Polar ring galaxies as tests of gravity

Journal article

Authors/Editors

Angus, Garry

Research Areas

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Publication Details

Author list: Lughausen F, Famaey B, Kroupa P, Angus G, Combes F, Gentile G, Tiret O, Zhao H

Publisher: Oxford University Press

Place: OXFORD

Publication year: 2013

Journal: Monthly Notices of the Royal Astronomical Society (0035-8711)

Journal acronym: MON NOT R ASTRON SOC

Volume number: 432

Issue number: 4

Start page: 2846

End page: 2853

Number of pages: 8

ISSN: 0035-8711

eISSN: 1365-2966

Languages: English-Great Britain (EN-GB)

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Abstract

Polar ring galaxies are ideal objects with which to study the three-dimensional shapes of galactic gravitational potentials since two rotation curves can be measured in two perpendicular planes. Observational studies have uncovered systematically larger rotation velocities in the extended polar rings than in the associated host galaxies. In the dark matter context, this can only be explained through dark haloes that are systematically flattened along the polar rings. Here, we point out that these objects can also be used as very effective tests of gravity theories, such as those based on Milgromian dynamics (also known as Modified Newtonian Dynamics or MOND). We run a set of polar ring models using both Milgromian and Newtonian dynamics to predict the expected shapes of the rotation curves in both planes, varying the total mass of the system, the mass of the ring with respect to the host and the size of the hole at the centre of the ring. We find that Milgromian dynamics not only naturally leads to rotation velocities being typically higher in the extended polar rings than in the hosts, as would be the case in Newtonian dynamics without dark matter, but that it also gets the shape and amplitude of velocities correct. Milgromian dynamics thus adequately explains this particular property of polar ring galaxies.

Keywords

Dark matter, galaxies: general, galaxies: individual: NGC 4650A, galaxies: kinematics and dynamics, gravitation

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