Papers by Valérie de Lapparent
Astronomy & Astrophysics, 2021
Context. Current models of galaxy evolution are constrained by the analysis of catalogs containin... more Context. Current models of galaxy evolution are constrained by the analysis of catalogs containing the flux and size of galaxies extracted from multiband deep fields. However, these catalogs contain inevitable observational and extraction-related biases that can be highly correlated. In practice, taking all of these effects simultaneously into account is difficult, and therefore the derived models are inevitably biased as well. Aims. To address this issue, we use robust likelihood-free methods to infer luminosity function parameters, which is made possible by the massive compression of multiband images using artificial neural networks. This technique makes the use of catalogs unnecessary when observed and simulated multiband deep fields are compared and model parameters are constrained. Because of the efficient data compression, the method is not affected by the required binning of the observables inherent to the use of catalogs. Methods. A forward-modeling approach generates galaxies of multiple types depending on luminosity function parameters rendered on photometric multiband deep fields that include instrumental and observational characteristics. The simulated and the observed images present the same selection effects and can therefore be properly compared. We trained a fully convolutional neural network to extract the most model-parameter-sensitive summary statistics out of these realistic simulations, shrinking the dimensionality of the summary space to the number of parameters in the model. Finally, using the trained network to compress both observed and simulated deep fields, the model parameter values were constrained through population Monte Carlo likelihood-free inference. Results. Using synthetic photometric multiband deep fields similar to previously reported CFHTLS and WIRDS D1/D2 deep fields and massively compressing them through the convolutional neural network, we demonstrate the robustness, accuracy, and consistency of this new catalog-free inference method. We are able to constrain the parameters of luminosity functions of different types of galaxies, and our results are fully compatible with the classic catalog-extraction approaches.
Le programme-cle ESO-Sculpteur a fourni le tout premier catalogue avec photometrie CCD et spectro... more Le programme-cle ESO-Sculpteur a fourni le tout premier catalogue avec photometrie CCD et spectroscopie de fente pour un releve systematique d’environ un millier de galaxies. Son taux de completude eleve permet une cartographie fiable des vides et feuillets interceptes le long de la ligne de visee jusqu’a z~0.5. En distinguant les populations de galaxies geantes et naines, nous proposons des analyses originales des fonctions de luminosite et de correlation, ainsi que la detection d’une evolution marquee des galaxies spirales tardives et des irregulieres. Un suivi infrarouge moyen permet de deduire une modelisation des comptages avec evolution « minimale ». Une sur-densite est detectee a z~0.44 dans le releve ESO-Sculpteur, precedee par une sous-densite a z~0.36. Ces structures definissent des regions de contraste ~2 sur 170 a 200 Mpc le long de la ligne de visee. En prenant en compte le regroupement spatial mesure des galaxies, on evalue le niveau de significativite de la sur-densit...
Astronomy & Astrophysics, 2017
Context. Current constraints on models of galaxy evolution rely on morphometric catalogs extracte... more Context. Current constraints on models of galaxy evolution rely on morphometric catalogs extracted from multi-band photometric surveys. However, these catalogs are altered by selection effects that are difficult to model, that correlate in non trivial ways, and that can lead to contradictory predictions if not taken into account carefully. Aims. To address this issue, we have developed a new approach combining parametric Bayesian indirect likelihood (pBIL) techniques and empirical modeling with realistic image simulations that reproduce a large fraction of these selection effects. This allows us to perform a direct comparison between observed and simulated images and to infer robust constraints on model parameters. Methods. We use a semi-empirical forward model to generate a distribution of mock galaxies from a set of physical parameters. These galaxies are passed through an image simulator reproducing the instrumental characteristics of any survey and are then extracted in the same way as the observed data. The discrepancy between the simulated and observed data is quantified, and minimized with a custom sampling process based on adaptive Markov chain Monte Carlo methods. Results. Using synthetic data matching most of the properties of a Canada-France-Hawaii Telescope Legacy Survey Deep field, we demonstrate the robustness and internal consistency of our approach by inferring the parameters governing the size and luminosity functions and their evolutions for different realistic populations of galaxies. We also compare the results of our approach with those obtained from the classical spectral energy distribution fitting and photometric redshift approach. Conclusions. Our pipeline infers efficiently the luminosity and size distribution and evolution parameters with a very limited number of observables (three photometric bands). When compared to SED fitting based on the same set of observables, our method yields results that are more accurate and free from systematic biases.
