Observation have shown the existence of billions of galaxies in our Universe spanning a wide mass range and having different morphologies. The simulation of realistic galaxies from cosmological initial conditions has been formidable challenge. On the other hand, there are now large catalogs of galactic data available from the local Universe to as far back as redshift z=4. They make it possible to compare galaxy formation models with observations, throughout their evolution. The rotation velocity, size, luminosity, stellar mass, total halo mass, mass of neutral hydrogen gas and total baryon mass are observationally well determined. Together, the relations between these properties provides stringent constraints which simulations of galaxy formation must satisfy.
By with WANG Liang
Figure 5. Stellar mass versus halo mass at redshift z = 0 for main simulations (blue points) together with lower mass galaxies in the zoom-in region (green and red points). The solid black line and shaded region shows the relation from Kravtsov et al. (2014) derived using halo abundance matching. Our simulation matches this very well. The dashed lines show extrapolations of the abundance matching relations. For reference, the dotted line shows the cosmic baryon fraction of mass associated with the dark matter halo, indicating that our simulations convert only a small fraction of the available gas into stars, as observed
The Partner group of Purple Mountain Observatory and Max Planck Institute for Astronomy lauched NIHAO (Numerical Investigatigation of a Hundred Astrophysical Objects) project to produce a sample of 100 hydrodynamical cosmological zoom-in simulations with halo masses ranging from dwarf to Milky Way mass galaxies. The simulations adopt a flat Lambda CDM cosmology with parameters and used GASOLINE2 code, which is an improved version of GASOLINE including a fully parallel gravitational N-body and smoothed particle hydrodynamics scheme. The initial conditons are refined to guarantee each halo is resolved with at least 500,000 particles. These galaxies have a resolution of 100 times larger than recent large cosmological simulations like EAGLE or ILLUSTRIS. The simulated galaxies from NIHAO project, which have same treatment of star formation and stellar feedback, reproduced the stellar mass - halo mass relation, star formation rate - stellar mass relation and their evolution. Moreover, the rotation curves of galaxies from NIHAO sample show a gradual transition based on mass that represents a change in the halo response.
NIHAO project create the first high resolution hydrodynamic simulations with large galaxy sample. The successful reproducing the observed inefficiency of galaxy formation across cosmic time indicates that stellar feedback is the chief piece of physics required to limit the efficiency of star formation in galaxies less massive than the Milky Way. It is also reasonable to assume this galaxy sample have accurate physical properties of galaxies which can provide more knowledge about the theory of galaxy formation and evolution.
This work was published on Monthly Notice of the Royal Astronomical Society. The first author is Liang Wang, co-authors are Aaron Dutton, Greg Stinson, Andrea Maccio, Camilla Penzo, Ben Keller and James Wadsley.
The link of this paper is: http://mnras.oxfordjournals.org/content/454/1/83
(Information Source: Purple Mountain Observatory, CAS)
