Spatially resolved spectroscopy of the globular cluster RZ 2109 and the nature of its black hole

TL;DR

This study uses spatially resolved spectroscopy to analyze the [OIII] emission in globular cluster RZ 2109, revealing an extended nebula incompatible with an intermediate mass black hole, suggesting a stellar mass black hole with a strong wind.

Contribution

First spatially resolved spectroscopy of RZ 2109's nebula, providing new insights into its morphology and challenging previous black hole models.

Findings

[OIII] emission has a half-light radius of 3-7 pc.

Extended nebula inconsistent with intermediate mass black hole models.

Supports a stellar mass black hole with a strong wind as the ionization source.

Abstract

We present optical HST/STIS spectroscopy of RZ 2109, a globular cluster in the elliptical galaxy NGC 4472. This globular cluster is notable for hosting an ultraluminous X-ray source as well as associated strong and broad [OIII] 4959, 5007 emission. We show that the HST/STIS spectroscopy spatially resolves the [OIII] emission in RZ 2109. While we are unable to make a precise determination of the morphology of the emission line nebula, the best fitting models all require that the [OIII] 5007 emission has a half light radius in the range 3-7 pc. The extended nature of the [OIII] 5007 emission is inconsistent with published models that invoke an intermediate mass black hole origin. It is also inconsistent with the ionization of ejecta from a nova in the cluster. The spatial scale of the nebula could be produced via the photoionization of a strong wind driven from a stellar mass black hole accreting at roughly its Eddington rate.