📝 SummarXiv

Abstract

Relatively blue light extends beyond a spiral disk from a radius of ~5 kpc out to ~14 kpc from the center of NGC 1275. Analyses of its spectrum and broadband colors reveal a population of young stars having sub-solar metallicities superposed on a dominant population of old stars having super-solar metallicities. The young stars have a characteristic age of ~160 Myr and may span ages of a few hundred Myr, similar to that of stars comprising the central spiral disk, and a total mass about one-third that of this disk for a combined stellar mass (at birth) of ~4 $\times$ 10$^9$ $\rm M_\odot$. A multitude of arc-like features embedded in the extended blue light have brightnesses comparable to the somewhat older (~500 Myr) super star clusters (SSCs) projected against the central spiral disk. The SSCs have a relatively shallow mass function, suggesting that the tidal disruption of an initially larger population that we estimate could have had an initial total mass (far) exceeding ~1 $\times$ 10$^9$ $\rm M_\odot$ gave rise to the extended blue light -- the arc-like features corresponding to stellar streams tracing disrupted star clusters -- and perhaps also the central spiral disk. We speculate that, beginning about 500 Myr ago, an enhanced episode of AGN activity in NGC 1275, leaving still visible X-ray bubbles, induced vigorous cooling of the intracluster medium to fuel the formation of numerous star clusters: many were tidally disrupted to leave bluish light at the inner region of this galaxy, with the survivors being the SSCs projected against the central spiral disk.