Formation of Blue-cored Dwarf Early-type Galaxies in a Cluster Environment: A Kinematical Perspective

Abstract

The presence of blue cores in some dwarf early-type galaxies (dEs) in galaxy clusters suggests the scenario of late-type galaxy infall and subsequent transformation into red, quiescent dEs. We present Gemini Multi-Object Spectrographs long-slit spectroscopy of two dEs with blue cores (dE(bc)s), EVCC 591 and EVCC 516, located at the core and outskirt of the Virgo cluster, respectively. We obtained their internal kinematics along the major axis out to, at least, ~ 1 effective radius. EVCC 591 shows evidence of a kinematically decoupled core (KDC) with a size of 2" (160 pc), exhibiting an inverted pattern for velocity with respect to the main body of its host galaxy. The rotation curve of the stellar component in the inner region of EVCC 591 is steeper than that in the rest of the galaxy. On the other hand, overall velocity profiles of stellar and ionized gas components of EVCC 516 show no signature of significant rotation. The occurrence of a KDC and zero rotation in the internal kinematics along with the central star formation support the scenario of gas-rich dwarf-dwarf mergers in the formation of these two dE(bc)s. Furthermore, evolution of dE(bc)s in a cluster environment into ordinary dEs with KDCs is possible based on their structural properties. We suggest that at least some of the dE(bc)s in the Virgo cluster were formed through dwarf-dwarf mergers in lower density environments before they subsequently fell into the cluster; they were then quenched by subsequent effects within the cluster environment.