ALFALFA Discovery of the Nearby Gas-Rich Dwarf Galaxy Leo~P. II. Optical Imaging Observations

TL;DR

This paper reports optical imaging observations of Leo P, a nearby gas-rich dwarf galaxy discovered by ALFALFA, revealing its stellar population, distance, and star formation activity, highlighting its extreme properties among low-mass systems.

Contribution

First optical imaging study of Leo P, providing detailed stellar population data, distance estimate, and evidence of ongoing star formation in a very low-mass, gas-rich galaxy.

Findings

Distance to Leo P is between 1.5 and 2.0 Mpc.

Leo P is the lowest-mass galaxy with significant gas and star formation.

Identified an HII region indicating active star formation.

Abstract

We present results from ground-based optical imaging of a low-mass dwarf galaxy discovered by the ALFALFA 21-cm HI survey. Broadband (BVR) data obtained with the WIYN 3.5-m telescope at Kitt Peak National Observatory (KPNO) are used to construct color-magnitude diagrams of the galaxy's stellar population down to V_0 ~ 25. We also use narrowband H-alpha imaging from the KPNO 2.1-m telescope to identify an HII region in the galaxy. We use these data to constrain the distance to the galaxy to be between 1.5 and 2.0 Mpc. This places Leo P within the Local Volume but beyond the Local Group. Its properties are extreme: it is the lowest-mass system known that contains significant amounts of gas and is currently forming stars.