Eight New Milky Way Companions Discovered in First-Year Dark Energy Survey Data

TL;DR

This paper reports the discovery of eight new Milky Way companions in the Dark Energy Survey data, including potential ultra-faint satellite galaxies, using a new likelihood-based detection algorithm and completeness analysis.

Contribution

It introduces a novel likelihood-based method for detecting and characterizing stellar over-densities in survey data, leading to new Milky Way companion discoveries.

Findings

Discovered eight new Milky Way companions in DES data.

Identified several likely ultra-faint satellite galaxies.

Developed a likelihood-based algorithm for stellar over-density detection.

Abstract

We report the discovery of eight new Milky Way companions in ~1,800 deg^2 of optical imaging data collected during the first year of the Dark Energy Survey (DES). Each system is identified as a statistically significant over-density of individual stars consistent with the expected isochrone and luminosity function of an old and metal-poor stellar population. The objects span a wide range of absolute magnitudes (M_V from -2.2 mag to -7.4 mag), physical sizes (10 pc to 170 pc), and heliocentric distances (30 kpc to 330 kpc). Based on the low surface brightnesses, large physical sizes, and/or large Galactocentric distances of these objects, several are likely to be new ultra-faint satellite galaxies of the Milky Way and/or Magellanic Clouds. We introduce a likelihood-based algorithm to search for and characterize stellar over-densities, as well as identify stars with high satellite membership probabilities. We also present completeness estimates for detecting ultra-faint galaxies of varying luminosities, sizes, and heliocentric distances in the first-year DES data.