Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

Primordial non-Gaussianity (PNG) is one of the most powerful probes of the early universe, and measurements of the large-scale structure of the universe have the potential to transform our understanding of this area. However, relating measurements of the late-time universe to the primordial perturbations is challenging due to the nonlinear processes that govern the evolution of the universe. To help address this issue, we release a large suite of N-body simulations containing four types of PNG: QUIJOTE-PNG. These simulations were designed to augment the QUIJOTE suite of simulations that explored the impact of various cosmological parameters on large-scale structure observables. Using these simulations, we investigate how much information on PNG can be extracted by extending power spectrum and bispectrum measurements beyond the perturbative regime at z = 0.0. This is the first joint analysis of the PNG and cosmological information content accessible with power spectrum and bispectrum measurements of the nonlinear scales. We find that the constraining power improves significantly up to kmax 0.3 Mpc h » -1 , with diminishing returns beyond as the statistical probes signal-to-noise ratios saturate. This saturation emphasizes the importance of accurately modeling all the contributions to the covariance matrix. Further, we find that combining the two probes is a powerful method of breaking the degeneracies with the ΛCDM parameters

Abstract:

Cluster galaxies exhibit substantially lower star formation rates than field galaxies today, but it is conceivable that clusters were sites of more active star formation in the early universe. Herein, we present an interpretation of the star formation history (SFH) of group/cluster galaxies based on the large-scale cosmological hydrodynamic simulation, Horizon-AGN. We find that massive galaxies in general have small values of e-folding timescales of star formation decay (i.e., "mass quenching") regardless of their environment, while low-mass galaxies exhibit prominent environmental dependence. In massive host halos (i.e., clusters), the e-folding timescales of low-mass galaxies are further decreased if they reside in such halos for a longer period of time. This "environmental quenching" trend is consistent with the theoretical expectation from ram pressure stripping. Furthermore, we define a "transition epoch" as where cluster galaxies become less star-forming than field galaxies. The transition epoch of group/cluster galaxies varies according to their stellar and host-cluster halo masses. Low-mass galaxies in massive clusters show the earliest transition epoch of ∼7.6 Gyr ago in lookback time. However, this decreases to ∼5.2 Gyr for massive galaxies in low-mass clusters. Based on our findings, we can describe a cluster galaxy's SFH with regard to the cluster halo-to-stellar mass ratio.