Sorce, J. G., Courtois, H. M., Gottlöber, S., Hoffman, Y., Tully, R. B., 2014, Monthly Notices of the Royal Astronomical Society
, 437, 4 , 3586 Published: February 2014
Peculiar velocities, obtained from direct distance measurements, are data of choice to achieve constrained simulations of the Local Universe reliable down to a scale of a few megaparsec. Unlike redshift surveys, peculiar velocities are direct tracers of the underlying gravitational field as they trace both baryonic and dark matter. This paper presents the first attempt to use solely observational peculiar velocities to constrain cosmological simulations of the nearby Universe. In order to set up initial conditions, a Reverse Zel'dovich Approximation (RZA) is used to displace constraints from their positions at z = 0 to their precursors' locations at higher redshifts. An additional new feature replaces original observed radial peculiar velocity vectors by their full 3D reconstructions provided by the Wiener-Filter (WF) estimator. Subsequently, the constrained realization (CR) of Gaussian fields technique is applied to build various realizations of the initial conditions. The WF/RZA/CR method is first tested on realistic mock catalogues built from a reference simulation similar to the Local Universe. These mocks include errors on peculiar velocities, on data point positions and a large continuous zone devoid of data in order to mimic galactic extinction. Large-scale structures are recovered with a typical accuracy of 5 h-1 Mpc in position, the best realizations reaching a 2-3 h-1 Mpc precision, the limit imposed by the RZA linear theory. Then, the method is applied to the first observational radial peculiar velocity catalogue of the project Cosmicflows. This paper is a proof of concept that the WF/RZA/CR method can be applied to observational peculiar velocities to successfully build constrained initial conditions.
We present the results of a set of numerical simulations aimed at studying reionization at the galactic scale. We use a high-resolution realization of the formation of the Milky Way (MW)-M31 system to simulate the reionization of the Local Group. The reionization calculation was performed with the post-processing radiative transfer code ATON and the underlying cosmological simulation was performed as part of the CLUES project (http://www.clues-project.org). We vary the source models to bracket the range of source properties used in the literature. We investigate the structure and propagation of the galactic ionization fronts by a visual examination of our reionization maps. Within the progenitors, we find that reionization is patchy and proceeds locally inside-out. The process becomes patchier with decreasing source photon output. It is generally dominated by one major H II region and one to four additional isolated smaller bubbles, which eventually overlap. Higher emissivity results in faster and earlier local reionization. In all models, the reionization of the MW and M31 are similar in duration, i.e., between 203 Myr and 22 Myr depending on the source model, placing their z reion between 8.4 and 13.7. In all models except the most extreme, the MW and M31 progenitors reionize internally, ignoring each other despite being relatively close to each other, even during the epoch of reionization. Only in the case of strong supernova feedback suppressing star formation in halos less massive than 109 M ⊙, and using our highest emissivity, do we find that the MW is reionized by M31.
Libeskind, N. I., Di Cintio, A., Knebe, A., Yepes, G., Gottlöber, S., Steinmetz, M., Hoffman, Y., Martinez-Vaquero, L. A., 2013, Publications of the Astronomical Society of Australia
, 30 , e039 Published: July 2013
The differences between cold dark matter (CDM) and warm dark matter (WDM) in the formation of a group of galaxies are examined by running two identical simulations, where in the WDM case the initial power spectrum has been altered to mimic a 1-keV dark matter particle. The CDM initial conditions were constrained to reproduce at z = 0 the correct local environment within which a `Local Group' (LG) of galaxies may form. Two significant differences between the two simulations are found. While in the CDM case a group of galaxies that resembles the real LG forms, the WDM run fails to reproduce a viable LG, instead forming a diffuse group which is still expanding at z = 0. This is surprising since, due to the suppression of small-scale power in its power spectrum, WDM is naively expected to only affect the collapse of small haloes and not necessarily the dynamics on a scale of a group of galaxies. Furthermore, the concentration of baryons in halo centre is greater in CDM than in WDM and the properties of the discs differ.
Di Cintio, A., Knebe, A., Libeskind, N. I., Brook, C., Yepes, G., Gottlöber, S., Hoffman, Y., 2013, Monthly Notices of the Royal Astronomical Society
, 431, 2 , 1220 Published: May 2013
We use dark matter only and full hydrodynamical Constrained Local Universe Simulations of the formation of the Local Group to study the density profile of subhaloes of the simulated Milky Way and Andromeda galaxies. We show that the Einasto model provides the best description of the subhaloes' density profile, as opposed to the more commonly used Navarro, Frenk & White profile or any generalization of it. We further find that the Einasto shape parameter nE is strongly correlated with the total subhalo mass, pointing towards the notion of a non-universality of the subhaloes' density profile. We observe that the effect of mass-loss due to tidal stripping, in both the dark matter only and the hydrodynamical run, is the reduction of the shape parameter nE between the infall and the present time. Assuming now that the dwarf spheroidals (dSphs) of our Galaxy follow the Einasto profile and using the maximum and minimum values of nE from our hydrodynamical simulation as a gauge, we can improve the observational constraints on the Rmax-Vmax pairs obtained for the brightest satellite galaxies of the Milky Way. When considering only the subhaloes with -13.2 ≲ MV ≲ -8.8, i.e. the range of luminosity of the classical dwarfs, we find that all our simulated objects are consistent with the observed dSphs if their haloes follow the Einasto model with 1.6 ≲ nE ≲ 5.3. The numerically motivated Einasto profile for the observed dSphs will alleviate the recently presented `massive failures' problem.
Recent observations constrained the tangential velocity of M31 with respect to the Milky Way to be v M31, tan < 34.4 km s-1and the radial velocity to be in the range v M31, rad = -109 ± 4.4 km s-1. In this study we use a large volume high-resolution N-body cosmological simulation (Bolshoi) together with three constrained simulations to statistically study this kinematics in the context of the Λ cold dark matter (ΛCDM). The comparison of the ensembles of simulated pairs with the observed Local Group (LG) at the 1σ level in the uncertainties has been done with respect to the radial and tangential velocities, the reduced orbital energy (e tot), angular momentum (l orb), and the dimensionless spin parameter, λ. Our main results are (1) the preferred radial and tangential velocities for pairs in ΛCDM are v r = -80 ± 20 km s-1 and v t = 50 ± 10 km s-1, (2) pairs around that region are 3-13 times more common than pairs within the observational values, (3) 15%-24% of LG-like pairs in ΛCDM have energy and angular momentum consistent with observations, while (4) 9%-13% of pairs in the same sample show similar values in the inferred dimensionless spin parameter. It follows that within current observational uncertainties the quasi-conserved quantities that characterize the orbit of the LG, i.e., e tot, l orb, and λ, do not challenge the standard ΛCDM model, but the model is in tension with regard to the actual values of the radial and tangential velocities. This might hint to a problem of the ΛCDM model to reproduce the observed LG.
