Environmental dependence of bulge-dominated galaxy sizes in hierarchical models of galaxy formation. Comparison with the local Universe

We compare state-of-the-art semi-analytic models of galaxy formation as well as advanced sub-halo abundance matching models with a large sample of early-type galaxies from SDSS at z < 0.3. We focus our attention on the dependence of median sizes of central galaxies on host halo mass. The data do not show any difference in the structural properties of early-type galaxies with environment, at fixed stellar mass. All hierarchical models considered in this work instead tend to predict a moderate to strong environmental dependence, with the median size increasing by a factor of about 1.5-3 when moving from low to high mass host haloes. At face value the discrepancy with the data is highly significant, especially at the cluster scale, for haloes above log Mhalo > 14. The convolution with (correlated) observational errors reduces some of the tension. Despite the observational uncertainties, the data tend to disfavour hierarchical models characterized by a relevant contribution of disc instabilities to the formation of spheroids, strong gas dissipation in (major) mergers, short dynamical friction timescales, and very short quenching timescales in infalling satellites. We also discuss a variety of additional related issues, such as the slope and scatter in the local size-stellar mass relation, the fraction of gas in local early-type galaxies, and the general predictions on satellite galaxies.Comment: 27 pages, 14 figures, 2 tables. MNRAS, in pres

Avoiding Progenitor Bias: The Structural and Mass Evolution of Brightest Group and Cluster Galaxies in Hierarchical Models since z≾1

The mass and structural evolution of massive galaxies is one of the hottest topics in galaxy formation. This is because it may reveal invaluable insights into the still debated evolutionary processes governing the growth and assembly of spheroids. However, direct comparison between models and observations is usually prevented by the so-called progenitor bias, i.e., new galaxies entering the observational selection at later epochs, thus eluding a precise study of how pre-existing galaxies actually evolve in size. To limit this effect, we here gather data on high-redshift brightest group and cluster galaxies, evolve their (mean) host halo masses down to z = 0 along their main progenitors, and assign as their "descendants" local Sloan Digital Sky Survey central galaxies matched in host halo mass. At face value, the comparison between high redshift and local data suggests a noticeable increase in stellar mass of a factor of ≳ 2 since z ~ 1, and of ≳ 2.5 in mean effective radius. We then compare the inferred stellar mass and size growth with those predicted by hierarchical models for central galaxies, selected at high redshifts to closely match the halo and stellar mass bins as in the data. Only hierarchical models characterized by very limited satellite stellar stripping and parabolic orbits are capable of broadly reproducing the stellar mass and size increase of a factor of ~2-4 observed in cluster galaxies since z ~ 1. The predicted, average (major) merger rate since z ~ 1 is in good agreement with the latest observational estimates

