We investigate the effect of long-range scalar interactions in dark matter (DM) models of cosmic structure formation with a particular focus on the formation times of haloes. Utilizing N-body ...simulations with 5123 DM particles we show that in our models DM haloes form substantially earlier: tracing objects up to redshift z ∼ 6 we find that the formation time, as characterized by the redshift z1/2 at which the halo has assembled half of its final mass, is gradually shifted from z1/2 ≈ 1.83 in the fiducial Λ cold dark matter (ΛCDM) model to z1/2 ≈ 2.54 in the most extreme scalar-interaction model. This is accompanied by a shift of the redshift that marks the transition between merger and steady accretion epochs from z* ≈ 4.32 in the ΛCDM haloes to z* ≈ 6.39 in our strongest interaction model. In other words, the scalar-interacting model employed in this work produces more structures at high redshifts, prolonging at the same time the steady accretion phases. These effects taken together can help the ΛCDM model to account for a high-redshift reionization as indicated by the Wilkinson Microwave Anisotropy Probe (WMAP) data and can alleviate issues related to the survival of the thin-disc-dominated galaxies at low redshifts.
Phase-space density profiles in scale-free cosmologies Knollmann, Steffen R.; Knebe, Alexander; Hoffman, Yehuda
Monthly Notices of the Royal Astronomical Society,
December 2008, Letnik:
391, Številka:
2
Journal Article
Recenzirano
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We use a set of high-resolution simulations of scale-free Einstein-de Sitter cosmologies to investigate the logarithmic slope of the phase-space density profile Q(r) =ρ(r)/σ3(r) of dark matter (DM) ...haloes. The initial conditions for the simulations are determined by a power-law power spectrum of the form P(k) ∝kn. We compute the Q(r) profiles using the radial, tangential and full velocity dispersion, and the velocity anisotropy parameter, β(r). We express Q(r) as a single power-law Q(r) ∝rα and derive a median slope α in each simulation and for each definition of Q. Our main findings are: (i) the various Q(r) profiles follow a power law to a good approximation. (ii) The slopes depend on the concentration parameter c of the DM haloes, where for c≳ 10 the slopes steepen with rising concentration and for c≲ 10 the trend flattens and even turns around. (iii) The asymptotic value of β as r→Rvir increases with the value of c. (iv) In accordance with Zait, Hoffman & Shlosman, αrad becomes more negative as the asymptotic value of β at the virial radius increases. (iv) This introduces a weak dependence of the Q(r) slopes on the slope of the power spectrum.
We discuss the rest-frame UV emission between 5 < z < 7 from the MareNostrum High-z Universe, an smoothed particle hydrodynamics simulation done with more than 2 billion particles. Cosmological ...simulations of galaxy formation generally overpredict the UV rest-frame luminosity function at high redshift, both at the bright and faint ends. In this Letter, we explore a dust attenuation model where a larger extinction is applied to star populations younger than a given age, mimicking the effect of a clumpy interstellar medium. We show that this scenario fits reasonably well both the UV luminosity functions and the UV continuum slopes derived from observations. The model assumes a large obscuration for stars younger than 25 Myr from the gas clouds where they should be embedded at their formation time. We find that the optical depth in these clouds should be between 30 and 100 times larger than the mean optical depth for the homogeneous part of the interstellar medium. These values are one order of magnitude larger than those estimated in local galaxies. Therefore, we conclude that Λ cold dark matter predictions for the high-z UV emission can accommodate the current observations if we consider a dust extinction model based on the assumption of a clumpy environment at high redshift.
AHF: AMIGA'S HALO FINDER Knollmann, Steffen R.; Knebe, Alexander
The Astrophysical journal. Supplement series,
06/2009, Letnik:
182, Številka:
2
Journal Article
Recenzirano
Cosmological simulations are the key tool for investigating the different processes involved in the formation of the universe from small initial density perturbations to galaxies and clusters of ...galaxies observed today. The identification and analysis of bound objects, halos, is one of the most important steps in drawing useful physical information from simulations. In the advent of larger and larger simulations, a reliable and parallel halo finder, able to cope with the ever-increasing data files, is a must. In this work we present the freely available MPI parallel halo finder AHF. We provide a description of the algorithm and the strategy followed to handle large simulation data. We also describe the parameters a user may choose in order to influence the process of halo finding, as well as pointing out which parameters are crucial to ensure untainted results from the parallel approach. Furthermore, we demonstrate the ability of AHF to scale to high-resolution simulations.
Dark matter halo profiles in scale-free cosmologies Knollmann, Steffen R.; Power, Chris; Knebe, Alexander
Monthly notices of the Royal Astronomical Society,
04/2008, Letnik:
385, Številka:
2
Journal Article
ABSTRACT Using clara (code for Lyman alpha radiation analysis) we constrain the escape fraction of Lyman α radiation in galaxies in the redshift range 5 z 7, based on the MareNostrum High-z Universe, ...a smoothed particle hydrodynamics cosmological simulation with more than two billion particles. We approximate Lyman α emitters (LAEs) as dusty gaseous slabs with Lyman α radiation sources homogeneously mixed in the gas. Escape fractions for such a configuration and for different gas and dust contents are calculated using our newly developed radiative transfer code clara. The results are applied to the MareNostrum High-z Universe numerical galaxies. The model shows a weak redshift evolution and good agreement with estimations of the escape fraction as a function of reddening from observations at z 2.2 and z 3. We extend the slab model by including additional dust in a clumpy component in order to reproduce the ultraviolet (UV) continuum luminosity function (LF) and UV colours at redshifts z > rsim 5. The LAE LF, based on the extended clumpy model, reproduces broadly the bright end of the LF derived from observations at z 5 and z 6. At z 7, our model overpredicts the LF by roughly a factor of 4, presumably because the effects of the neutral intergalactic medium are not taken into account. The remaining tension between the observed and simulated faint end of the LF, both in the UV continuum and Lyman α at redshifts z 5 and z 6, points towards an overabundance of simulated LAEs hosted in haloes of masses 1.0 × 1010≤Mh≤ 4.0 × 1010h-1M. Given the difficulties in explaining the observed overabundance by dust absorption, a probable origin of the mismatch is the high star formation rate in the simulated haloes around the quoted mass range. A more efficient supernova feedback should be able to regulate the star formation process in the shallow potential wells of these haloes. PUBLICATION ABSTRACT
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