NGC 3741: the dark halo profile from the most extended rotation curve |
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| Authors: | Gianfranco Gentile Paolo Salucci Uli Klein Gian Luigi Granato |
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| Institution: | Department of Physics and Astronomy, University of New Mexico, 800 Yale Blvd NE, Albuquerque, NM 87131, USA;SISSA, via Beirut 4, 34014 Trieste, Italy;Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany;INAF –Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy |
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| Abstract: | We present new H i observations of the nearby dwarf galaxy NGC 3741. This galaxy has an extremely extended H i disc, which allows us to trace the rotation curve out to unprecedented distances in terms of the optical disc: we reach 42 B -band exponential scalelengths or about 7 kpc. The H i disc is strongly warped, but the warp is very symmetric. The distribution and kinematics are accurately derived by building model data cubes, which closely reproduce the observations. In order to account for the observed features in the data cube, radial motions of the order of 5–13 km s?1 are needed. They are consistent with an inner bar of several hundreds of pc and accretion of material in the outer regions.
The observed rotation curve was decomposed into its stellar, gaseous and dark components. The Burkert dark halo (with a central constant density core) provides very good fits. The dark halo density distribution predicted by the Λ cold dark matter (CDM) theory fails to fit the data, unless NGC 3741 is a 2.5σ exception to the predicted relation between concentration parameter and virial mass and at the same time a high value of the virial mass (though poorly constrained) of 1011 M⊙ . Noticeably, modified Newtonian dynamics (MOND) seems to be consistent with the observed rotation curve. Scaling up the contribution of the gaseous disc also gives a good fit. |
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| Keywords: | galaxies: kinematics and dynamics galaxies: spiral dark matter |
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