Le grandes structures dans la distribution des galaxies
A redshift survey of galaxies with z ⪅ 0.6 using multi-object spectroscopy. Profile of key programme
Through the steady acquisition of redshifts of galaxies, our understanding of the large-scale gal... more Through the steady acquisition of redshifts of galaxies, our understanding of the large-scale galaxy distribution has evolved drastically during the past decade. Most recently, the Centre for Astrophysics (CfA) redshift survey (B =5 15.5) has suggested a new picture of the galaxy distribution: galaxies appear to be distributed on thin shells surrounding vast regions with diameters between 20 and 50 h-1 Mpc (Ho = 100 h km S-1 Mpc-1) devoid of bright galaxies (de Lapparent, Geiler, and Huchra 1986). This new interpretation of the galaxy distribution is consistent with the detection of a 60 h-1 Mpc void in Boötes (Kirshner et al. 1981) and with the alternation of peaks and - 100 h-1 Mpc wide valleys in deep pencil-beam probes (Koo, Kron, and Szalay 1987). Shell-like structures are also detected in redshift surveys of HI galaxies (Haynes and Giovanelli 1986).
The Center for Astrophysics redshift survey - Statistical measures of large-scale clustering
The extension of the Center for Astrophysics Redshift Survey will eventually cover the northern s... more The extension of the Center for Astrophysics Redshift Survey will eventually cover the northern sky with |bII| ≥ 40° and mB(0) ≤ 15.5. The complete portion of the survey contains 1770 galaxies in a 135°(r.a.)×12°(dec.) strip centered at the north galactic pole. The distribution of galaxies contains large voids (≤50 h-1Mpc) separated by thin sheets, suggesting a "bubble-like" topology: (1) most of the galaxies lie in portions of surfaces which extend naturally from the southern 6° of the slice into the northern half; (2) no corresponding filaments are present in projection on the sky.
The mean density from the galaxy distribution
Some of the characteristics of the galaxy distribution in the CfA redshift survey extension are r... more Some of the characteristics of the galaxy distribution in the CfA redshift survey extension are reviewed, and their implications on the mean mass density of the universe are discussed. This survey shows that the largest structures in the galaxy distribution pose problems for determination of the mean density of matter underlying structures of galaxies. New surveys designed for sampling efficiently many more structures than in the nearby surveys will provide tighter constraints on the distribution and mean density of matter in the universe.
Mapping the large-scale galaxy distribution
The observed large-scale structure of the universe
Nature and size of detected structures. Statistical characterization of these structures. Design ... more Nature and size of detected structures. Statistical characterization of these structures. Design of surveys for reliable detection.
the threshold where the excesses are not very significant anymore. The continuum magnitudes of th... more the threshold where the excesses are not very significant anymore. The continuum magnitudes of the WR stars are typically 20-21 mags and there are probably many more which are fainter. Although present day instrumentation clearly allows individual WR stars to be observed at distances beyond 1 Mpc, we find that we use it close to its limitations. In the longer term it will be necessary to use larger telescopes such as the VLT in order to complete the survey.
The large-scale structure of the universe: from galaxies to superclusters
Significant progress has been achieved over the past 10 years in the understanding of the large-s... more Significant progress has been achieved over the past 10 years in the understanding of the large-scale distribution of galaxies. The three-dimensional distribution has a cell-like structure characterized by the alternation of sheets and voids, and with the topological properties of a "sponge". These results have stimulated a renewed interest in mapping the large-scale structure of the Universe. Large projects are being designed and will provide within 5 years a detailed description of the clustering of galaxies up to distances of several billion light-years away.
