case western reserve university



Massive galaxies and EROs at z=1-3 in cosmological hydrodynamic simulations: Is the hierarchical CDM model wrong?

Ken Nagamine (UC San Diego)

Recently there have been several claims that the hierarchical cold dark matter (CDM) model might have a difficulty in producing massive galaxies that have been found at redshift z=1-2 by near-IR observations. In order to test these claims, we study the properties of massive galaxies at z=1-3 in two different types of cosmological hydrodynamic simulations. In particular, I focus on colors, stellar masses, and star formation histories of galaxies, and describe how the hydrodynamic simulations achieve the production of 10^11 Msun galaxies by z=2. Unlike the current semi-analytic models of galaxy formation, our models predict the peak of the Madau plot to be at z>=5 and higher stellar mass density at z>1 than the current observational estimates. Our models suggest that the current observations could be missing as much as 50% of the stellar masses at high redshift. We also study the number density of Extremely Red Objects (EROs), and find that our simulations can account for the observed space density of EROs at z=1-2 if a uniform extinction of E(B-V)=0.4 is assumed. However, it still remains to be seen whether the simulations can produce enough 'dead massive EROs'.