Abstract
We present N-body simulations of a new class of self-interacting dark matter models, which do not violate any astrophysical constraints due to a non-power-law velocity dependence of the transfer cross section which is motivated by a Yukawa-like new gauge boson interaction. Specifically, we focus on the formation of a Milky Way-like dark matter halo taken from the Aquarius project and re-simulate it for a couple of representative cases in the allowed parameter space of this new model. We find that for these cases, the main halo only develops a small core (~1 kpc) followed by a density profile identical to that of the standard cold dark matter scenario outside of that radius. Neither the subhalo mass function nor the radial number density of subhaloes are altered in these models but there is a significant change in the inner density structure of subhaloes resulting in the formation of a large density core. As a consequence, the inner circular velocity profiles of the most massive subhaloes differ significantly from the cold dark matter predictions and we demonstrate that they are compatible with the observational data of the brightest Milky Way dSphs in such a velocity-dependent self-interacting dark matter scenario. Specifically, and contrary to the cold dark matter case, there are no subhaloes that are more concentrated than what is inferred from the kinematics of the Milky Way dSphs. We conclude that these models offer an interesting alternative to the cold dark matter model that can reduce the recently reported tension between the brightest Milky Way satellites and the dense subhaloes found in cold dark matter simulations.
Highlights
Astrophysical processes that inhibit star formation are able to solve the “missing satellite” problem (e.g. Koposov et al 2009), but the tension with dwarf galaxies in the field remains despite attempts to explain it without modifying the Cold Dark Matter (CDM) model (Ferrero et al 2011)
In this work we only focus on the recently discovered problem pointed out by Boylan-Kolchin et al (2011a,b) and demonstrate how velocity-dependent SIDM (vdSIDM) models can reduce the discrepancy between observation and theoretical prediction
We emphasise that the objective of this paper is to present an initial exploration of the vdSIDM models discussed in Section 2.1 and show explicitly that contrary to the CDM case, these vdSIDM models do not predict a number of subhaloes which are too concentrated to host the bright dwarf spheroidals (dSphs)
Summary
Astrophysical processes that inhibit star formation are able to solve the “missing satellite” problem (e.g. Koposov et al 2009), but the tension with dwarf galaxies in the field remains despite attempts to explain it without modifying the CDM model (Ferrero et al 2011). Koposov et al 2009), but the tension with dwarf galaxies in the field remains despite attempts to explain it without modifying the CDM model (Ferrero et al 2011) It remains to be seen if galaxy formation models based on N-body simulations that seem to provide a good fit to the luminosity function at low masses (Guo et al 2011) are successful in reproducing the HI observations of the velocity function. Current observations of LSB galaxies (Kuzio de Naray & Spekkens 2011) and MW dwarf spheroidals (dSphs) (Walker & Penarrubia 2011) seem to confirm the presence of density cores in low-mass haloes Since these galaxies are DM-dominated, it is challenging to invoke baryonic processes as the main mechanisms responsible of altering so drastically the inner density profile of haloes. This is one of the most serious challenges faced by the CDM model and can perhaps be solved by invoking WDM (Lovell et al.2011) or, alternatively, naturally avoided in certain SIDM models as we explore in this work
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