Astronomy and Astrophysics
The UH8K wide field camera of the CFHT was used to image 0.68 deg2 of sky. From these images, ~ 2... more The UH8K wide field camera of the CFHT was used to image 0.68 deg2 of sky. From these images, ~ 20,000 galaxies were detected to completeness magnitudes V<23.5 and I<22.5. The angular correlation function of these galaxies is well represented by the parameterization omega (theta ) = A_W theta -delta . The slope delta =~ -0.8 shows no significant variation over the range of magnitude. The amplitude A_W decreases with increasing magnitude in a way that is most compatible with a Lambda CDM model (Omega_0 = 0.2, Lambda =0.8) with a hierarchical clustering evolution parameter epsilon >0. We infer a best-fit spatial correlation length of r00 =~ 5.85+/-0.5 h-1 Mpc at z=0. The peak redshift of the survey (I<=22.5) is estimated to be zpeak ~ 0.58, using the blue-evolving luminosity function from the CFRS and the flat Lambda cosmology, and r_0(zpeak) =~ 3.5+/-0.5 h-1 Mpc. We also detect a significant difference in clustering amplitude for the red and blue galaxies, quantitatively ...
Le Point sur... Astronomie I
Le point sur Astronomie I and Le point sur Astronomie II are the references of the Comptes Rendus... more Le point sur Astronomie I and Le point sur Astronomie II are the references of the Comptes Rendus de l'Académie des Sciences now gathered in a book series. They consist of review articles in English or French, requested by the Editor-in-Chief in charge of Astronomy in the Comptes Rendus. Each volume presents: A collection of articles written by specialists, the recent years' greatest results, and a detailed bibliography
Monthly Notices of the Royal Astronomical Society, 2014
A large-scale hydrodynamical cosmological simulation, Horizon-AGN, is used to investigate the ali... more A large-scale hydrodynamical cosmological simulation, Horizon-AGN, is used to investigate the alignment between the spin of galaxies and the cosmic filaments above redshift 1.2. The analysis of more than 150 000 galaxies per time step in the redshift range 1.2 < z < 1.8 with morphological diversity shows that the spin of low-mass blue galaxies is preferentially aligned with their neighbouring filaments, while high-mass red galaxies tend to have a perpendicular spin. The reorientation of the spin of massive galaxies is provided by galaxy mergers, which are significant in their mass build-up. We find that the stellar mass transition from alignment to misalignment happens around 3 × 10 10 M. Galaxies form in the vorticity-rich neighbourhood of filaments, and migrate towards the nodes of the cosmic web as they convert their orbital angular momentum into spin. The signature of this process can be traced to the properties of galaxies, as measured relative to the cosmic web. We argue that a strong source of feedback such as active galactic nuclei is mandatory to quench in situ star formation in massive galaxies and promote various morphologies. It allows mergers to play their key role by reducing post-merger gas inflows and, therefore, keeping spins misaligned with cosmic filaments.
SPIE Proceedings, 1998
The Large Zenith Telescope is a zenith-pointing telescope with a 6-meter diameter rotating mercur... more The Large Zenith Telescope is a zenith-pointing telescope with a 6-meter diameter rotating mercury mirror. Located in mountains near Vancouver, Canada, it is expected to see first light in 1998. Equipped with a low-noise driftscanning CCD camera, the telescope will survey a 17-arcmin-wide strip of sky using a set of medium-band filters. The data are expected to provide spectral energy distributions and photometric redshifts for over a million galaxies which will form a base for studies of galaxy evolution and large-scale structure.
