Large-scale analysis of the SDSS-III DR8 photometric luminous galaxies angular correlation function

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Large-scale structure of the fast solar wind

Breen, Andrew; Bisi, M.M.; Fallows, R.A.; Habbal, S.R., (2007) 'Large-scale structure of the fast solar wind', Journal of Geophysical Research 112(A6) pp.A06101 RAE2008

A study of the large-scale structure of the wind of WR 134

Diverses méthodes ont été utilisées pour étudier les étoiles Wolf-Rayet (WR) dans le but de comprendre les phénomènes physiques variés qui prennent place dans leur vent dense. Pour étudier la variabilité qui n'est pas strictement périodique et ayant des caractéristiques différentes d'une époque à l'autre, il faut observer pendant des périodes de temps suffisamment longues en adopter un échantillonnage temporel élevé pour être en mesure d'identifier les phénomènes physiques sous-jacents. À l'été 2013, des astronomes professionnels et amateurs du monde entier ont contribué à une campagne d'observation de 4 mois, principalement en spectroscopie, mais aussi en photométrie, polarimétrie et en interférométrie, pour observer les 3 premières étoiles Wolf-Rayet découvertes: WR 134 (WN6b), WR 135 (WC8) et WR 137 (WC7pd + O9). Chacune de ces étoiles est intéressante à sa manière, chacune présentant une variété différente de structures dans son vent. Les données spectroscopiques de cette campagne ont été réduites et analysées pour l'étoile présumée simple WR 134 pour mieux comprendre le comportement de sa variabilité périodique à long terme dans le cadre d'une étude des régions d'interactions en corotation (CIRs) qui se retrouvent dans son vent. Les résultats de cette étude sont présentés dans ce mémoire.

Large Scale Structure of Metric Spaces

How the mathematical concept of Coarse Geometries is useful to analysing the Web

Discovery of a large-scale wall in the direction of Abell 22

We report on the discovery of a large-scale wall in the direction of Abell 22. Using photometric and spectroscopic data from the Las Campanas Observatory and Anglo-Australian Telescope Rich Cluster Survey, Abell 22 is found to exhibit a highly unusual and striking redshift distribution. We show, by examining the galaxy distributions both in redshift space and on the colour-magnitude plane, that Abell 22 exhibits a foreground wall-like structure. A search for other galaxies and clusters in the nearby region using the 2dF Galaxy Redshift Survey data base suggests that the wall-like structure is a significant large-scale, non-virialized filament which runs between two other Abell clusters either side of Abell 22. The filament stretches over at least > 40 h(-1) Mpc in length and 10 h(-1) Mpc in width at the redshift of Abell 22.

Structure and dynamics of the Shapley Supercluster - Velocity catalogue, general morphology and mass

We present results of our wide-field redshift survey of galaxies in a 285 square degree region of the Shapley Supercluster (SSC), based on a set of 10 529 velocity measurements (including 1201 new ones) on 8632 galaxies obtained from various telescopes and from the literature. Our data reveal that the main plane of the SSC (v approximate to 14 500 km s(-1)) extends further than previous estimates, filling the whole extent of our survey region of 12 degrees by 30 degrees on the sky (30 x 75 h(-1) Mpc). There is also a connecting structure associated with the slightly nearer Abell 3571 cluster complex (v approximate to 12 000 km s(-1)). These galaxies seem to link two previously identified sheets of galaxies and establish a connection with a third one at v = 15 000 km s(-1) near RA = 13(h). They also tend to fill the gap of galaxies between the foreground Hydra-Centaurus region and the more distant SSC. In the velocity range of the Shapley Supercluster (9000 km s(-1) < cz < 18 000 km s(-1)), we found redshift-space overdensities with b(j) < 17.5 of similar or equal to 5.4 over the 225 square degree central region and similar or equal to 3.8 in a 192 square degree region excluding rich clusters. Over the large region of our survey, we find that the intercluster galaxies make up 48 per cent of the observed galaxies in the SSC region and, accounting for the different completeness, may contribute nearly twice as much mass as the cluster galaxies. In this paper, we discuss the completeness of the velocity catalogue, the morphology of the supercluster, the global overdensity, and some properties of the individual galaxy clusters in the Supercluster.

