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Concept

Spitzer (télescope spatial)

Résumé

Spitzer ou SIRTF (Space Infrared Telescope Facility) est un télescope spatial infrarouge développé par la NASA. Il est le dernier des quatre « Grands Observatoires » aux caractéristiques complémentaires réalisés par la NASA pour répondre aux grandes interrogations scientifiques de la fin du dans le domaine de l'astrophysique. Son rôle est principalement d'observer la création de l'Univers, la formation et l'évolution des galaxies primitives, la genèse des étoiles et des planètes et l'évolution de la composition chimiques de l'Univers qui sont des phénomènes principalement visibles dans l'infrarouge. Ce projet de télescope infrarouge est lancé en 1984 par la NASA. Au cours de son développement, la taille de Spitzer est fortement revue à la baisse (masse abaissée de à moins d'une tonne) pour faire face à des réductions budgétaires qui touchent l'agence spatiale. Ses capacités sont néanmoins nettement supérieures à ses prédécesseurs, IRAS (1983) et ISO (1995), grâce à plusieurs choix t

Source officielle

https://fr.wikipedia.org/wiki/Spitzer_(t%C3%A9lescope_spatial)

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Large scale structures around medium mass galaxy clusters at intermediate redshift

François Henri Ambroise Rérat

Theory predicts that galaxies are not randomly distributed in the Universe. They form a complex network of filamentary structures, the Cosmic Web, divided in clusters, groups, filaments and walls. This picture has been confirmed by the large galaxy redshift surveys. Galaxy properties like morphology and star formation rates are strongly influenced by their environment. The most radical transformations are observed in galaxy clusters, located at the intersection of filaments. Nevertheless, the location where the environment starts to play a role and the main physical phenomenon responsible for these changes are still unknown. The aim of this thesis is to determine where and how galaxies are affected by the environment, at local and global scales. We gathered high quality photometry in the 5 optical bands

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with MegaCam on the Canada-France-Hawaii Telescope for 3 medium mass galaxy clusters at intermediate redshift, with a spatial extent on the sky plane reaching 8 to 13 times the cluster virial radii. These clusters were selected to represent as much as possible progenitors of clusters in the local Universe. The core of these clusters have rich ancillary data from the ESO Distant Cluster Survey. The redshift and mass ranges of these clusters, combined to the wide field of the observations make this study unique. We computed photometric redshifts to map the galaxy distribution around the clusters. We were able to identify overdense regions forming groups and filaments, unveiling for the first time the large scale structures in such details for this type of clusters. We studied the fraction of galaxies in the red sequence in different environments, namely in the field, filaments and groups. We find that significant quenching processes are already at work in filaments, even at large cluster-centric distances. We also show that the local neighborhood of galaxies has a stronger impact on galaxy colors than the global environment. An optical spectroscopic follow-up with the VIsible MultiObject Spectrograph on the Very Large Telescope confirms our photometric results. In particular, the fraction of galaxies with detected \otwo emission line is smaller with increasing density. We also find that the star formation rate, determined from [OII], is in average weaker in groups and clusters than in lower density environments. This thesis opens new perspectives to study the way galaxies populate the Cosmic Web. Combined to weak-lensing analysis and cosmological simulations, it will allow a deeper understanding of the structure formation and their baryonic content. It is a first step before extending the results to much larger samples, with the help of the upcoming all-sky cosmological surveys such as Euclid or the Square Kilometer Array.

EPFL2015

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We present the Spitzer-IRAC/MIPS Extragalactic survey (SIMES) in the South Ecliptic Pole field. The large area covered (7.7 deg(2)), together with one of the lowest Galactic cirrus emissions in the entire sky and a very extensive coverage by Spitzer, Herschel, Akari, and GALEX, make the SIMES field ideal for extragalactic studies. The elongated geometry of the SIMES area (approximate to 4: 1), allowing for significant cosmic variance reduction, further improves the quality of statistical studies in this field. Here we present the reduction and photometric measurements of the Spitzer/IRAC data. The survey reaches depths of 1.93 and 1.75 mu Jy (1 sigma) at 3.6 and 4.5 mu m, respectively. We discuss the multiwavelength IRAC-based catalog, completed with optical, mid-, and far-IR observations. We detect 341,000 sources with F-3.6 mu m >= 3 sigma. Of these, 10% have an associated 24 mu m counterpart, while 2.7% have an associated SPIRE source. We release the catalog through the NASA/IPAC Infrared Science Archive. Two scientific applications of these IRAC data are presented in this paper. First, we compute integral number counts at 3.6 mu m. Second, we use the [3.6]-[4.5] color index to identify galaxy clusters at z > 1.3. We select 27 clusters in the full area, a result consistent with previous studies at similar depth.

Iop Publishing Ltd2016

Chargement

We combine Hubble Space Telescope (HST) G102 and G141 near-IR (NIR) grism spectroscopy with HST/WFC3UVIS, HST/WFC3-IR, and Spitzer/IRAC [3.6 mu m] photometry to assemble a sample ofmassive (log(M-star/M-circle dot) similar to 11.0) and quenched (specific star formation rate < 0.01 Gyr-1) galaxies at z similar to 1.5. Our sample of 41 galaxies is the largest with G102+G141 NIR spectroscopy for quenched sources at these redshifts. In contrast to the local universe, z similar to 1.5 quenched galaxies in the high-mass range have a wide range of stellar population properties. We find that their spectral energy distributions (SEDs) are well fitted with exponentially decreasing star formation histories and short star formation timescales (tau

American Astronomical Society2013

Chargement

Large scale structures around medium mass galaxy clusters at intermediate redshift

François Henri Ambroise Rérat

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EPFL2015