Day 673

Sunday.

1406.0508
Cosmic web alignments with the shape, angular momentum and peculiar velocities of dark matter haloes
Forero-Romero, Contreras, Padilla

Study the alignment of the DM haloes with the cosmic web characterized by the tidal and velocity shear fields.  Focus on the alignment of their shape, angular momentum and peculiar velocities.  Use a cosmological N-body simulation that allows to study DM haloes spanning almost 5 orders of magnitude in mass (1e9 to14)/h Msun and spatial scales of (0.5-1.0)/h Mpc to define the cosmic web.  Find that the halo shape presents the strongest alignment along the smallest tidal eigenvector, i.g., along filaments and walls, with a signal that gets stronger as the halo mass increases.  In the case of the velocity shear field only massive haloes >1e12 /h Msun tend to have their shapes aligned along the largest tidal eigenvector; that is, perpendicular to filaments and walls.  For the angular momentum, find alignment signals only for haloes more massive than 1e12/h Msun both in the tidal and velocity shear webs where the preferences are for it to be parallel to the middle eigenvector; that is, perpendicular to filaments and walls.  Finally, the peculiar velocities show a strong alignment along the smallest tidal eigenvector for all masses; halos move along filaments and walls.  In the velocity shear the same alignment is present but weaker and only for haloes less massive than 1e12/h Msun.  Results clearly show that the two different algorithms used to define the cosmic web describe different physical aspects of non-linear collapse and should be used in a complementary way to understand the effect of the cosmic web on galaxy evolution.

1406.0129
The Gaia inertial reference farm and the tilting of the Milky Way disk
Perryman, Spergel, Lindegren

While the precise relationship between the MW disk and the symmetry planes of the DM halos remains somewhat uncertain, a time-varying disk orientation wrt an inertial reference frame seems probable.  Hierarchical structure formation models predict that the DM halo is triaxial and tumbles with a characteristic rate of ~2 rad/Hubble time (~30 muas/yr).  These models also predict a time-dependenet accretion of gas, such that the angular momentum vector of the disk should be misaligned with that of the halo.  These effects, as well as tidal effects of the LMC, will result in the rotation of the angular momentum vector of the disk population wrt the quasar reference frame.  Assess the accuracy with which the positions and proper motions from Gaia can be referred to a kinematically non-rotating system, and show that the spin vector of the transformation from any rigid self-consistent catalog frame to the quasi-inertial system defined by quasars should be defined to better than 1muas/yr.  Determination of this inertial frame by Gaia will reveal any signature of the disk orientation varying with time, improve models of the potential and dynamics of the MW, test theories of gravity, and provide new insights into the orbital evolution of the Sagittarius dwarf galaxy and the Magellanic Clouds.

1406.0323
Dynamical, biological, and anthropic consequences of equal lunar and solar angular radii
Balbus

Equal angular radii means tidal forces from these bodies being comparable, implying strong temporal modulation.  Conductive to the formation of a network of isolated tidal pools ([particularly?] in the Devonian period, when the first tetrapods appeared on land)  landing support to A.S.Romer's classic idea that the evaporation of shallow pools was an evolutionary impetus for the development of chiridian limbs in aquatic tetrapodomorphs.