Search for extratidal features around 17 globular clusters in the Sloan Digital Sky Survey

Abstract

Context. The dynamical evolution of a single globular cluster and also of the entire Galactic globular cluster system has been studied theoretically in detail. In particular, simulations show how the "lost" stars are distributed in tidal tails emerging from the clusters. Aims. We investigate the distribution of Galactic globular cluster stars on the sky to identify such features as tidal tails. The Sloan Digital Sky Survey provides consistent photometry of a large part of the sky to study the projected two-dimensional structure of the 17 globular clusters in its survey area. Methods. We used a color-magnitude weighted counting algorithm to map (potential) cluster member stars on the sky. Results. We recover the already known tidal tails of Pal 5 and NGC 5466. For NGC 4147 we find a two-arm morphology. Possible indications of tidal tails are also seen around NGC 5053 and NGC 7078, confirming earlier suggestions. Moreover, we find potential tails around NGC 5904 and Pal 14. Especially for Palomar clusters other than Pal 5, deeper data are needed to confirm or to rule out the existence of tails. For many of the remaining clusters in our sample we observe a pronounced extratidal halo, which is particularly large for NGC 7006 and Pal 1. In some cases, the extratidal halos may be associated with the stream of the Sagittarius dwarf spheroidal galaxy (e.g., NGC 4147, NGC 5024, NGC 5053).