The long life of ultra diffuse galaxies inside low-density dark matter halos: the case of AGC 114905

TL;DR

This study uses numerical simulations to show that ultra diffuse galaxy AGC 114905 remains stable within low-density dark matter halos, challenging previous assumptions about its instability and suggesting such galaxies can persist unperturbed in atypical halos.

Contribution

The paper demonstrates through simulations that UDG AGC 114905 is stable in low-density dark matter halos, revising previous instability assumptions based on new observational data.

Findings

AGC 114905 remains stable over 5 Gyr in simulations

Discrepancies with previous studies are due to hotter, more massive halos

UDGs can evolve unperturbed in low-density dark matter halos

Abstract

It has long been known that, in the absence of a dark matter (DM) halo, galaxy discs tend to develop global gravitational instabilities that strongly modify their initial structure. The recent discovery of gas-rich ultra diffuse galaxies (UDGs) that seem to live in DM halos with very low concentrations, a very atypical configuration in the standard cosmological framework, poses therefore a crucial question: is the small contribution from such DM halos sufficient to stabilize the UDG discs? In this work we investigate this question, focusing on the extreme UDG AGC 114905, which previous works found to be unstable. Here, we revisit these studies, using idealised numerical simulations with AREPO of a system composed by a stellar disc, a gas disc and a DM halo in initial equilibrium with each other and with properties based on slightly revised observational data of AGC 114905. We explore different scenarios for the DM halo and we run our simulations for 5 Gyr. We find that in all cases the stellar and the gas discs are stable and that their initial density distributions and kinematic properties remain unchanged during the course of the simulation. We discuss how the apparent discrepancy with previous works (where the UDG developed instabilities) is due to our discs being dynamically hotter and living in slightly more massive DM halos, in accordance with the new observational constraints, previously unavailable. Our findings demonstrate that AGC 114905 (and likely other similar UDGs) can evolve unperturbed in halos that challenge current cosmological models.