1,027 research outputs found
Galactic halos in cosmology with long-range scalar DM interaction
Based on a set of cosmological N-body simulations we analyze properties of
the dark matter haloes (DM) in a galaxy mass range () in modified \lcdm cosmology with additional dynamically
screened scalar interactions in DM sector. Our simulations show that scalar
interactions support picture of the Island Universe. Rapid structure formation
processes are shifted into higher redshifts resulting in a much smaller
accretion and merging rates for galactic haloes at low redshifts. Finally, we
present how this "fifth" force affects halo properties, like density profile,
triaxiality, ellipticities and the spin parameter.Comment: 4 pages, 2 figures, printed in Annalen Phys.19:351-354,2010,
subsituted with the accepted versio
The dynamical state of dark matter haloes in cosmological simulations - I. Correlations with mass assembly history
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©2011 RAS © 2011 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.Using a statistical sample of dark matter haloes drawn from a suite of cosmological N-body simulations of the cold dark matter (CDM) model, we quantify the impact of a simulated halo's mass accretion and merging history on two commonly used measures of its dynamical state, the virial ratio η and the centre of mass offset Δr. Quantifying this relationship is important because the degree to which a halo is dynamically equilibrated will influence the reliability with which we can measure characteristic equilibrium properties of the structure and kinematics of a population of haloes. We begin by verifying that a halo's formation redshift zform correlates with its virial mass Mvir and we show that the fraction of its recently accreted mass and the likelihood of it having experienced a recent major merger increase with increasing Mvir and decreasing Zform. We then show that both η and Δr increase with increasing Mvir and decreasing zform, which implies that massive recently formed haloes are more likely to be dynamically unrelaxed than their less massive and older counterparts. Our analysis shows that both η and Δr are good indicators of a halo's dynamical state, showing strong positive correlations with recent mass accretion and merging activity, but we argue that Δr provides a more robust and better defined measure of dynamical state for use in cosmological N-body simulations at z≃ 0. We find that Δr≲ 0.04 is sufficient to pick out dynamically relaxed haloes at z= 0. Finally, we assess our results in the context of previous studies, and consider their observational implicationsAK is supported by the Spanish Ministerio de Ciencia e Innovación (MICINN) in Spain through the Ramon y Cajal programme as well as the grants AYA 2009-13875-C03-02, AYA2009-12792-C03-03, CSD2009- 00064 and CAMS2009/ESP-1496. He acknowledges support by the MICINN under the Consolider-Ingenio, SyeC project CSD- 2007-0005
The luminosities of backsplash galaxies in constrained simulations of the Local Group
We study the differences and similarities in the luminosities of bound,
infalling and the so-called backsplash (Gill et al. 2005) galaxies of the Milky
Way and M31 using a hydrodynamical simulation performed within the Constrained
Local UniversE Simulation (CLUES) project. The simulation models the formation
of the Local Group within a self-consistent cosmological framework. We find
that even though backsplash galaxies passed through the virial radius of their
host halo and hence may have lost a (significant) fraction of their mass, their
stellar populations are hardly affected. This leaves us with comparable
luminosity functions for infalling and backsplash galaxies and hence little
hope to decipher their past (and different) formation and evolutionary
histories by luminosity measurements alone. Nevertheless, due to the tidal
stripping of dark matter we find that the mass-to-light ratios have changed
when comparing the various populations against each other: they are highest for
the infalling galaxies and lowest for the bound satellites with the backsplash
galaxies in-between.Comment: 9 pages, 10 figures, 1 table, accepted for publication in MNRA
Part-per-billion measurement of the electric quadrupole transition isotope shifts between Ca and Ca
We report a precise measurement of the isotope shifts in the SD electric quadrupole transition at 729~nm in the Ca. The measurement has been made via high-resolution laser
spectroscopy of co-trapped ions, finding measured shifts of
2,771,872,467.6(7.6), 5,340,887,394.6(7.8), and 9,990,381,870.0(6.3) Hz between
Caand Ca, respectively. By exciting the two
isotopes simultaneously using frequency sidebands derived from a single laser
systematic uncertainties resulting from laser frequency drifts are eliminated.
This permits far greater precision than similar previously published
measurements in other alkaline-earth systems. The resulting measurement
precision provides a benchmark for tests of theoretical isotope shift
calculations, and also offers a step towards probing New Physics via isotope
shift spectroscopy.Comment: 9 pages, 7 figure
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