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

Abstract

We present 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 $0.05a_{{}_0}$, the estimated gravitational field from large-scale structure. We show that isophotes in the face-on view can differ from circular at the 50% 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 reported by observers. This plausibly reconciles AGC 114905 with MOND expectations.

arXiv comment8 pages, 2 figures, 2 tables. Published in the Monthly Notices of the Royal Astronomical Society in this form. Face-on videos available at https://youtu.be/VkZq2Se0_lU (isolated) and https://youtu.be/3wC3yRkrXnc (including an external field of a_0/20)

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• From galactic bars to the Hubble tension: weighing up the astrophysical evidence for Milgromian gravity
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• Distinguishing Dark Matter, Modified Gravity, and Modified Inertia with the Inner and Outer Parts of Galactic Rotation Curves
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• Broader view of bimetric MOND
• Newtonian Fractional-Dimension Gravity and Galaxies without Dark Matter