The star formation history and dynamics of the ultra-diffuse galaxy dragonfly 44 in MOND and MOG

Hosein Haghi, Vahid Amiri, Akram Hasani Zonoozi, Indranil Banik, Pavel Kroupa, Moritz Haslbauer

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


The observed line-of-sight velocity dispersion σ los of the ultra-diffuse galaxy Dragonfly 44 (DF44) requires a Newtonian dynamical mass-to-light ratio of solar units. This is well outside the acceptable limits of our stellar population synthesis (SPS) models, which we construct using the integrated galactic initial mass function (IGIMF) theory. Assuming DF44 is in isolation and using Jeans analysis, we calculate σ los profiles of DF44 in Milgromian dynamics (MOND) and modified gravity (MOG) theories without invoking dark matter. Comparing with the observed kinematics, the best-fitting MOND model has and a constant orbital anisotropy of In MOG, we first fix its two theoretical parameters α and μ based on previous fits to the observed rotation curve data of The HI Nearby Galaxy Survey (THINGS). The DF44 σ los profile is best fit with, larger than plausible SPS values. MOG produces a σ los profile for DF44 with acceptable M dyn/L I and isotropic orbits if α and μ are allowed to vary. MOND with the canonical a 0 can explain DF44 at the 2.40σ confidence level (1.66%) if considering both its observed kinematics and typical star formation histories in an IGIMF context. However, MOG is ruled out at 5.49σ (P-value of 4.07 ? 10-8) if its free parameters are fixed at the highest values consistent with THINGS data.

Original languageEnglish
Article numberL25
JournalAstrophysical Journal Letters
Issue number1
Early online date11 Oct 2019
Publication statusPublished - Oct 2019


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