A new astrophysical solution to the Too Big To Fail problem: Insights from the MORIA simulations

Abstract

Aims. We test whether or not realistic analysis techniques of advanced hydrodynamical simulations can alleviate the Too Big To Fail problem (TBTF) for late-type galaxies. TBTF states that isolated dwarf galaxy kinematics imply that dwarfs live in halos with lower mass than is expected in a A cold dark matter universe. Furthermore, we want to identify the physical mechanisms that are responsible for this observed tension between theory and observations.

Methods. We use the MORIA suite of dwarf galaxy simulations to investigate whether observational effects are involved in TBTF for late-type field dwarf galaxies. To this end, we create synthetic radio data cubes of the simulated MORIA galaxies and analyse their HI kinematics as if they were real, observed galaxies.

Results. We find that for low-mass galaxies, the circular velocity profile inferred from spatially resolved HI kinematics often underestimates the true circular velocity profile, as derived directly from the enclosed mass. Fitting the HI kinematics of MORIA dwarfs with a theoretical halo profile results in a systematic underestimate of the mass of their host halos. We attribute this effect to the fact that the interstellar medium of a low-mass late-type dwarf is continuously stirred by supernova explosions into a vertically puffed-up, turbulent state to the extent that the rotation velocity of the gas is simply no longer a good tracer of the underlying gravitational force field. If this holds true for real dwarf galaxies as well, it implies that they inhabit more massive dark matter halos than would be inferred from their kinematics, solving TBTF for late-type field dwarf galaxies.