74 research outputs found
Algoritmo para la exploración de todos los valores posibles en el problema del agente viajero (TPS)
El siguiente artículo muestra algunas aplicaciones empleadas para probar soluciones acerca del problema del agente viajero y busca mostrar ejemplos de algoritmos desarrollados para este fin, en esta primera parte el de fuerza bruta y en la siguiente los basados en algoritmos heurísticos
Algoritmo para la exploración de todos los valores posibles en el problema del agente viajero (TPS)
El siguiente artículo muestra algunas aplicaciones empleadas para probar soluciones acerca del problema del agente viajero y busca mostrar ejemplos de algoritmos desarrollados para este fin, en esta primera parte el de fuerza bruta y en la siguiente los basados en algoritmos heurísticos
The Redshift Evolution of LCDM Halo Parameters: Concentration, Spin, and Shape
We present a detailed study of the redshift evolution of dark matter halo
structural parameters in a LambdaCDM cosmology. We study the mass and redshift
dependence of the concentration, shape and spin parameter in Nbody simulations
spanning masses from 10^{10} Msun/h to 10^{15} Msun/h and redshifts from 0 to
2. We present a series of fitting formulas that accurately describe the time
evolution of the concentration-mass relation since z=2. Using arguments based
on the spherical collapse model we study the behaviour of the scale length of
the density profile during the assembly history of haloes, obtaining physical
insights on the origin of the observed time evolution of the concentration mass
relation. We also investigate the evolution with redshift of dark matter halo
shape and its dependence on mass. Within the studied redshift range the
relation between halo shape and mass can be well fitted by a power law. Finally
we show that although for z=0 the spin parameter is practically mass
independent, at increasing redshift it shows a increasing correlation with
mass.Comment: 12 pages, 11 figures, accepted to MNRAS, minor changes to previous
versio
Weak lensing peak count as a probe of f(R) theories
Weak gravitational lensing by galaxy clusters on faint higher redshift
galaxies has been traditionally used to study the cluster mass distribution and
as a tool to identify clusters as peaks in the shear maps. However, it becomes
soon clear that peaks statistics can also be used as a way to constrain the
underlying cosmological model due to its dependence on both the cosmic
expansion rate and the growth rate of structures. This feature makes peak
statistics particularly interesting from the point of view of discriminating
between General Relativity and modified gravity. Here we consider a general
class of theories and compute the observable mass function based on the
aperture mass statistics. We complement our theoretical analysis with a Fisher
matrix forecast of the constraints that an Euclid\,-\,like survey can impose on
the model parameters. We show that peak statistics alone can in
principle discriminate between General Relativity and models and
strongly constrain the parameters that are sensitive to the non-linear
growth of structure. However, further analysis is needed in order to include
possible selection function in the peaks redshift determination.Comment: 17 pages, 9 figures, 1 table, accepted for publication on MNRAS on
Jan 14, 2013; updated to match the published versio
Properties of Dark Matter Haloes and their Correlations: the Lesson from Principal Component Analysis
We study the correlations between the structural parameters of dark matter
haloes using Principal Component Analysis (PCA). We consider a set of eight
parameters, six of which are commonly used to characterize dark matter halo
properties: mass, concentration, spin, shape, overdensity, and the angle
() between the major axis and the angular momentum vector. Two
additional parameters (\x_{off} and ) are used to describe the
degree of `relaxedness' of the halo. We find that we can account for much of
the variance of these properties with halo mass and concentration, on the one
hand, and halo relaxedness on the other. Nonetheless, three principle
components are usually required to account for most of the variance. We argue
that halo mass is not as dominant as expected, which is a challenge for halo
occupation models and semi-analytic models that assume that mass determines
other halo (and galaxy) properties. In addition, we find that the angle
is not significantly correlated with other halo parameters, which may
present a difficulty for models in which galaxy disks are oriented in haloes in
a particular way. Finally, at fixed mass, we find that a halo's environment
(quantified by the large-scale overdensity) is relatively unimportant.Comment: 14 pages, 8 figures; minor revisions; MNRAS, in pres
A mass-dependent density profile for dark matter haloes including the influence of galaxy formation
