Joel R. Primack

TL;DR: It is shown that a repulsive Λ gives a smaller final radius of a virialized cluster than a vanishing Λ, and the possibility of measuring the density parameter Ω0 and the cosmological constant λ0 from dynamical tests using linear and non-linear spherical models.

TL;DR: In the early universe, light neutrinos would have been 'hot', moving at nearly the speed of light as discussed by the authors, with masses of a few electronvolts (eV) or less.

TL;DR: In this paper, the authors argue that the most useful definition is that a set of galaxies is homologous if they are the same in all respects up to three dimensional scaling constants which may differ from one galaxy to the next.

Abstract: We investigate the nature and evolution of substructure within the SSA22 protocluster region at $z=3.09$ using cosmological simulations. A redshift histogram constructed from current spectroscopic observations of the SSA22 protocluster reveals two separate peaks at $z = 3.065$ (blue) and $z = 3.095$ (red). Based on these data, we report updated overdensity and mass calculations for the SSA22 protocluster. We find $\delta_{b,gal}=4.8 \pm 1.8$, $\delta_{r,gal}=9.5 \pm 2.0$ for the blue and red peaks, respectively, and $\delta_{t,gal}=7.6\pm 1.4$ for the entire region. These overdensities correspond to masses of $M_b = (0.76 \pm 0.17) \times 10^{15} h^{-1} M_{\odot}$, $M_r = (2.15 \pm 0.32) \times 10^{15} h^{-1} M_{\odot}$, and $M_t=(3.19 \pm 0.40) \times 10^{15} h^{-1} M_{\odot}$ for the red, blue, and total peaks, respectively. We use the Small MultiDark Planck (SMDPL) simulation to identify comparably massive $z\sim 3$ protoclusters, and uncover the underlying structure and ultimate fate of the SSA22 protocluster. For this analysis, we construct mock redshift histograms for each simulated $z\sim 3$ protocluster, quantitatively comparing them with the observed SSA22 data. We find that the observed double-peaked substructure in the SSA22 redshift histogram corresponds not to a single coalescing cluster, but rather the proximity of a $\sim 10^{15}h^{-1} M_{\odot}$ protocluster and at least one $>10^{14} h^{-1} M_{\odot}$ cluster progenitor. Such associations in the SMDPL simulation are easily understood within the framework of hierarchical clustering of dark matter halos. We finally find that the opportunity to observe such a phenomenon is incredibly rare, with an occurrence rate of $8h^3 \mbox{ Gpc}^{-3}$.

TL;DR: In this article, the authors present a new algorithm for generating merger trees and halo catalogs which explicitly ensures consistency of halo properties (mass, position, and velocity) across timesteps.