Pegasus V/Andromeda XXXIV–a newly discovered ultrafaint dwarf galaxy on the outskirts of Andromeda

Journal Article · 26 July 2022 · Monthly Notices of the Royal Astronomical Society: Letters

DOI: https://doi.org/10.1093/mnrasl/slac063 · OSTI ID:1878238

Collins, Michelle L. M. ; Charles, Emily J. E.; Martínez-Delgado, David; Monelli, Matteo; Karim, Noushin; Donatiello, Giuseppe; Tollerud, Erik J.; Boschin, Walter

ABSTRACT We report the discovery of an ultrafaint dwarf in the constellation of Pegasus. Pegasus V (Peg V)/Andromeda XXXIV was initially identified in the public imaging data release of the DESI Legacy Imaging Surveys and confirmed with deep imaging from Gemini/GMOS-N. The colour–magnitude diagram shows a sparse red giant branch (RGB) population and a strong overdensity of blue horizontal branch stars. We measure a distance to Peg V of $$D=692^{+33}_{-31}$$ kpc, making it a distant satellite of Andromeda with MV = −6.3 ± 0.2 and a half-light radius of rhalf = 89 ± 41 pc. It is located ∼260 kpc from Andromeda in the outskirts of its halo. The RGB is well fitted by a metal-poor isochrone with [Fe/H] = −3.2, suggesting it is very metal poor. This, combined with its blue horizontal branch, could imply that it is a reionization fossil. This is the first detection of an ultrafaint dwarf outside the deep Pan-Andromeda Archaeological Survey area, and points to a rich, faint satellite population in the outskirts of our nearest neighbour.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
• Sponsoring Organization: Chinese Academy of Sciences (CAS); National Natural Science Foundation of China (NSFC); National Science Foundation (NSF); USDOE; USDOE Office of Science (SC)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1878238
• Journal Information: Monthly Notices of the Royal Astronomical Society: Letters, Journal Name: Monthly Notices of the Royal Astronomical Society: Letters Journal Issue: 1 Vol. 515; ISSN 1745-3925
• Publisher: Oxford University PressCopyright Statement
• Country of Publication: United Kingdom
• Language: English