Day 773

Tuesday.

410.6818
At the Argo simulation: II. The early build-up of the Hubble sequence
Fiacconi, Feldmann, Mayer

22 high z>3 galaxies in Argo cosmo zoom-in sim of grog-sized halo in high resolution (1e4 Msun, 100 pc): Identify major mergers as the main trigger for the formation of bulges, and the steepening of the circular velocity curves.  Minor mergers and non-axisymmetric perturbations (stellar bars) drive the bulge growth in some cases.  The specific angular momenta of the simulated disc components fairly match the values inferred from nearby galaxies of similar M* once the expected redshift evolution of disc sizes is accounted for.  Conclude that morphological transformations of high z galaxies of intermediate mass are likely triggered by processes similar to those at low z and result in an early build-up of the Hubble sequence.

1410.6826
Baryonic effects on weak-lensing two-point statistics and its cosmological implications
Mohammed, Martizzi, Teyssier, Amara

Develop an extension of the Halo model that describes analytically the corrections to the matter PS due to the physics of baryons.  Extend these correction to the WL shear angular power spectrum.  Within each halo, baryonic model accounts for : 1) a central galaxy, the major stellar component whose properties are derived from abundance matching techniques; 2) a hot plasma in hydrostatic equilibrium and 3) an adiabatically-contracted DM component.  This analytic approach allows comparison of the model to the DM-only case.  The basic assumptions are tested against the hydrodynamical simulations of Martizzi+ 2014, with which a remarkable agreement is found.  The baryonic model has only one free parameter, M_crit, the critical halo mass that marks the transition between feedback-dominated haloes, mostly devoid of gas, and gas rich haloes, in which AGN feedback effects become weaker.  Explore the entire cosmological parameter space, using the angular power spectrum in 3 z bins as the observable, assuming a Euclid-like survey.  Derive the corresponding constraints on the cosmological parameters, as well as the possible bias introduced by neglecting the effects of baryonic physics.  Find that, up to ell_max=4000, baryonic physics plays very little role in the cosmo parameter estimation.  However, if one goes up to ell_max=8000, the marginalized errors on the cosmo parameters can be significantly reduced, but neglecting baryonic physics can lead to bias in the recovered cosmological parameters up to 10 sigma.  These biases are removed if one takes into account the main baryonic parameter, M_crit, which can also be determined up to 1-2%, along with the other cosmological parameters.

1410.6955
A new model to predict weak lensing peak counts I. comparison with $N$-body simulations
Lin, Kilbinger

WL peak counts has been shown to be a powerful tool for cosmo.  It provides non-Gaussian information of LSS, complementary to second order statistics.  Propose a new flexible method to predict WL peak counts, which can be adapted to realistic scenarios, such as a real source distribution, intrinsic galaxy alignment, mass effects, photo-z errors from surveys, etc.  The new model is also suitable for applying the tomography technique and NL filters.  A probabilistic approach to model peak counts is pretend.  First, sample halos from a MF.  Second, assign them NFW profiles.  Third, place haloes randomly on the field of view.  The creation of these "fast sims" requires much less computing time compared to N-body runs.  Then, perform ray-tracing through these fast simulation boxes and select peaks from WL maps to predict peak number counts.  The computation is achieved by CAMELUS algorithm, which is made available at cosmostat.org.  Compare results to N-body sims to validate the model.  Find that the approach is in good agreement with full N-body runs.  Show that the lensing signal dominates shape noise and Poisson noise for peaks with SNR between 4 and 6.  Counts from the same SNR range are sensitive to Omega_m and sigma_8.  Show how the model can discriminate between various combinations of these two parameters.  Offer a powerful tool to study WL peaks.  The potential of the forward model is its high flexibility, making the use of peak counts under realistic survey conditions feasible.

1410.7175
Dark matter inner slope and concentration in galaxies: from the Fornax dwarf to M87
Mamon et al

Apply 2 new methods that model the distribution of observed tracers in projected phase space to lift the mass/velocity anisotropy (VA) degeneracy and deduce constraints on the mass profiles of galaxies, as well as their VA.  First show how a distribution function based method applied to the satellite kinematics of otherwise isolated SDSS galaxies shows convincing observational evidence of age matching: red galaxies have more concentrated DM haloes than blue galaxies of the same stellar or halo mass.  Then, applying the MAMPOSSt technique to M87 (traced by its red and blue globular clusters) find that very cuspy DM is favored, unless priors are released on DM or stellar mass (leading to unconstrained slope).  For the Fornax dSph (traced by its metal-rich and metal-poor stars), the inner DM slope is unconstrained, with weak evidence for a core if the stellar mass is fixed.  This highlights how priors are crucial for DM modeling.  Finally, find that blue GCs around M87 and metal-rich stars in Fornax have tangential outer VA.