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

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] λλ4959, 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 data sets; the change in L[O III] λ5007 is lsim10% 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] λ5007 line velocity structure can be described by a two-component model with most of the flux contributed by a bipolar conical outflow of about 1600 km s^-1, and the remainder from a Gaussian component with an FWHM of several hundred km s^-1.