1505.07833
An accurate halo model for fitting non-linear cosmological power spectra and baryonic feedback models
Mead, Peacock, Heymans, Joudaki, Heavens
Present an optimized variant of the halo model, designed to produce accurate matter power spectra well into the NL regime for a wide range of cosmo models. To do this, introduce physically-motivated free parameters into the halo-model formalism and fit these to data from high-resolution N-body simulations. For a variety of LCDM and wCDM models the halo-model power is accurate to ~5& for k<10 h/Mpc and z<2. Compare the results with recent revisions of the popular HALOFIT model and show that these predictions are more accurate. An advantage of the new halo model is that it can be adapted to account for the effects of baryonic feedback on the PS. Demonstrate this by fitting the halo model to PS from the OWLS hydro sim suite via parameters that govern halo internal structure. Able to fit all feedback models investigated at the 5% level using only 2 free parameters, and place limits on the range of these halo parameters for feedback models investigated by the OWLS simulations. Accurate predictions to high-k are vital for WL surveys, and these halo parameters could be considered nuisance parameters to marginalize over in future analysis to mitigate uncertainty regarding the details of feedback, the limits found on these parameters provide a prior. Finally, investigate how lensing observables predicted by the model compare to those from simulations and from HALOFIT for a range of k-cuts and feedback models and quantify the angular scales at which these effects become important. Code to calculate PS from the model presented in this paper can be found at github.com.
1505.07840
Hierarchical cosmic shear power spectrum inference
Alsing, Heavens, Jaffe, Kiessling, Wandelt, Hoffmann
Develop a Bayesian hierarchical modeling approach for cosmic shear power spectrum inference, jointly sampling from the poster distribution of the cosmic shear field and its (tomographic) PS. Inference of the shear PS is a powerful intermediate product for acoustic shear analysis, since it requires very few model assumptions and can be used to perform inference on a wide range of cosmological models a posteriori without loss of information. Show that joint posterior for the shear map and PS can be sampled effectively by Gibbs sampling, iteratively drawing samples from the map and PS, each conditional on the other. This approach neatly circumvents difficulties associated with complicated survey geometry and masks that plague frequentist PS estimators, since the PS inference provides prior information about the field in masked regions at every sampling step. Demonstrate this approach for inference of tomographic shear E-mode, B-mode and EB-cross PS from a simulated galaxy shear catalogue with a number of important features; galaxies distributed on the sky and in z with photometric redshift uncertainties, realistic random ellipticity noise for every galaxy and a complicated survey mask . The obtained posterior distributions for the tomographic PS coefficient recover the underlying simulated PS for both E- and B-modes, where the latter are recovered at a level of 1-2 orders of magnitude below the ellipticity noise level.
1505.07861
Redshift-space clustering of SDSS galaxies --- luminosity dependence, halo occupation distribution, and velocity bias
Guo, Zheng, Zehavi, Behroozi, ... et al
Present the measurements and modeling of the small-to-intermediate scale (0.1-25 Mpc/h) projected and 3d z-space 2PCFs of local galaxies in the SDSS DR7. Find a clear dependence of galaxy clustering on luminosity in both projected and z spaces, generally being stronger for more luminous samples. The measurements are successfully interpreted within the HOD framework with central and satellite velocity bias parameters to describe galaxy kinematics inside haloes and to model z-space distortion (RSD) effects. In agreement with previous studies, find that more luminous galaxies reside in more massive haloes. Including the z-space 2PCFs helps tighten the HOD constraints. Moreover, find that luminous central galaxies are not at rest at the halo centers, with the velocity dispersion about 30% that of the DM. Such a relative motion may reflect the consequence of galaxy and halo mergers, and find that central galaxies in lower mass haloes tend to be more relaxed with respect to their host haloes. The motion of satellite galaxies in luminous samples is consistent with their following that of the DM. For faint samples, satellites tend to have slower motion, with velocity dispersion inside haloes about 85% that of the DM. Discuss possible applications of the velocity bias constraints on studying galaxy evolution and cosmology. In the appendix, characterize the distribution of galaxy redshift measurement errors, which is well described by a Gaussian-convolved double exponential distribution.
1505.07875
On the intergalactic temperature-density relation
McQuinn, Sanderbeck
Cosmo sims of the low-density IGM exhibit a strikingly tight power-law relation between temperature and density that holds over two decades in density. It is found that this relation should roughly apply Delta z~1-2 after a reionization event, and this limiting behavior has motivated the power-law parameteriztions used in most analyses of the Lya forest. This relation has been explained by using equations linearized in the baryonic overdensity (which does not address why a tight power-law relation holds over two decades in density) or by equating the photo heating rate with the cooling rate from cosmo expansion (which is shown to be incorrect). Previous explanations also did not address why recombination cooling and Compton cooling off of the cosmic microwave background, which are never negligible, do not alter the character of this relation. Provide an understanding for why a tight power-law relation arises for unshocked gas at all densities for which collisional cooling is unimportant. Also use results to comment on (1) how quickly fluctuations in temperature redshift away after reionization processes, (2) how much shock heating occurs in the low-density IGM, and (3) how the temperatures of collapsing gas parcel evolve.
1505.08131
A demonstration of position angel-only weak lensing shear estimators on the GREAT3 simulations
Whittaker, Brown, Battye
Develop and apply the position angle-only shear estimator of Whittaker+2014 to realistic galaxy images. This is done by demonstrating the method on the simulations of the GREAT3 challenge, which include contributions from anisotropic PSFs. Measure the position angles of the galaxies using 3 distinct methods - the integrated light method, quadruple moments of surface brightness, and using model-based ellipticity measurements provided by IM3SHAPE. A weighting scheme is adopted to address biases in the position angle measurements which arise in the presence of an anisotropic PSF. Biases on the shear estimates, due to measurement errors on the position angles and correlations between the measurement errors and the true position angles, are corrected for using simulated galaxy images and an iterative procedure. The properties of the simulations are estimated using the deep field images provided as part of the challenge. A method is developed to match the distributions of galaxy fluxes and half-light radii from the deep fields to the corresponding distributions in the field of interest. Recover angle-only shear estimates with a performance close to current well-established model and moments-based methods for all 3 angle measurement techniques. The Q-values for all 3 methods are found to be Q~400. The code is freely available online.
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