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03-09-2009
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Today's colloquium: Dark matter in early-type galaxies: mapping dark haloes with integral-field spectrography (A.-M. Weijmans, Leiden)

Submitter: Jean-Mathias Griessmeier
Description:
From galaxy formation theory we expect galaxies to be embedded in massive dark matter haloes. For spiral and dwarf galaxies this has indeed been observationally confirmed, by modeling the kinematics from the large cold gas discs that often surround these galaxies. These gas discs are however rare in elliptical galaxies. We therefore have to resort to other tracers when we want to probe dark matter haloes around these systems, and these are not always easily accessible. As a result, dark haloes for only a handful of early-type galaxies have been mapped.

In this talk I will give an overview of the methods that can be used to find dark matter in early-type galaxies. I will give special attention to early-type galaxy NGC 2974, where we combine integral-field ionised gas kinematics with the HI kinematics of its large gas ring, to determine the dark matter content of this galaxy. I will then focus on using integral-field spectrographs as 'photon-collectors' to obtain spectra in the outer parts of galaxies. From these spectra we can not only obtain the velocity profile and construct mass models to constrain the dark halo, but also infer the properties of the stellar halo population. I will show some recent results from this new technique, based on spectra from the SAURON and PPAK instruments, and discuss future prospects.

The image above pictures the early-type galaxy NGC 3379 (underlying image in V-band) with the use of integral-field spectroscopy in the central part of the galaxy (the velocity map) and at large radii (where the instrument is a photon-collector and a single spectrum is obtained).
Copyright: A.-M. Weijmans
 
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