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Abstract:
We use high spatial resolution stellar velocity maps from the Gemini integral-field spectrograph (IFS) and wide-field velocity maps from the McDonald Mitchell IFS to study the stellar velocity profiles and kinematic misalignments from ~200 pc to ~20 kpc in 20 early-type galaxies (ETGs) with stellar mass M * > 1011.7 M ⊙ in the MASSIVE survey. While 80% of the galaxies have low spins (λ < 0.1) and low rotational velocities (<50 km s−1) in both the central region and the main body, we find a diverse range of velocity features and misalignment angles. For the 18 galaxies with measurable central kinematic axes, 10 have well aligned kinematic axis and photometric major axis, and the other eight galaxies have misalignment angles that are distributed quite evenly from 15° to the maximal value of 90°. There is a strong correlation between central kinematic misalignment and galaxy spin, where all four galaxies with significant spins have well aligned kinematic and photometric axes, but only 43% of the low-spin galaxies are well aligned. The central and main-body kinematic axes within a galaxy are not always aligned. When the two kinematic axes are aligned (~60% of the cases), they are either also aligned with the photometric major axis or orthogonal to it. We find 13 galaxies to also exhibit noticeable local kinematic twists, and one galaxy to have a counterrotating core. A diverse assembly history consisting of multiple gas-poor mergers of a variety of progenitor mass ratios and orbits is likely to be needed to account for the predominance of low spins and the wide range of central and main-body velocity features reported here for local massive ETGs.
