Internal dynamics, structure and formation of dwarf elliptical galaxies

Dwarf elliptical (dE) galaxies are the most common galaxy type in nearby galaxy clusters. How these objects formed remains an open question, and many basic properties of dEs have yet to be quantified. The first part of this thesis is a Keck/ESI study of the internal dynamics of six Virgo Cluster dEs. We model their observed velocity dispersion profiles using HST /WFPC2 surface photometry and spherically-symmetric dynamical models. Global mass-to-light ratios are determined to be in the range 3 ≤ Υ _V ≤ 6, implying the absence of a significant dark matter component inside an effective radius. We rule out central black holes more massive than ∼10⁷ M_⊙ . For the five nucleated dEs in our sample, kinematic and photometric properties were determined for the central nucleus separately from the underlying host dE galaxy. These nuclei are as bright as or brighter than the most luminous Galactic globular clusters and lie near the region of Fundamental Plane space occupied by globular clusters. The second part of this thesis focuses on the velocity profiles and stellar content of 17 Virgo Cluster dEs. We find an unexpected dichotomy in the degree of rotational support: 4 out of the 17 dEs are roughly consistent with rotational flattening, while the remaining galaxies have no detectable major-axis rotation. Despite this apparent dichotomy, we find that these galaxies are remarkably similar in terms of their structure, stellar content, and local environments, posing a significant challenge to theoretical models of their formation. Compared to classical ellipticals, dEs appear to be on average a few Gyr younger, somewhat more metal poor, and with lower, roughly solar, α/Fe ratios. In the third and final part of this thesis, we present spectroscopic evidence for a counter-rotating core in NGC 770, a low-luminosity elliptical galaxy that is a satellite of a field spiral galaxy. We present photometric evidence of a central disk in this system and find a weak stellar population gradient between the counter-rotating region and main galaxy body. We suggest that the counter-rotating core in NGC 770 was formed via gas infall and subsequent star formation during interactions with its gas-rich spiral companion.