Signature of systemic rotation in 21 galactic globular clusters from APOGEE-2

¹ Instituto de Astrofísica, Facultad de Ciencias Exactas, Universidad Andrés Bello, Fernández Concha 700, Las Condes, Santiago, Chile
e-mail: ilariapetralia28@gmail.com
² Vatican Observatory, Vatican City State 00120, Italy
³ Departamento de Fisica, Universidade Federal de Santa Catarina, Trinidade, 88040-900 Florianopolis, Brazil
⁴ Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, Chile
⁵ Centro de Investigación en Astronomía, Universidad Bernardo O’Higgins, Avenida Viel, 1497 Santiago, Chile
⁶ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK

Received: 24 July 2023
Accepted: 26 March 2024

Abstract

Context. Traditionally, globular clusters (GCs) have been assumed to be quasi-relaxed non-rotating systems, characterized by spherical symmetry and orbital isotropy. However, in recent years, a growing set of observational evidence has been unveiling an unexpected dynamical complexity in Galactic GCs. Indeed, kinematic studies have demonstrated that a measurable amount of internal rotation is present in many present-day GCs.

Aims. The objective of this work is to analyse the APOGEE-2 value-added catalog (VAC) DR17 data of a sample of 21 GCs to extend the sample exhibiting signatures of systemic rotation and better understand the kinematic properties of GCs overall. Also, we aim to identify the fastest rotating GC from the sample of objects with suitable measurements.

Methods. From the sample of 23 GCs included in this work, the presence of systemic rotation was detected in 21 of the GCs, using three different methods. All these methods use the radial velocity referred to the cluster systemic velocity (Ṽ_r). Using the first method, it was possible to visually verify the clear-cut signature of systemic rotation; whereas using the second and third methods, it was possible to determine the amplitude of the rotation curve (A_rot) and the position angle (PA) of the rotation axis.

Results. This study shows that 21 GCs have a signature of systemic rotation. For these clusters, the rotation amplitude and the position angle of the rotation axis (PA₀) have been calculated. The clusters cover a remarkable range of rotational amplitudes, from 0.77 km s⁻¹ to 13.85 km s⁻¹.