Typhon: A Polar Stream from the Outer Halo Raining through the Solar Neighborhood

Abstract We report on the discovery in Gaia DR3 astrometric and spectroscopic catalog of a new polar stream that is found as an overdensity action space. This structure unique it has extremely large apocenter distance, reaching beyond 100 kpc, yet detected coherent moving solar neighborhood with width ∼4 kpc. A subsample these stars was fortuitously observed by LAMOST mean metallicity 〈 stretchy="false">[ Fe stretchy="true">/ H stretchy="false">] stretchy="false">〉 = − 1.60 0.16 + 0.15 dex possesses resolved dispersion $\sigma ([\mathrm{Fe}/{\rm{H}}])={0.32}_{-0.06}^{+0.17}$?> σ stretchy="false">( stretchy="false">) 0.32 0.06 0.17 dex. The physical stream, dispersion, vertical spread indicate progenitor dwarf galaxy. existence such highly radial at their pericenters vicinity Sun suggests many other galaxy fragments may be lurking outer halo.