The Kinematics of Thick Disks in Nine External Galaxies

Abstract

We present kinematic measurements of thin and thick disk components in a sample of nine edge-on galaxies. We extract stellar and ionized gas rotation curves at and above the galaxies' midplanes using the Ca II triplet absorption features and H-alpha emission lines measured with the GMOS spectrographs on Gemini North and South. For the higher mass galaxies in the sample, we fail to detect differences between the thin and thick disk kinematics. In the lower mass galaxies, there is a wide range of thick disk behavior including thick disks with substantial lag and one counter-rotating thick disk. We compare our rotation curves with expectations from thick disk formation models and conclude that the wide variety of thick disk kinematics favors a formation scenario where thick disk stars are accreted or formed during merger events as opposed to models that form thick disks through gradual thin disk heating.

17 pages, 9 figures, accepted for publication in ApJ

References in corpus (6)

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• On local dark matter density
• A monolithic collapse origin for the thin/thick disc structure of ESO 243-49
• Properties of thick discs formed in clumpy galaxies
• The Contribution of Spiral Arms to the Thick Disk along the Hubble Sequence