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.
In previous works we proposed the Reverse Zeldovich Approximation (RZA) method, which can be used to estimate the cosmological initial conditions underlying the galaxy distribution in the Local Universe using peculiar velocity data. In this paper, we apply the technique to run constrained cosmological simulations from the RZA-reconstructed initial conditions, designed to reproduce the large-scale structure of the Local Universe. We test the method with mock peculiar velocity catalogues extracted from a reference simulation. We first reconstruct the initial conditions of this reference simulation using the mock data, and then run the reconstructed initial conditions forward in time until z = 0. We compare the resulting constrained simulations with the original simulation at z = 0 to test the accuracy of this method. We also compare them with constrained simulations run from the mock data without the addition of RZA, i.e. using only the currently established constrained realizations (CRs) method. Our resimulations are able to correctly recover the evolution of the large-scale structure underlying the data. The results show that the addition of RZA to the CRs method significantly improves both the reconstruction of the initial conditions and the accuracy of the obtained constrained resimulations. Haloes from the original simulation are recovered in the resimulations with an average accuracy of ≈2 Mpc h-1 on their position and a factor of 2 in mass, down to haloes with a mass of ≈1014 M⊙ h-1. In comparison, without RZA the resimulations recover only the most massive haloes with masses of ≈5 × 1014 M⊙ h-1 and higher, and with a systematic shift on their position of about ≈ 10 Mpc h- 1 due to the cosmic displacement field. We show that with the additional Lagrangian reconstruction step introduced by the RZA, this shift can be removed.
