長峯 健太郎氏（University of Nevada, Las Vegas）

「Testing Lambda CDM model with Cosmological Simulations:
massive galaxies and cosmic star formation history」

- abstract -
Today, theorists are challenged by the overwhelming wealth of observational data on galaxies, which must be analyzed and interpreted in a cosmological context. The goal of our work is to bridge the gap between the observation and theory of galaxy formation using cosmological hydrodynamic simulations.

The concordance Lambda cold dark matter (CDM) model, which has been very successful in explaining various observations, is currently challenged by two major issues in galaxy formation: one is the existence of massive galaxies at z~6, and the other is the existence of ``dead & red'' extremely red objects (EROs) at z=1-3. Using two different types of cosmological simulations (smoothed particle hydrodynamics [SPH] and total variation diminishing [TVD]), I will discuss our current understanding of these population of galaxies and issues with simulations. Turning to a purely analytic model of cosmic SF history, we recently developed the two-component `Fossil' model based on the observed colors and luminosity densities of SDSS galaxies at z~0. This model exhibits roughly constant SFR density at z=3-6. These two models (i.e. the hydro simulations and the Fossil model) both predict that 60-70% of stellar masses in the Universe were already in place by z=2, in contrast with current observational constraints. The Fossil model also predicts that the bulge component mostly formed at z>1.5.

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