Pressure from dark matter annihilation and the rotation curve of spiral galaxies

Abstract

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2011 RAS ©2011 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.The rotation curves of spiral galaxies are one of the basic predictions of the cold dark matter paradigm, and their shape in the innermost regions has been hotly debated over the last decades. The present work shows that dark matter annihilation into electron-positron pairs may affect the observed rotation curve by a significant amount. We adopt a model-independent approach, where all the electrons and positrons are injected with the same initial energy E0~mdmc2 in the range from 1 MeV to 1 TeV and the injection rate is constrained by INTEGRAL, Fermi and HESS data. The pressure of the relativistic electron-positron gas is determined by solving the diffusion-loss equation, considering inverse Compton scattering, synchrotron radiation, Coulomb collisions, bremsstrahlung and ionization. For values of the gas density and magnetic field that are representative of the Milky Way, it is estimated that pressure gradients are strong enough to balance gravity in the central parts if E0 < 1GeV. The exact value depends somewhat on the astrophysical parameters, and it changes dramatically with the slope of the dark matter density profile. For very steep slopes, as those expected from adiabatic contraction, the rotation curves of spiral galaxies would be affected on ~kpc scales for most values of E0. By comparing the predicted rotation curves with observations of dwarf and low surface brightness galaxies, we show that the pressure from dark matter annihilation may improve the agreement between theory and observations in some cases, but it also imposes severe constraints on the model parameters (most notably, the inner slope of halo density profile, as well as the mass and the annihilation cross-section of dark matter particles into electron-positron pairs)This work has been funded by DFG Research Grant AS 312/1-1 (Germany).YA also acknowledges support from project AYA 2007-67965-C03-03 (MEC, Spain

Dark matter annihilation feedback in cosmological simulations – II. The influence on gas and halo structure

“…Another less explored avenue of investigation into dark matter annihilation raises the question if any energy released by the decay and subsequent interaction of the annihilation products could play an active role in late structure-formation (Ascasibar 2007). The expected interaction products in the form of particles and photons deposit their energy in to the nearby baryonic material of galaxies and the intergalactic medium, and a number of studies show that Dark Matter Annihilation Feedback (DMAF) could affect gas flows, cosmic rays and early star formation (Ripamonti et al 2007;Natarajan et al 2008;Wechakama & Ascasibar 2011;Schön et al 2015Schön et al , 2018.…”

Effects of Chameleon Scalar Field on Rotation Curves of the Galaxies

“…In the equation of motion of the chameleon scalar field, we will set the pressure of matter to zero by assuming that the matter in the universe is in the dust form and ignoring the possible annihilation pressure of dark matter and such [20]. The effective pressure thus only comes from the scalar field.…”

Accelerated expansion of the Universe in the presence of dark matter pressure

“…However, the DM as one of the significant portion of the Universe can affect the astrophysical systems through its pressure [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. The observations of rotation curves together with the gravitational lensing can determine the equation of state (EOS) of DM [25].…”