Conference paper Open Access

The extended Planetary Nebula Spectrograph (ePN.S) Early Type Galaxy Survey: the Kinematic Diversity of Stellar Halos

Pulsoni, Claudia; Gerhard, Ortwin; Arnaboldi, Magda; Coccato, Lodovico

In this contribution we report on a kinematic study for 33 early type galaxies (ETGs) into their outer halos (average 6 effective radii, Re).  We use planetary nebulae (PNe) as tracers of the main stellar population at large radii, where absorption line spectroscopy is no longer feasible.  The ePN.S survey is the largest survey to-date of ETG kinematics with PNe, based on data from the Planetary Nebula Spectrograph (PN.S), counter-dispersed imaging, and high-resolution PN spectroscopy. We find that ETGs typically show a kinematic transition between inner regions and halos. Slow rotators have increased  rotational support at large radii. Most of the ePN.S fast rotators show a decrease in rotation, due to the fading of the stellar disk in the outer, more slowly rotating spheroid. 30% of these fast rotators are dominated by rotation also at large radii, 40% show kinematic twists or misalignments, indicating a transition from oblate to triaxial in the halo. Despite this variety of kinematic behaviors, the ePN.S ETG halos have similar angular momentum content, independently of fast/slow rotation of the central regions. Estimated kinematic transition radii in units of Re are ~1-3 Re and anti-correlate with stellar mass. These results are consistent with cosmological simulations and support a two-phase formation scenario for ETGs.

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