Erasing Dark Matter Cusps in Cosmological Galactic Halos with Baryons

Abstract

We study the central dark matter (DM) cusp evolution in cosmological galactic halos. Models with and without baryons (baryons+DM, hereafter BDM model, and pure DM, PDM model, respectively) are advanced from identical initial conditions. The DM cusp properties are contrasted by a direct comparison of pure DM and baryonic models. We find a divergent evolution between the PDM and BDM models within the inner ~10 kpc region. The PDM model forms a R^{-1} cusp as expected, while the DM in the BDM model forms a larger isothermal cusp R^{-2} instead. The isothermal cusp is stable until z~1 when it gradually levels off. This leveling proceeds from inside out and the final density slope is shallower than -1 within the central 3 kpc (i.e., expected size of the R^{-1} cusp), tending to a flat core within ~2 kpc. This effect cannot be explained by a finite resolution of our code which produces only a 5% difference between the gravitationally softened force and the exact Newtonian force of point masses at 1 kpc from the center. Neither is it related to the energy feedback from stellar evolution or angular momentum transfer from the bar. Instead it can be associated with the action of DM+baryon subhalos heating up the cusp region via dynamical friction and forcing the DM in the cusp to flow out and to `cool' down. The process described here is not limited to low z and can be efficient at intermediate and even high z.Comment: 4 pages, 4 figures, accepted for publication by the Astrophysical Journal Letters. Minor corrections following the referee repor

Density profile of dark matter haloes and galaxies in the horizon–agn simulation: the impact of AGN feedback

“…Focusing first on the highest redshifts (z > 2), HAGN and HnoAGN profiles are clearly much steeper than HDM ones. As previously mentioned, this is mainly due to the galaxy formation process: radiative cooling and subsequent star formation lead to a steepening of the DM density profile of DM haloes due to adiabatic contraction (Blumenthal et al 1986;Gnedin et al 2004), in agreement with previous works (e.g., Gustafsson et al 2006;Romano-Díaz et al 2008Abadi et al 2010Pedrosa et al 2010;Tissera et al 2010;Duffy et al 2010). Note that the mean slopes of HAGN and HnoAGN halo density profiles are very close at z ∼ 5 suggesting that AGN feedback has not had an important impact yet by this redshift.…”

Angular Momentum in Dwarf Galaxies

“…This produces flattening of the cusp in agreement with previous studies based on the DF driven flattening (El-Zant et al 2001Romano-Diaz et al 2008) and the SF driven flattening (Navarro et al 1996;Mashchenko et al 2006Mashchenko et al , 2008.…”

“…In the present paper we studied the angular momentum catastrophe in the framework of interaction among baryons and dark matter through dynamical friction (El-Zant et al 2001Romano-Diaz et al 2008DP09;Cole et al 2011). We followed the proto-structure evolution with the DP09 semi-analytical model taking into account the effect of adiabatic contraction, dynamical friction and the exchange of angular momentum between baryons and DM, ordered and random angular momentum.…”

“…In order to see if the interaction between the baryonic clumps and DM through a dynamical friction (El-Zant et al 2001Romano-Diaz et al 2008Cole et al 2011) are able to modify the spin parameter distribution and the angular momentum distribution in a system made of baryons and DM, we use the model introduced in DP09.…”

“…The last is the discrepancy among the cuspy density profiles obtained in simulations (Navarro et al 1996(Navarro et al , 1997(Navarro et al , 2010 and the cored density profiles observed (Burkert 1995; The previous problems can be also solved through another mechanism, namely the transfer of energy and angular momentum from the baryonic clumps to DM through a dynamical friction (El-Zant et al 2001Romano-Diaz et al 2008Del Popolo & Hiotelis 2014;Del Popolo et al 2014;Cole et al 2011;Inoue & Saitoh 2011).…”