Star Formation in the Outer Filaments of NGC 1275

TL;DR

This study investigates star formation in the outer filaments of NGC 1275, revealing young star clusters likely formed due to buoyant radio bubbles influencing the H alpha filaments, distinct from inner galaxy star formation.

Contribution

It provides the first detailed analysis of outer star clusters in NGC 1275, linking their formation to radio bubble activity and filament dynamics, which is a novel insight.

Findings

Outer star clusters are younger than 100 million years.

Young clusters are concentrated along H alpha filaments.

Formation likely triggered by buoyant radio bubbles.

Abstract

We present photometry of the outer star clusters in NGC 1275, the brightest galaxy in the Perseus cluster. The observations were taken using the Hubble Space Telescope Advanced Camera for Surveys. We focus on two stellar regions in the south and south-east, far from the nucleus of the low velocity system (~22 kpc). These regions of extended star formation trace the H alpha filaments, drawn out by rising radio bubbles. In both regions bimodal distributions of colour (B-R)_0 against magnitude are apparent, suggesting two populations of star clusters with different ages; most of the H alpha filaments show no detectable star formation. The younger, bluer population is found to be concentrated along the filaments while the older population is dispersed evenly about the galaxy. We construct colour-magnitude diagrams and derive ages of at most 10^8 years for the younger population, a factor of 10 younger than the young population of star clusters in the inner regions of NGC 1275. We conclude that a formation mechanism or event different to that for the young inner population is needed to explain the outer star clusters and suggest that formation from the filaments, triggered by a buoyant radio bubble either rising above or below these filaments, is the most likely mechanism.