Discovery of a new Local Group Dwarf Galaxy Candidate in UNIONS: Bo\"otes V

Understand

We present the discovery of Bo\"otes V, a new ultra-faint dwarf galaxy candidate.

• This satellite is detected as a resolved overdensity of stars during an ongoing search for new Local Group dwarf galaxy candidates in the UNIONS photometric dataset.
• It has a physical half-light radius of 26.9$^{+7.5}_{-5.4}$ pc, a $V$-band magnitude of $-$4.5 $\pm$ 0.4 mag, and resides at a heliocentric distance of approximately 100 kpc.
• We use Gaia DR3 astrometry to identify member stars, characterize the systemic proper motion, and confirm the reality of this faint stellar system.