Intracluster stellar populations are a natural result of tidal interactions in galaxy clusters .
Measuring these populations is difficult , but important for understanding the assembly of the most massive galaxies .
The Coma cluster of galaxies is one of the nearest truly massive galaxy clusters , and is host to a correspondingly large system of globular clusters ( GCs ) .
We use imaging from the HST/ACS Coma Cluster Survey to present the first definitive detection of a large population of intracluster GCs ( IGCs ) that fills the Coma cluster core and is not associated with individual galaxies .
The GC surface density profile around the central massive elliptical galaxy , NGCÂ 4874 , is dominated at large radii by a population of IGCs that extend to the limit of our data ( R < 520 Â kpc ) .
We estimate that there are 47000 \pm 1600 ( random ) ^ { +4000 } _ { -5000 } ( systematic ) IGCs out to this radius , and that they make up \sim 70 \% of the central GC system , making this the largest GC system in the nearby Universe .
Even including the GC systems of other cluster galaxies , the IGCs still make up \sim 30 – 45 \% of the GCs in the cluster core .
Observational limits from previous studies of the intracluster light ( ICL ) suggest that the IGC population has a high specific frequency .
If the IGC population has a specific frequency similar to high- S _ { N } dwarf galaxies , then the ICL has a mean surface brightness of \mu _ { V } \approx 27 { mag arcsec } ^ { -2 } and a total stellar mass of roughly 10 ^ { 12 } \mathcal { M } _ { \odot } within the cluster core .
The ICL makes up approximately half of the stellar luminosity and one-third of the stellar mass of the central ( NGC4874+ICL ) system .
The color distribution of the IGC population is bimodal , with blue , metal-poor GCs outnumbering red , metal-rich GCs by a ratio of 4:1 .
The inner GCs associated with NGCÂ 4874 also have a bimodal distribution in color , but with a redder metal-poor population .
The fraction of red IGCs ( 20 % ) , and the red color of those GCs , implies that IGCs can originate from the halos of relatively massive , L ^ { \ast } galaxies , and not solely from the disruption of dwarf galaxies .