Abstract
We use observations of gas-rich dwarf galaxies to derive constraints on dark matter scattering with ordinary matter. We require that heating/cooling due to DM interacting with gas in the Leo T dwarf galaxy not exceed the ultra-low radiative cooling rate of the gas. This enables us to set $(i)$ stronger bounds than all the previous literature on ultra-light hidden photon DM for nearly all of the mass range $10^{-23}\lesssim m_\mathrm{DM} \lesssim 10^{-10}$ eV, $(ii)$ limits on sub-GeV millicharged DM which add to the constraints on the recent EDGES 21cm absorption anomaly, and $(iii)$ constraints on DM-baryon interactions directly at low relative velocities $v_\mathrm{rel}\sim 17$ km/s. Our study opens a new direction at using observations of gas-rich dwarf galaxies from previous, current and upcoming optical and 21cm surveys to probe physics beyond the standard model.
Highlights
The particle nature of dark matter (DM) and its origin is still a mystery
In addition to using Leo T to add to the constraints on DM interactions in the cosmic dawn and on millicharged DM more generally, we report constraints on ultralight hidden photon DM (HPDM)
We indicate, with the dashed gray line of Fig. 3, the value of ε such that the characteristic DM energy loss/gain time is comparable to the Leo T lifetime: ðd ln E=dtÞ−1 ≈ 10 Gyr; the millicharge coupling must be smaller than this
Summary
The particle nature of dark matter (DM) and its origin is still a mystery. The EDGES Collaboration reported observations suggesting the temperature of gas during the cosmic dawn of the Universe was roughly half the expected value [1]. Ongoing and future 21 cm surveys (like WALLABY [64] and SKA [65]), and optical surveys (like DES [66,67,68,69], the SAGA survey [70,71], DESI [72], HSC [73], MSE [74], Rubin observatory [75,76], and the Roman telescope [77]) will find and characterize an even larger number of these galaxies This motivates finding new ways to use gas-rich dwarfs to probe physics beyond the standard model. We eschew use of the HVNO clouds and instead use the robustly observed gas clouds of Ref. [89] which are in tranquil environments corotating with the Galactic disk and not close to the Galactic Center
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