Robbert Verbeke - January 26, 2018

Too-Big-To-Fail is in the eye of the beholder - Insights from realistic dwarf
galaxy simulations

We test whether advanced galaxy models and analysis techniques of simulations
can alleviate the Too-Big-To-Fail problem (TBTF) for late-type galaxies, which
states that isolated dwarf galaxy kinematics imply that dwarfs live in
lower-mass halos than is expected in a Lambda-CDM universe. Furthermore, we want to
explain this apparent tension between theory and observations.

To do this, we have used the MoRIA (Models of Realistic dwarfs In Action) 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.

We find that for low-mass galaxies, the circular velocity profile inferred from
the HI kinematics often under-estimates 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 underestimation
of the total 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.

As a recent result, we discuss how the results from the MoRIA galaxies compare
to simulations using different technique, such as zoom simulations and using the
AMR code Ramses.