Day 1158

Monday.

1609.07147

What galaxy masses perturb the local cosmic expansion?

Peñarrubia, Fattahi

Use 12 cosmo N-body sims of Local Group systems (Sawala+2016) to inspect the relation between the viral mass of the main halos (Mvir,1 and Mvir,2), the mass derived from the relative motion of the halo pair (Mtim), and that inferred from the local Hubble flow (Mlhf).  Show that within the Spherical Collapse Model (SCM), which provides an idealized description of structure formation in an expanding Universe, the correspondence between the 3 mass estimates is exact, i.e. Mlhf=Mtim=Mvir,1+Mvir,2.  However, comparison with Apostle sims reveals that, contrary to what the SCM states, a relative large fraction of the mass that perturbs the local Hubble flow and drives the relative trajectory of the main galaxies is not contained within Rvir, and that the amount of "extra-viral" mass tends to increase in galaxies with a slow accretion rate.  In addition, find that modeling the peculiar velocities around the Local Group returns an unbiased constraint on the viral mass ratio of the main galaxy pair (fm=M1/M2~Mvir1/Mvir2), as well as the individual masses of the main galaxies (M1 and M2) without a priori assumptions on the matter distribution nor the equilibrium state of these systems.  Adopting Deimer+Kravtsov (2014) outer halo profile, which scales as rho~R^-4 at R>~Rvir, indicates that M1 and M2 roughly correspond to the asymptotically-convergent (total) masses of the individual haloes.  In contrast, find that estimates of Mvir based on the dynamics of tracers at R>>Rvir require a prior information on the internal matter distribution and the growth rate of the main galaxies, both of which are typically difficult to quantify.

1609.07474

Scaling in global tidal dissipation of the Earth-Moon system

van Putten

The Moon migrated to r_leftmoon~3.8e10 cm over a characteristic time r/v=1e10 Gyr by tidal interaction with the Earth's oceans at a present velocity of v=3.8cm/yr.  Derive scaling of global dissipation that covers the entire history over the past 4.52 Gyr.  Off-resonance tidal interactions at relatively short tidal periods in the past reveal the need for scaling with amplitude.  The global properties of the complex spatio-temprial dynamics and dissipation in broad spectrum ocean waves is modeled by damping e=hF/(2Q0), where h is the tidal wave amplitude, F is the tidal frequency, and Q0 is the Q-factor at the present time.  It satisfies Q0~14 for consistency of migration time and age of the Moon consistent wth observations for a near-resonance state today.  It shows a startlingly fast eviction of the Moon from an unstable near-synchronous orbit close to the Roche limit, probably in a protolunar disk.  Rapid spin down of the Earth from an initial ~30% of break-up by the moon favored early formation of a clement global climate.  Our theory suggests moons may be similarly advantageous to potentially habitable exoplanets.