Monday.
1312.1242
Practical cosmology with lenses
Eales
How lensed systems can be used for cosmology, taking into account the difficulty of separately measuring the values of the cosmological parameters, the statistical properties of the DM halos and the properties of the source population. First show: if one assumes a standard cosmological mode, samples of lenses can be used to test models for the evolution of the distribution of DM haloes in a way that is independent of the properties of the source population; even the existing sample of lenses in Herschel is enough to formally rule out 3 of the most popular models of the evolving population of DM haloes. Independently of the evolution of the halos, observations of a sample of 100 lensed systems would be enough to estimate Omega-Lambda with a precision of 5% and observations of 1000 lenses would be enough to estimate w, the parameter in the EoS of dark energy with a precision similar to that obtained from the Planck observations of CMB. While the fraction of submillimetre sources that are lensed depends weakly on the specific halo mass function that is used in the model, it depends very strongly on the evolution of the submillimetre luminosity function of the source population. Measurements of the lensing fraction can be used to investigate galaxy evolution in a way that is independent of the properties of the intervening halos. [not clear what about the lens system that can determine these claimed properties.]
1312.1252
Non-Gaussianity of the cosmic infrared background anisotropies II : predictions of the bispectrum and constrains forecast
Pénin, Lacasa, Aghanim
Use full analytical computation of the bispectrum based on the halo model together with the halo occupation number, derive the bispectrum of the CIB anisotropies that trace the clustering of dusty-SF galaxies. Focus on Planck and Herschel wavelengths. Explore the bispectrum behavior as a function of several models of evolution of galaxies and show that it is strongly sensitive to that ingredient. Contrary to the power spectrum, the bispectrum at the four wavelengths, seems dominated by low redshift galaxies. Such a contribution can be hardly limited by applying low flux cuts ["cannot be limited by"?]. Also discuss the contributions of halo mass as a function of the redshift and the wavelength, recovering that each term [each term of what? z and lambda?] is sensitive to a different mass range. Show that the CIB bispectrum is a strong contaminant of the CMB bispectrum at 850 um and higher. Finally, a Fisher analysis of the PS, bispectrum alone and of the combination of both shows that degeneracies on the HOD parameters are broken by including the bispectrum information, leading to tight constraints even when including foreground residuals.
1312.1287
Using neural networks to estimate redshift distributions. An application to DFHTLenS
Bonnett
Using neural networks (NN) to estimate the redshift distribution of a galaxy sample, able to obtain PDF for each galaxy using a classification NN. Applied to 58k galaxies in CFHTLenS that have spectroscopic redshifts from DEEP2, VVDS and VIPERS. Show that the stacked PDF's give an excellent representation of the true N(z) using information from 5,4, or 3 photometric bands. Show that the fractional error due to using N(z_phot) instead of N(z_thruth) is <=1 on the lensing power spectrum P_kappa in several tomographic bins. Investigate how well this method performs when few training samples are available and show that in this regime the NN slightly overestimates the N(z) at high z [you'd think that that would depend on how the NN was trained, though!]. The case where the training sample is not representative of the full data set is investigated. An IPython notebook accompanying this paper is available on bitbucket.org/christopher_bonnett/nn_notebook.
1312.1292
Halo modelling in chameleon theories
Lombriser, Koyama, Li
Analyze modeling techniques for LSS formed in scalar-tensor theories of constant Brans-Dicke parameter which match the concordance model background expansion history and produce a chameleon suppression of the gravitational modification in high-density regions. use a mass and environment dependent chameleon spherical collapse model [chameleon spherical collapse model!], the Sheth-Tormen halo mass function and linear halo bias, the NFW halo density profile, and the halo model. Using the spherical collapse model, extrapolate a chameleon mass-concentration scaling relation from a LCDM prescription calibrated to N-body simulations. Also provide constraints on the model parameters to ensure viability on local scales. Test description of the halo mass function and nonlinear matter power spectrum against the respective observers extracted from large-volume and high-resolution N-body simulations in the limiting case of f(R) gravity, corresponding to a vanishing Brans-Dicke parameter. Find good agreement between the two; the halo model provides a good qualitative description of the shape of the relative enhancement of the f(R) matter power spectrum wrt LCDM caused by the extra attractive gravitational force but fails to recover the correct amplitude. Introducing an effective linear PS in the computation of the two-halo term to account for an underestimation of the chameleon suppression at intermediate scales, can accurately reproduce the measurements from the N-body simulations.
1312.1300
Planck 2013 results. XXXI. All-sky model of thermal dust emission
Planck Collabroation
Present an all-sky model of dust emission from Planck 857, 545 and 353 GHz, and IRAS 100 micron data. Use modified BB fit to the data; present all-sky maps of the optical depth, temperature, and spectral index over the 353-3000 GHz range. Model is a tight representation of the data at 5 arcmin. Shows variations of the order of 30% compared with the widely-used model of Finkbeiner, Davis and Schlegel. The Planck data allow estimation of the dust temperature uniformly over the whole sky, providing an improved estimate of the dust optical depth compared to previous all-sky dust model, especially in high-contrast molecular regions. An increase of the dust opacity at 353 GHz, tau_353/N_H, from the diffuse to the denser ISM is reported. It is associated with the decrease in the observed dust temperature, T_obs, that could be due at least in part to the increased dust opacity. Also report an excess of dust emission at HI column densities lower than 1e20 cm^-2 that could be the signature of dust in the warm ionized medium. In the diffuse ISM at high Galactic latitude, report an anti-correlation between tau_353/N_H and T_obs while the dust specific luminosity (the total dust emission integrated over frequency, the radiance, per H atom) stays about constant. The implication is that in the diffuse high-latitude ISM tau_353 is not as reliably a tracer of dust column density as concluded it is in molecular clouds where the correlation of tau_353 with dust extinction estimated using color excess measurements on stars is strong. Tot estimate Galactic E(B-V) in extragalactic fields at high latitude, develop a new method based on the thermal dust radiance, instead of the dust optical depth, calibrated to E(B-V) using reddening measurements of quasars deduced from SDSS data.
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