The Next Generation Virgo Cluster Survey (NGVS). XXXII. A Search for Globular Cluster Substructures in the Virgo Galaxy Cluster Core

Abstract

Substructure in globular cluster (GC) populations around large galaxies is expected in galaxy formation scenarios that involve accretion or merger events, and it has been searched for using direct associations between GCs and structure in the diffuse galaxy light, or with GC kinematics. Here, we present a search for candidate substructures in the GC population around the Virgo cD galaxy M87 through the analysis of the spatial distribution of the GC colors. The study is based on a sample of ∼ 1800 bright GCs with high-quality u, g, r, i, z, K s photometry, selected to ensure a low contamination by foreground stars or background galaxies. The spectral energy distributions of the GCs are associated with formal estimates of age and metallicity, which are representative of its position in a 4-D color-space relative to standard single stellar population models. Dividing the sample into broad bins based on the relative formal ages, we observe inhomogeneities which reveal signatures of GC substructures. The most significant of these is a spatial overdensity of GCs with relatively young age labels, of diameter ∼ 0.1 deg (∼ 30 kpc), located to the south of M87. The significance of this detection is larger than about 5σ after accounting for estimates of random and systematic errors. Surprisingly, no large Virgo galaxy is present in this area, that could potentially host these GCs. But candidate substructures in the M87 halo with equally elusive hosts have been described based on kinematic studies in the past. The number of GC spectra available around M87 is currently insufficient to clarify the nature of the new candidate substructure.

Fossil stellar streams and their globular cluster populations in the E-MOSAICS simulations

“…Observations of the GC population outside 30 kpc of the centre of M31 have shown that a large fraction of these GCs are situated on streams (Mackey et al 2010) and this has also been found to be the case for other galaxies outside the Local Group (e.g. Romanowsky et al 2012;Powalka et al 2018). As is the case for the Sagittarius dwarf, our simulations predict that the mean age of these GCs is younger than the other GCs associated with these galaxies.…”

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE)

“…The Hα filament is located at the southeast edge of the cavity formed by the counter-jet. (Powalka et al 2018), seem to suggest that the ionised gas filament is the remnant of a gas-rich galaxy which has recently been accreted by M 87, as first proposed by Sparks et al (1993), or has crossed the halo losing most of its gas reservoir after a rampressure-stripping event (Mayer et al 2006). The rough estimate of the total mass of the ionised gas in the filament (M filament 6.9 × 10 7 M ) is comparable to that of the gas that would have been associated with the observed dusty filaments if this dust had been accreted from an external object (M gas,dust 2 × 10 7 M ).…”

The Next Generation Virgo Cluster Survey (NGVS). XXXI. The Kinematics of Intracluster Globular Clusters in the Core of the Virgo Cluster

“…11). This analysis was motivated by the recent finding of a correlation between GC color-color relations and environment, and interpreted as driven by different stellar abundance ratios (Powalka et al 2016b(Powalka et al , 2018, altough interpretations related to different underlying ages are also given, e.g. Usher et al (2015); Powalka et al (2018) ).…”