The Influence of the Bar on the Dynamics of Globular Clusters in the Central Region of the Milky Way. Frequency Analysis of Orbits According to Gaia EDR3 Data

Abstract

This work is devoted to studying the influence of the bar on the orbital dynamics of globular clusters. The orbits of 45 globular clusters in the central galactic region with a radius of 3.5 kpc were analyzed using spectral dynamics methods in order to identify objects captured by the bar. To form the 6D phase space required for orbit integration, the most accurate astrometric data to date from the Gaia satellite (EDR3), as well as new refined average distances to globular clusters, were used. Since the parameters of the Milky Way bar are known with very great uncertainty, the orbits were constructed and their frequency analysis was carried out by varying the mass, length and angular velocity of rotation of the bar in a wide range of values with a fairly small step. The integration of orbits was carried out at 2.5 billion years ago. As a result, bar-supporting globular clusters were identified for each set of bar parameters. For the first time, an analytical expression has been obtained for the dependence of the dominant frequency $f_{X}$ on the angular velocity of rotation of the bar. In addition, the probabilities of globular clusters being captured by the bar were determined when the bar parameters were varied in certain ranges of values according to a random distribution law. A list of 14 globular clusters with the most significant capture probabilities is given, with five GCs—NGC 6266, NGC 6569, Terzan 5, NGC 6522, NGC 6540—showing the probability of capture by the bar $P\geq 0.2$. A conclusion is made about the regularity of the orbits of globular clusters based on the calculation of approximations of the maximum characteristic Lyapunov exponents.