Search results for "Universe"
showing 10 items of 2171 documents
The 2014 KIDA network for interstellar chemistry
2015
Chemical models used to study the chemical composition of the gas and the ices in the interstellar medium are based on a network of chemical reactions and associated rate coefficients. These reactions and rate coefficients are partially compiled from data in the literature, when available. We present in this paper kida.uva.2014, a new updated version of the kida.uva public gas-phase network first released in 2012. In addition to a description of the many specific updates, we illustrate changes in the predicted abundances of molecules for cold dense cloud conditions as compared with the results of the previous version of our network, kida.uva.2011.
The impact from survey depth and resolution on the morphological classification of galaxies
2015
We consistently analyse for the first time the impact of survey depth and spatial resolution on the most used morphological parameters for classifying galaxies through non-parametric methods: Abraham and Conselice-Bershady concentration indices, Gini, M20moment of light, asymmetry, and smoothness. Three different non-local data sets are used, Advanced Large Homogeneous Area Medium Band Redshift Astronomical (ALHAMBRA) and Subaru/XMMNewton Deep Survey (SXDS, examples of deep ground-based surveys), and Cosmos Evolution Survey (COSMOS, deep space-based survey). We used a sample of 3000 local, visually classified galaxies, measuring their morphological parameters at their real redshifts (z ~ 0)…
The filter wheel and filters development for the X-IFU instruments onboard Athena
2016
Athena is the large mission selected by ESA in 2013 to investigate the science theme “Hot and Energetic Universe” and presently scheduled for launch in 2028. One of the two instruments located at the focus of the 12 m-long Athena telescope is the X-ray Integral Field Unit (X-IFU). This is an array of TES microcalorimeters that will be operated at temperatures of 50 mK in order to perform high resolution spectroscopy with an energy resolution down to 2.5 eV at energies < 7 keV. In order to cope with the large dynamical range of X-ray fluxes spanned by the celestial objects Athena will be observing, the X-IFU will be equipped with a filter wheel. This will allow the user to fine tune the i…
SATELLITES AROUND MASSIVE GALAXIES SINCE z ∼ 2: CONFRONTING THE MILLENNIUM SIMULATION WITH OBSERVATIONS
2012
Minor merging has been postulated as the most likely evolutionary path to produce the increase in size and mass observed in the massive galaxies since z$\sim$2. In this Letter, we test directly this hypothesis comparing the population of satellites around massive galaxies in cosmological simulations versus the observations. We use state-of-the-art, publically available, Millennium I and II simulations and the associated semi-analytical galaxy catalogues to explore the time evolution of the fraction of massive galaxies that have satellites, the number of satellites per galaxy, the projected distance at which the satellite locate from the host galaxy, and the mass ratio between the host galax…
On the full Boltzmann equations for leptogenesis
2009
We consider the full Boltzmann equations for standard and soft leptogenesis, instead of the usual integrated Boltzmann equations which assume kinetic equilibrium for all species. Decays and inverse decays may be inefficient for thermalising the heavy-(s)neutrino distribution function, leading to significant deviations from kinetic equilibrium. We analyse the impact of using the full kinetic equations in the case of a previously generated lepton asymmetry, and find that the washout of this initial asymmetry due to the interactions of the right-handed neutrino is larger than when calculated via the integrated equations. We also solve the full Boltzmann equations for soft leptogenesis, where t…
XMM-Newton First-Light Observations of the Hickson Galaxy Group 16
2000
This paper presents the XMM-Newton first-light observations of the Hickson-16 compact group of galaxies. Groups are possibly the oldest large-scale structures in the Universe, pre-dating clusters of galaxies, and are highly evolved. This group of small galaxies, at a redshift of 0.0132 (or 80 Mpc) is exceptional in the having the highest concentration of starburst or AGN activity in the nearby Universe. So it is a veritable laboratory for the study of the relationship between galaxy interactions and nuclear activity. Previous optical emission line studies indicated a strong ionising continuum in the galaxies, but its origin, whether from starbursts, or AGN, was unclear. Combined imaging and…
Probing the creatable character of some significant universe models
2008
An unambiguous physical definition of creatable universes was recently proposed. According to it, flat and closed Friedmann-Robertson-Walker (FRW) backgrounds can be created as quantum vacuum fluctuations, whereas open backgrounds are not creatable. Here, physically motivated perturbations of closed and flat backgrounds are analyzed. Various creatable perturbed FRW universes are thus found. Some of them involve scalar and tensor perturbations with appropriate spectra, whereas other ones are Bianchi models.
Filaments in observed and mock galaxy catalogues
2010
Context. The main feature of the spatial large-scale galaxy distribution is an intricate network of galaxy filaments. Although many attempts have been made to quantify this network, there is no unique and satisfactory recipe for that yet. Aims. The present paper compares the filaments in the real data and in the numerical models, to see if our best models reproduce statistically the filamentary network of galaxies. Methods. We apply an object point process with interactions (the Bisous process) to trace and describe the filamentary network both in the observed samples (the 2dFGRS catalogue) and in the numerical models that have been prepared to mimic the data.We compare the networks. Result…
The exposure of the hybrid detector of the Pierre Auger Observatory
2010
The Pierre Auger Observatory is a detector for ultra-high energy cosmic rays. It consists of a surface array to measure secondary particles at ground level and a fluorescence detector to measure the development of air showers in the atmosphere above the array. The ‘‘hybrid” detection mode combines the information from the two subsystems. We describe the determination of the hybrid exposure for events observed by the fluorescence telescopes in coincidence with at least one water-Cherenkov detector of the surface array. A detailed knowledge of the time dependence of the detection operations is crucial for an accurate evaluation of the exposure. We discuss the relevance of monitoring data coll…
The Fluorescence Detector of the Pierre Auger Observatory
2010
The Pierre Auger Observatory is a hybrid detector for ultra-high energy cosmic rays. It combines a surface array to measure secondary particles at ground level together with a fluorescence detector to measure the development of air showers in the atmosphere above the array. The fluorescence detector comprises 24 large telescopes specialized for measuring the nitrogen fluorescence caused by charged particles of cosmic ray air showers. In this paper we describe the components of the fluorescence detector including its optical system, the design of the camera, the electronics, and the systems for relative and absolute calibration. We also discuss the operation and the monitoring of the detecto…