The CFA Redshift Survey
Proceedings of The International Astronomical Union, 1988
The first CfA Survey is now over 90% spectroscopically complete. Over 60% of all galaxies exhibit... more The first CfA Survey is now over 90% spectroscopically complete. Over 60% of all galaxies exhibit detectable emission lines. The authors have also completed five slices of the Center for Astrophysics (CfA) redshift survey extension. The geometry of the structures in the first slice persists; galaxies are distributed on thin surfaces of "bubble-like" structures. Galaxy voids fill ≡80% of the
Large Scale Structures of the Universe, 1988
We compare the luminosity function and the two-point spatial correlation function for the two sli... more We compare the luminosity function and the two-point spatial correlation function for the two slices 1 of the CfA redshift survey extension to m#(0) < 15.5 [S h < RA. < 17 h and 26.5° < DEC. < 38.5°], with those for the early survey 2 limited to m B (0) < 14.5 [6 n > 40°, and DEC. > 0°]. The derived properties of the two samples agree within the errors. The parameters of the luminosity function are M * =-19.1±0.1 and a =-1.2±0.1 for the 15.5 sample, and M * =-19.3±0.1 and a =-1.1 ±0.1 for the 14.5 sample. We use an inhomogeneity-independent method to calculate the luminosity function. 3 ' 4 The slopes of the correlation functions for the two samples are-1.5 ± 0.35, 5 shallower than the canonical slope of-1.8. 6 The correlation lengths are 7.5 ± 5h~l Mpc, 5 larger than the correlation length of 5A-1 Mpc matched to the theoretical models. 7,8,9 Because of the 25% uncertainty in the mean density of the 15.5 sample, the correlation function is indeterminate on scales larger than ~ 20A-1 Mpc.
Astronomy and Astrophysics Supplement Series, 1997
The Large Zenith Telescope Survey whose construction is almost completed (first light expected in... more The Large Zenith Telescope Survey whose construction is almost completed (first light expected in spring 2002) near Vancouver (Canada) is designed to observed a total strip of ∼ 17 ′ ×120 • in 40 narrowband filters spanning 4000-10000Å. It will gather the spectrophotometric energy distributions of ca. 10 6 galaxies to redshifts z ∼ 1, with redshift accuracy σ z = 0.01 at s/n=10, σ z = 0.04 at s/n=3, ca. 10 5 stars, and a large sample of QSOs, variable stars, and transient objects of the solar system. The survey is optimized for studying of the evolution of both the luminosity function and the clustering of galaxies to a redshift z ∼ 1. It will also provide a complete and homogeneous sample of stars at various galactic latitudes useful for studying galactic structure, and it will be a good instrument for the monitoring of variable objects.
The UH8K wide field camera of the CFHT was used to image 0.68 deg 2 of sky. From these images, ∼2... more The UH8K wide field camera of the CFHT was used to image 0.68 deg 2 of sky. From these images, ∼20,000 galaxies were detected to completeness magnitudes V < 23.5 and I < 22.5. The angular correlation function of these galaxies is well represented by the parameterization ω(θ) = A W θ −δ. The slope δ ≃ −0.8 shows no significant variation over the range of magnitude. The amplitude A W decreases with increasing magnitude in a way that is most compatible with a ΛCDM model (Ω 0 = 0.2, Λ = 0.8) with a hierarchical clustering evolution parameter ǫ > 0. We infer a best-fit spatial correlation length of r 00 ≃ 5.85 ± 0.5 h −1 Mpc at z = 0. The peak redshift of the survey (I ≤ 22.5) is estimated to be z peak ∼ 0.58, using the blue-evolving luminosity function from the CFRS and the flat Λ cosmology, and r 0 (z peak) ≃ 3.5 ± 0.5 h −1 Mpc. We also detect a significant difference in clustering amplitude for the red and blue galaxies, quantitatively measured by correlation lengths of r 00 = 5.3 ± 0.5 h −1 Mpc and r 00 = 1.9 ± 0.9 h −1 Mpc respectively, at z = 0.
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Papers by Valérie de Lapparent