ÉVOLUTION DES PROPRIÉTÉS STRUCTURELLES DES GALAXIES DE TYPE PRÉCOCE DANS DIFFÉRENTS ENVIRONNEMENTS

The mass assembly of massive galaxies is still an open question. In particular, there is a large debate about the evolution leading to the formation of massive early-type galaxies (ETGs) observed today, since the discovery of massive passive galaxies at z ~ 1-2 more compact than their local counter-parts. Two physical processes are usually invoked to explain the size growth of these galaxies : gas expulsion or dry minor mergers, but none of them is able to reproduce all the observed trends. Environment is an additional variable that can be used to disentangle between different scenarios and which has been poorly explored up to now. In that contex, z > 1 is an interesting epoch to study environmental dependence of the sizes of ETGs since the first massive clusters start to appear at that time. If galaxies ending-up in these massive structures have for some reason been processed differently or more rapidly than galaxies living in the field, the effects should be visible at that time. In this work, I analyze the mass-size relation and size evolution of passive early-type galaxies in a sample of nine massive galaxy clusters in the redshift range 0.8 1 semble être le moment idéal pour étudier la dépendance entre la taille et l'environnement puisque c'est le moment où les amas de galaxies massifs apparaissent. Si les galaxies finissant dans ces structures denses ont été transformées différemment que celles finissant dans le champ, les effets devraient être visibles à ce moment là. Dans ce travail de thèse, j'ai analysé la relation masse-taille et l'évolution en taille des galaxies passives de type précoce dans un échantillon de 9 amas de galaxies massifs, dans l'intervalle 0, 8 < z < 1, 6, et comparé à un échantillon homogène de galaxies de champ. Toutes les propriétés telles que la taille, la masse et la morphologie sont estimées de la même manière dans les échantillons de galaxies d'amas et de champ. La sélection des galaxies d'amas comprend les galaxies classifiées comme type précoce ayant une masse supérieure à 3 * 10^10 M sun et peuplant la séquence rouge déterminée pour chaque amas de galaxies. Les galaxies de champ ont été sélectionnées en respectant les mêmes critères. Le principal résultat est que nous ne détectons pas de différences significatives dans la relation masse-taille ni dans l'évolution de la taille des galaxies de type précoce vivant dans le champ et dans les amas. Nos résultats, combinés avec les récents résultats de la littérature, suggèrent une très faible dépendance de la taille des galaxies de type précoce avec l'environnement à grande échelle depuis z ~ 1, 5. L'absence de dépendance avec l'environnement est aussi indépendante de l'intervalle de masse considéré. Nous détectons en revanche une dépendance de la taille avec la morphologie : les galaxies lenticulaires paraîssent en moyenne plus compactes que les galaxies elliptiques à masse stellaire fixée. Elles semblent avoir une évolution en taille plus forte que les elliptiques depuis z ~ 1, 5 : elles sont ~ 40% plus petites à z = 1 et seulement ~ 10% plus petites à z = 0. Les galaxies elliptiques, quant à elles, dominent uniquement la population de galaxies au-delà de 10^11 Msun . Finalement, nous comparons nos résultats avec les prédictions des modèles semi-analytiques de Guo et al. (2011) et Shankar et al. (2013) basés sur les arbres de fusions de la simulation Millénium. Globalement, nos résultats sur l'évolution en taille des ETGs sont compatibles à 1 sigma avec ces modèles. Cela permet de mettre quelques contraintes sur les propriétés des modèles d'évolution de galaxie

Evolution des propriétés structurelles des galaxies de type précoce dans différents environnements

A large debate takes place about the evolution leading to the formation of massive early-type galaxies (ETGs) observed today, since the discovery of massive passive galaxies at z~l-2 more compact than their local counterparts. Gas expulsion or dry minor mergers are invoked to explain the size growth of these galaxies, but none of them can reproduce all the observed trends. Environment is an extra variable used to disentangle the two scenarios and has been poorly explored up to now. z>l is an interesting epoch to study environmental dependence of ETG sizes since massive clusters start to appear. If galaxies ending-up in these massive structures have been processed differently than galaxies in the field, the effects should be visible at that time. I analyze the mass-size relation (MSR) and size evolution of passive ETGs in a sample of 9 clusters at 0.8 l est idéale pour étudier la dépendance de la taille avec l'environnement puisque les amas massifs apparaissent. Si les ETGs finissant dans ces structures ont été transformées autrement que les ETGs de champ, les effets doivent être visibles à ce moment là. J'analyse la relation masse-taille (MSR) et l'évolution en taille des ETGs dans un échantillon de 9 amas à 0,8 < z < 1,6, comparé à un échantillon homogène du champ. Toutes les propriétés sont estimées de la même façon. La sélection dans les amas et le champ inclut les ETGs avec une masse supérieure à 3.10 M , se trouvant sur la séquence rouge. Nous ne détectons pas de différences claires dans la MSR ni dans l'évolution en taille des ETGs de champ et d'amas. Nos résultats, avec les récents travaux, suggèrent une très faible dépendance de la taille des ETGs avec l'environnement depuis z~l,5, indépendamment de l'intervalle de masse. Nous trouvons une dépendance morphologique. Les galaxies lenticulaires paraissent en moyenne plus compactes que les elliptiques à masse fixée et semblent évoluer plus rapidement depuis z~l,5. Nous comparons nos résultats avec les prédictions de deux modèles semi-analytiques qui montrent un comportement compatible à l-2 .PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Wind and Wave Expert Centre at LATMOS (CAL/VAL Activities)

International audienc

The SWIM instrument, a wave scatterometer on CFOSAT mission

International audienceSWIM is part of the CFOSAT satellite mission payload. It is designed for the measurement of directional ocean wave spectra. It is a Ku-band real-aperture radar with 6 rotating fan-beams pointing near nadir. The main characteristics of the instrument, data, products are presented in this paper, as well as performances estimated from simulations

