Overestimated inclinations of Milgromian disc galaxies: the case of the ultradiffuse galaxy AGC 114905

Abstract

We present two hydrodynamical star-forming simulations in the Milgromian dynamics (MOND) framework of a gas-rich disc galaxy with properties similar to AGC 114905, which has recently been argued to have a rotation curve (RC) that is inconsistent with the MOND prediction. Our first model considers the galaxy in isolation, while our second model includes an external field of 0.05a0, the estimated gravitational field from large-scale structure. We show that isophotes in the face-on view can differ from circular at the 50 per cent level. This could mislead observers into overestimating the inclination i between disc and sky planes. Because RCs require a correction factor of 1/sin i, the actual RC could be much higher than that reported by observers. This plausibly reconciles AGC 114905 with MOND expectations.