Discovery of a New Local Group Dwarf Galaxy Candidate in UNIONS: Boötes V
Abstract
We present the discovery of Boötes V, a new ultra-faint dwarf galaxy (UFD) 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 data set. It has a physical half-light radius of ${26.9}_{-5.4}^{+7.5}$ pc, a V-band magnitude of -4.5 ± 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. The brightest star in this system was followed up using Gemini GMOS-N long-slit spectroscopy and is measured to have a metallicity of [Fe/H] = -2.85 ± 0.10 dex and a heliocentric radial velocity of v r = 5.1 ± 13.4 km s-1. Boötes V is larger (in terms of scale radius), more distant, and more metal-poor than the vast majority of globular clusters. It is likely that Boötes V is an UFD, though future spectroscopic studies will be necessary to definitively classify this object.
- Publication:
-
The Astronomical Journal
- Pub Date:
- August 2023
- DOI:
- 10.3847/1538-3881/acdd77
- arXiv:
- arXiv:2209.08242
- Bibcode:
- 2023AJ....166...76S
- Keywords:
-
- Dwarf galaxies;
- Local Group;
- Broad band photometry;
- Milky Way stellar halo;
- 416;
- 929;
- 184;
- 1060;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 13 pages, 7 figures, 3 tables. Accepted for publication in the AAS Journals. Please note that this paper was submitted in coordination with the work of William Cerny et al. 2022. These authors independently discovered this same satellite so our two research groups have coordinated the submission of these discovery papers