arXiv subjects

Felipe A. Marin

Publications and source records attributed to Felipe A. Marin.

5 recordsLinked to original sources

arXiv2016

The 2-degree Field Lensing Survey: photometric redshifts from a large new training sample to r<19.5

We present a new training set for estimating empirical photometric redshifts of galaxies, which was created as part of the 2dFLenS project. This training set is located in a 700 sq deg area of the KiDS South field and is randomly selected and nearly complete at r<19.5. We investigate the photometric redshift performance obtained with ugriz photometry from VST-ATLAS and W1/W2 from WISE, based on several empirical and template methods. The best redshift errors are obtained with kernel-density estimation, as are the lowest biases, which are consistent with zero within statistical noise. The 68th percentiles of the redshift scatter for magnitude-limited samples at r<(15.5, 17.5, 19.5) are (0.014, 0.017, 0.028). In this magnitude range, there are no known ambiguities in the colour-redshift map, consistent with a small rate of redshift outliers. In the fainter regime, the KDE method produces p(z) estimates per galaxy that represent unbiased and accurate redshift frequency expectations. The p(z) sum over any subsample is consistent with the true redshift frequency plus Poisson noise. Further improvements in redshift precision at r<20 would mostly be expected from filter sets with narrower passbands to increase the sensitivity of colours to small changes in redshift.

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arXiv2016

2dFLenS and KiDS: Determining source redshift distributions with cross-correlations

We develop a statistical estimator to infer the redshift probability distribution of a photometric sample of galaxies from its angular cross-correlation in redshift bins with an overlapping spectroscopic sample. This estimator is a minimum variance weighted quadratic function of the data: a quadratic estimator. This extends and modifies the methodology presented by McQuinn & White (2013). The derived source redshift distribution is degenerate with the source galaxy bias, which must be constrained via additional assumptions. We apply this estimator to constrain source galaxy redshift distributions in the Kilo-Degree imaging survey through cross-correlation with the spectroscopic 2-degree Field Lensing Survey, presenting results first as a binned step-wise distribution in the range z < 0.8, and then building a continuous distribution using a Gaussian process model. We demonstrate the robustness of our methodology using mock catalogues constructed from N-body simulations, and comparisons with other techniques for inferring the redshift distribution.

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arXiv2016

The 2-degree Field Lensing Survey: design and clustering measurements

We present the 2-degree Field Lensing Survey (2dFLenS), a new galaxy redshift survey performed at the Anglo-Australian Telescope. 2dFLenS is the first wide-area spectroscopic survey specifically targeting the area mapped by deep-imaging gravitational lensing fields, in this case the Kilo-Degree Survey. 2dFLenS obtained 70,079 redshifts in the range z < 0.9 over an area of 731 sq deg, and is designed to extend the datasets available for testing gravitational physics and promote the development of relevant algorithms for joint imaging and spectroscopic analysis. The redshift sample consists first of 40,531 Luminous Red Galaxies (LRGs), which enable analyses of galaxy-galaxy lensing, redshift-space distortion, and the overlapping source redshift distribution by cross-correlation. An additional 28,269 redshifts form a magnitude-limited (r < 19.5) nearly-complete sub-sample, allowing direct source classification and photometric-redshift calibration. In this paper, we describe the motivation, target selection, spectroscopic observations, and clustering analysis of 2dFLenS. We use power spectrum multipole measurements to fit the redshift-space distortion parameter of the LRG sample in two redshift ranges 0.15 < z < 0.43 and 0.43 < z < 0.7 as beta = 0.49 +/- 0.15 and beta = 0.26 +/- 0.09, respectively. These values are consistent with those obtained from LRGs in the Baryon Oscillation Spectroscopic Survey. 2dFLenS data products will be released via our website http://2dflens.swin.edu.au.

astro-ph.CO↗

arXiv2015

The Gigaparsec WiggleZ Simulations: Characterising scale dependant bias and associated systematics in growth of structure measurements

We use the Gigaparsec WiggleZ (GiggleZ) simulations to characterise galaxy bias and its scale dependence for a range of redshifts and halo masses in a standard $Λ$LCDM cosmology. Assuming bias converges to a scale independent form at large scales, we develop a phenomenological model which fully expresses the mass and redshift dependence of bias and its scale dependence in real or redshift space. We then use this to illustrate how scale-dependent bias can systematically skew measurements of the growth-rate of cosmic structure obtained from redshift-space distortion measurements. When data is fit only to scales $k_{\rm max}{\le}0.1$ $[h^{-1} \rm{Mpc}]^{-1}$, we find that these effects are significant only for large biases ($b{\gtrsim}3$) at large redshifts ($z{\gtrsim}1$). However, when smaller scales are incorporated ($k_{\rm max}{\le}0.2$ $[h^{-1} \rm{Mpc}]^{-1}$) to increase measurement precision, the combination of reduced statistical uncertainty and increased scale dependent bias can result in highly significant systematics for most large halos across all redshifts. We identify several new interesting aspects of bias, including a significant large-scale bias boost for small halos at low-redshifts due to substructure effects ($\sim$20\% for Milky Way-like systems) and a nearly redshift-independent halo mass (corresponding to a redshift-space bias of ${\sim}1.5$) for which halo bias has little-or-no scale dependence on scales greater than $3$ $[h^{-1} {\rm Mpc}]$. This suggests an optimal strategy of targeting bias ${\sim}{1.5}$ systems for clustering studies which are dominated by systematic uncertainties in how observed halo (or galaxy) distributions map to their underlying mass distribution, such as cosmological measurements of neutrino masses. Code for generating our fitting formula is publicly available at http://gbpoole.github.io/Poole_2014a_code/ (Abridged)

astro-ph.CO↗

arXiv2015

nIFTy Cosmology: Galaxy/halo mock catalogue comparison project on clustering statistics

We present a comparison of major methodologies of fast generating mock halo or galaxy catalogues. The comparison is done for two-point and the three-point clustering statistics. The reference catalogues are drawn from the BigMultiDark N-body simulation. Both friend-of-friends (including distinct halos only) and spherical overdensity (including distinct halos and subhalos) catalogs have been used with the typical number density of a large-volume galaxy surveys. We demonstrate that a proper biasing model is essential for reproducing the power spectrum at quasilinear and even smaller scales. With respect to various clustering statistics a methodology based on perturbation theory and a realistic biasing model leads to very good agreement with N-body simulations. However, for the quadrupole of the correlation function or the power spectrum, only the method based on semi-N-body simulation could reach high accuracy (1% level) at small scales, i.e., r<25 Mpc/h or k>0.15 h/Mpc. Full N-body solutions will remain indispensable to produce reference catalogues. Nevertheless, we have demonstrated that the far more efficient approximate solvers can reach a few percent accuracy in terms of clustering statistics at the scales interesting for the large-scale structure analysis after calibration with a few reference N-body calculations. This makes them useful for massive production aimed at covariance studies, to scan large parameter spaces, and to estimate uncertainties in data analysis techniques, such as baryon acoustic oscillation reconstruction, redshift distortion measurements, etc.

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