56 research outputs found
Dwarf Dark Matter Halos
We study properties of dark matter halos at high redshifts z=2-10 for a vast
range of masses with the emphasis on dwarf halos with masses 10^7-10^9 Msun/h.
We find that the density profiles of relaxed dwarf halos are well fitted by the
NFW profile and do not have cores. We compute the halo mass function and the
halo spin parameter distribution and find that the former is very well
reproduced by the Sheth & Tormen model while the latter is well fitted by a
lognormal distribution with lambda_0 = 0.042 and sigma_lambda = 0.63. We
estimate the distribution of concentrations for halos in mass range that covers
six orders of magnitude from 10^7 Msun/h to 10^13} Msun/h, and find that the
data are well reproduced by the model of Bullock et al. The extrapolation of
our results to z = 0 predicts that present-day isolated dwarf halos should have
a very large median concentration of ~ 35. We measure the subhalo circular
velocity functions for halos with masses that range from 4.6 x 10^9 Msun/h to
10^13 Msun/h and find that they are similar when normalized to the circular
velocity of the parent halo. Dwarf halos studied in this paper are many orders
of magnitude smaller than well-studied cluster- and Milky Way-sized halos. Yet,
in all respects the dwarfs are just down-scaled versions of the large halos.
They are cuspy and, as expected, more concentrated. They have the same spin
parameter distribution and follow the same mass function that was measured for
large halos.Comment: Accepted to be pusblished by ApJ, 12 pages, 8 figures, LaTeX
(documentclass preprint2). Differences with respect to the previous
submission are: (i) abstract was modified slightly to make it more
transparent to the reader, (ii) an extra figure has been added, and (3) some
minor modifications to the main text were also don
Bars and Cold Dark Matter Halos
The central part of a dark matter halo reacts to the presence and evolution
of a bar. Not only does the halo absorb angular momentum from the disk, it can
also be compressed and have its shape modified. We study these issues in a
series of cosmologically motivated, highly resolved N-body simulations of
barred galaxies run under different initial conditions. In all models we find
that the inner halo's central density increases. We model this density increase
using the standard adiabatic approximation and the modified formula by Gnedin
et al. and find that halo mass profiles are better reproduced by this latter.
In models with a strong bar, the dark matter in the central region forms a
bar-like structure (``dark matter bar''), which rotates together with the
normal bar formed by the stellar component (``stellar bar''). The
minor-to-major axial ratio of a halo bar changes with radius with a typical
value 0.7 in the central disk region. DM bar amplitude is mostly a function of
the stellar bar strength. Models in which the bar amplitude increases or stays
roughly constant with time, initially large (40%-60%) misalignment between the
halo and disk bars quickly decreases with time as the bar grows. The halo bar
is nearly aligned with the stellar bar (~10 degrees lag for the halo) after ~2
Gyr. The torque, which the halo bar exerts on the stellar bar, can serve as a
mechanism to regulate the angular momentum transfer from the disk to the halo.Comment: Modified version after referee's suggestions. 17 pages, 12 figures,
accepted by Ap
Formation and structure of halos in a warm dark matter cosmology
(Abridged) Using high-resolution cosmological N-body simulations, we study
how the density profiles of dark matter halos are affected by the filtering of
the density power spectrum below a given scale length and by the introduction
of a thermal velocity dispersion. In the warm dark matter (WDM) scenario, both
the free-streaming scale, R_f, and the velocity dispersion, v_w, are determined
by the mass m_w of the WDM particle. We find that v_w is too small to affect
the density profiles of WDM halos. Down to the resolution attained in our
simulations, there is not any significant difference in the density profiles
and concentrations of halos obtained in simulations with and without the
inclusion of v_w. The density profiles of halos with masses down to ~0.01 the
filtering mass M_f can be described by the NFW shape; significant soft cores
are not formed. Nevertheless, the concentrations of these halos are lower than
those of the CDM counterparts and are approximately independent of mass. The
lower concentrations of WDM halos with respect to their CDM counterparts can be
accounted for their late formation epoch. Overall, our results point to a
series of advantages of a WDM model over the CDM one. In addition to solving
the substructure problem, a WDM model with R_f~0.16 Mpc (m_w~0.75 kev; flat
cosmology with Omega_L=h=0.7) also predicts concentrations, a Tully-Fisher
relation, and formation epochs for small halos which seems to be in better
agreement with observations, relative to CDM predictions.Comment: Accepted for publication in ApJ. 34 pages, figs. 1a,1b, and 1c given
in separate files (high resolution versions available at
ftp://ftp.astroscu.unam.mx/pub/temporal/). Major modifications after referees
Report (more simulations and new figures are presented), but main conclusions
remain the sam
Cosmological neutrinos
The current status of neutrino cosmology is reviewed, from the question of
neutrino decoupling and the presence of sterile neutrinos to the effects of
neutrinos on the cosmic microwave background and large scale structure.
