Testing $\hat{I}›$CDM With Dwarf Galaxy Morphology

Abstract

The leading tensions to the collisionless cold dark matter (CDM) paradigm are the "small-scale controversies", discrepancies between observations at the dwarf-galactic scale and their simulational counterparts. In this work we consider methods to infer 3D morphological information on Local Group dwarf spheroidals, and test the fitness of CDM+hydrodynamics simulations to the observed galaxy shapes. We find that the subpopulation of dwarf galaxies with mass-to-light ratio $\gtrsim 100M_{\odot }/L_{\odot }$ reflects an oblate morphology. This is discrepant with the dwarf galaxies with mass-to-light ratio $\lesssim 100M_{\odot }/L_{\odot }$, which reflect prolate morphologies, and more importantly with simulations of CDM-sourced galaxies which are explicitly prolate. Although more simulations and data are called for, if evidence of oblate pressure-supported stellar distributions persists, we argue that an underlying oblate non-CDM dark matter halo may be required, and present this as motivation for future studies.

29 pages, 17 figures, Astrophys. J. 2020, 900 (2020) no.1