Velocity Structure and Variability of [O III] Emission in Black Hole Host Globular Cluster RZ2109

TL;DR

This study investigates the velocity structure and variability of [O III] emission lines in the globular cluster RZ2109, revealing a stable emission profile dominated by bipolar outflows over nearly a year.

Contribution

It provides the first detailed analysis of the velocity structure and variability of [O III] emission in a black hole-hosting globular cluster using multi-facility observations.

Findings

[O III] emission lines show less than 10% variability over 467 days.

The velocity profile is consistent with a bipolar conical outflow at about 1,600 km/s.

The emission structure can be modeled with a two-component system including outflows and a Gaussian component.

Abstract

We present a multi-facility study of the optical spectrum of the extragalactic globular cluster RZ2109, which hosts a bright black hole X-ray source. The optical spectrum of RZ2109 shows strong and very broad [O III]\lambda \lambda 4959,5007 emission in addition to the stellar absorption lines typical of a globular cluster. We use observations over an extended period of time to constrain the variability of these [O III] emission lines. We find that the equivalent width of the lines is similar in all of the datasets; the change in L[O III]\lambda 5007 is \ltsim 10% between the first and last observations, which were separated by 467 days. The velocity profile of the line also shows no significant variability over this interval. Using a simple geometric model we demonstrate that the observed [O III]\lambda 5007 line velocity structure can be described by a two component model with most of the flux contributed by a bipolar conical outflow of about 1,600 km/s, and the remainder from a Gaussian component with a FWHM of several hundred km/s.