Poster Abstract
Sagittarius dwarf Spheroidal (Sgr dSph) galaxy is a satelite of the Milky Way. Martı́nez-Delgado et al. (2002) detected two tidal debris in the northern streams of the Sgr dSph galaxy suggesting that the Sgr dSph and Milky Way halo are merging and Sgr dSph galaxy. Sgr dSph galaxy have many globular clusters and some of the Milky way clusters, example Pal 12, may have been part of the cluster in the past (Cohen 2004). The wrok from many authors in the past have shown that Pal 12, Pal 3, Terzan 7, NGC 6715, Arp 2, NGC 5634, Terzan 8, Whiting 1 and Berkeley 29 are associated with the galaxy (Sbordone et al. (2005), Monaco et al. (2005), Bellazzini et al. (2008), Law & Majewski (2010), Sbordone et al. (2015), Carretta et al. (2017), Carraro et al. (2007)). Association of NGC 5053 with the galaxy is still ambiguise (Sbordone et al. (2015), Tang et al. (2018)). We are using Gaia DR2 data along Harris (1996) catalog to analyse the extra-tidal feature of the clusters. We select the extra -tidal stars based on three main criteria: 1. star should be atleast tidal radius away from the center of the cluster but not more than 5*TR away; 2. PM of the star must match the PM of the cluster within 3 sigma error; 3: Star must lie on the CMD of the cluster. Our primary analysis points at promising results for Terzan 7, Arp 2, M54, NGC 4147, Terzan 8, NGC 2419 ang NGC 5634.
Plain text summary
Globular clusters (GCs) are very old (almost as old as the Universe!) and carry chemical and dynamical information about the initial conditions of their host galaxy. Also, given their typical stellar mass (of the order of 10^4-10^5 solar masses), these systems have shorter dynamical time scales, and various dynamical processes (relaxation, mass segregation, core-collapse etc) can be studied looking at the distribution of stars in their outskirt regions. We chose Sagittarius dwarf Spheroidal (Sgr dSph) galaxy for our analysis because its long stellar streams, emerging from its disruption, are quite prominent evidence of on-going accretion of a satellite galaxy onto the Milky Way. Besides the different arms of its stellar stream, the Sgr galaxy brought several globular clusters into the Milky Way. Hence, the extra-tidal region around these clusters can give us some idea about the various forces acting on the clusters. List of member GCs is taken from Bellazzini et al 2020, 636, A107. According to their finding, M 54, Terzan 8, Terzan 7, Arp 2, Pal 12, Whiting 1 are confirmed members of Sgr dSph galaxy, NGC 2419, NGC 5634, NGC 4147 are likely members and NGC 6284, Pal 2 are probably not the members of the galaxy. Extra-tidal stars are the stars which lie outside the tidal radius (rt) of the cluster. Extra-tidal stars around the clusters were selected based on following three criteria: 1.Stars which have a projected distance to the cluster center inside rt<r<5rt, where rt is the tidal radius of the cluster. 2.Proper motion (PM) of the star must match with the PM of the cluster considering dispersion in the PM of the cluster and individual error in the PM of the star. 3.Stars that lie on the color-magnitude diagram of the cluster (i.e., are part of the same stellar population). For details about astrometric cleaning of the data and selection process, please refer to Kundu et al 2019, MNRAS, 483, 1Public Engagement and Outreach and\or Kundu et al 2019, 2019, MNRAS, 489, 4565. The mean PM was determined by fitting Gaussian to the PM distribution of the cluster population in R.A. and Dec, separately. Results of our fit matched with the literature values from Vasiliev E., 2019, MNRAS, 484, 2832. Isochrones are taken from http://stev.oapd.inaf.it/cgi-bin/cmd and tr from Mackey, A. D. & Van Den Bergh, S. 2005, MNRAS, 360, 631–645. Out of the 10 globular clusters analyzed in our work 7 clusters show the signatures of extra-tidal stars. We found considerable extra-tidal stars outside the Jacobi radius of these 7 clusters which means that these stars are completely detached from the clusters. Stars which are outside the Jacobi radius are completely out of the cluster’s gravitational potential and hence are not attached to the cluster anymore. Stars which are outside the rt but inside the Jacobi radius of the clusters have higher chance of escaping the cluster potential. The analysis seems accurate for NGC 4147, Terzan 8, NGC 5634 and NGC 2419. Most of the extra-tidal stars for all these clusters (except NGC 4147) lie outside the Jacobi radius. For NGC 4147, NGC 5634 and NGC 2419 most of the extra-tidal stars lie in a direction which is opposite to the PM of the cluster and away from the Galactic center. Presence of extra-tidal stars in the clusters indicates that they could be experiencing high gravitational forces from the Sgr dSph galaxy, Milky Way and/or both. Near future spectroscopy surveys such as WEAVE, MOONs, SDSS-V and 4-MOST will help to disentangle the chemodynamics properties of the outermost regions of these GCs and other, for the moment we are examining available high-resolution near-infrared data such as APOGEE-2.
Poster Title
Globular clusters from the Sagittarius dwarf Spheroidal galaxy
