Di Cintio, A., Knebe, A., Libeskind, N. I., Yepes, G., Gottlöber, S., Hoffman, Y., 2011, Monthly Notices of the Royal Astronomical Society
, 417, 1 , L74 Published: October 2011
Using Constrained Local UniversE Simulations (CLUES) of the formation of the Local Group in a cosmological context, we investigate the recently highlighted problem that the majority of the most massive dark subhaloes of the Milky Way (MW) are too dense to host any of its bright satellites. In particular, we examine the influence of baryonic processes and find that they leave a twofold effect on the relation between the peak of the rotation curve and its position (Vmax and Rmax). Satellites with a large baryon fraction experience adiabatic contraction, thus decreasing Rmax while leaving Vmax more or less unchanged. Subhaloes with smaller baryon fractions undergo a decrease in Vmax possibly due to outflows of material. Furthermore, the situation of finding subhaloes in simulations that lie outside the confidence interval for possible hosts of the bright MW dwarf spheroidals appears to be far more prominent in cosmologies with a high σ8 normalization and depends on the mass of the host. We conclude that the problem cannot be simply solved by including baryonic processes and hence demands further investigations.
Iliev, I. T., Moore, B., Gottlöber, S., Yepes, G., Hoffman, Y., Mellema, G., 2011, Monthly Notices of the Royal Astronomical Society
, 413, 3 , 2093 Published: May 2011
We present the first detailed structure formation and radiative transfer simulations of the reionization history of our cosmic neighbourhood. To this end, we follow the formation of the Local Group of galaxies and nearby clusters by means of constrained simulations, which use the available observational constraints to construct a representation of those structures which reproduces their actual positions and properties at the present time. We find that the reionization history of the Local Group is strongly dependent on the assumed photon production efficiencies of the ionizing sources, which are still poorly constrained. If sources are relatively efficient, i.e. the process is 'photon-rich', the Local Group is primarily ionized externally by the nearby clusters. Alternatively, if the sources are inefficient, i.e. reionization is 'photon-poor' the Local Group evolves largely isolated and reionizes itself. The mode of reionization, external versus internal, has important implications for the evolution of our neighbourhood, in terms of e.g. its satellite galaxy populations and primordial stellar populations. This therefore provides an important avenue for understanding the young universe by detailed studies of our nearby structures.
Knebe, A., Libeskind, N. I., Knollmann, S. R., Martinez-Vaquero, L. A., Yepes, G., Gottlöber, S., Hoffman, Y., 2011, Monthly Notices of the Royal Astronomical Society
, 412, 1 , 529 Published: March 2011
We study the differences and similarities in the luminosities of bound, infalling and the so-called backsplash galaxies of the Milky Way and M31 using a hydrodynamical simulation performed within the Constrained Local UniversE Simulation (CLUES) project. The simulation models the formation of the Local Group within a self-consistent cosmological framework. We find that even though backsplash galaxies passed through the virial radius of their host halo and hence may have lost a (significant) fraction of their mass, their stellar populations are hardly affected. This leaves us with comparable luminosity functions for infalling and backsplash galaxies and hence little hope to decipher their past (and different) formation and evolutionary histories by luminosity measurements alone. Nevertheless, due to the tidal stripping of dark matter we find that the mass-to-light ratios have changed when comparing the various populations against each other: they are highest for the infalling galaxies and lowest for the bound satellites with the backsplash galaxies in between.
Libeskind, N. I., Knebe, A., Hoffman, Y., Gottlöber, S., Yepes, G., Steinmetz, M., 2011, Monthly Notices of the Royal Astronomical Society
, 411, 3 , 1525 Published: March 2011
Using a high-resolution dark matter (DM) simulation of the Local Group, conducted within the framework of the Constrained Local UniversE Simulation (CLUES) project, we investigate the nature of how satellites of the Milky Way (MW) and M31 are accreted. Satellites of these two galaxies are accreted anisotropically on to the main haloes, entering the virial radius of their hosts, from specific 'spots' with respect to the large-scale structure. Furthermore, the material which is tidally stripped from these accreted satellites is also, at z= 0, distributed anisotropically and is characterized by an ellipsoidal subvolume embedded in the halo. The angular pattern created by the locus of satellite infall points and the projected z= 0 stripped dark matter is investigated within a coordinate system determined by the location of the Local Group companion and the simulated Virgo cluster across concentric shells ranging from 0.1 to 5 rvir. Remarkably, the principal axis of the ellipsoidal subvolume shows a coherent alignment extending from well within the halo to a few rvir. A spherical harmonics transform applied to the angular distributions confirms the visual impression: namely, the angular distributions of both the satellites entry points and stripped DM for both haloes are dominated by the l= 2 quadrupole term, whose major principal axis is approximately aligned across the shells considered. It follows that the outer (r > 0.5rvir) structure of the main haloes of the Local Group composed of stripped material is closely related to the cosmic web, within which it is embedded. Given the very plausible hypothesis that an important fraction of the stellar halo of the MW has been accreted from satellite galaxies, the present results can be directly applied to the stellar halo of the MW and M31. We predict that the remnants of tidally stripped satellites should be embedded in streams of material composed of dark matter and stars. The present results can therefore shed light on the existence of satellites embedded within larger streams of matter, such as the Segue 2 satellite.
Cuesta, A. J., Jeltema, T. E., Zandanel, F., Profumo, S., Prada, F., Yepes, G., Klypin, A., Hoffman, Y., Gottlöber, S., Primack, J., Sánchez-Conde, M. A., Pfrommer, C., 2011, The Astrophysical Journal
, 726, 1 , L6 Published: January 2011
We present all-sky simulated Fermi maps of γ-rays from dark matter (DM) decay and annihilation in the local universe. The DM distribution is obtained from a constrained cosmological simulation of the neighboring large-scale structure provided by the CLUES project. The DM fields of density and density squared are then taken as an input for the Fermi observation simulation tool to predict the γ-ray photon counts that Fermi would detect in 5 years of an all-sky survey for given DM models. Signal-to-noise ratio (S/N) sky maps have also been obtained by adopting the current Galactic and isotropic diffuse background models released by the Fermi Collaboration. We point out the possibility for Fermi to detect a DM γ-ray signal in local extragalactic structures. In particular, we conclude here that Fermi observations of nearby clusters (e.g., Virgo and Coma) and filaments are expected to give stronger constraints on decaying DM compared to previous studies. As an example, we find a significant S/N in DM models with a decay rate fitting the positron excess as measured by PAMELA. This is the first time that DM filaments are shown to be promising targets for indirect detection of DM. On the other hand, the prospects for detectability of annihilating DM in local extragalactic structures are less optimistic even with extreme cross-sections. We make the DM density and density squared maps publicly available online.