Particular emphasis is put on cosmological neutrino mass measurements.Comment: 21 pages, 4 figures, review for NJP focus issue on neutrino
Refined physical parameters for Chariklo's body and rings from stellar occultations observed between 2013 and 2020
Context. The Centaur (10199) Chariklo has the first ring system discovered around a small object. It was first observed using stellar occultation in 2013. Stellar occultations allow sizes and shapes to be determined with kilometre accuracy, and provide the characteristics of the occulting object and its vicinity. Aims. Using stellar occultations observed between 2017 and 2020, our aim is to constrain the physical parameters of Chariklo and its rings. We also determine the structure of the rings, and obtain precise astrometrical positions of Chariklo. Methods. We predicted and organised several observational campaigns of stellar occultations by Chariklo. Occultation light curves were measured from the datasets, from which ingress and egress times, and the ring widths and opacity values were obtained. These measurements, combined with results from previous works, allow us to obtain significant constraints on Chariklo's shape and ring structure. Results. We characterise Chariklo's ring system (C1R and C2R), and obtain radii and pole orientations that are consistent with, but more accurate than, results from previous occultations. We confirm the detection of W-shaped structures within C1R and an evident variation in radial width. The observed width ranges between 4.8 and 9.1 km with a mean value of 6.5 km. One dual observation (visible and red) does not reveal any differences in the C1R opacity profiles, indicating a ring particle size larger than a few microns. The C1R ring eccentricity is found to be smaller than 0.022 (3σ), and its width variations may indicate an eccentricity higher than ~0.005. We fit a tri-axial shape to Chariklo's detections over 11 occultations, and determine that Chariklo is consistent with an ellipsoid with semi-axes of 143.8-1.5+1.4, 135.2-2.8+1.4, and 99.1-2.7+5.4 km. Ultimately, we provided seven astrometric positions at a milliarcsecond accuracy level, based on Gaia EDR3, and use it to improve Chariklo's ephemeris.Fil: Morgado, B.E.. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Sicardy, Bruno. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Braga Ribas, Felipe. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; Brasil. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia. Universidade Tecnologia Federal do Parana; BrasilFil: Desmars, Josselin. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Gomes Júnior, Altair Ramos. Universidade de Sao Paulo; BrasilFil: Bérard, D.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Leiva, Rodrigo. Universidad de Chile; Chile. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Vieira Martins, Roberto. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; Brasil. Universidade Federal do Rio de Janeiro; BrasilFil: Benedetti Rossi, G.. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia. Universidade Federal de Sao Paulo; BrasilFil: Santos Sanz, Pablo. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Camargo, Julio Ignacio Bueno. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Duffard, R.. Universidade Federal do Rio de Janeiro; BrasilFil: Rommel, F.L.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Assafin, M.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Boufleur, R.C.. Universidad Nacional de Córdoba; ArgentinaFil: Colas, F.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Kretlow, Mike. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Beisker, W.. University of North Carolina; Estados UnidosFil: Sfair, Rafael. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Snodgrass, Colin. University of Edinburgh; Reino UnidoFil: Morales, N.. Pontificia Universidad Católica de Chile; Chile. Universidad Católica de Chile; ChileFil: Fernández Valenzuela, E.. Pontificia Universidad Católica de Chile; Chile. Universidad Católica de Chile; ChileFil: Amaral, L.S.. Massachusetts Institute of Technology; Estados UnidosFil: Amarante, A.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Artola, R.A.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Backes, M.. Universidad Nacional de Córdoba; ArgentinaFil: Bath, K. L.. University of North Carolina; Estados UnidosFil: Bouley, S.. University of St. Andrews; Reino UnidoFil: Garcia Lambas, Diego Rodolfo. 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: Schneiter, Ernesto Matías. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Ingeniería Económica y Legal; Argentina. 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; Argentin
Stellar polytropes and Navarro-Frenk-White halo models: comparison with observations
Motivated by the possible conflict between the Navarro-Frenk-White(NFW) model
predictions for the dark matter contents of galactic systems and its
correlation with baryonic surface density, we will explore an alternative
