CLUES Publications

Publications retrieved from NASA ADS and sorted by publication date in reverse order

More from CLUES library at ADS

The sizes of minivoids in the local Universe: an argument in favour of a warm dark matter model?
Tikhonov, A. V., Gottlöber, S., Yepes, G., Hoffman, Y., 2009, Monthly Notices of the Royal Astronomical Society , 399, 3 , 1611
Published: November 2009
doi:10.1111/j.1365-2966.2009.15381.x
Abstract:
Using high-resolution simulations within the cold dark matter (CDM) and warm dark matter (WDM) models, we study the evolution of small-scale structure in the local volume, a sphere of 8-Mpc radius around the Local Group. We compare the observed spectrum of minivoids in the local volume with the spectrum of minivoids determined from the simulations. We show that the ΛWDM model can easily explain both the observed spectrum of minivoids and the presence of low-mass galaxies observed in the local volume, provided that all haloes with circular velocities greater than 20 km s-1 host galaxies. On the contrary, within the ΛCDM model the distribution of the simulated minivoids reflects the observed one if haloes with maximal circular velocities larger than 35kms-1 host galaxies. This assumption is in contradiction with observations of galaxies with circular velocities as low as 20 km s-1 in our local Universe. A potential problem of the ΛWDM model could be the late formation of the haloes in which the gas can be efficiently photoevaporated. Thus, star formation is suppressed and low-mass haloes might not host any galaxy at all.
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Martinez-Vaquero, L. A., Yepes, G., Hoffman, Y., Gottlöber, S., Sivan, M., 2009, Monthly Notices of the Royal Astronomical Society , 397, 4 , 2070
Published: August 2009
doi:10.1111/j.1365-2966.2009.15093.x
Abstract:
Using a suite of N-body simulations in different cold dark matter (CDM) scenarios, with cosmological constant (ΛCDM) and without (OCDM, SCDM), we study the Hubble flow (σH) in Local Volumes (LV) around Local Group (LG) like objects found in these simulations, and compare the numerical results with the most recent observations. We show that ΛCDM and OCDM models exhibit the same behaviour of σH. Hence, we demonstrate that the observed coldness of the Hubble flow is not likely to be a manifestation of the dark energy, contrary to previous claims. The coldness does not constitute a problem by itself but it poses a problem to the standard ΛCDM model only if the mean density within the LV is greater than twice the mean matter cosmic density. The lack of blueshifted galaxies in the LV, outside of the LG can be considered as another manifestation of the coldness of the flow. Finally, we show that the main dynamical parameter that affects the coldness of the flow is the relative isolation of the LG, and the absence of nearby Milky Way like objects within a distance of about 3Mpc.
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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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