A research team led by University of Arizona’s Steward Observatory astronomers presents a new catalog of 40,502 globular cluster candidates in Centaurus A, an elliptical galaxy located 13 million light-years away in the constellation of Centaurus, recommending follow-up observations focused on a set of 1,900 that are most likely to be true globular clusters.
This DEC image shows Centaurus A, a giant galaxy located some 13 million light-years away in the constellation of Centaurus. Image credit: CTIO / NOIRLab / DOE / NSF / AURA / M. Soraisam, University of Illinois at Urbana-Champaign & NOIRLab / T.A. Rector, University of Alaska Anchorage & NOIRLab / M. Zamani, NOIRLab / D. de Martin, NOIRLab.
Centaurus A is a visually stunning, elliptical galaxy featuring a relativistic jet spewing from a supermassive black hole at its center and spectacular streams of scattered stars left behind by past collisions and mergers with smaller galaxies orbiting Centaurus A.
Also known as NGC 5128, the galaxy is too far away to allow astronomers to see individual stars, but star clusters can be identified as such and used as fossil evidence of the galaxy’s tumultuous evolution.
“Centaurus A has been a leading target for extragalactic globular cluster studies due to its richness and proximity to Earth, but the majority of studies have focused on the inner 40,000 parsecs (about 130,500 light-years) of the galaxy, leaving the outer reaches of the galaxy largely unexplored,” said Allison Hughes, a doctoral student in the Department of Astronomy and Steward Observatory at the University of Arizona.
Hughes and colleagues surveyed globular cluster candidates out to a projected radius of approximately 150,000 parsecs (489,235 light-years) from the center of Centaurus A.
They analyzed data from the Panoramic Imaging Survey of Centaurus and Sculptor, the Gaia Data Release 2, and the NOAO Source Catalog.
Ranking the candidates based on the likelihood that they are true globular clusters, they found that approximately 1,900 are highly likely to be confirmed as such and should be the highest priority for follow-up spectroscopic confirmation.
“Centaurus A’s structure tells astronomers that it went through several major mergers with other galaxies, leading to its glob-like appearance with river-like regions that have many more stars than the surrounding areas,” Hughes said.
“Globular clusters serve as evidence of processes that happened a long time ago.”
“For example, if you see a line of these globular clusters that all have similar metallicity and move with similar radial velocity, we know they must have come from the same dwarf galaxy or some similar object that collided with Centaurus A and is now in the process of being assimilated.”
The team’s paper was published in the Astrophysical Journal.
Allison K. Hughes et al. 2021. NGC 5128 Globular Cluster Candidates Out to 150 kpc: A Comprehensive Catalog from Gaia and Ground-based Data. ApJ 914, 16; doi: 10.3847/1538-4357/abf63c