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The shape of the dark matter halo in the early-type galaxy NGC 2974 |
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| Authors: | Anne-Marie Weijmans Davor Krajnovi&#; Glenn van de Ven † Tom A Oosterloo Raffaella Morganti P T de Zeeuw |
| Institution: | Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA Leiden, the Netherlands;Denys Wilkinson Building, University of Oxford, Keble Road, Oxford;Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540, USA;Netherlands Foundation for Research in Astronomy, Postbus 2, 7990 AA Dwingeloo, the Netherlands;Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, the Netherlands;European Southern Observatory, Karl-Schwarzschild Strasse 2, 85748 Garching bei Munchen, Germany |
| Abstract: | We present H i observations of the elliptical galaxy NGC 2974, obtained with the Very Large Array. These observations reveal that the previously detected H i disc in this galaxy is in fact a ring. By studying the harmonic expansion of the velocity field along the ring, we constrain the elongation of the halo and find that the underlying gravitational potential is consistent with an axisymmetric shape. We construct mass models of NGC 2974 by combining the H i rotation curve with the central kinematics of the ionized gas, obtained with the integral-field spectrograph SAURON. We introduce a new way of correcting the observed velocities of the ionized gas for asymmetric drift, and hereby disentangle the random motions of the gas caused by gravitational interaction from those caused by turbulence. To reproduce the observed flat rotation curve of the H i gas, we need to include a dark halo in our mass models. A pseudo-isothermal sphere provides the best model to fit our data, but we also tested an NFW halo and modified Newtonian dynamics, which fit the data marginally worse. The mass-to-light ratio M / L |
| Keywords: | galaxies: elliptical and lenticular cD galaxies: haloes galaxies: individual: NGC 2974 galaxies: kinematics and dynamics dark matter |