Cores in Dwarf Galaxies from Dark Matter with a Yukawa Potential

TL;DR

It is shown that cold dark matter particles interacting through a Yukawa potential could naturally explain the recently observed cores in dwarf galaxies without affecting the dynamics of objects with a much larger velocity dispersion, such as clusters of galaxies.

Abstract

We show that cold dark matter particles interacting through a Yukawa potential could naturally explain the recently observed cores in dwarf galaxies without affecting the dynamics of objects with a much larger velocity dispersion, such as clusters of galaxies. The velocity dependence of the associated cross-section as well as the possible exothermic nature of the interaction alleviates earlier concerns about strongly interacting dark matter. Dark matter evaporation in low-mass objects might explain the observed deficit of satellite galaxies in the Milky Way halo and have important implications for the first galaxies and reionization.

Figures (2)

• Figure 1: Dependence of the self-interaction cross-section ($\sigma$) on the relative velocity ($v$) for dark matter interacting through a Yukawa potential. The normalizations of $\sigma$ and $v$ are set by free parameters in the underlying Lagrangian (see Appendix), and we show two possible curves peaking at $v_\sigma = 10~{\rm km~s^{-1}}$ and $=100~{\rm km~s^{-1}}$ ( blue, solid and purple, dashed, respectively).
• Figure 2: Astrophysical constraints on the normalization of the self-interaction cross-section ($\sigma_{\rm max}$) as a function of the velocity at which the peak collision rate is obtained ($v_{\sigma}$) in Fig. 1. The red solid line is normalized to have ${\langle \sigma \rangle}_{max}/m_\chi \approx 6\times 10^{-25}~{\rm cm^2/GeV}$ at $v_{\rm dwarf}\approx 10~{\rm km~s^{-1}}$, which should be regarded as the minimum interaction necessary to flatten the cores of dwarf galaxies. Additional lines indicate upper limits on the cross-section based on astrophysical considerations: X-ray cluster ellipticity ( blue, dashed), limiting $(\sigma_{max}/m_\chi) \stackrel{<}{\sim} 4\times 10^{-26}~{\rm cm^2/GeV}$ at $v\sim 10^3 {\rm km~s^{-1}}$; destruction of dwarf sub-halos through collisions with high velocity particles from a larger parent halo in which these dwarfs are embedded ( green, dotted), limiting $(\sigma_{max}/m_\chi)\stackrel{<}{\sim} 5 \times 10^{-25}~{\rm cm^2/GeV}$Gnedin:2000ea at $v\sim 200 {\rm km~s^{-1}}$; and requiring the number of scatters in dwarfs to be less than $\sim 10^2$ during the age of the Universe to avoid the gravothermal catastrophe ( purple, dash-dotted). Related limits are summarized in Buckley:2009in.