NGC 2419 -- Another Remnant of Accretion by the Milky Way

TL;DR

This study analyzes the chemical composition of stars in NGC 2419, revealing a calcium abundance spread that supports its origin as a remnant of a dwarf galaxy accreted by the Milky Way.

Contribution

It provides the first detailed chemical abundance analysis of NGC 2419's stars, confirming its complex history and supporting its classification as an accreted dwarf galaxy remnant.

Findings

Detected a ~0.2 dex spread in calcium abundance among cluster stars.

Confirmed the cluster's status as a remnant of an accreted dwarf galaxy.

Demonstrated the effectiveness of combining moderate and high-resolution spectra.

Abstract

We isolate a sample of 43 upper RGB stars in the extreme outer halo Galactic globular cluster NGC 2419 from two Keck/DEIMOS slitmasks. The probability that there is more than one contaminating halo field star in this sample is extremely low. Analysis of moderate resolution spectra of these cluster members, as well as of our Keck/HIRES high resolution spectra of a subsample of them, demonstrates that there is a small but real spread in Ca abundance of ~ 0.2 dex within this massive metal-poor globular cluster. This provides additional support to earlier suggestions that NGC 2419 is the remnant of a dwarf galaxy accreted long ago by the Milky Way.