Thorsten Lisker et al 2009 ApJ 706 L124 doi:10.1088/0004-637X/706/1/L124
Thorsten Lisker1, Joachim Janz1,2,8, Gerhard Hensler3, Suk Kim4, Soo-Chang Rey4, Simone Weinmann5, Chiara Mastropietro6, Oliver Hielscher1, Sanjaya Paudel1 and Ralf Kotulla7
Show affiliationsIn the light of the question whether most early-type dwarf (dE) galaxies in clusters formed through infall and transformation of late-type progenitors, we search for an imprint of such an infall history in the oldest, most centrally concentrated dE subclass of the Virgo cluster: the nucleated dEs that show no signatures of disks or central residual star formation. We select dEs in a (projected) region around the central elliptical galaxies, and subdivide them by their line-of-sight velocity into fast-moving and slow-moving ones. These subsamples turn out to have significantly different shapes: while the fast dEs are relatively flat objects, the slow dEs are nearly round. Likewise, when subdividing the central dEs by their projected axial ratio into flat and round ones, their distributions of line-of-sight velocities differ significantly: the flat dEs have a broad, possibly two-peaked distribution, whereas the round dEs show a narrow single peak. We conclude that the round dEs probably are on circularized orbits, while the flat dEs are still on more eccentric or radial orbits typical for an infalling population. In this picture, the round dEs would have resided in the cluster already for a long time, or would even be a cluster-born species, explaining their nearly circular orbits. They would thus be the first generation of Virgo cluster dEs. Their shape could be caused by dynamical heating through repeated tidal interactions. Further investigations through stellar population measurements and studies of simulated galaxy clusters would be desirable to obtain definite conclusions on their origin.
galaxies: clusters: individual (Virgo); galaxies: dwarf; galaxies: elliptical and lenticular, cD; galaxies: evolution; galaxies: kinematics and dynamics; galaxies: structure
98.56.Wm Dwarf galaxies (elliptical, irregular, and spheroidal)
98.62.Lv Stellar content and populations; radii; morphology and overall structure
98.62.Hr Spiral arms and bars; galactic disks
98.62.Ai Origin, formation, evolution, age, and star formation
Issue 1 (2009 November 20)
Received 2009 June 4, accepted for publication 2009 October 15
Published 2009 November 3
Thorsten Lisker et al 2009 ApJ 706 L124
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