Zhijie Qu, Rui Huang, Joel N. Bregman, Jiang-Tao Li
We report a large-scale ($r\approx 20^\circ$) X-ray and Sunyaev-Zeldovich(SZ)-bright diffuse enhancement toward M31, which might be a Local Hot Bridgeconnecting the Milky Way (MW) with M31. We subtract the Galactic emission fromthe all-sky O VII and O VIII emission line measurement survey, and find thatthe emission of these two ions is enhanced within $r\approx20^\circ$ aroundM31. The mean emission enhancements are $5.6\pm 1.3$ L.U., and $2.8\pm0.6$ L.U.for O VII and O VIII, respectively ($>4\sigma$ for both ions). We also extractthe SZ signal around M31, which suggests a surface brightness $y$ of$2-4\times10^{-7}$, an enhancement $>2.5\sigma$ (and a best fit of$5.9\sigma$). These three measurements trace the hot gas with a temperature$\log~T({\rm K})> 6$, showing similar plateau shapes (flat within$\approx15^\circ$, and zero beyond $\approx30^\circ$). A single-phaseassumption leads to a temperature of $\log~T({\rm K})=6.34\pm0.03$, which isdetermined by the O VII/O VIII line ratio. Combining X-ray and SZ measurements,we suggest that this feature is unlikely to be the hot halo around M31 (toomassive) or in the MW (too high pressure and X-ray bright). The plateau shapemay be explained by a cylinder connecting the MW and M31 (the Local HotBridge). We constrain its length to be about 400 kpc, with a radius of 120 kpc,a density of $\approx 2\times10^{-4}-10^{-3} ~\rm cm^{-3}$, and a metallicityof $0.02-0.1~ Z_\odot$. The baryon mass is $\gtrsim10^{11}~M_\odot$, and theoxygen mass is about $\gtrsim10^8~M_\odot$, which contribute to the baryon ormetal budget of the Local Group.