Testing self-interacting dark matter with galaxy warps

Abstract

Self-interacting dark matter (SIDM) is an able alternative to collisionless dark matter. If dark matter does have self-interactions, we would expect this to cause a separation between the collisionless stars and the dark matter halo of a galaxy as it falls through a dark matter medium. For stars arranged in a disk, this would generate a U-shaped warp. The magnitude of this warping depends on the SIDM cross section, type of self-interaction, relative velocity of galaxy and background, halo structure, and density of the dark matter medium. In this paper, we set constraints on long-range (light mediator) dark matter self-interaction by means of this signal. We begin by measuring U-shaped warps in $3,213$ edge-on disk galaxies within the Sloan Digital Sky Survey. We then forward-model the expected warp from SIDM on a galaxy-by-galaxy basis by combining models of halo structure, density and velocity field reconstructions, and models for the dark matter interactions. We find no evidence for a contribution to the warps from SIDM. Our constraints are highly dependent on the uncertain velocities of our galaxies: for a normalized Rutherford-like cross section we find $\tilde{\sigma }/m_{\mathrm{DM}}\lesssim 3\times 10^{-13}{\mathrm{cm}}^2/\mathrm{g}$ at fixed velocity $v=300km/s$ -- a bound that scales roughly linearly with increasing $v$. In the appendix we translate these bounds into limits on the momentum transfer cross section, finding ${\sigma }_T(300km/s)/{\mathrm{m}}_{\mathrm{DM}}\lesssim 0.1{\mathrm{cm}}^2/\mathrm{g}$. [abridged]

v2: minor modifications + appendix with results in terms of the momentum transfer cross section

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