We introduce a mass-dependent density profile to describe the distribution of dark matter within galaxies, which takes into account the stellar-to-halo mass dependence of the response of dark matter to baryonic processes. The study is based on the analysis of hydrodynamically simulated galaxies from dwarf to Milky Way mass, drawn from the Making Galaxies In a Cosmological Context project, which have been shown to match a wide range of disc scaling relationships. We find that the best-fitting parameters of a generic double power-law density profile vary in a systematic manner that depends on the stellar-to-halo mass ratio of each galaxy. Thus, the quantity M⋆/Mhalo constrains the inner (γ) and outer (β) slopes of dark matter density, and the sharpness of transition between the slopes (α), reducing the number of free parameters of the model to two. Due to the tight relation between stellar mass and halo mass, either of these quantities is sufficient to describe the dark matter halo profile including the effects of baryons. The concentration of the haloes in the hydrodynamical simulations is consistent with N-body expectations up to Milky Way-mass galaxies, at which mass the haloes become twice as concentrated as compared with pure dark matter runs. This mass-dependent density profile can be directly applied to rotation curve data of observed galaxies and to semi-analytic galaxy formation models as a significant improvement over the commonly used NFW profile
XUE. Molecular inventory in the inner region of an extremely irradiated Protoplanetary Disk
We present the first results of the eXtreme UV Environments (XUE) James Webb
Space Telescope (JWST) program, that focuses on the characterization of planet
forming disks in massive star forming regions. These regions are likely
representative of the environment in which most planetary systems formed.
Understanding the impact of environment on planet formation is critical in
order to gain insights into the diversity of the observed exoplanet
populations. XUE targets 15 disks in three areas of NGC 6357, which hosts
numerous massive OB stars, among which some of the most massive stars in our
Galaxy. Thanks to JWST we can, for the first time, study the effect of external
irradiation on the inner ( au), terrestrial-planet forming regions of
proto-planetary disks. In this study, we report on the detection of abundant
water, CO, CO, HCN and CH in the inner few au of XUE 1, a highly
irradiated disk in NGC 6357. In addition, small, partially crystalline silicate
dust is present at the disk surface. The derived column densities, the
oxygen-dominated gas-phase chemistry, and the presence of silicate dust are
surprisingly similar to those found in inner disks located in nearby,
relatively isolated low-mass star-forming regions. Our findings imply that the
inner regions of highly irradiated disks can retain similar physical and
chemical conditions as disks in low-mass star-forming regions, thus broadening
the range of environments with similar conditions for inner disk rocky planet
formation to the most extreme star-forming regions in our Galaxy.Comment: Accepted for publication in ApJ Letters. 20 pages, 7 figure
Galaxy cluster mass reconstruction project - I. Methods and first results on galaxy-based techniques
This paper is the first in a series in which we perform an extensive comparison of various galaxy-based cluster mass estimation techniques that utilize the positions, velocities and colours of galaxies. Our primary aim is to test the performance of these cluster mass estimation techniques on a diverse set of models that will increase in complexity. We begin by providing participating methods with data from a simple model that delivers idealized clusters, enabling us to quantify the underlying scatter intrinsic to these mass estimation techniques. The mock catalogue is based on a Halo Occupation Distribution (HOD) model that assumes spherical Navarro, Frenk and White (NFW) haloes truncated at R₂₀₀, with no substructure nor colour segregation, and with isotropic, isothermal Maxwellian velocities. We find that, above 1014Mʘ, recovered cluster masses are correlated with the true underlying cluster mass with an intrinsic scatter of typically a factor of 2. Below 1014Mʘ, the scatter rises as the number of member galaxies drops and rapidly approaches an order of magnitude. We find that richness-based methods deliver the lowest scatter, but it is not clear whether such accuracy may simply be the result of using an over-simplistic model to populate the galaxies in their haloes. Even when given the true cluster membership, large scatter is observed for the majority non-richness-based approaches, suggesting that mass reconstruction with a low number of dynamical tracers is inherently problematic
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