We present the discovery of [O III] λ5007 emission associated with the black hole X-ray binary recently identified in a globular cluster in the Virgo elliptical galaxy NGC 4472. This object is the first confirmed black hole X-ray binary in a globular cluster. The identification of [O III] λ5007 emission from the black hole hosting globular cluster is based on two independent fiber spectra obtained at the VLT with FLAMES, which cover a wavelength range of 5000-5800 Å at a spectral resolution of about 6000. In each of these spectra we find an emission line at 5031.2 Å with an uncertainty of several tenths of an angstrom. These are consistent with [O III] 15007 emission at the 1475 ± 7 km s-1 radial velocity of the globular cluster previously determined from an analysis of its absorption lines. This agreement within the small uncertainties argues strongly in favor of the interpretation of the line as [O III] λ5007 emission from the black hole hosting globular cluster. We also find that the emission line most likely has a velocity width of several hundred km s. Such a velocity width rules out a planetary nebula explanation for the [O III] λ5007 emission and implicates the black hole as the source of the power driving the nebular emission.
- Galaxies: individual (NGC 4472)
- Galaxies: star clusters
- Globular clusters: general
- X-rays: binaries
- X-rays: galaxies: clusters