Angular Momentum Distribution in Galaxies and Inner Haloes Profile

Abstract

In this paper, we extend the Romanowsky and Fall (2012) results concerning the stellar angular momentum to the mass range 10³ ≲ M_*/M_⊙ ≲ 10¹², and using this result, we calculate the inner slope, α of haloes density profiles in terms of V_rot, by using a previous model of Del Popolo, taking into account the interactions between dark matter and baryons through dynamical friction. Using the McConnachie sample, and that of Romanowsky and Fall, based only on observations, we show that in the quoted sample the rotationally supported galaxies, and the pressure supported ones are divided by a break atM_* ≃ 10^7.8M_⊙. Then we show that the slope α flattens monotonically, from α ≃ − 1 to α ≃ 0. The flattening is due to the increase of specific angular momentum moving fromMilkyWay-type galaxies to disk dwarf galaxies. Since at M_* < 10^7.8M_⊙, non-rotational supported galaxies start to dominate, the inner slope steepens again. The paper also extends the main result of Del Popolo (2016) to morphologies different from spheroids, and disks, taking into account the different morphologies delimited by the quoted ones. We finally compared our results with Di Cintio SPH simulations. The two models differ mainly at stellar masses smaller than M_* ≲ 10^7.8M_⊙. In our model the inner slope is flatter than in simulations. This imply that even finding a cored, α ≃ 0.4, profile in dSphs with masses slightly smaller than ≃10⁶M_⊙ will not imply necessarily a problem for the ΛCDM mode, as predicted by some simulations. To check which one of the two model was better describing data in this region, we used the LITTLE THINGS data, and compared the two models through a χ², finding that our model gives a better description of the data.