An updated census of the Vast Polar Structure member galaxies

Abstract

The Vast Polar Structure (VPOS) is a thin, planar arrangement of dwarf galaxies oriented almost perpendicular to the Milky Way (MW) disc. Since its discovery, the census of VPOS member galaxies has progressively expanded thanks to continuous findings of new dwarfs in the vicinity of the MW and increasingly precise measurements of their phase-space coordinates. In this work, we present the largest census to date of VPOS member galaxies, building on a sample of 73 MW dwarfs for which positional and kinematic data are available in the literature. Based on their orbital poles, we identify 22 VPOS members: 12 MW satellites, the Large Magellanic Cloud (LMC), and 9 LMC satellites. With the exception of Bootes III, Kim 1, and Sculptor, all the on-plane dwarfs are co-rotating. Our revised census increases the known VPOS member population by nearly 50%, introducing Delve 4, Kim 1, Kim 3, Eridanus III, Pictor II, and YMCA-1 (3 MW and 3 LMC satellites, respectively) as new on-plane dwarfs. From this updated census, we revise the structural parameters of the VPOS, confirming its planar ($c/a \sim$0.27) and remarkably thin ($\sim$15 kpc) nature.