A WIDE-FIELD PHOTOMETRIC SURVEY FOR EXTRATIDAL TAILS AROUND FIVE METAL-POORGLOBULAR CLUSTERS IN THE GALACTIC HALO

摘要

Wide-field deep images obtained with the Megacam of the Canada—France—Hawaii Telescope are used toinvestigate the spatial configuration of stars around five metal-poor globular clusters M15, M30, M53, NGC 5053,and NGC 5466, in a field-of-view —3°. Applying a mask filtering algorithm to the color—magnitude diagrams of theobserved stars, we sorted cluster's member star candidates that are used to examine the characteristics of the spatialstellar distribution surrounding the target clusters. The smoothed surface density maps and the overlaid isodensitycontours indicate that all of the five metal-poor globular clusters exhibit strong evidence of extratidal overdensityfeatures over their tidal radii, in the form of extended tidal tails around the clusters. The orientations of the observedextratidal features show signatures of tidal tails tracing the clusters' orbits, inferred from their proper motions, andeffects of dynamical interactions with the Galaxy. Our findings include detections of a tidal bridge-like featureand an envelope structure around the pair of globular clusters M53 and NGC 5053. The observed radial surfacedensity profiles of target clusters have a deviation from theoretical King models, for which the profiles show a breakat 0.5-0.7r,, extending the overdensity features out to 1.5-2r,. Both radial surface density profiles for differentangular sections and azimuthal number density profiles confirm the overdensity features of tidal tails around thefive metal-poor globular clusters. Our results add further observational evidence that the observed metal-poor haloglobular clusters originate from an accreted satellite system, indicative of the merging scenario of the formation ofthe Galactic halo.