Wave spectrum retrieval from SWIM data: speckle spectrum estimation Session: " Wave retrieval and applications "

International audienceThe Chinese and French Space Agencies propose to jointly carry out an innovative mission, CFOSAT (China France Oceanography Satellite project) devoted to the monitoring of the ocean surface and its related science and applications. CFOSAT will embark both a wind and a wave scatterometers, enabling a simultaneous measure of the wind and the wave vectors with a global coverage for the first time. The launch is planned for mid-2018

SWIM: the first spaceborne wave scatterometer

International audienceThis paper provides an overview of the SWIM (Surface Waves Investigation and Monitoring) instrument which will be one of the two payload instruments carried by CFOSAT (China France Oceanography SATellite) with a planned launch date in mid 2018. SWIM is a real aperture wave scatterometer operated at near-nadir incidence angles and dedicated to the measurement of directional spectra of ocean waves. The SWIM flight model is currently being assembled and tested, its performance is being assessed and its prototype data processing algorithm is being developed. The aim of this paper is to provide a complete overview on the motivations and scientific requirements of this mission, together with a description of the design and characteristics of the SWIM instrument, and the analysis of its expected performances based on a pre-launch study. An end-to-end simulator has been developed to evaluate the quality of the data products, thus allowing the overall performance of the instrument to be assessed. Simulations run with two subsets of full orbit subsets show that the performances of the instrument and the inversion algorithms will meet the scientific requirements for the mission

Partitioning ocean wave spectra obtained from SAR observations or from the future real aperture wave scatterometer SWIM on CFOSAT

ISBN: 978-92-9221-305-3International audienceIn oceanography, one of the important products that can be provided from satellites is the directional spectrum of ocean waves (also called 2D spectrum), which describes the energy of the surface ocean waves as a function of wave number and direction of propagation. This information is essential for wave forecast systems, improvement of wave models, wave climate studies and scientific studies related to the ocean/atmosphere interface, coastal and marginal ice zone processes. This has motivated the specification of SAR instruments to deliver 2D wave spectra (ERS, ENVISAT, SENTINEL-1, RADARSAT, etc.), and the future CFOSAT mission [1] which will embark the wave scatterometer SWIM (low incidence real aperture scanning scatterometer) to provide directional wave spectra with wavelengths from 70 to 600 m.Because directional spectra contain a large amount of information, a way to use this information is usually to decompose the two-dimensional spectra into several partitions, each of them characterizing a “wave component”. For example partitioning wave spectra is a way to distinguish swell components from wind sea components that have different spectral characteristics and correspond to different wave evolutions (swell waves, in opposite to wind sea waves, re defined as ocean waves which are no longer under the influence of the local wind). Partitioning is a key issue for a good retrieval of wave parameters such as significant wave height, peak direction and wavelength, of the different wave components in a 2D wave spectrum.Partitioning methods of wave spectra have originally been developed for analysing outputs of wave forecasting numerical models. The most famous method is the watershed method proposed by Hanson and Phillips [2]. Extending the application of this method to satellite data raises several difficulties because of the presence of noise in the data, which makes the result of the partitioning rather sensitive to the noise.Our presentation will address this issue in the context of 2D wave spectra observed from i) SAR (Sentinel-1), ii) simulated wave spectra expected from SWIM observations (including noise effects) and iii) observed wave spectra from the airborne wave scatterometer KuROS [3]. We will compare different adaptations of the watershed principle to account for noise effects. Furthermore, we will present results obtained from an alternative method, namely a method based on a Bayesian approach. In opposite to the watershed method, the bayesian method presents the advantage of taking explicitly into account noise into the partitioning process and can even be used to estimate the noise floor. After explaining both methods and showing comparative results, we will discuss the pros, cons and limits of both partitioning techniques

KuROS: A new airborne Ku-band Doppler radar for observation of the ocean surface

International audienceWe have designed and developed a new airborne Ku-band Doppler radar, called KuROS, to prepare the CFOSAT satellite mission for measuring ocean surface wind and waves. The main characteristics of this new radar are presented, and first results obtained from a campaign held in 2013 illustrated. Both intensity and Doppler information are used to estimate the directional spectra of ocean waves. Radar cross-section and directional spectra are assessed trough comparisons with independent information