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 ≲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]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 1600kms^-1, and the remainder from a Gaussian component with an FWHM of several hundredkms ^-1.