arXiv subjects

C. Yeche

Publications and source records attributed to C. Yeche.

4 recordsLinked to original sources

arXiv2021

Finding Strong Gravitational Lenses in the DESI DECam Legacy Survey

We perform a semi-automated search for strong gravitational lensing systems in the 9,000 deg$^2$ Dark Energy Camera Legacy Survey (DECaLS), part of the DESI Legacy Imaging Surveys (Dey et al.). The combination of the depth and breadth of these surveys are unparalleled at this time, making them particularly suitable for discovering new strong gravitational lensing systems. We adopt the deep residual neural network architecture (He et al.) developed by Lanusse et al. for the purpose of finding strong lenses in photometric surveys. We compile a training set that consists of known lensing systems in the Legacy Surveys and DES as well as non-lenses in the footprint of DECaLS. In this paper we show the results of applying our trained neural network to the cutout images centered on galaxies typed as ellipticals (Lang et al.) in DECaLS. The images that receive the highest scores (probabilities) are visually inspected and ranked. Here we present 335 candidate strong lensing systems, identified for the first time.

astro-ph.GA↗

arXiv2016

SDSS-IV eBOSS emission-line galaxy pilot survey

The Sloan Digital Sky Survey IV extended Baryonic Oscillation Spectroscopic Survey (SDSS-IV/eBOSS) will observe 195,000 emission-line galaxies (ELGs) to measure the Baryonic Acoustic Oscillation standard ruler (BAO) at redshift 0.9. To test different ELG selection algorithms, 9,000 spectra were observed with the SDSS spectrograph as a pilot survey based on data from several imaging surveys. First, using visual inspection and redshift quality flags, we show that the automated spectroscopic redshifts assigned by the pipeline meet the quality requirements for a reliable BAO measurement. We also show the correlations between sky emission, signal-to-noise ratio in the emission lines, and redshift error. Then we provide a detailed description of each target selection algorithm we tested and compare them with the requirements of the eBOSS experiment. As a result, we provide reliable redshift distributions for the different target selection schemes we tested. Finally, we determine an target selection algorithms that is best suited to be applied on DECam photometry because they fulfill the eBOSS survey efficiency requirements.

astro-ph.CO↗

arXiv2011

Simulations of BAO reconstruction with a quasar Lyman-alpha survey

The imprint of Baryonic Acoustic Oscillations (BAO) on the matter power spectrum can be constrained using the neutral hydrogen density in the intergalactic medium as a tracer of the matter density. One of the goals of the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS-III) is to derive the Hubble expansion rate and the angular scale from the BAO signal in the IGM. To this aim, the Lyman-alpha forest of 10^5 quasars will be observed in the redshift range 2.2<z<3.5 and over 10,000 deg^2. We simulated the BOSS QSO survey to estimate the statistical accuracy on the BAO scale determination provided by such a large scale survey. In particular, we discuss the effect of the poorly constrained estimate of the unabsorbed intrinsic quasar spectrum. The volume of current N-body simulations being too small for such studies, we resorted to Gaussian random field (GRF) simulations. We validated the use of GRFs by comparing the output of GRF simulations with that of the Horizon N-body simulation with the same initial conditions. Realistic mock samples of QSO Lyman-αforest were generated; their power spectrum was computed and fitted to obtain the BAO scale. The rms of the results for 100 different simulations provides an estimate of the statistical error expected from the BOSS survey. We confirm the results from Fisher matrix estimate. In the absence of error on the unabsorbed quasar spectrum, the BOSS quasar survey should measure the BAO scale with an error of the order of 2.3%, or the transverse and radial BAO scales separately with errors of the order of 6.8% and 3.9%, respectively. The significance of the BAO detection is assessed by an average Δχ^2=17 but for individual realizations Δχ^2 ranges from 2 t o 35. The error on the unabsorbed quasar spectrum increases the error on the BAO scale by 10 to 20% and results in a sub percent bias.

astro-ph.CO↗

arXiv2005

Cosmology with wide-field SZ cluster surveys: Selection and Systematic Effects

The cosmological potential of large-scale structure observations for cosmology have been extensively discussed in the litterature. In particular, it has recently been shown how Sunyaev-Zel'dovich (SZ) cluster surveys can be used to constrain dark energy parameters. In this paper, we study whether selection and systematics effects will limit future wide-field SZ surveys from achieving their cosmological potential. For this purpose, we use a sky simulation and an SZ-cluster detection software presented in Pires et al. (2005), using the future Olimpo, APEX and Planck surveys as a concrete examples. We show that the SZ-cluster selection function and contamination of SZ-cluster catalogues are more complex than is usually assumed. In particular, the simulated field-to-field detected cluster counts is a factor 3 larger than the expected Poisson fluctuations. We also study the impact of missing redshift information and of the uncertainty of the scaling relations for low mass clusters. We quantify, through hypothesis tests, how near-future SZ experiments can be used to discriminate between different structure formation models. Using a maximum likelihood approach, we then study the impact of these systematics on the joint measurement of cosmological models and of cluster scaling relations.

astro-ph↗