A Pair of Bootes: A New Milky Way Satellite

TL;DR

This paper reports the discovery of a new faint Milky Way satellite near Boötes, identified through data mining of SDSS data, characterized as an old, metal-poor stellar system with properties between globular clusters and dwarf galaxies.

Contribution

It introduces a new Milky Way satellite discovered via a data mining algorithm in SDSS data, expanding knowledge of faint galactic satellites.

Findings

Discovered a new stellar overdensity near Boötes.

Estimated the satellite's magnitude and size, placing it between globular clusters and dwarf galaxies.

Confirmed the stellar population as old and metal-poor.

Abstract

As part of preparations for a southern sky search for faint Milky Way dwarf galaxy satellites, we report the discovery of a stellar overdensity in the Sloan Digital Sky Survey Data Release 5, lying at an angular distance of only 1.5 degrees from the recently discovered Bo{\"o}tes dwarf. The overdensity was detected well above statistical noise by employing a sophisticated data mining algorithm and does not correspond to any catalogued object. Overlaid isochrones using stellar population synthesis models show that the color-magnitude diagram of that region has the signature of an old (12 Gyr), metal-poor (${\rm Fe/H}\approx-2.0$) stellar population at a tentative distance of 60 kpc, evidently the same heliocentric distance as the Bo\"otes dwarf. We estimate the new object to have a total magnitude of $M_{V}\sim-3.1\pm1.1$ mag and a half-light radius of $r_{h}=4'.1\pm1'.6$ ($72\pm28$ pc) placing it in an apparent $40<r_{h}<100$ pc void between globular clusters and dwarf galaxies, occupied only by another recently discovered Milky Way Satellite, Coma Berenices.