Evidence for the rapid formation of low mass early-type galaxies in dense environments

TL;DR

This study shows that low-mass early-type galaxies in dense environments like the Virgo Cluster form their stars rapidly, especially near the cluster center, linking their properties to their surroundings and globular cluster formation.

Contribution

It provides new evidence that environment influences star formation timescales in low-mass galaxies, using [$ extalpha$/Fe] ratios and globular cluster data.

Findings

Galaxies near Virgo's center have higher [$ extalpha$/Fe] ratios.

A correlation exists between [$ extalpha$/Fe] and globular cluster specific frequency.

Environment controls star formation timescales in dense regions for low-mass galaxies.

Abstract

We explore the environmental dependence of star formation timescales in low mass galaxies using the [$\alpha$/Fe] abundance ratio as an evolutionary clock. We present integrated [$\alpha$/Fe] measurements for 11 low mass ($M_\star \sim 10^9~M_\odot$) early-type galaxies (ETGs) with a large range of cluster-centric distance in the Virgo Cluster. We find a gradient in [$\alpha$/Fe], where the galaxies closest to the cluster center (the cD galaxy, M87) have the highest values. This trend is driven by galaxies within a projected radius of 0.4~Mpc (0.26 times the virial radius of Virgo~A), all of which have super-solar [$\alpha$/Fe]. Galaxies in this mass range exhibit a large scatter in the [$\alpha$/Fe]--$\sigma$ diagram, and do not obviously lie on an extension of the relation defined by massive ETGs. In addition, we find a correlation between [$\alpha$/Fe] and globular cluster specific frequency ($S_N$), suggesting that low-mass ETGs that formed their stars over a short period of time, were also efficient at forming massive star clusters. The innermost low-mass ETGs in our sample have [$\alpha$/Fe] values comparable to that of M87, implying that environment is the controlling factor for star formation timescales in dense regions. These low-mass galaxies could be the surviving counterparts of the objects that have already been accreted into the halo of M87, and may be the link between present-day low-mass galaxies and the old, metal-poor, high-[$\alpha$/Fe], high-$S_N$ stellar populations seen in the outer halos of massive ETGs.