Simulations of star-forming main-sequence galaxies in Milgromian gravity

Abstract

We conduct hydrodynamical MOND simulations of isolated disc galaxies over the stellar mass range M⋆/M⊙ = 107 − 1011 using the adaptive mesh refinement code phantom of ramses (por), an adaptation of the ramses code with a Milgromian gravity solver. The scale lengths and gas fractions are based on observed galaxies, and the simulations are run for 5 Gyr. The main aim is to see whether existing sub-grid physics prescriptions for star formation and stellar feedback reproduce the observed main sequence, and Kennicutt-Schmidt relation that captures how the local and global star formation rates relate to other properties. Star formation in the models starts soon after initialisation and continues as the models evolve. The initialized galaxies indeed evolve to a state which is on the observed main sequence, and the Kennicutt-Schmidt relation. The available formulation of sub-grid physics is therefore adequate and leads to galaxies that largely behave like observed galaxies, grow in radius, and have flat rotation curves − provided we use Milgromian gravitation. Furthermore, the strength of the bars tends to be inversely correlated with the stellar mass of the galaxy, whereas the bar length strongly correlates with the stellar mass. Irrespective of the mass, the bar pattern speed stays constant with time, indicating that dynamical friction does not affect the bar dynamics. The models demonstrate Renzo’s rule and form structures at large radii, much as in real galaxies. In this framework, baryonic physics is thus sufficiently understood to not pose major uncertainties in our modelling of global galaxy properties.

On the Decline of Star Formation during the Evolution of Galaxies

“…only consider late-type galaxies with a certain amount of cold and star-forming gas. So with our sample of galaxies, we cannot predict whether the low surface brightness galaxies in our simulation fall below the KS relation as found in observational studies (Bigiel et al 2008;Nagesh et al 2023).…”

Inside MOND: testing gravity with stellar accelerations

“…Our goal here is to compare the accelerations seen in explicit MONDian realisations of disk galaxies to those expected from the Newtonian potential of a galaxy with the same baryonic component and a spherical dark matter halo chosen to match the accelerations seen in the disk. We work with the endpoints of MONDian simulations of galaxies formed via spherical collapse [21] and galaxies initialised in non-expanding backgrounds that pay closer attention to the impact of star-formation and feedback [22]. These galaxies have masses running from O(10 9 ) to O(10 11 ) solar masses, which is close to the baryonic mass of the Milky Way at the upper end.…”

“…The simulated galaxies are listed in table 1, drawn from refs. [21] and [22]. Both papers use a modified version [36] of the RAMSES code [37].…”

“…[21] show that gravitational collapse in a MONDian scenario can yield exponential disk galaxies with radially symmetric stellar distributions. Including more detailed internal dynamics leads to the formation of substructure [22] in the outer parts of the galaxy. The larger halos have N ∼ 10 6 mass points.…”

The Relevance of Dynamical Friction for the MW/LMC/SMC Triple System

“…The law of gravitation fundamentally defines the formation and evolution of galaxies. For example, by mergers being much rarer in Milgromian gravitation (i.e., without DM), galaxies evolve largely in isolation [27][28][29], and the formation of cosmological structures proceeds differently than in the DM-based models [5,30,31]. It is thus of paramount importance to test for the existence of DM halos around galaxies.…”