Inferring the photometric and size evolution of galaxies from image simulations

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. 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. 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 Monte Carlo Markov Chain methods. Using synthetic data matching most of the properties of a CFHTLS 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.Our pipeline infers efficiently the luminosity and size distribution and evolution parameters with a very limited number of observables (3 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.Comment: 24 pages, 12 figures, accepted for publication in A&

The EFIGI catalogue of 4458 nearby galaxies with detailed morphology

Accepted for publication in Astronomy and Astrophysics, 27 pages, 7 tables, 32 colour figures. Data available at http://www.efigi.orgInternational audienceNow that large databases of resolved galaxy images are provided by modern imaging surveys, advanced morphological studies can be envisioned, urging for well defined calibration samples. We present the EFIGI catalogue, a multiwavelength database specifically designed for a dense sampling of all Hubble types. The catalogue merges data from standard surveys and catalogues (Principal Galaxy Catalogue, Sloan Digital Sky Survey, Value-Added Galaxy Catalogue, HyperLeda, and the NASA Extragalactic Database) and provides detailed morphological information. Imaging data are obtained from the SDSS DR4 in the u, g, r, i, and z bands for a sample of 4458 PGC galaxies, whereas photometric and spectroscopic data are obtained from the SDSS DR5 catalogue. Point-Spread Function models are derived in all five bands. Composite colour images of all objects are visually examined by a group of astronomers, and galaxies are staged along the Hubble sequence and classified according to 16 morphological attributes describing their structure, texture, as well as environment and appearance on a five-level scale. The EFIGI Hubble sequence shows remarkable agreement with the RC3 Revised Hubble Sequence. The main characteristics and reliability of the catalogue are examined, including photometric completeness, type mix, systematic trends and correlations. The final EFIGI database is a large sub-sample of the local Universe, with a dense sampling of Sd, Sdm, Sm and Im types compared to magnitude-limited catalogues. We estimate the photometric catalogue to be more than ~ 80% complete for galaxies with 10 < g < 14. More than 99.5% of EFIGI galaxies have a known redshift in the HyperLeda and NED databases

Spectroscopie, spectrophotométrie, et morphométrie : mérites et faiblesses pour la caractérisation des populations de galaxies et leur distribution spatiale

Le programme-clé ESO-Sculpteur a fourni le tout premier catalogue avec photométrie CCD et spectroscopie de fente pour un relevé systématique d’environ un millier de galaxies. Son taux de complétude élevé permet une cartographie fiable des vides et feuillets interceptés le long de la ligne de visée jusqu’à z~0.5. En distinguant les populations de galaxies géantes et naines, nous proposons des analyses originales des fonctions de luminosité et de corrélation, ainsi que la détection d’une évolution marquée des galaxies spirales tardives et des irrégulières. Un suivi infrarouge moyen permet de déduire une modélisation des comptages avec évolution « minimale ». Une sur-densité est détectée à z~0.44 dans le relevé ESO-Sculpteur, précédée par une sous-densité à z~0.36. Ces structures définissent des régions de contraste ~2 sur 170 à 200 Mpc le long de la ligne de visée. En prenant en compte le regroupement spatial mesuré des galaxies, on évalue le niveau de significativité de la sur-densité à 2.6 à 3.3. Si elle s’étendait transversalement sur 2 × 2 deg2, cette structure pourrait atteindre une niveau de significativité de 4 à 5. Des pinceaux profonds ayant la même géométrie sur le ciel que le relevé ESO-Sculpteur sont extraits des simulations “Millennium”, et confirment que la probabilité de détecter une telle sur-densité dans un volume cosmologique est de l’ordre du pourcent.En outre, je teste les performances des méthodes de décalages vers le rouge « photométriques » pour la détection de ces très grandes fluctuations de densité, en complétant la photométrie optique par la photométrie infrarouge simulée par ZPEG à partir des mesures optiques et des ajustements des scénarios évolutifs de PÉGASE.2. On montre que les biais systématiques dans l’ajustement des spectres peuvent empêcher la détection des très grandes structures, même si les erreurs aléatoires de la photométrie causent un étalement en décalage spectral sur des échelles bien inférieures. On compare aussi les performances des ajustements de spectres synthétiques avec la classification spectrale par composante principale. Je montre enfin la présence d’effets systématiques sur la classification spectrale causés par l’orientation des fentes de spectroscopie.Je présente ensuite les caractéristiques du catalogue morphologique de galaxies proches EFIGI. Par l’ajustement de profils convolués à doubles composantes de bulbe et de disque, nous dérivons de nouvelles magnitudes totales qui mettent en évidence des pertes de flux de 0.5 à 10 magnitudes dans les mesures photométriques produites par le relevé SDSS pour ces objets proches; celle-ci sont causées par un mauvais ajustement du fond de ciel autour des grandes galaxies, et par un morcellement des objets sans bulbe dominant. Ces nouvelles mesures exhibent un décalage continu dans le diagramme couleur-magnitude des différents types morphologiques de galaxies, qui contraste avec la notion de bi-modalité. Je montre aussi que les couleurs des bulbes des galaxies spirales sont proches des couleurs des galaxies elliptiques, avec un rougissement des bulbes des galaxies Sb et Sbc, les plus riches en poussières. En revanche, on observe un bleuissement progressif des couleurs des disques, depuis ceux des lenticulaires, de même couleur que leurs bulbes, vers les disques des spirales les plus tardives.J’utilise ainsi les catalogues ESO-Sculpteur et EFIGI pour illustrer les enjeux et difficultés dans la caractérisation des différents types de galaxies dans l’Univers proche et lointain par une analyse des fonctions de luminosité. Celles-ci sont biaisées par les confusions entre les différents types morphologiques de galaxies qui se produisent lorsque la séparation est basée sur la classification spectrale, sur les couleurs, ou sur les types spectrophotométriques. Ces effets peuvent avoir des répercussions majeures dans la dérivation de contraintes observationnelles sur l’évolution des galaxies

