Formation and evolution of dwarf early-type galaxies in the Virgo cluster II. Kinematic Scaling Relations

TL;DR

This study analyzes the kinematic scaling relations of Virgo dwarf early-type galaxies, revealing their distinct properties and suggesting they are more closely related to late-type galaxies than to massive ellipticals.

Contribution

It provides a detailed comparison of dEs with Es and dSphs using multiple scaling relations, highlighting their unique position and dark matter content.

Findings

dEs bend the Faber-Jackson relation towards lower velocity dispersions

dEs are offset from the Fundamental Plane of Es, indicating different mass-to-light ratios

dEs have a dark matter fraction >~ 42% within half-light radii

Abstract

We place our sample of 18 Virgo dwarf early-type galaxies (dEs) on the V-K - velocity dispersion, Faber-Jackson, and Fundamental Plane (FP) scaling relations for massive early-type galaxies (Es). We use a generalized velocity dispersion, which includes rotation, to be able to compare the location of both rotationally and pressure supported dEs with those of early and late-type galaxies. We find that dEs seem to bend the Faber-Jackson relation of Es to lower velocity dispersions, being the link between Es and dwarf spheroidal galaxies (dSphs). Regarding the FP relation, we find that dEs are significantly offset with respect to massive hot stellar systems, and re-casting the FP into the so-called kappa-space suggests that this offset is related to dEs having a total mass-to-light ratio higher than Es but still significantly lower than dSph galaxies. Given a stellar mass-to-light ratio based on the measured line indices of dEs, the FP offset allows us to infer that the dark matter fraction within the half light radii of dEs is on average >~ 42% (uncertainties of 17% in the K band and 20% in the V band), fully consistent with an independent estimate in an earlier paper in this series. We also find that dEs in the size-luminosity relation in the near-infrared, like in the optical, are offset from early-type galaxies, but seem to be consistent with late-type galaxies. We thus conclude that the scaling relations show that dEs are different from Es, and that they further strengthen our previous findings that dEs are closer to and likely formed from late-type galaxies.