Big fish, small fish: Two New Ultra-Faint Satellites of the Milky Way

TL;DR

This paper reports the discovery of two ultra-faint Milky Way satellites, Pisces II and Segue 3, using Sloan Digital Sky Survey data and follow-up imaging, revealing their structural properties and distances.

Contribution

It introduces two new ultra-faint satellites of the Milky Way, expanding knowledge of its satellite system and providing detailed structural measurements.

Findings

Pisces II is about 180 kpc away with a 60 pc half-light radius.

Segue 3 is 16 kpc away with a 3 pc half-light radius.

Both objects are ultra-faint, with Segue 3 being a star cluster and Pisces II a dwarf galaxy.

Abstract

We report the discovery of two new Milky Way satellites in the neighboring constellations of Pisces and Pegasus identified in data from the Sloan Digital Sky Survey. Pisces II, an ultra-faint dwarf galaxy lies at the distance of ~180 kpc, some 15 degrees away from the recently detected Pisces I. Segue 3, an ultra-faint star cluster lies at the distance of 16 kpc. We use deep follow-up imaging obtained with the 4-m Mayall telescope at Kitt Peak National Observatory to derive their structural parameters. Pisces II has a half-light radius of ~60 pc, while Segue 3 is twenty times smaller at only 3pc.