Detection of the Tidal Tail of the Globular Cluster Pal 5 with SDSS Commissioning Data

We have analysed commissioning data of the Sloan Digital Sky Survey (SDSS) in a 2.5^o wide equatorial band in order to search for tidal debris around the distant halo globular cluster Palomar 5. SDSS provides deep multi-color photometry in the u',g',r',i' and z' bands. These data have been used to locate the cluster population in multi-color-magnitude space and to efficiently separate extratidal cluster stars from the field population by means of a cell-count algorithm. The tidal extension of the cluster is traced by stars from about 0.5 mag above to 2 mag below the cluster main-sequence turn-off. We find clear evidence for a symmetrical two-sided tail which extends at least 1.5^o in north-eastern and south-western direction and is likely to continue further on beyond the edges of the currently available field. The orientation of the tail which is along constant galactic latitude provides an efficient constraint on the direction of the clusters tangential space motion. The spatial structure of the tail closely resembles the characteristic structures seen in numerically simulated cluster tails. Integrating the overdensity of stars in the region of the tail we find that the extra-tidal part of the cluster population equals about 50% of the current stellar content inside the cluster in the same magnitude range. We conclude that the cluster has experienced very heavy mass-loss during the last passages through the inner Galaxy.