Pal 13: its moderately extended low-density halo and its accretion history

Abstract

We present results on the basis of Dark Energy Camera Legacy Survey (DECaLS) DR8 astrometric and photometric data sets of the Milky Way globular cluster Pal 13. Because of its relative small size and mass, there has not been yet a general consensus about the existence of extra-tidal structures around it. While some previous results claim for the absence of such features, others have shown that the cluster is under the effects of tidal stripping. From DECaLS g, r magnitudes of stars placed along the cluster Main Sequence in the color-magnitude diagram -previously corrected by interstellar reddening-, we built the cluster stellar density map. The resulting density map shows nearly smooth contours around Pal 13 out to ≈ 1.6 times the most recent estimate of its Jacobi radius, derived by taking into account its variation along its orbital motion. This outcome favors the presence of stars escaping the cluster, a phenomenon frequently seen in globular clusters that have crossed the Milky Way disc a comparable large number of times. Particularly, the orbital high eccentricity and large inclination angle of this accreted globular cluster could have been responsible for the relatively large amount of cluster mass lost.

Multiple populations in low mass globular clusters: Palomar 13

“…The existence of MPs in Pal 13 supports the statement that this phenomenon is not unique in Galactic GCs formed in − situ (e.g., Li & de Grijs 2019;Milone et al 2020). Besides its proposed accreted origin, Pal 13 is suggested to be experiencing tidal stripping (Yepez et al 2019;Piatti & Fernández-Trincado 2020). Hamren et al (2013) found that Pal 13 has lost a considerable amount of mass, which is related to its low present-day cluster mass.…”

“…This indicates MPs exist in the GC Pal 13. This GC recently attracts attention because of its revealed peculiarity under deep photometric observations, e.g., high binary fraction (Clark et al 2004), experiencing tidal dissolution (Piatti & Fernández-Trincado 2020), and the discovery of tidal tails (Shipp et al 2020). Our novel discovery of MPs in Palomar 13 is consistent with the suggested large mass loss, assuming that MPs are preferentially formed in large initial mass GCs (Conroy & Spergel 2011).…”

“…Due to its large distance, several detailed features of Pal 13 have been discovered just recently (e.g. Piatti & Fernández-Trincado 2020;Shipp et al 2020) and more are still waiting for further investigation, the estimation of total mass loss or initial mass of Pal 13 should be illuminative for future studies. Besides Pal 13, several remote, low mass GCs, including Whiting 1 and Eridanus GC, also show evidence of tidal tails or extra-tidal structures (Carballo-Bello et al 2014;Myeong et al 2017).…”

“…B11 found the dynamical mass inside the half-light radius to be 1.3 +2.7 −1.3 × 10 3 M . More interestingly, this GC is possibly under dissolution (Piatti & Fernández-Trincado 2020;Shipp et al 2020). We carefully discuss its implications in Section 3.…”

The elusive tidal tails of the Milky Way globular cluster NGC 7099

“…Because of two-body relaxation, less massive stars are candidates to escape the cluster more easily than more massive ones (Balbinot & Gieles 2018). Hence, fainter cluster main sequence (MS) stars are usually used to search for extra-tidal structures around globular clusters (see Piatti & Fernández-Trincado 2020, and references therein). We, therefore, take advantage of the well-delineated MS shown in Fig.…”