxy content of
the Sloan Great Wall (SGW). We use the luminosity density field to determine
superclusters in the SGW, and the fourth Minkowski functional V_3 and the
morphological signature (the K_1-K_2 shapefinders curve) to show the different
morphologies of the SGW, from a single filament to a multibranching, clumpy
planar system. The richest supercluster in the SGW, SCl~126 and especially its
core resemble a very rich filament, while another rich supercluster in the SGW,
SCl~111, resembles a "multispider" - an assembly of high density regions
connected by chains of galaxies. Using Minkowski functionals we study the
substructure of individual galaxy populations determined by their color in
these superclusters. We assess the statistical significance of the results with
the halo model and smoothed bootstrap. We study the galaxy content and the
properties of groups of galaxies in two richest superclusters of the SGW,
paying special attention to bright red galaxies (BRGs) and to the first ranked
galaxies in SGW groups. About 1/3 of BRGs are spirals. The scatter of colors of
elliptical BRGs is smaller than that of spiral BRGs. About half of BRGs and of
first ranked galaxies in groups have large peculiar velocities. Groups with
elliptical BRGs as their first ranked galaxies populate superclusters more
uniformly than the groups, which have a spiral BRG as its first ranked galaxy.
The galaxy and group content of the core of the supercluster SCl~126 shows
several differences in comparison with the outskirts of this supercluster and
with the supercluster SCl~111. Our results suggest that the formation history
and evolution of individual neighbour superclusters in the SGW has been
different.Comment: Comments: 26 pages, 20 figures, accepted for publication in Ap
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 Cold Dark Matter 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 fewer 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.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat
Análisis estadísticos de superestructuras en el Universo /
Tesis (Doctor en Astronomía)--Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física, 2011.En esta tesis se presenta un nuevo método para determinar la probabilidad de encontrar eventos extremos en la distribución de materia oscura fría. En nuestra aproximación usamos un conjunto de simulaciones de N-Cuerpos para encontrar estructuras extremas, concluyendo que la frecuencia de estos eventos es bien descripta por la distribución de Gumbel. Esto permite enfrentar la dificultad de la falta de muestras estadísticamente confiables de estos eventos, anticipando la probabilidad de encontrarlos en una dada distribución, sin la necesidad de hacer suposiciones sobre la forma detallada de la distribución subyacente. La aplicación de dicha técnica a los supercúmulos de galaxias permite analizar la validez del modelo ΛCDM.
En este trabajo también se llevó a cabo un estudio detallado sobre la dependencia del clustering de las galaxias con las superestructuras. La comparación de dicho clustering de
galaxias, diferenciando entre las galaxias situadas dentro y fuera de superestructuras, brinda valiosa información sobre la evolución conjunta de las estructuras más masivas presentes
actualmente en el Universo y las galaxias. Mediante este análisis, se encuentra que la estructura interna de los grupos y cúmulos es un indicador sensible de las diferentes historias de
agregación jerárquica dentro y fuera de superestructuras