Day 337

Wednesday.

1211.4031
Effective conductance method for the primordial recombination spectrum
Ali-Haimoud

A fast way to compute the spectrum, separating the cosmology (cheap) from cosmology-independent part (expensive).  1e4 times faster.

1211.4128
A local bias approach to the clustering of discrete density peaks
Desjacques

Show: 2pt correlation function of maxima of homogeneous and isotropic Gaussian random field can be thought of (to 2nd order) as arising from a local bias expansion formulated in terms of rotationally invariant variables.  This expansion relies on a unique smoothing scale (Lagrangian radius of dark matter haloes).  Advantage: circumvents the difficult computation of joint probability distributions.  Demonstrate that the bias factors associated with these rotational invariants can be computed using a peak-BG spit argument.  Bias factors are orthogonal polynomials averaged over spatial locations that satisfy the peak constraint.  Asphericity in the peak profile contributes to the clustering at quadratic and higher order, with bias factors given by generalized Laguerre polynomials.  Useful to model the clustering of discrete tracers (eg peaks) with more realistic collapse prescriptions involving the tidal shear.

1211.4253
Hubble parameter measurement constraints on dark energy
Farooq, Mania, Ratra

21 H(z) points from past literature to constrain model parameters on time-evolving DE cosmologies.  Constraints now almost as restrictive as that from SNIa (Suzuki+ 2012).  Joint analysis of H(z), BAO and SNIa data favors a spatially-flat cosmological model by a cosmological constant, but does not exclude slowly-evolving DE.

1211.4308
On the scatter in the relation between stellar mass and halo mass: random or halo formation time dependent?
Wang, De Lucia, Weinmann

HOD fit of both stellar MF and correlation function of galaxies by definition; SAM built on the same DM halo merger trees than empirical model still have difficulties in reproducing the observational data simultaneously.  Compare relation between M* of galaxies and their host halo mass in the 3 models (1 HOD and 2 SAM); find that they are different.  Rescaled DLB07 SAM does ok, SAM model Guo11 still over-predicts the clustering of low-mass galaxies.  This indicates that the detail of how galaxies populate the scatter in the M*-M_halo relation does play an important role in determining the correlation functions of galaxies.  While the M* of galaxies in HOD (Wang) model depends only on halo mass and is randomly distributed within the scatter, galaxy M* depends also on the halo formation time in SAMs.  At fixed value of infall mass, galaxies that lie above the median M*-M_halo relation reside in haloes that formed earlier, while galaxies that lie below the median relation reside in haloes that formed later.  This effect much stronger in Guo11, which explains the over-clustering of low mass galaxies ing Guo11.  Results illustrate that the assumption of random scatter in the relation between stellar and halo mass as employed by current HOD an abundance matching models may be problematic in case a significant assembly bias exists in the real Universe.

1211.4345
Cosmic microwave background filters and the dark-flow measurement
Atrio-Barandela, Kashlinsky, Ebeling, Kocevski

Large-scale peculiar velocities from cumulative kSZ effect identified a bulk flow of galaxy clusters at 600-1000 km/s on scales of 0.5-1 Gpc, roughly aligned with the all-sky CMB dipole.  The signal originates from a residual dipole in the direction of galaxy clusters; amplitude increases with the X-ray luminosity of the clusters.  Data must be filtered to remove the primary CMB (increases S/N).  Filtering important to get signal.  Results from alternative filters consistent with measurement [x-ray?], when filters are normalized to the data.  The discrepancies can be traced to the assumptions on cluster profile and extent that reduce the efficiency of the filter and the possible existence of tSZ residual dipoles.  PLANCK maps will be important to probe the bulk flows as well as to remove spurious dipole signals and further identify the filtering schemes appropriate for this measurement.

1211.4356
Magnetic fields during high redshift structure formation
Schleicher et al

High-res cosmo sims of primordial haloes with 1e7 Msun; turbulent structures and complex morphologies.  Turbulence implies the efficient amplification of B-fields via the small-scale dynamo.  Field strengths of ~1e-5 G can be expected at number densities of ~5/cm^3.