THINGS about MOND

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 a 0 , and find a median value very close to the one determined in previous studies, a 0 = (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 a 0 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.

HALOGAS: Extraplanar gas in NGC 3198

“…Famaey & McGaugh 2012 and references therein), even though on larger scales it also needs some invisible mass. The galaxy studied in the present paper, NGC 3198, was claimed to show tension with MOND (Bottema et al 2002;Gentile et al 2011). It is an ideal case study for MOND because of its inclination (perfectly suited for kinematical studies, see Begeman 1989), its relative closeness, the fact that it is a late-type spiral galaxy with regular and symmetric kinematics, and the accurate determination of its distance using Cepheids (Kelson et al 1999;Freedman et al 2001).…”

“…It is a late-type spiral that is traditionally considered as one of the benchmark galaxies for rotation curve A&A 554, A125 (2013) Sellwood & Sánchez (2010), Gentile et al (2011). The distance of NGC 3198 has been determined to be 13.8 Mpc using Cepheids (Kelson et al 1999;Freedman et al 2001; see also Macri et al 2001), which are usually considered to be one of the most precise distance indicators.…”

Isolated and non-isolated dwarfs in terms of modified Newtonian dynamics

“…We adopted the "simple" MOND interpolating function (Famaey & Binney 2005), which is known to best match other galaxy rotation curves (Gentile et al 2011), finding that V cor becomes:…”

“…The isolated galaxy KK 246, on the other hand, has a maximum velocity consistent with MOND, despite having a very high mass discrepancy: its dynamical-to-baryonic mass ratio is ≈15. We note that despite its many successes in terms of global scaling relations and dozens of individual galaxy rotation curves, a few galaxies indeed remain challenging for MOND (for instance NGC 3198, see Gentile et al 2011), but none as much as the published rotation curve of Holmberg II.…”

Distant star clusters of the Milky Way in MOND

“…Different interpolating functions have been suggested, such as the simple function, μ(x) = x/(1+ x) (Famaey & Binney 2005) and the standard interpolation function, μ(x) = x/ √ 1 + x 2 (Milgrom 1983). Because the simple function fits galactic rotation curves better than the standard function (Gentile et al 2011), in this paper we use the simple function. The value of the curl field H depends on the boundary conditions and the spatial mass distribution and vanishes only for some special symmetries (Bekenstein & Milgrom 1984).…”