arXiv subjects

Carles Sánchez

Publications and source records attributed to Carles Sánchez.

11 recordsLinked to original sources

arXiv2026

Weak lensing, Big Magnification: Recovering hidden lensing information from galaxy positions

Galaxy clustering and weak gravitational lensing are powerful cosmological probes, traditionally combined through galaxy clustering and galaxy-galaxy lensing in a $2\times2$pt analysis. An alternative is the foreground-background clustering cross-correlation induced by lensing magnification, but measurements have achieved lower signal-to-noise than shear-based lensing. We show that, for deep photometric samples, cancellation between galaxies with positive and negative magnification responses can suppress this signal. Using DES Year 6 photometry and Balrog synthetic-source injections, we explore high-redshift ($z\simeq0.7$-$2.5$) samples split by the sign and amplitude of their magnification response. This separation reduces cancellation and can increase both signal-to-noise and cosmological constraining power. We call the combination of foreground clustering and foreground-background cross-correlations with response-selected background samples BigMag. Forecasts with DES-like simulated data vectors show that, for an optimistic sample configuration and sufficiently precise response calibration, BigMag can achieve constraining power comparable to traditional $2\times2$pt using galaxy positions alone. The same samples also enhance inverse galaxy-galaxy lensing (IGGL), a position-shear correlation dominated by magnification when the position sample lies behind the shape sample. Combining BigMag and IGGL further self-calibrates the magnification responses and yields marginalized $S_8$ constraints comparable to traditional $3\times2$pt analyses, and tighter for the more precise calibration scenarios considered here. The framework also enables near-zero-response samples for traditional $3\times2$pt and geometric lensing-ratio analyses. These results motivate further optimization and validation of galaxy selections to realize magnification as a complementary cosmological probe. [Abrg.]

astro-ph.CO↗

arXiv2024

Inverse Galaxy-Galaxy Lensing: Magnification, Intrinsic Alignments and Cosmology

Current and upcoming imaging galaxy surveys are pushing galaxy samples to higher and higher redshifts. This push will be more pronounced for lens galaxies, for which we only need to measure galaxy positions, not shapes. As a result, we will increasingly often have lens galaxy samples at redshifts higher than those of source galaxies, changing the traditional configuration of galaxy-galaxy lensing (GGL). In this paper, we explore this situation, where lens galaxies are behind source galaxies, which we call inverse galaxy-galaxy lensing (IGGL). We take projected lens and source sample specifications from the Vera Rubin Observatory LSST Dark Energy Science Collaboration (DESC) to compare astrophysical and cosmological constraints between traditional GGL and IGGL. We find IGGL to behave in a different way than GGL, being especially sensitive to lensing magnification, intrinsic alignments (IA) and cosmology, but largely independent of galaxy bias (as opposed to traditional GGL). In this way, we find IGGL can provide independent and robust cosmological constraints without combination with galaxy clustering, and can also probe IA at high redshift and baryonic effects at small scales without being entwined with the effects of non-linear galaxy bias. When combined with cosmic shear, we find IGGL to improve $S_8$ constraints by 25\% compared to cosmic shear alone, while also providing tighter and more robust constraints on IA and baryons.

astro-ph.CO↗

arXiv2023

Cosmology with imaging galaxy surveys: the impact of evolving galaxy bias and magnification

The joint analysis of galaxy clustering and galaxy-shear cross-correlations (galaxy-galaxy lensing) in imaging surveys constitutes one of the main avenues to obtain cosmological information. Analyses from Stage III surveys have assumed constant galaxy bias and weak lensing magnification coefficients within redshift bins. We use simple models of bias and magnification evolution to show that plausible levels of evolution impact cosmological parameter inference significantly for Stage IV surveys and possibly for current datasets as well. The distance weighting factors in galaxy-galaxy lensing cause it to have a different effective mean redshift within a lens bin than galaxy clustering. If the evolution is not included carefully in the theory modeling, this produces an apparent de-correlation of clustering and lensing even on large scales and leads to biased cosmological constraints. The level of bias is sensitive to the redshift and the width of the lens redshift distributions: for magnitude-limited-like samples it is comparable to the statistical precision even for the full DES survey, and exceeds it for Rubin-LSST. We find that ignoring the evolution can lead to approximately $1σ$ biases in the cosmological constraints in future Rubin-LSST analyses. We describe how these effects can be mitigated from the modeling and data sides, in particular by using cross-correlations to constrain the evolution parameters. We also demonstrate that the combination of galaxy clustering and CMB lensing does not suffer from this problem, due to the different distance weighting.

astro-ph.CO↗

arXiv2022

Combining cosmic shear data with correlated photo-$z$ uncertainties: constraints from DESY1 and HSC-DR1

