THINGS about MOND

¹ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281, 9000 Gent, Belgium
e-mail: gianfranco.gentile@ugent.be
² Observatoire Astronomique, Université de Strasbourg, CNRS UMR 7550, 67000 Strasbourg, France
³ AIfA, Universtät Bonn, 53121 Bonn, Germany
⁴ Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa

Received: 25 June 2010
Accepted: 5 November 2010

Abstract

We present an analysis of 12 high-resolution galactic rotation curves from The HI Nearby Galaxy Survey (THINGS) in the context of modified Newtonian dynamics (MOND). These rotation curves were selected to be the most reliable for mass modelling, and they are the highest quality rotation curves currently available for a sample of galaxies spanning a wide range of luminosities. We fit the rotation curves with the “simple” and “standard” interpolating functions of MOND, and we find that the “simple” function yields better results. We also redetermine the value of a₀, and find a median value very close to the one determined in previous studies, a₀ = (1.22  ±  0.33)  ×  10^-8 cm s^-2. Leaving the distance as a free parameter within the uncertainty of its best independently determined value leads to excellent quality fits for 75% of the sample. Among the three exceptions, two are also known to give relatively poor fits in Newtonian dynamics plus dark matter. The remaining case (NGC 3198) presents some tension between the observations and the MOND fit, which might, however, be explained by the presence of non-circular motions, by a small distance, or by a value of a₀ at the lower end of our best-fit interval, 0.9  ×  10^-8 cm s^-2. The best-fit stellar M/L ratios are generally in remarkable agreement with the predictions of stellar population synthesis models. We also show that the narrow range of gravitational accelerations found to be generated by dark matter in galaxies is consistent with the narrow range of additional gravity predicted by MOND.