Morphological properties of superclusters of galaxies

We studied superclusters of galaxies in a volume-limited sample extracted from the Sloan Digital Sky Survey Data Release 7 and from mock catalogues based on a semi-analytical model of galaxy evolution in the Millennium Simulation. A density field method was applied to a sample of galaxies brighter than M(r) = -21+5 log h(100) to identify superclusters, taking into account selection and boundary effects. In order to evaluate the influence of the threshold density, we have chosen two thresholds: the first maximizes the number of objects (D1) and the second constrains the maximum supercluster size to similar to 120 h(-1) Mpc (D2). We have performed a morphological analysis, using Minkowski Functionals, based on a parameter, which increases monotonically from filaments to pancakes. An anticorrelation was found between supercluster richness (and total luminosity or size) and the morphological parameter, indicating that filamentary structures tend to be richer, larger and more luminous than pancakes in both observed and mock catalogues. We have also used the mock samples to compare supercluster morphologies identified in position and velocity spaces, concluding that our morphological classification is not biased by the peculiar velocities. Monte Carlo simulations designed to investigate the reliability of our results with respect to random fluctuations show that these results are robust. Our analysis indicates that filaments and pancakes present different luminosity and size distributions.

Intercluster filaments of galaxies programme: Abundance and distribution of filaments in the 2dFGRS catalogue

Filaments of galaxies are known to stretch between galaxy clusters at all redshifts in a complex manner. In this Letter, we present an analysis of the frequency and distribution of intercluster galaxy filaments selected from the 2dF Galaxy Redshift Survey. Out of 805 cluster-cluster pairs, we find at least 40 per cent have bona fide filaments. We introduce a filament classification scheme and divide the filaments into several types according to their visual morphology: straight (lying on the cluster-cluster axis; 37 per cent), warped or curved (lying off the cluster-cluster axis; 33 per cent), sheets (planar configurations of galaxies; 3 per cent), uniform (1 per cent) and irregular (26 per cent). We find that straight filaments are more likely to reside between close cluster pairs and they become more curved with increasing cluster separation. This curving is toward a larger mass concentration in general. We also show that the more massive a cluster is, the more likely it is to have a larger number of filaments. Our results are found to be consistent with a cold dark matter cosmology.

Large-scale velocity structures in the Horologium-Reticulum supercluster

We present 547 optical redshifts obtained for galaxies in the region of the Horologium-Reticulum supercluster (HRS) using the 6 degrees field (6dF) multifiber spectrograph on the UK Schmidt Telescope at the Anglo-Australian Observatory. The HRS covers an area of more than 12 degrees x 12 degrees on the sky centered at approximately alpha = 03(h)19(m), delta = 50 degrees 02'. Our 6dF observations concentrate on the intercluster regions of the HRS, from which we describe four primary results. First, the HRS spans at least the redshift range from 17,000 to 22,500 km s(-1). Second, the overdensity of galaxies in the intercluster regions of the HRS in this redshift range is estimated to be 2.4, or delta rho/(rho) over bar similar to 1: 4. Third, we find a systematic trend of increasing redshift along a southeast-northwest spatial axis in the HRS, in that the mean redshift of HRS members increases by more than 1500 km s(-1) from southeast to northwest over a 12 degrees region. Fourth, the HRS is bimodal in redshift with a separation of similar to 2500 km s(-1) (35 Mpc) between the higher and lower redshift peaks. This fact is particularly evident if the above spatial-redshift trend is fitted and removed. In short, the HRS appears to consist of two components in redshift space, each one exhibiting a similar systematic spatial-redshift trend along a southeast-northwest axis. Lastly, we compare these results from the HRS with the Shapley supercluster and find similar properties and large-scale features.

