Wide-Field Stellar Distributions around the Remote Young Galactic Globular Clusters Palomar 3 and Palomar 4

Abstract

In a search for tidal extension features and/or streams of the probable parent satellite galaxies around the remote young globular clusters Pal 3 and Pal 4, we used wide-field VI photometry of an area a $ 1=3 Â 1=3 around Pal 3 and an area a $ 1=3 Â 0=9 around Pal 4, obtained with the CFH12K mosaic CCD. Applying the CMD-mask algorithm to stars in the vicinity of the clusters, we selected member star candidates that were used to examine the characteristics of the spatial distribution of stars around Pal 3 and Pal 4. The isodensity contours in the Gaussian-smoothed spatial stellar density maps around the clusters, and the KolmogorovSmirnov test applied to the corresponding luminosity functions, indicate tidal halos around Pal 3 at distances of up to $4r t , and around Pal 4 of up to $6r t . The stellar distribution around Pal 3 suggests north-south elongations along the directions of the Galactic center and anticenter, and a northeast extension in the direction of the cluster's proper motion. In the vicinity of Pal 4 an extension of a tail around the cluster in the opposite direction to the Galactic center and a possible extension of stars toward the Galactic center have also been detected in the isodensity maps and in the angular luminosity functions. We discuss the relevance of the spatial distribution of stars in possible streams around Pal 3 and Pal 4 to these spatial correlations and to the space orbits of the possible parent satellite galaxies.

Roche lobe shapes for testing MOND-like modified gravities

“…Outer globulars on long period orbits also have time to fill the instantaneous Roche lobe by two-body relaxation (Bellazzini 2004). Globular clusters as a class generally exhibit extra-tidal stars under deep observations; a sharp break of the star count profile and/or sometimes two-dimensional confirmation of unvirialised structures outside the King radius have been shown for globular clusters in the Milky Way, Andromeda, and other galaxies (Leon et al 2000;Lehmann & Scholz 1997;Sohn et al 2003;Harris et al 2002). To be generous we assume the instantaneous Roche lobe has a filling factor F 1 ∼ 0.01−1, or F −1/3 ∼ F −1/3 1 ∼ 1−5.…”

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

“…An interesting structure of the contour lines is visible at the cluster's western edge. Sohn et al (2003) studied the 2D morphology of Pal 3 and Pal 4 using CFH12K wide-field photometry. For Pal 3 they detect some extensions in the direction towards the Galactic center and anti-center which are not more prominent than 1σ over the background.…”

In search of massive single-population globular clusters

“…On the basis of the chemical and structural characteristics of the cluster, that is, the absence of s ‐process elements and anticorrelations (admittedly, an absence not yet safely established) we may consider Pal 3 as a good candidate to an FG‐only cluster. For what concerns the dynamical evolution, let us note however that Sohn et al (2003) found a weak evidence of tidal extensions around the cluster, out to ∼4 times the tidal (truncation) radius. In view of the long relaxation times at the centre and at r h (7 × 10 9 and 8 × 10 9 yr, respectively) and the estimated extremely long destruction time, we think that, in any case, such extra‐tidal objects should constitute a minor side effect.…”