Day 582

Thursday.

1401.4454
Simulations of cosmic rays in large-scale structures: numerical and physical effects
Vazza, Gheller, Brüggen

Non-thermal (relativistic) particles are injected into the cosmos by structure formation shock waves, AGN and stellar explosions.  Present sims (up to 2048^3) using a two-fulid model in ENZO, including dynamical effects of CR protons and cover a range of theoretically motivated acceleration efficiencies.  For the bulk of the cosmic volume the modeling of CR processes is rather stable wrt resolution if minimum cell resolution ~ 100 kpc/h is used.  However, the results for the innermost cluster regions depend on the assumptions for the baryonic physics.  Inside clusters, non-radiative runs at high res tend to produce an energy density of CRs that are below available upper limits from the FERMI satellite, while the radiative runs are found to produce a higher budget of CRs.  Show that weak (M=<3-5) shocks and shock-reacceleration are crucial to set the level of CRs in the innermost region of clusters, while in the outer regions the level of CR energy is mainly set via direct injection by stronger shocks, and is less sensitive to cooling and feedback from AGN and SNe.

1401.4457
Scattering outcomes of close-in planets: constraints on planet migration
Petrovich, Tremaine, Rafikov

Many exoplanets in close-in orbits are observed to have relatively high eccentricities and large stellar obliquities.  Explore the possibility that these result from planet-planet scattering by studying the dynamical outcomes from a large number of orbit integrations in systems with 2 and 3 gas-giant planets in close-in orbits (0.05 AU<a<0.15 AU).  Find that at these orbital separations, unstable systems generally lead to planet-planet collisions in which the collision product is a plant on a low-eccentricity, low-incination orbit.  This result is inconsistent with the observations.  Conclude that eccentricity and inclination excitation from planet-planet scattering must precede migration of planets into short-period orbits.  This results constrains theories of planet migration: the semi-major axis must shrink by 1-2 orders of magnitude without damping the eccentricity and inclination.

1401.4459
An uncertainty principle for star formation. I. Why galactic star formation relations break down below a certain spatial scale
Kruijssen, Longmore

Galactic scaling relations between the (surface densities of) the gas mass and the SFR are known to develop substantial scatter or even change form when considered below a certain spatial scale.  Quantify how this behavior should be expected due to the incomplete statistical sampling of independent SF regions.  Other included limiting factors are the incomplete sampling of SF tracers from the stellar IMF and the spatial drift between gas and stars.  Present a simple uncertainty principle explaining how the scatter of SF relations depends on the spatial scale and predicts a scale-dependent bias of the gas depletion time-scale when centering an aperture on gas or SF tracer peaks.  Show how the scatter and bias are sensitive to the physical size and time-scales involved in the SF process (such as its duration of the molecular cloud lifetime), and illustrate how formalism provides a powerful tool to constrain these largely unknown quantities.  Thanks to its general form, the uncertainty principle can also be applied to other astrophysical systems, e.g. addressing the time-evolution of SF cores, protoplanetary disks, or galaxies and their nuclei.

1401.4469
A cosmic web filament revealed in Lyman-alpha emission around a luminous high-redshift quasar
Cantalupo, .. Prochaska, Hennawi, Madau, et al

Report observation of a cosmic web filament in Ly-a emission, discovered during a survey for cosmic gas fluorescently "illuminated" by bright quasars at z=2.3.  With a projected size of approximately 460 physical kpc, the Ly-a emission surrounding the radio-quiet quasar UM287 extends well beyond the virial radius of any plausible associated DM halo.  The estimated cold gas mass of the nebula from the observed emission is at least 10x larger than what is typically found by cosmological simulations, suggesting that a population of intergalactic gas clumps with sub-kpc sizes may be missing within current numerical models.