A Hero's Dark Horse: Discovery of an Ultra-Faint Milky Way Satellite in Pegasus

TL;DR

This paper reports the discovery of Pegasus III, an ultra-faint, old, and metal-poor dwarf galaxy satellite of the Milky Way, identified through star overdensity detection and confirmed with deep photometry, contributing to understanding of galaxy formation.

Contribution

The paper introduces the discovery of Pegasus III, a new ultra-faint dwarf galaxy satellite, using a novel overdensity detection algorithm and deep photometry confirmation.

Findings

Pegasus III is an old, metal-poor dwarf galaxy at 205 kpc.

It has a half-light radius of about 78 pc.

Its luminosity places it among dwarf galaxies on the size-luminosity plane.

Abstract

We report the discovery of an ultra-faint Milky Way satellite galaxy in the constellation of Pegasus. The concentration of stars was detected by applying our overdensity detection algorithm to the SDSS-DR 10 and confirmed with deeper photometry from the Dark Energy Camera at the 4-m Blanco telescope. Fitting model isochrones indicates that this object, Pegasus III, features an old and metal-poor stellar population ([Fe/H]$\sim-2.1$) at a heliocentric distance of $205\pm20$ kpc. The new stellar system has an estimated half-light radius of $r_h=78^{+30}_{-24}$ pc and a total luminosity of $M_{V}\sim-4.1\pm0.5$ that places it into the domain of dwarf galaxies on the size--luminosity plane. Pegasus III is spatially close to the MW satellite Pisces II. It is possible that the two might be physically associated, similar to the Leo IV and Leo V pair. Pegasus III is also well aligned with the Vast Polar Structure, which suggests a possible physical association.