Cross-Identification Performance from Simulated Detections: GALEX and SDSS

We investigate the quality of associations of astronomical sources from multi-wavelength observations using simulated detections that are realistic in terms of their astrometric accuracy, small-scale clustering properties and selection functions. We present a general method to build such mock catalogs for studying associations, and compare the statistics of cross-identifications based on angular separation and Bayesian probability criteria. In particular, we focus on the highly relevant problem of cross-correlating the ultraviolet Galaxy Evolution Explorer (GALEX) and optical Sloan Digital Sky Survey (SDSS) surveys. Using refined simulations of the relevant catalogs, we find that the probability thresholds yield lower contamination of false associations, and are more efficient than angular separation. Our study presents a set of recommended criteria to construct reliable cross-match catalogs between SDSS and GALEX with minimal artifacts.Comment: 7 pages, 9 figures; ApJ in pres

The UV-Optical Color Dependence of Galaxy Clustering in the Local Universe

We measure the UV-optical color dependence of galaxy clustering in the local universe. Using the clean separation of the red and blue sequences made possible by the NUV - r color-magnitude diagram, we segregate the galaxies into red, blue and intermediate "green" classes. We explore the clustering as a function of this segregation by removing the dependence on luminosity and by excluding edge-on galaxies as a means of a non-model dependent veto of highly extincted galaxies. We find that \xi (r_p, \pi) for both red and green galaxies shows strong redshift space distortion on small scales -- the "finger-of-God" effect, with green galaxies having a lower amplitude than is seen for the red sequence, and the blue sequence showing almost no distortion. On large scales, \xi (r_p, \pi) for all three samples show the effect of large-scale streaming from coherent infall. On scales 1 Mpc/h < r_p < 10 Mpc/h, the projected auto-correlation function w_p(r_p) for red and green galaxies fits a power-law with slope \gamma ~ 1.93 and amplitude r_0 ~ 7.5 and 5.3, compared with \gamma ~ 1.75 and r_0 ~ 3.9 Mpc/h for blue sequence galaxies. Compared to the clustering of a fiducial L* galaxy, the red, green, and blue have a relative bias of 1.5, 1.1, and 0.9 respectively. The w_p(r_p) for blue galaxies display an increase in convexity at ~ 1 Mpc/h, with an excess of large scale clustering. Our results suggest that the majority of blue galaxies are likely central galaxies in less massive halos, while red and green galaxies have larger satellite fractions, and preferentially reside in virialized structures. If blue sequence galaxies migrate to the red sequence via processes like mergers or quenching that take them through the green valley, such a transformation may be accompanied by a change in environment in addition to any change in luminosity and color.Comment: accepted by MNRA

Clustering Properties of Rest-Frame UV-Selected Galaxies. II. Migration of Star Formation Sites with Cosmic Time from GALEX and CFHTLS

We analyze the clustering properties of ultraviolet-selected galaxies by using GALEX-SDSS data at z 2 (10^(12) M_⊙ ≤ M_(min) ≤ 10^(13) M_⊙, located in high-density regions) to less massive halos at low redshift (M_(min) ≤ 10^(12) M_⊙, located in low-density regions). This result extends the "downsizing" picture (shift of the star formation activity from high stellar mass systems at high z to low stellar mass at low z) to the dark matter distribution

Spatial Clustering from GALEX-SDSS samples: Star Formation History and large-scale clustering

We measure the projected spatial correlation function w_p(r_p) from a large sample combining GALEX ultraviolet imaging with the SDSS spectroscopic sample. We study the dependence of the clustering strength for samples selected on (NUV - r)_abs color, specific star formation rate (SSFR), and stellar mass. We find that there is a smooth transition in the clustering of galaxies as a function of this color from weak clustering among blue galaxies to stronger clustering for red galaxies. The clustering of galaxies within the "green valley" has an intermediate strength, and is consistent with that expected from galaxy groups. The results are robust to the correction for dust extinction. The comparison with simple analytical modeling suggests that the halo occupation number increases with older star formation epochs. When splitting according to SSFR, we find that the SSFR is a more sensitive tracer of environment than stellar mass.Comment: Accepted for publication in ApJ; 14 pages, 17 figures, 4 table

GALEX-SDSS Catalogs for Statistical Studies

We present a detailed study of the Galaxy Evolution Explorer's photometric catalogs with special focus on the statistical properties of the All-sky and Medium Imaging Surveys. We introduce the concept of primaries to resolve the issue of multiple detections and follow a geometric approach to define clean catalogs with well-understood selection functions. We cross-identify the GALEX sources (GR2+3) with Sloan Digital Sky Survey (DR6) observations, which indirectly provides an invaluable insight about the astrometric model of the UV sources and allows us to revise the band merging strategy. We derive the formal description of the GALEX footprints as well as their intersections with the SDSS coverage along with analytic calculations of their areal coverage. The crossmatch catalogs are made available for the public. We conclude by illustrating the implementation of typical selection criteria in SQL for catalog subsets geared toward statistical analyses, e.g., correlation and luminosity function studies.Comment: 12 pages, 15 figures, accepted to Ap

Reconstruction and simulation of neocortical microcircuitry

We present a first-draft digital reconstruction of the microcircuitry of somatosensory cortex of juvenile rat. The reconstruction uses cellular and synaptic organizing principles to algorithmically reconstruct detailed anatomy and physiology from sparse experimental data. An objective anatomical method defines a neocortical volume of 0.29 ± 0.01 mm3 containing ∼31,000 neurons, and patch-clamp studies identify 55 layer-specific morphological and 207 morpho-electrical neuron subtypes. When digitally reconstructed neurons are positioned in the volume and synapse formation is restricted to biological bouton densities and numbers of synapses per connection, their overlapping arbors form ∼8 million connections with ∼37 million synapses. Simulations reproduce an array of in vitro and in vivo experiments without parameter tuning. Additionally, we find a spectrum of network states with a sharp transition from synchronous to asynchronous activity, modulated by physiological mechanisms. The spectrum of network states, dynamically reconfigured around this transition, supports diverse information processing strategies

La distribution spatiale des galaxies sélectionnées en ultraviolet intrinsèque de z =1 à z = 0 (formation stellaire et environnement)

Le taux de formation stellaire décroît fortement depuis 7 milliards d'années. Cette évolution reste un problème ouvert aujourd'hui, mais des contraintes peuvent être apportées par l'étude des liens entre les galaxies formant des étoiles et leur environnement. En effet, dans le cadre du scénario hiérarchique de formation des structures, l'environnement joue un rôle majeur dans la formation puis l'évolution des galaxies. Pendant cette thèse, j'ai mesuré la distribution spatiale (qui permet de relier à l'environnement) des galaxies sélectionnées en ultraviolet (qui sonde la formation stellaire) dans l'Univers récent à l'aide de différents échantillons, principalement construits à partir des données du satellite GALEX. Ces résultats, en combinaison avec ceux obtenus à partir de galaxies de l'Univers lointain également sélectionnées dans l'ultraviolet, permettent de discuter la migration des lieux principaux de la formation stellaire au cours de l'évolution de l'Univers. Les résultats présentés ici montrent ainsi que la formation stellaire a migré des régions fortement surdenses dans l'Univers lointain vers les régions faiblement surdenses dans l'Univers récent.AIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF