Pegasus V -- a newly discovered ultra-faint dwarf galaxy on the outskirts of Andromeda

TL;DR

Pegasus V is a newly discovered ultra-faint dwarf galaxy near Andromeda, characterized by its sparse stellar population, very low metallicity, and location in the galaxy's outskirts, indicating a potentially ancient origin.

Contribution

This paper reports the first detection of an ultra-faint dwarf galaxy outside the Pan-Andromeda Archaeological Survey area, expanding knowledge of Andromeda's faint satellite population.

Findings

Pegasus V is approximately 692 kpc from Earth.

It has an absolute magnitude of -6.3 and a half-light radius of 89 pc.

The galaxy is very metal-poor with [Fe/H] ≈ -3.2.

Abstract

We report the discovery of an ultra-faint dwarf in the constellation of Pegasus. Pegasus~V (Peg~V) 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 over-density 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 $M_V=-6.3\pm0.2$ and a half-light radius of $r_{\rm half}=89\pm41$~pc. It is located $\sim260$~kpc from Andromeda in the outskirts of its halo. The RGB is well-fit 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 reionisation fossil. This is the first detection of an ultra-faint dwarf outside the deep Pan-Andromeda Archaeological Survey area, and points to a rich, faint satellite population in the outskirts of our nearest neighbour.