Recent Formation of a Spiral Disk Hosting Progenitor Globular Clusters at the center of the Perseus Brightest Cluster Galaxy: II. Progenitor Globular Clusters

TL;DR

This paper investigates the origin and properties of central super star clusters in NGC 1275, showing they are likely progenitor globular clusters formed from cooling flow gas, and identifies a recent spiral disk hosting these clusters.

Contribution

It reveals a new formation scenario for progenitor globular clusters within a spiral disk at the galaxy's center, linked to residual cooling flow gas.

Findings

Central SSCs are more massive and have a shallower mass function than outer SSCs.

Central SSCs are approximately 500 Myr old, indicating recent formation.

A spiral disk hosting progenitor globular clusters has recently formed at NGC 1275's center.

Abstract

We address the nature and origin of Super Star Clusters (SSCs) discovered by Holtzman et al. (1992) within a radius of $\sim$$5\,\rm kpc$ from the center of NGC 1275, the giant elliptical galaxy at the center of the Perseus Cluster. We show that, in contrast with the much more numerous population of SSCs subsequently discovered up to $\sim$$30\,\rm kpc$ from the center of this galaxy, the central SSC population have maximal masses an order of magnitude higher and a mass function with a shallower power-law slope. Furthermore, whereas the outer SSC population have ages spanning a few $\rm Myr$ to at least $\sim$$1\,\rm Gyr$, the central SSC population have ages strongly concentrated around $\sim$$500 \rm \, Myr$ with a $1\,\sigma$ dispersion of $\sim$$100\,\rm Myr$. These SSCs share a close spatial and temporal relationship with the "central spiral," which also has a radius $\sim$$5\,\rm kpc$ centered on NGC 1275 and a characteristic stellar age of $\sim$$150\,\rm Myr$ (Paper I). We argue that both the central SSC population and the central spiral formed from gas deposited by a residual cooling flow, with the SSCs forming first followed by the formation of the stellar body of the central spiral $\sim$$300$-$400\,\rm Myr$ later. The ages of the central SSC population imply that they are able to withstand very strong tidal fields near the center of NGC 1275, making them genuine progenitor globular clusters. Evidently, a spiral disk hosting progenitor globular clusters has recently formed at the center of a giant elliptical galaxy.