The dynamics of the bulge dominated galaxy NGC 7814 in MOND

TL;DR

This study tests Modified Newtonian Dynamics (MOND) against the galaxy NGC 7814, demonstrating that accurate bulge-disk decomposition and precise mass-to-light ratios are crucial for matching observed rotation curves.

Contribution

The paper presents a detailed MOND model of NGC 7814 using improved bulge-disk decomposition and a grid-based Poisson solver, achieving excellent rotation curve fits with minimal free parameters.

Findings

MOND can accurately reproduce the galaxy's rotation curve with proper mass modeling.

The fit quality is highly sensitive to bulge-disk decomposition accuracy.

Precise measurements of galaxy components are essential for testing gravity theories.

Abstract

The bulge dominated galaxy NGC 7814 provides one of the strongest dynamical tests possible for Modified Newtonian Dynamics (MOND). Spitzer 3.6 micron photometry fixes the bulge parameterisation and strongly constrains the properties of the sub-dominant stellar disk. Furthermore, the distance is known to better than 5 percent, virtually eliminating it as a free parameter. The rotation curve is easily measured, since the H I (and stellar) disks are edge on, and both the receding and approaching sides agree very well. In this paper we explore the agreement between the model and observed rotation curves in MOND given that the only two free parameters available are the mass-to-light ratios of the bulge and disk. We use a grid based MOND Poisson solver that accurately solves for the MOND gravity and produces our model rotation curves from a given mass distribution. The input to the Poisson solver is a 3D distribution of N particles which is generated from modelling the observed distribution of stars and gas in the galaxy. By ensuring a superior fit to the radial surface brightness profile than previous works, by virtue of a double Sersic fit to the bulge, we were able to produce excellent fits to the rotation curve with typical values for both mass-to-light ratios. We conclude that the model rotation curve of a mass distribution in MOND is extremely sensitive to the bulge-disk decomposition and even slight deviation from the observed mass distribution can produce large differences in the model rotation curve.