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A major quest in cosmology is the understanding of the nature of dark energy. It is now well known that a combination of cosmological probes is required to break the underlying degeneracies on cosmological parameters. In this paper, we present a method, based on a frequentist approach, to combine probes without any prior constraints, taking full account of the correlations in the parameters. As an application, a combination of current SNIa and CMB data with an evolving dark energy component is first compared to other analyses. We emphasise the consequences of the implementation of the dark energy perturbations on the result for a time varying equation of state. The impact of future weak lensing surveys on the measurement of dark energy evolution is then studied in combination with future measurements of the cosmic microwave background ...
Le NRT (Nançay Radio Telescope) est l'un des trois radiotélescopes "single-dish" de la classe des 100m dans le monde. De nouvelles techniques observationnelles ainsi que des besoins scientifiques nouveaux pour de grands relevés aveugles ont émergés ces dernières années, et doivent utiliser des grands champs de vue. En particulier, la technologie des réseaux d'antennes au foyer est au cœur des recherches et développements de préparation à SKA. Nous présentons le projet FAN (Focal Array at Nançay) qui consiste en l'étude et la réalisation d'un premier prototype d'antenne à réseau phasé installé au foyer du NRT, qui utilise une chaîne de réception et d'acquisition développée par les laboratoires LAL /IN2P3 et SPP/IRFU/CEA. L'antenne est utilisée pour des observations de test depuis la fin 2010. Le système FAN et son fonctionnement sont dé...
La cartographie de l'univers en radio, à travers l'observation de la raie à 21 cm de l'hydrogène atomique, constitue une approche complémentaire aux relevés optiques pour l'étude des grandes structures, et en particulier des oscillations acoustiques baryoniques (BAO). Nous proposons une méthode originale de la mesure de la distribution de l'hydrogène atomique neutre à travers une cartographie à 3 dimensions de l'émission du gaz à 21 cm, sans passer par l'identification des sources compactes (galaxies . . . ). Cette méthode nécessite un instrument à grande sensibilité et ayant une grande largeur de bande instantanée (≿ 100 MHz), alors qu'elle peut se contenter d'une résolution angulaire moyenne (10 arcmin). L'instrument devra avoir une surface de collection de quelques milliers de m2 et quelques centaines de lobes simultanés. Ces contrai...
3D mapping of matter distribution in the Universe through the 21 cm radio emission of atomic hydrogen (HI) is a complementary approach to optical surveys for the study of the Large Scale Structures, in particular for measuring the BAO (Baryon Acoustic Oscillation) scale up to redshifts z≲3, and therefore constraining dark energy parameters. We propose a novel method to map the HI mass distribution in three dimensions in radio, without detecting or identifying individual compact sources. This method would require an instrument with a large instantaneous bandwidth (≳100 MHz) and high sensitivity, while a rather modest angular resolution (∼10 arcmin) should be sufficient. These requirements can be met by a dense interferometric array or a phased array (FPA) in the focal plane of a large primary reflector, representing a total collecting a...
3D mapping of matter distribution in the universe through the 21 cm radio emission of atomic hydrogen is a complementary approach to optical surveys for the study of the Large Scale Structures, in particular for measuring the BAO (Baryon Acoustic Oscillation) scale up to redshifts z <~ 3 and constrain dark energy. We propose to carry such a survey through a novel method, called intensity mapping, without detecting individual galaxies radio emission. This method requires a wide band instrument, 100 MHz or larger, and multiple beams, while a rather modest angular resolution of 10 arcmin would be sufficient. The instrument would have a few thousand square meters of collecting area and few hundreds of simultaneous beams. These constraints could be fulfilled with a dense array of receivers in interferometric mode, or a phased array at the...
Context. Baryonic acoustic oscillations (BAO) and their effects on the matter power spectrum can be studied using the Lyman-α absorption signature of the matter density field along quasar (QSO) lines of sight. A measurement sufficiently accurate to provide useful cosmological constraints requires the observation of ~105 quasars in the redshift range 2.2 < z < 3.5 over ~8000 deg2. Such a survey is planned by the Baryon Oscillation Spectroscopic Survey (BOSS) project of the Sloan Digital Sky Survey (SDSS-III). Aims: We assess one of the challenges for this project, that of building from five-band imaging data a list of targets that contains the largest number of quasars in the required redshift range. In practice, we perform a stellar rejection of more than two orders of magnitude with a selection efficiency for quasars better than 50% t...
Context. Baryonic acoustic oscillations (BAO) and their effects on the matter power spectrum can be studied using the Lyman-α absorption signature of the matter density field along quasar (QSO) lines of sight. A measurement sufficiently accurate to provide useful cosmological constraints requires the observation of ~105 quasars in the redshift range 2.2 < z < 3.5 over ~8000 deg2. Such a survey is planned by the Baryon Oscillation Spectroscopic Survey (BOSS) project of the Sloan Digital Sky Survey (SDSS-III). Aims: We assess one of the challenges for this project, that of building from five-band imaging data a list of targets that contains the largest number of quasars in the required redshift range. In practice, we perform a stellar rejection of more than two orders of magnitude with a selection efficiency for quasars better than 50% t...
Large Scale Structures (LSS) in the universe can be traced using the neutral atomic hydrogen HI through its 21cm emission. Such a 3D matter distribution map can be used to test the Cosmological model and to constrain the Dark Energy properties or its equation of state. A novel approach, called intensity mapping can be used to map the HI distribution, using radio interferometers with large instantaneous field of view and waveband. In this paper, we study the sensitivity of different radio interferometer configurations, or multi-beam instruments for the observation of large scale structures and BAO oscillations in 21cm and we discuss the problem of foreground removal. For each configuration, we determine instrument response by computing the (u,v) or Fourier angular frequency plane coverage using visibilities. The (u,v) plane response is ...
The BAO radio instrument is a demonstrator of a radio telescope dedicated to cosmological studies and dark energy observation. It will analyze the signal emitted by the hydrogen in the universe with the aim of the detection of BAO's (Baryon Acoustic Oscillations). The instrument will use cylindrical reflectors or a large number of small dishes associated with a digital beam-former correlator. The electronic chain covers a large frequency range (1.5 GHz) and has a high throughput rate (~300 MB/s).
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