On soft limits of large-scale structure correlation functions

We study soft limits of correlation functions for the density and velocity fields in the theory of structure formation. First, we re-derive the (resummed) consistency conditions at unequal times using the eikonal approximation. These are solely based on symmetry arguments and are therefore universal. Then, we explore the existence of equal-time relations in the soft limit which, on the other hand, depend on the interplay between soft and hard modes. We scrutinize two approaches in the literature: the time-flow formalism, and a background method where the soft mode is absorbed into a locally curved cosmology. The latter has been recently used to set up (angular averaged) 'equal-time consistency relations'. We explicitly demonstrate that the time-flow relations and 'equal-time consistency conditions'are only fulfilled at the linear level, and fail at next-to-leading order for an Einstein de-Sitter universe. While applied to the velocities both proposals break down beyond leading order, we find that the 'equal-time consistency conditions'quantitatively approximates the perturbative results for the density contrast. Thus, we generalize the background method to properly incorporate the effect of curvature in the density and velocity fluctuations on short scales, and discuss the reasons behind this discrepancy. We conclude with a few comments on practical implementations and future directions.

Real or virtual large-scale structure?

Modeling the development of structure in the universe on galactic and larger scales is the challenge that drives the field of computational cosmology. Here, photorealism is used as a simple, yet expert, means of assessing the degree to which virtual worlds succeed in replicating our own.

Large- and small-scale structure of the intermediate- and high-velocity clouds towards the LMC and SMC.

We employ Ca II K and Na I D interstellar absorption-line spectroscopy of early-type stars in the Large and Small Magellanic Clouds (LMC, SMC) to investigate the large- and small-scale structure in foreground intermediate- and high-velocity clouds (I/HVCs). Data include FLAMES-GIRAFFE Ca II K observations of 403 stars in four open clusters, plus FEROS or UVES spectra of 156 stars in the LMC and SMC. The FLAMES observations are amongst the most extensive probes to date of Ca II structures on ∼20 arcsec scales in Magellanic I/HVCs. From the FLAMES data within a 0 ∘.∘.∘.5 field of view, the Ca II K equivalent width in the I/HVC components towards three clusters varies by factors of ≥10. There are no detections of molecular gas in absorption at intermediate or high velocities, although molecular absorption is present at LMC and Galactic velocities towards some sightlines. The FEROS/UVES data show Ca II K I/HVC absorption in ∼60 per cent of sightlines. The range in the Ca II/Na I ratio in I/HVCs is from –0.45 to +1.5 dex, similar to previous measurements for I/HVCs. In 10 sightlines we find Ca II/O I ratios in I/HVC gas ranging from 0.2 to 1.5 dex below the solar value, indicating either dust or ionization effects. In nine sightlines I/HVC gas is detected in both H I and Ca II at similar velocities, implying that the two elements form part of the same structure.

Influence of small-scale inhomogeneities on the cosmological consistency tests

The current cosmological dark sector (dark matter plus dark energy) is challenging our comprehension about the physical processes taking place in the Universe. Recently, some authors tried to falsify the basic underlying assumptions of such dark matterdark energy paradigm. In this Letter, we show that oversimplifications of the measurement process may produce false positives to any consistency test based on the globally homogeneous and isotropic ? cold dark matter (?CDM) model and its expansion history based on distance measurements. In particular, when local inhomogeneity effects due to clumped matter or voids are taken into account, an apparent violation of the basic assumptions (Copernican Principle) seems to be present. Conversely, the amplitude of the deviations also probes the degree of reliability underlying the phenomenological DyerRoeder procedure by confronting its predictions with the accuracy of the weak lensing approach. Finally, a new method is devised to reconstruct the effects of the inhomogeneities in a ?CDM model, and some suggestions of how to distinguish between clumpiness (or void) effects from different cosmologies are discussed.

Galaxies and large scale structure at high redshifts

It is now straightforward to assemble large samples of very high redshift (z ∼ 3) field galaxies selected by their pronounced spectral discontinuity at the rest frame Lyman limit of hydrogen (at 912 Å). This makes possible both statistical analyses of the properties of the galaxies and the first direct glimpse of the progression of the growth of their large-scale distribution at such an early epoch. Here I present a summary of the progress made in these areas to date and some preliminary results of and future plans for a targeted redshift survey at z = 2.7–3.4. Also discussed is how the same discovery method may be used to obtain a “census” of star formation in the high redshift Universe, and the current implications for the history of galaxy formation as a function of cosmic epoch.