The Saga of M81: Global View of a Massive Stellar Halo in Formation

Understand

Recent work has shown that Milky Way-mass galaxies display an incredible range of stellar halo properties, yet the origin of this diversity is unclear.

• The nearby galaxy M81 $-$ currently interacting with M82 and NGC 3077 $-$ sheds unique light on this problem.
• We present a Subaru Hyper Suprime-Cam survey of the resolved stellar populations around M81, revealing M81's stellar halo in never-before-seen detail.
• We resolve the halo to unprecedented $V$-band equivalent surface brightnesses of 33 mag arcsec$^{-2}$, and produce the first-ever global stellar mass density map for a Milky Way-mass stellar halo outside of the Local Group.