Testing anthropic reasoning for the cosmological constant with a realistic galaxy formation model

Abstract

The anthropic principle is one of the possible explanations for the cosmological constant ($\Lambda$) problem. In previous studies, a dark halo mass threshold comparable with our Galaxy must be assumed in galaxy formation to get a reasonably large probability of finding the observed small value, $P(<$${\Lambda }_{\mathrm{obs}})$, though stars are found in much smaller galaxies as well. Here we examine the anthropic argument by using a semi-analytic model of cosmological galaxy formation, which can reproduce many observations such as galaxy luminosity functions. We calculate the probability distribution of $\Lambda$ by running the model code for a wide range of $\Lambda$, while other cosmological parameters and model parameters for baryonic processes of galaxy formation are kept constant. Assuming that the prior probability distribution is flat per unit $\Lambda$, and that the number of observers is proportional to stellar mass, we find $P(<$${\Lambda }_{\mathrm{obs}})=6.7\%$ without introducing any galaxy mass threshold. We also investigate the effect of metallicity; we find $P(<$${\Lambda }_{\mathrm{obs}})=9.0\%$ if observers exist only in galaxies whose metallicity is higher than the solar abundance. If the number of observers is proportional to metallicity, we find $P(<$${\Lambda }_{\mathrm{obs}})=9.7\%$. Since these probabilities are not extremely small, we conclude that the anthropic argument is a viable explanation, if the value of $\Lambda$ observed in our universe is determined by a probability distribution.

6 pages, 4 figures, accepted for publication in MNRAS

References in corpus (8)

• Dark Energy and the Accelerating Universe
• The Mass-Metallicity Relation at z~2
• The Milky Way's Circular Velocity Curve to 60 kpc and an Estimate of the Dark Matter Halo Mass from Kinematics of ~2400 SDSS Blue Horizontal Branch Stars
• A primer on hierarchical galaxy formation: the semi-analytical approach
• The End of the Reionization Epoch Probed by Ly-alpha Emitters at z=6.5 in the Subaru Deep Field
• Lyman Alpha Emitters in the Hierarchically Clustering Galaxy Formation
• Anthropic Distribution for Cosmological Constant and Primordial Density Perturbations
• Testing anthropic predictions for Lambda and the CMB temperature