Speaker
Mr
Robbert Verbeke
(UGent)
Description
In the ΛCDM model, cosmic structure forms in a hierarchical fashion. According to this paradigm,
even low-mass dwarf galaxies grow via smooth accretion and mergers. Given the low masses of dwarf
galaxies and their even smaller progenitors, the UV background is expected to have a significant
influence on their gas content and, consequently, their star formation histories. Generally, cosmological
simulations predict that most dwarf systems with circular velocities below ~30 km/s do not form
significant amounts of stars or contain gas and are "dark" galaxies (Sawala et al. 2013, 2014; Hopkins
et al. 2014; Shen et al. 2014). This is in contradiction with the recent discovery of low-mass yet gas-
rich dwarf galaxies, such as Leo P (Skillman et al. 2013) and Pisces A (Tollerud et al. 2014).
Moreover, Tollerud et al. (2014) point out that most isolated dark-matter halos down to circular
velocities of ~15 km/s contain neutral gas, in contradiction with the predictions of current simulations.
Based on a suite of simulations of the formation and evolution of dwarf galaxies we show that, if the
first peak of star formation can be sufficiently reduced, e.g. by inclusion of Pop III stars in the
simulations, the resulting dwarf galaxies have severely suppressed star-formation rates while holding
on to their gas reservoirs. Moreover, we show that, although instrumental in shaping these galaxies,
only a few Pop III stars are expected to still reside within the simulated dwarfs at z=0, in agreement
with observed extremely metal-poor stars in dwarf galaxies. We show that there is a marked difference
between a galaxy's "total" star-formation history and the one read from the stars in the center of the
galaxy, since most of the oldest stars have been ejected from the galaxy in merger events.
To determine the observational properties of the simulations, we mimic the ways observers would
determine them as best as possible. When doing this, our feedback model leads to the formation of
realistic low-mass, gas-rich dwarfs with a broad range of star formation histories and which adhere to
the observed scaling relations, such as the baryonic Tully-Fisher relation.
Summary
In short, when properly mocking the observable properties, the simulations presented here are for the first time able to reproduce the observed properties of low-mass, gas-rich dwarfs such as Leo T, Leo P and Pisces A.
Primary author
Mr
Robbert Verbeke
(UGent)
