The tidal tails of the ultrafaint globular cluster Palomar 1

Abstract

Using the optimal filter technique applied to Sloan Digital Sky Survey photometry, we have found extended tails stretching about 1° (or several tens of half-light radii) from either side of the ultrafaint globular cluster Palomar 1. The tails contain roughly as many stars as does the cluster itself. Using deeper Hubble Space Telescope data, we see that the isophotes twist in a characteristic S-shape on moving outwards from the cluster centre to the tails. We argue that the main mechanism forming the tails may be relaxation-driven evaporation and that Pal 1 may have been accreted from a now disrupted dwarf galaxy ~500 Myr ago. © 2010 The Authors. Journal compilation © 2010 RAS.