Science

Mission spatiale de cosmologie observationnelle EUCLID

Near-Infrared Spectro-Photometer

Euclid est une mission spatiale de l”ESA destinée à étudier, via diverses sondes cosmologiques (cisaillement gravitationnel, oscillations acoustiques de baryons, etc.), le contenu sombre – énergie et matière noires – de l’Univers, et dont le décollage est prévu pour mi 2023.

Je participe au Euclid Consortium depuis 2012, essentiellement dans le domaine du traitement et de l’analyse des données en provenance du spectrographie sans fente NISP, et en tant que responsable scientifique à l’IP2I; plus spécifiquement:

  • Co-lead de l’activité de réduction des données de spectrographie sans fente (PF-SIR),

  • Deputy calibration scientist, en charge de la spectroscopie.

NISP simulated exposure.

Liens

  • EUCL-IPN-TN-8-001 Impact of spectral covariance on line fitting

    I look for the impact of the spectral covariance on the line fitting procedure. It appears that the maximum-likelihood estimates — for all line parameters — are equally un-biased when using the correct full-covariance χ² definition and the simpler pure-diagonal one (i.e. neglecting spectral correlations). However, best-fit parameter uncertainties — on line flux, position/redshift and width — are systematically under-estimated by ~40% when using the uncorrelated χ², while properly estimated when minimizing the statistically correct χ². The use of spectral covariance is therefore of crucial importance to derive statistically controlled spectral quantities such as redshift and line fluxes.

  • EUCL-IPN-TN-8-002 Adaptive Emission Line Detection

    To derive spectral quantities such as redshift, the first step in the process of precision emission line adjustment in a galaxy spectrum is to detect potential emission lines in a robust and systematic way. I present in this note a collection of algorithms developed for that purpose, including optimal spectrum combination, adaptive fitting and robust M-estimators.

  • EUCL-IPN-TN-8-003 Outlier detection in small samples using pull-clipping

    We present and tests different algorithms to compute the mean of very small samples (n = 4) in presence of a small fraction of outliers. The favorite choice appears to be the inverse-variance weighted mean of pull-clipped values, both more robust and statistically efficient (from 10% to 40%) than the median.

  • Grism-based Spectrograph Modeling

    This module implements the spectrograph optical model used for the SuperNova Integral Field Spectrograph Lantz04 data-reduction pipeline, and presented in Copin00. It provides a flexible chromatic mapping between the input focal plane and the output detector plane, based on an effective simplified ray-tracing model of the key optical elements defining the spectrograph (collimator, prism, grating, camera), described by a restricted number of physically-motivated distortion parameters.

  • Euclid Spectroscopy Analysis Software

    This code addresses the different modules in SGS-SPE PE-5300 Spectral Features Measurement.

Modélisation directe de la spectrographie sans fente

Je développe dans le cadre de l’expérience Euclid une expertise sur la modélisation directe (forward modeling) de la spectrographie sans fente, parfois appelée imagerie dispersée.

Cinématique des galaxies

  • Forward modeling of galaxy kinematics in slitless spectroscopy (Outini & Copin, 2020, A&A 633, 43O)

    Slitless spectroscopy has long been considered as a complicated and confused technique. Nonetheless, with the advent of Hubble Space Telescope (HST) instruments characterized by a low sky background level and a high spatial resolution (most notably WFC3), slitless spectroscopy has become an adopted survey tool to study galaxy evolution from space. We investigate its application to single object studies to measure not only redshift and integrated spectral features, but also spatially resolved quantities such as galaxy kinematics. We build a complete forward model to be quantitatively compared to actual slitless observations. This model depends on a simplified thin cold disk galaxy description – including flux distribution, intrinsic spectrum and kinematic parameters – and on the instrumental signature. It is used to improve redshifts and constrain basic rotation curve parameters, i.e. plateau velocity v0 (in km/s) and central velocity gradient w0 (in km/s/arcsec). The model is tested on selected observations from 3D-HST and GLASS surveys, to estimate redshift and kinematic parameters on several galaxies measured with one or more roll angles. Our forward approach allows to mitigate the self-contamination effect, a primary drawback of slitless spectroscopy, and therefore has the potential to increase precision on redshifts. In a limited sample of well-resolved spiral galaxies from HST surveys, it is possible to significantly constrain galaxy rotation curve parameters. This proof-of-concept work is promising for future large slitless spectroscopic surveys such as EUCLID and WFIRST.

  • Presentation at the The Art of Measuring Galaxy Physical Properties conference En

  • Mesure de la cinématique interne des galaxies en spectroscopie sans fente, thèse de M. Outini Fr

Caractérisation atmosphérique LSST

Je travaille, en collaboration avec Jérémy Neveu et al., sur l’utilisation de la spectrographie sans fente pour la caractérisation de la transmission atmosphérique pour LSST.

Spectro-photométrie des supernovæ de type Ia

Design Dianna LaFerry

Les supernovæ thermonucléaires (dites de type Ia) sont des chandelles standard à portée cosmologique, et ont permis la découverte de l’expansion accélérée de l’Univers (prix Nobel de physique 2011)

Depuis sa création en 2001, je suis impliqué dans le projet international Nearby SuperNova Factory de suivi spectro-photométrique de SNe Ia proches, où je suis data scientist, responsable du traitement des données du SuperNova Integral Field Spectrograph.

Spectrographie à champ intégral

Mon expertise instrumentale est la spectrographie à champ intégral (integral-field spectrography), parfois appelée spectrographie 3D.

Galaxies de type précoce

J’ai longtemps été impliqué dans le projet SAURON, dont l’objectif principal est l’étude des mécanismes de formation et d’évolution des galaxies de type précoce à partir d’observations 3D sur un spectrographe à champ panoramique dédié.