Globular Clusters of the Galaxy: Chemical Composition vs Kinematics

Abstract

A comprehensive statistical analysis of the relationship between the chemical and spatially kinematic parameters of the globular clusters of the Galaxy has been performed. The data of the authors compilation catalog contain astrophysical parameters for 157 clusters and the relative abundances of α-elements for 69 clusters. For 121 clusters, the data are supplemented by spatially kinematic parameters taken from the literature. The phenomenon of reddening of horizontal branches of low-metal accreted globular clusters is discussed. We consider the contradiction between the criteria for clusters to belong to the subsystems of the thick disk and the halo in terms of chemical and kinematic properties. It consists in the fact that, regardless of belonging to the galactic subsystems by kinematics, almost all metallic ([Fe/H] > −1.0) clusters are located close to the center and plane of the Galaxy, while among the less metallic of both subsystems there are many distant ones. Differences in the abundances of α-elements in the stellar objects of the Galaxy and the surrounding low-mass dwarf satellite galaxies confirm the wellknown conclusion that all globular clusters and field stars of the accreted halo are remnants of galaxies of higher mass than the current environment of the Galaxy. A possible exception is a distant low-metal cluster with low relative abundance of α-elements Rup 106. stars and dwarf satellite galaxies, which we use for comparison.For all 157 globular clusters, we calculated the rectangular coordinates from positions and distances from [7], and for 115 of them-from [8]. We supplemented the data for the last 115 clusters with cylindrical velocity components, taking them from the authors of [8], and for the clusters Ter 4, Pal 3, Pal 5, Pal 13, NGC6528 and NGC7006 calculated them from their proper motions, radial velocities and distances from [7]. As a result, the number of clusters with known velocities increased by more than two-thirds compared to our previous work MKG19 and totals 121 objects. Among them are 63 clusters with the found abundances of chemical elements. The rectangular velocity components in a cylindrical coordinate system, the center of which is placed in the center of the Galaxy, were obtained on the basis of modern deep surveys (see studies [8], [9]). Previously, cross-identification was performed for objects of the catalogs USNO-B1, (U. S. Naval Observatory A1.0 catalogue), 2MASS (Two Micron All-Sky Survey), URAT1 (The First U. S. Naval Observatory (USNO) Astrometric Robotic Telescope Catalog), ALLWISE (The Wide-field Infrared Survey Explorer et IPAC), UCAC5 (New Proper Motions using GaiaDR1) and GaiaDR1 (based on the Tycho-Gaia Astrometric Solution) with subsequent reduction to the system Gaia DR1 TGAS (Tycho Gaia Astrometric Solution). In so doing, the difference of epochs was up to 65 years, the velocity of the Sun relative to the galactic center was taken equal to (U, V, W ) = (−10, 12 + 237, 7) km s −1 , and its galactic distance -R GC = 8.3 kpc. The average internal error declar...

Globular Clusters Lost by the Sagittarius Dwarf Spheroidal Galaxy

“…This is possible if Sgr was much more massive in the past and its debris would then occupy a large range of distances. Evidence in favor of this assumption is discussed by [66,97,99], but our method does not use this assumption, since in the LM10 model the initial mass of Sgr dSph is small, 6 × 10 8 M .…”

Physical and Chemical Properties of Galactic Global Clusters with Various Origins Identified from the Gaia DR2 Data

“…Recall that in [5], [6], [7] we identified clusters as genetically related (i. e., born from the same protogalactic cloud) if they were in direct orbits and stayed within 15 kpc from the galactic center. In addition, these clusters should demonstrate the same residual velocities as the field stars of the Galaxy's disk subsystems (i. e., close to circular) and not be considered the remnants of known satellite galaxies disrupted at that time.…”

“…In addition, these clusters should demonstrate the same residual velocities as the field stars of the Galaxy's disk subsystems (i. e., close to circular) and not be considered the remnants of known satellite galaxies disrupted at that time. Although we considered all counter-orbiting clusters to be accreted, nevertheless, the majority of clusters identified as genetically related using such different approaches to kinematic data coincided (compare Table 1 in [4] and [6]). Note that, unlike Massari et al [4], we added the bulge clusters to the thick disk, while those authors had all the stellar objects of the proper halo subsystem in the disk subsystem.…”

“…1c. The diagram shows that almost all clusters (except ESO452-SC11) with metallicity −1.5 < [Fe/H] < −1.0 belonging to the bulge and disk lie in a narrow layer above the tilted line drawn "by eye", which separates the positions of these clusters and accreted ones (see also [5,6]). Note that all the clusters of the low-energy group also lie above this line.…”

“…In [5], [6], [7] we calculated the probabilities of the clusters belonging to the subsystems of the thick disk and halo using the method described by Bensby et al [8] with the aid of ground-based measurements of their residual velocities. Only the clusters that belonged to the thick disk were considered to be genetically related to a single protogalactic cloud; as for the halo, we kept only the clusters in direct orbits within 15 kpc from the galactic center.…”