The Active Assembly of the Virgo Cluster: Indications for Recent Group Infall From Early-type Dwarf Galaxies

Abstract

Virgo is a dynamically young galaxy cluster with substructure in its spatial and kinematic distribution. Here, we simultaneously study the phase-space distribution and the main characteristics of Virgo's galaxies, particularly its most abundant galaxy population -the early-type dwarfs -to understand their environmental transformation histories. Aside from known correlations with morphological types -like the larger average clustercentric distance of late-type galaxies -we find an intriguing behavior of early types with magnitudes −17 ≥ M r ≥ −18. They show a large velocity spread and an asymmetric phase-space distribution, similar to the late-type galaxies and different from the early types just one magnitude brighter/fainter. Furthermore, we find a close phase-space aggregation of early-type dwarfs at large clustercentric distance and high relative velocity. Nearly all of them show signatures of disk components and their colors imply stellar ages that are younger than the population average. They are not located closely together but spread azimuthally around the cluster center. We show that this is expected from simulations of an infalling galaxy group that slowly gets dispersed after its first pericentric passage. We thus conclude that these galaxies are recent arrivals, and that the peculiar phase-space distribution of early-type dwarfs is evidence for the ongoing growth of this galaxy population. Studying galaxies based on their phase space correlations is a unique way to compare the properties of recent and older cluster members, and to understand which environment most influenced their present-day characteristics.

On the accretion of a new group of galaxies on to Virgo: I. Internal kinematics of nine in-falling dEs

“…A recently accreted group of galaxies in the Virgo cluster was discovered by Lisker et al (2018), based on the clustering of nine dEs with −17 ≥ M r > −18 in a particular region of the observer's phase-space plane. These relatively young dEs (based on their NUV-r colour) are found at a projected cluster-centric distance of ≈ 1.5 Mpc with respect to M87, and move with line-of-sight velocities of ≈ 700 km s −1 relative to Virgo.…”

The Fornax Deep Survey with the VST

“…Clusters of galaxies are excellent sites to study the effects of the environment on the galaxy structure and on the star formation rate (e.g. Trujillo et al 2001;Lewis et al 2002;Aguerri et al 2004;Gutiérrez et al 2004;Méndez-Abreu et al 2012;Aguerri 2016;Merluzzi et al 2016;Lisker et al 2018). There are several types of environmental mechanisms that can act, also simultaneously, on the cluster members, which induce strong changes in the stellar distribution and gas content.…”

The effect of ram-pressure stripping on dwarf galaxies

“…Morphological transformations of DGs by RPS does not only happen in rich galaxy clusters but also in galaxy groups (GGs) where relative velocities and inter-galactic gas densities are lower. Since galaxy clusters accumulate mass also by the infall of GGs (Lisker et al 2018), DGs can be already pre-processed when they enter the cluster environment. This paper is structured as followed: section 2 provides the simulations ingredients, section 3 provides the numerical setup, section 4 describes the DGs model, in section 5 the results are presented which are discussed in section 6, and finally the conclusions in section 7.…”