An accurate calibration of the source redshift distribution $p(z)$ is a key aspect in the analysis of cosmic shear data. This, one way or another, requires the use of spectroscopic or high-quality photometric samples. However, the difficulty to obtain colour-complete spectroscopic samples matching the depth of weak lensing catalogs means that the analyses of different cosmic shear datasets often use the same samples for redshift calibration. This introduces a source of statistical and systematic uncertainty that is highly correlated across different weak lensing datasets, and which must be accurately characterised and propagated in order to obtain robust cosmological constraints from their combination. In this paper we introduce a method to quantify and propagate the uncertainties on the source redshift distribution in two different surveys sharing the same calibrating sample. The method is based on an approximate analytical marginalisation of the $p(z)$ statistical uncertainties and the correlated marginalisation of residual systematics. We apply this method to the combined analysis of cosmic shear data from the DESY1 data release and the HSC-DR1 data, using the COSMOS 30-band catalog as a common redshift calibration sample. We find that, although there is significant correlation in the uncertainties on the redshift distributions of both samples, this does not change the final constraints on cosmological parameters significantly. The same is true also for the impact of residual systematic uncertainties from the errors in the COSMOS 30-band photometric redshifts. Additionally, we show that these effects will still be negligible in Stage-IV datasets. Finally, the combination of DESY1 and HSC-DR1 allows us to constrain the ``clumpiness'' parameter to $S_8 = 0.768^{+0.021}_{-0.017}$. This corresponds to a $\sim\sqrt{2}$ improvement in uncertainties with respect to either DES or HSC alone.

astro-ph.CO↗

arXiv2022

BronchoPose: an analysis of data and model configuration for vision-based bronchoscopy pose estimation

Vision-based bronchoscopy (VB) models require the registration of the virtual lung model with the frames from the video bronchoscopy to provide effective guidance during the biopsy. The registration can be achieved by either tracking the position and orientation of the bronchoscopy camera or by calibrating its deviation from the pose (position and orientation) simulated in the virtual lung model. Recent advances in neural networks and temporal image processing have provided new opportunities for guided bronchoscopy. However, such progress has been hindered by the lack of comparative experimental conditions. In the present paper, we share a novel synthetic dataset allowing for a fair comparison of methods. Moreover, this paper investigates several neural network architectures for the learning of temporal information at different levels of subject personalization. In order to improve orientation measurement, we also present a standardized comparison framework and a novel metric for camera orientation learning. Results on the dataset show that the proposed metric and architectures, as well as the standardized conditions, provide notable improvements to current state-of-the-art camera pose estimation in video bronchoscopy.

cs.CV↗

arXiv2021

Dark Energy Survey Year 1 Results: Constraining Baryonic Physics in the Universe

Measurements of large-scale structure are interpreted using theoretical predictions for the matter distribution, including potential impacts of baryonic physics. We constrain the feedback strength of baryons jointly with cosmology using weak lensing and galaxy clustering observables (3$\times$2pt) of Dark Energy Survey (DES) Year 1 data in combination with external information from baryon acoustic oscillations (BAO) and Planck cosmic microwave background polarization. Our baryon modeling is informed by a set of hydrodynamical simulations that span a variety of baryon scenarios; we span this space via a Principal Component (PC) analysis of the summary statistics extracted from these simulations. We show that at the level of DES Y1 constraining power, one PC is sufficient to describe the variation of baryonic effects in the observables, and the first PC amplitude ($Q_1$) generally reflects the strength of baryon feedback. With the upper limit of $Q_1$ prior being bound by the Illustris feedback scenarios, we reach $\sim 20\%$ improvement in the constraint of $S_8=σ_8(Ω_{\rm m}/0.3)^{0.5}=0.788^{+0.018}_{-0.021}$ compared to the original DES 3$\times$2pt analysis. This gain is driven by the inclusion of small-scale cosmic shear information down to 2.5 arcmin, which was excluded in previous DES analyses that did not model baryonic physics. We obtain $S_8=0.781^{+0.014}_{-0.015}$ for the combined DES Y1+Planck EE+BAO analysis with a non-informative $Q_1$ prior. In terms of the baryon constraints, we measure $Q_1=1.14^{+2.20}_{-2.80}$ for DES Y1 only and $Q_1=1.42^{+1.63}_{-1.48}$ for DESY1+Planck EE+BAO, allowing us to exclude one of the most extreme AGN feedback hydrodynamical scenario at more than $2 σ$.

astro-ph.CO↗

arXiv2020

Propagating sample variance uncertainties in redshift calibration: simulations, theory and application to the COSMOS2015 data

Cosmological analyses of galaxy surveys rely on knowledge of the redshift distribution of their galaxy sample. This is usually derived from a spectroscopic and/or many-band photometric calibrator survey of a small patch of sky. The uncertainties in the redshift distribution of the calibrator sample include a contribution from shot noise, or Poisson sampling errors, but, given the small volume they probe, they are dominated by sample variance introduced by large-scale structures. Redshift uncertainties have been shown to constitute one of the leading contributions to systematic uncertainties in cosmological inferences from weak lensing and galaxy clustering, and hence they must be propagated through the analyses. In this work, we study the effects of sample variance on small-area redshift surveys, from theory to simulations to the COSMOS2015 data set. We present a three-step Dirichlet method of resampling a given survey-based redshift calibration distribution to enable the propagation of both shot noise and sample variance uncertainties. The method can accommodate different levels of prior confidence on different redshift sources. This method can be applied to any calibration sample with known redshifts and phenotypes (i.e. cells in a self-organizing map, or some other way of discretizing photometric space), and provides a simple way of propagating prior redshift uncertainties into cosmological analyses. As a worked example, we apply the full scheme to the COSMOS2015 data set, for which we also present a new, principled SOM algorithm designed to handle noisy photometric data. We make available a catalog of the resulting resamplings of the COSMOS2015 galaxies.

