CLUES Publications

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The Velocity Function in the Local Environment from ΛCDM and ΛWDM Constrained Simulations
Zavala, J., Jing, Y. P., Faltenbacher, A., Yepes, G., Hoffman, Y., Gottlöber, S., Catinella, B., 2009, The Astrophysical Journal , 700, 2 , 1779
Published: August 2009
doi:10.1088/0004-637X/700/2/1779
Abstract:
Using constrained simulations of the local universe for generic cold dark matter (CDM) and for 1 keV warm dark matter (WDM), we investigate the difference in the abundance of dark matter halos in the local environment. We find that the mass function (MF) within 20 h -1 Mpc of the Local Group is ~2 times larger than the universal MF in the 109-1013 h -1 M sun mass range. Imposing the field of view of the ongoing H I blind survey Arecibo Legacy Fast ALFA (ALFALFA) in our simulations, we predict that the velocity function (VF) in the Virgo-direction region (VdR) exceeds the universal VF by a factor of 3. Furthermore, employing a scheme to translate the halo VF into a galaxy VF, we compare the simulation results with a sample of galaxies from the early catalog release of ALFALFA. We find that our simulations are able to reproduce the VF in the 80-300 km s-1 velocity range, having a value ~10 times larger than the universal VF in the VdR. In the low-velocity regime, 35-80 km s-1, the WDM simulation reproduces the observed flattening of the VF. In contrast, the simulation with CDM predicts a steep rise in the VF toward lower velocities; for V max = 35 km s-1, it forecasts ~10 times more sources than the ones observed. If confirmed by the complete ALFALFA survey, our results indicate a potential problem for the CDM paradigm or for the conventional assumptions about energetic feedback in dwarf galaxies.
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Forero-Romero, J. E., Hoffman, Y., Gottlöber, S., Klypin, A., Yepes, G., 2009, Monthly Notices of the Royal Astronomical Society , 396, 3 , 1815
Published: July 2009
doi:10.1111/j.1365-2966.2009.14885.x
Abstract:
In this paper, we propose a new dynamical classification of the cosmic web. Each point in space is classified in one of four possible web types: voids, sheets, filaments and knots. The classification is based on the evaluation of the deformation tensor (i.e. the Hessian of the gravitational potential) on a grid. The classification is based on counting the number of eigenvalues above a certain threshold, λth, at each grid point, where the case of zero, one, two or three such eigenvalues corresponds to void, sheet, filament or a knot grid point. The collection of neighbouring grid points, friends of friends, of the same web type constitutes voids, sheets, filaments and knots as extended web objects.

A simple dynamical consideration of the emergence of the web suggests that the threshold should not be null, as in previous implementations of the algorithm. A detailed dynamical analysis would have found different threshold values for the collapse of sheets, filaments and knots. Short of such an analysis a phenomenological approach has been opted for, looking for a single threshold to be determined by analysing numerical simulations.

Our cosmic web classification has been applied and tested against a suite of large (dark matter only) cosmological N-body simulations. In particular, the dependence of the volume and mass filling fractions on λth and on the resolution has been calculated for the four web types. We also study the percolation properties of voids and filaments.

Our main findings are as follows. (i) Already at λth = 0.1 the resulting web classification reproduces the visual impression of the cosmic web. (ii) Between 0.2 <~ λth <~ 0.4, a system of percolated voids coexists with a net of interconnected filaments. This suggests a reasonable choice for λth as the parameter that defines the cosmic web. (iii) The dynamical nature of the suggested classification provides a robust framework for incorporating environmental information into galaxy formation models, and in particular to semi-analytical models.

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Yepes, G., Gottlöber, S., Martínez-Vaquero, L. A., Hoffman, Y., Khalil, S., 2009, The Dark Side of the Universe: 4th International Workshop on the Dark Side of the Universe , 1115 , 80
Published: April 2009
doi:10.1063/1.3131533
Abstract:
Constrained simulations of the Local Universe are an invaluable tool to investigate in detail the nature of dark matter particles. Thanks to them, we can simulate the formation of dark halos in environments pretty much like the one our Milky Way happened to live. A direct comparison with observations of our Local Universe can be made in this way, minimizing the effects of cosmic variance in the simulations. In this paper we present the results of a comparison of high-resolution simulated Local Group (LG) objects done in 3 different dark matter scenarios: The standard Cold Dark Matter and two Warm Dark Matter models with particles masses ranging from 3 to 1 keV, that are still compatible with high-redshift observations. We focus here on the study of substructures and mass profiles for the CDM and WDM LG objects and draw some conclusions about the limits on the mass of warm dark matter particles to be compatible with the most recently discovered Milky Way ultra-faint satellites.
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Wojtak, R., Łokas, E. L., Mamon, G. A., Gottlöber, S., Klypin, A., Hoffman, Y., 2008, Monthly Notices of the Royal Astronomical Society , 388, 2 , 815
Published: August 2008
doi:10.1111/j.1365-2966.2008.13441.x
Abstract:
We study the distribution function (DF) of dark matter particles in haloes of mass range 1014-1015Msolar. In the numerical part of this work we measure the DF for a sample of relaxed haloes formed in the simulation of a standard Λ cold dark matter (ΛCDM) model. The DF is expressed as a function of energy E and the absolute value of the angular momentum L, a form suitable for comparison with theoretical models. By proper scaling we obtain the results that do not depend on the virial mass of the haloes. We demonstrate that the DF can be separated into energy and angular momentum components and propose a phenomenological model of the DF in the form . This formulation involves three parameters describing the anisotropy profile in terms of its asymptotic values (β0 and β∞) and the scale of transition between them (L0). The energy part fE(E) is obtained via inversion of the integral for spatial density. We provide a straightforward numerical scheme for this procedure as well as a simple analytical approximation for a typical halo formed in the simulation. The DF model is extensively compared with the simulations: using the model parameters obtained from fitting the anisotropy profile, we recover the DF from the simulation as well as the profiles of the dispersion and kurtosis of radial and tangential velocities. Finally, we show that our DF model reproduces the power-law behaviour of phase-space density Q = ρ(r)/σ3(r).
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Hoffman, Y., Martinez-Vaquero, L. A., Yepes, G., Gottlöber, S., 2008, Monthly Notices of the Royal Astronomical Society , 386, 1 , 390
Published: May 2008
doi:10.1111/j.1365-2966.2008.13034.x
Abstract:
To study the local Hubble flow, we have run constrained dark matter (DM) simulations of the Local Group (LG) in the concordance Λ cold dark matter (CDM) and open cold dark matter (OCDM) cosmologies, with identical cosmological parameters apart from the Λ term. The simulations were performed within a computational box of centred on the LG. The initial conditions were constrained by the observed peculiar velocities of galaxies and positions of X-ray nearby clusters of galaxies. The simulations faithfully reproduce the nearby large-scale structure, and in particular the Local Supercluster and the Virgo cluster. LG-like objects have been selected from the DM haloes so as to closely resemble the dynamical properties of the LG. Both the ΛCDM and OCDM simulations show very similar local Hubble flow around the LG-like objects. It follows that, contrary to recent statements, the dark energy (DE) does not manifest itself in the local dynamics.
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