Tailoring galaxies: Size–luminosity–surface brightness relations of bulges and disks along the morphological sequence

International audienceAims. We revisit the scaling relations between size, luminosity, and surface brightness as a function of morphology, for the bulge and disk components of the 3106 weakly inclined galaxies of the “Extraction de Formes Idéalisées de Galaxies en Imagerie” (EFIGI) sample, in the nearby Universe. Methods. The luminosity profiles from the Sloan Digital Sky Survey (SDSS) gri images were modeled as the sum of a Sérsic (bulge) and an exponential (disk) component for cD, elliptical (E), lenticular, and spiral galaxies, or as a single Sérsic profile for cD, E, dE, and irregular (Im) galaxies, by controlled profile fitting with the SourceXtractor++ software. Results. For the EFIGI sample, we remeasured the Kormendy (1977, ApJ, 218, 333) relation between effective surface brightness ⟨ μ ⟩ e and effective radius R e of elliptical galaxies, and show that it is also valid for the bulges (or Sérsic components) of galaxy types Sb and earlier. In contrast, there is a progressive departure toward fainter and smaller bulges for later Hubble types, as well as with decreasing bulge-to-total ratios ( B / T ) and Sérsic indices. This depicts a continuous transition from pseudo-bulges to classical ones, which we suggest to occur for absolute g magnitudes M g between −17.8 and −19.1. We also obtain partial agreement with the Binggeli et al. (1984, AJ, 89, 64) relations between effective radius and M g (known as “size–luminosity” relations, in log–log scale) for E and dE galaxies. There is a convex size–luminosity relation for the bulges of all EFIGI types. Both ⟨ μ ⟩ e − R e and R e − M g scaling relations are projections of a plane in which bulges are located according to their value of B / T , which partly determines the morphological type. Analogous scaling relations were derived for the disks of lenticular and spiral types, and the irregulars. The curvature of the size–luminosity relation for disks is such that while they grow, they first brighten and then stabilize in surface brightness. Moreover, we obtain the unprecedented result that the effective radii of both the bulges and disks of lenticular and spiral galaxies increase as power laws of B / T , with a steeper increase for the bulges. Both bulges and disks of lenticular galaxies have a similar and largely steeper increase with B / T than those for spirals. These relations propagate into a single scaling relation for the disk-to-bulge ratio of effective radii across ∼2 orders of magnitude in B / T , and for all types. We provide the parameters of all of these relations that can be used to build realistic mock images of nearby galaxies. The new convex size–luminosity relations are more reliable estimates of bulge, disk, and galaxy sizes at all magnitudes in the nearby Universe. Conclusions. This analysis describes the joint size and luminosity variations of bulges and disks along the Hubble sequence. The characteristics of the successive phases of disk and bulge size growth strengthen a picture of morphological evolution in which irregulars and late spirals merge to form earlier spirals, lenticulars, and eventually ellipticals

Aging of galaxies along the morphological sequence, marked by bulge growth and disk quenching

We revisit the color bimodality of galaxies using the extensive EFIGI morphological classification of nearby galaxies. The galaxy SDSS images in the g, r and i bands are decomposed as bulge+disk using SourceXtractor++. The spectral energy distributions made of our gri photometry complemented with GALEX NUV are fitted with ZPEG in order to estimate the stellar masses and specific star formations rates (sSFR) of whole galaxies as well as their bulge and disk components. The absolute NUV-r color versus stellar mass diagram shows a continuous relationship between the present sSFR of galaxies and their stellar mass, that spans all morphological types of the Hubble sequence. Irregular galaxies to Sab spirals make up the Blue Cloud, the Green Plain (formerly Valley) is made up of early-type spirals (S0a-Sa) while the Red Sequence contains all lenticular and elliptical galaxies, with systematically higher masses for the ellipticals. Galaxies across the Green Plain undergo a marked growth by a factor 2 to 3 in their bulge-to-total mass ratio and a systematic profile change from pseudo to classical bulges, as well as a significant reddening interpreted as star formation fading in their disks. Therefore, the Green Plain is a transition region, and we exclude a predominantly quick transit due to rapid quenching. We suggest that tracers of increased star formation (bright HII regions, spiral arms, flocculence) determine the limited scatter of the Main Sequence of star-forming galaxies. The high frequency of bars for all spirals as well as the stronger spiral arms and flocculence in the knee of the Green Plain suggest that internal dynamics, likely triggered by flybys or mergers, may be the key to the bulge growth of massive disk galaxies, marker of the aging of galaxies from star forming to quiescence. The Hubble sequence can then be considered as an inverse sequence of galaxy physical evolution.Comment: 25 pages, 27 figures. Submitted to A&A. Comments are welcom