astro-ph.CO↗

arXiv2019

Redshift inference from the combination of galaxy colors and clustering in a hierarchical Bayesian model $-$ Application to realistic $N$-body simulations

Photometric galaxy surveys constitute a powerful cosmological probe but rely on the accurate characterization of their redshift distributions using only broadband imaging, and can be very sensitive to incomplete or biased priors used for redshift calibration. Sánchez & Bernstein (2019) presented a hierarchical Bayesian model which estimates those from the robust combination of prior information, photometry of single galaxies and the information contained in the galaxy clustering against a well-characterized tracer population. In this work, we extend the method so that it can be applied to real data, developing some necessary new extensions to it, especially in the treatment of galaxy clustering information, and we test it on realistic simulations. After marginalizing over the mapping between the clustering estimator and the actual density distribution of the sample galaxies, and using prior information from a small patch of the survey, we find the incorporation of clustering information with photo-$z$'s to tighten the redshift posteriors, and to overcome biases in the prior that mimic those happening in spectroscopic samples. The method presented here uses all the information at hand to reduce prior biases and incompleteness. Even in cases where we artificially bias the spectroscopic sample to induce a shift in mean redshift of $Δ\bar z \approx 0.05,$ the final biases in the posterior are $Δ\bar z \lesssim0.003.$ This robustness to flaws in the redshift prior or training samples would constitute a milestone for the control of redshift systematic uncertainties in future weak lensing analyses.

astro-ph.CO↗

arXiv2018

Redshift inference from the combination of galaxy colors and clustering in a hierarchical Bayesian model

Powerful current and future cosmological constraints using high precision measurements of the large-scale structure of galaxies and its weak gravitational lensing effects rely on accurate characterization of the redshift distributions of the galaxy samples using only broadband imaging. We present a framework for constraining both the redshift probability distributions of galaxy populations and the redshifts of their individual members. We use a hierarchical Bayesian model (HBM) which provides full posterior distributions on those redshift probability distributions, and, for the first time, we show how to combine survey photometry of single galaxies and the information contained in the galaxy clustering against a well-characterized tracer population in a robust way. One critical approximation turns the HBM into a system amenable to efficient Gibbs sampling. We show that in the absence of photometric information, this method reduces to commonly used clustering redshift estimators. Using a simple model system, we show how the incorporation of clustering information with photo-$z$'s tightens redshift posteriors, and can overcome biases or gaps in the coverage of a spectroscopic prior. The method enables the full propagation of redshift uncertainties into cosmological analyses, and uses all the information at hand to reduce those uncertainties and associated potential biases.

astro-ph.CO↗

arXiv2016

Clustering and Bias Measurements of SDSS Voids

Using a void catalog from the SDSS survey, we present the first measurements of void clustering and the corresponding void bias. Over the range 30-200 Mpc/h the void auto-correlation is detected at 5-sigma significance for voids of radius 15-20 Mpc/h. We also measure the void-galaxy cross-correlation at higher signal-to-noise and compare the inferred void bias with the autocorrelation results. Void bias is constant with scale for voids of a given size, but its value falls from 5.6 +/- 1.0 to below zero as the void radius increases from 15 to 30 Mpc/h. The comparison of our measurements with carefully matched galaxy mock catalogs, with no free parameters related to the voids, shows that model predictions can be reliably made for void correlations. We study the dependence of void bias on tracer density and void size with a view to future applications. In combination with our previous lensing measurements of void mass profiles, these clustering measurements provide another step towards using voids as cosmological tracers.

astro-ph.CO↗

arXiv2014

Precise photometric redshifts with a narrow-band filter set: The PAU Survey at the William Herschel Telescope

The Physics of the Accelerating Universe (PAU) survey at the William Herschel Telescope (WHT) will use a new optical camera (PAUCam) with a large set of narrow-band filters to perform a photometric galaxy survey with a quasi-spectroscopic redshift precision of σ(z)/(1 + z) ~ 0.0035 and map the large-scale structure of the universe in three dimensions up to i_AB < 22.5-23.0. In this paper we present a detailed photo-z performance study using photometric simulations for 40 equally-spaced 12.5-nm-wide (FWHM) filters with a ~25% overlap and spanning the wavelength range from 450 nm to 850 nm, together with a ugrizY broad-band filter system. We then present the migration matrix r_ij, containing the probability that a galaxy in a true redshift bin j is measured in a photo-z bin i, and study its effect on the determination of galaxy auto- and cross-correlations. Finally, we also study the impact on the photo-z performance of small variations of the filter set in terms of width, wavelength coverage, etc., and find a broad region where slightly modified filter sets provide similar results, with the original set being close to optimal.

astro-ph.CO↗