Paper detail

No sign (yet) of intergalactic globular clusters in the Local Group

We present Gemini/GMOS imaging of twelve candidate intergalactic globular clusters (IGCs) in the Local Group, identified in a recent survey of the SDSS footprint by di Tullio Zinn & Zinn (2015). Our image quality is sufficiently high, at $\sim 0.4^{\prime\prime} - 0.7^{\prime\prime}$, that we are able to unambiguously classify all twelve targets as distant galaxies. To reinforce this conclusion we use GMOS images of globular clusters in the M31 halo, taken under very similar conditions, to show that any genuine clusters in the putative IGC sample would be straightforward to distinguish. Based on the stated sensitivity of the di Tullio Zinn & Zinn (2015) search algorithm, we conclude that there cannot be a significant number of IGCs with $M_V \le -6$ lying unseen in the SDSS area if their properties mirror those of globular clusters in the outskirts of M31 -- even a population of $4$ would have only a $\approx 1\%$ chance of non-detection.