The Peculiar Globular Cluster System of the S0 Galaxy NGC 7457

TL;DR

This study investigates the globular cluster system of NGC 7457, revealing a potentially unique intermediate-age subpopulation and unusual emission-line objects, suggesting complex formation history beyond typical bimodal distributions.

Contribution

It provides new evidence for a third, intermediate-age globular cluster subpopulation in NGC 7457, challenging the common bimodal paradigm in early-type galaxies.

Findings

Lack of clear bimodality in GC color distribution

Presence of two GCs with bright emission lines, likely planetary nebula and supernova remnant

Evidence for a possible intermediate-age GC subpopulation formed 2-3 Gyr ago

Abstract

We present HST photometry and Keck spectroscopy of globular clusters (GCs) in the nearby S0 galaxy NGC 7457. The V-I color-magnitude diagram of GCs lacks the clear bimodality present in most early-type galaxies; there may be a significant population of intermediate-color objects. Of 13 spectroscopically-observed GCs, two are unusually metal-rich and feature bright [O III] emission lines. We conclude that one probably hosts a planetary nebula and the other a supernova remnant. Such emission line objects should be more common in an intermediate-age stellar population than in an old one. We therefore suggest that, in addition to the typical old metal-rich and old metal-poor GC subpopulations, there may be a third subpopulation of intermediate age. Such a subpopulation may have been formed ~2-3 Gyr ago, in the same star-forming event that dominates the stellar population of the center of the galaxy.