paradigm for the description of dark matter halos. Such an alternative emerges
from Tsallis' non-extensive thermodynamics applied to self-gravitating systems
and leads to the so-called ``stellar polytrope'' (SP) model. We consider that
this could be a better approach to real structures rather than the isothermal
model, given the fact that the first one takes into account the non-extensivity
of energy and entropy present in these type of systems characterized by
long-range interactions. We compare a halo based on the Navarro-Frenk-White
(NFW) and one which follows the SP description. Analyzing the dark matter
contents estimated by means of global physical parameters of galactic disks,
obtained from a sample of actual galaxies, with the ones of the unobserved dark
matter halos, we conclude that the SP model is favored over the NFW model in
such a comparison.Comment: 21 pages, 4 figures. Accepted for publication in the Journal of
Cosmology and Astroparticle Physic
Sports graduate capabilities and competencies: a comparison of graduate and employer perceptions in six EU countries
The graduate employment market faces ever-increasing socio-economic and political pressures. Higher Education Institutions and the sport sector in the EU have an important role in contributing to graduate employment. The aims of the study were: (1) to assess general perceptions of employability, and (2) to assess sports graduates’ and employers’ perceptions of specific capabilities and competencies in order to identify possible improvements for sports graduate employability programmes. A cross-sectional survey of sports graduates and employers was administered in six EU countries including the UK, France, Germany, Spain, Greece and the Czech Republic to assess graduate and employer perceptions. A graduate capabilities and competencies framework was devised to assess personal, interpersonal, cognitive, role-specific and generic skills. Responses were elicited from 1132 sports graduates and 327 employers. There was generally a wide difference of opinion between employers and sports graduates in terms of the importance and possession of a number of capabilities and competencies. There is a need for the Higher Education sector and employers to take responsibility in ensuring that work experience, work placement and volunteering opportunities are embedded in curricula and to ensure the fitness of purpose of what and how graduate capabilities and competencies are assessed
Cosmology: small scale issues
The abundance of dark matter satellites and subhalos, the existence of
density cusps at the centers of dark matter halos, and problems producing
realistic disk galaxies in simulations are issues that have raised concerns
about the viability of the standard cold dark matter (LambdaCDM) scenario for
galaxy formation. This talk reviews these issues, and considers the
implications for cold vs. various varieties of warm dark matter (WDM). The
current evidence appears to be consistent with standard LambdaCDM, although
improving data may point toward a rather tepid version of LambdaWDM - tepid
since the dark matter cannot be very warm without violating observational
constraints.Comment: 7 pages, 1 figure, to appear in the proceedings of the 8th UCLA Dark
Matter Symposium, Marina del Rey, USA, 20-22 February 200
The mammalian gene function resource: the International Knockout Mouse Consortium.
In 2007, the International Knockout Mouse Consortium (IKMC) made the ambitious promise to generate mutations in virtually every protein-coding gene of the mouse genome in a concerted worldwide action. Now, 5 years later, the IKMC members have developed high-throughput gene trapping and, in particular, gene-targeting pipelines and generated more than 17,400 mutant murine embryonic stem (ES) cell clones and more than 1,700 mutant mouse strains, most of them conditional. A common IKMC web portal (www.knockoutmouse.org) has been established, allowing easy access to this unparalleled biological resource. The IKMC materials considerably enhance functional gene annotation of the mammalian genome and will have a major impact on future biomedical research
The mammalian gene function resource: The International Knockout Mouse Consortium
In 2007, the International Knockout Mouse Consortium (IKMC) made the ambitious promise to generate mutations in virtually every protein-coding gene of the mouse genome in a concerted worldwide action. Now, 5 years later, the IKMC members have developed highthroughput gene trapping and, in particular, gene-targeting pipelines and generated more than 17,400 mutant murine embryonic stem (ES) cell clones and more than 1,700 mutant mouse strains, most of them conditional. A common IKMC web portal (www.knockoutmouse.org) has been established, allowing easy access to this unparalleled biological resource. The IKMC materials considerably enhance functional gene annotation of the mammalian genome and will have a major impact on future biomedical research
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