However, this linear correlation breaks down in dwarf galaxies, where stars form very inefficiently on timescales that are much longer: 10-100 billion years. It is not yet clear whether the star forming gas in these dwarf galaxies consists mainly of molecules or atoms. Observations have not yet detected molecular gas but it has been speculated that an unseen molecular reservoir could dictate the star formation rate. This would provide an explanation for the longer star formation timescales in dwarf galaxies, which could be regulated by an inefficient transition from the atomic to molecular state.
Recently, scientists at MPA have investigated the star formation in dwarf galaxies using numerical hydro-dynamical simulations, which incorporate a wealth of relevant physical processes. In particular it is assumed that molecular hydrogen forms on dust grains and that interstellar UV starlight can destroy the molecules. The simulations were conducted at an unprecedented high resolution (with a spatial resolution of 2 Parsec and matter particles of 4 solar masses). The impact of individual supernova explosions is numerically resolved. Fig. 1 shows a snapshot of the gas surface density in one of the simulations at different spatial scales, demonstrating the complexity of the multi-phase gas structure.
Comparing the Kennicutt-Schmidt relation of these simulations with observations of dwarf galaxies one finds good agreement (Fig. 3). The longer timescales compared to spiral galaxies (which is about 2 billion years) is caused by the inability of gas to cool in the outer part of the galaxy. As explained above, this prevents the ISM to form the cold gas needed for effective star formation.
Authors: Chia-Yu Hu & Thorsten Naab - (Personal homepage)
(Stefanie Walch, Simon Glover, Paul Clark)
This work is supported by: