Univers observable | EPFL Graph Search

L'Univers observable est, en cosmologie, la partie visible de notre Univers. Il est donc une boule dont la limite est située à l'horizon cosmologique et dont la Terre constitue le centre. C'est ainsi une notion relative, d'autres observateurs situés ailleurs dans l'Univers n'ont pas la même boule observable, mais une similaire de même rayon. Du fait que notre Univers a un âge fini, de d'années, la lumière des objets célestes situés au-delà de l'horizon n'a pas eu le temps de parvenir jusqu'à nous et ces objets sont donc encore invisibles ; néanmoins, l'Univers observable s'agrandit par nature au cours du temps : le rayon de l'Univers visible est ainsi une seconde-lumière plus grand chaque seconde ou de manière équivalente une année-lumière plus grand chaque année, et ce indépendamment de l'expansion de l'Univers. Les objets les plus éloignés de l'Univers observable sont également ceux qui peuvent être observés dans leur état le plus primordial, le plus proche du Big Bang, car ce son

HAVC-II - Idiap Private Cloud (Technical Inside-Out)

Virtualizing resources – servers, storage, networks – is now part of every IT departments life. The benefits of virtualization no longer need to be demonstrated and, when played upon in a large scale, provide both the saddle and spurs with which the Cloud mantra has been riding towards its success. This document shall describe how Idiap took advantage of its infrastructure to build its own virtualization farm, which shall (shamelessly) be referred to as Idiap Private Cloud.

Idiap2015

Predictors and predictands of linear response in spatially extended systems

Umberto Maria Tomasini

The goal of response theory, in each of its many statistical mechanical formulations, is to predict the perturbed response of a system from the knowledge of the unperturbed state and of the applied perturbation. A new recent angle on the problem focuses on providing a method to perform predictions of the change in one observable of the system using the change in a second observable as a surrogate for the actual forcing. Such a viewpoint tries to address the very relevant problem of causal links within complex system when only incomplete information is available. We present here a method for quantifying and ranking the predictive ability of observables and use it to investigate the response of a paradigmatic spatially extended system, the Lorenz '96 model. We perturb locally the system and we then study to what extent a given local observable can predict the behaviour of a separate local observable. We show that this approach can reveal insights on the way a signal propagates inside the system. We also show that the procedure becomes more efficient if one considers multiple acting forcings and, correspondingly, multiple observables as predictors of the observable of interest.

SPRINGER HEIDELBERG2021

Cold gas in the cosmic web around galaxy clusters

Damien Louis Alexandre Spérone-Longin

Galaxies live in very different types of environment. Those different environments are relics from the evolution of the Universe since the Big Bang. This network of structures observed via large scale surveys is called Cosmic Web. Within this web, galaxies can be isolated, in a filament, in a group, or in a cluster. When part of a cluster of galaxies, their morphologies, gas content (cold and hot), and star formation activities is seen to be affected by other galaxies, or by the gas inside the cluster. However, the long-term effects of the local environment on galaxy evolution remain unclear. Also, it has been observed that a pre-processing is happening long before the galaxies enter the cluster cores, which could explain the build-up of the passive galaxy sequence, where galaxies have quenched star formation. The aim of this thesis is to see if and how the cold molecular gas reservoir of galaxies is modified when star formation activity is decreasing and if there is a link with the position of the galaxy in the CW around the cluster. We gathered unprecedented observations: the first and largest survey of the molecular gas content of galaxies in and around the same cluster environment at intermediate redshifts. These Atacama Large Millimeter Array observations are part of a larger survey called Spatially Extended ESO Distant Cluster Survey. We are focusing on two clusters at a redshift of 0.5, which benefit from previous deep photometric and spectroscopic observations. This will allow us to derive accurate stellar masses and star formation rates, in order to compare those galaxies to other surveys of the cold gas content of galaxies, either in the field or inside different clusters. We unveiled a new population of galaxies with normal star formation rates but less cold molecular gas than other galaxies at the same stellar mass. This could be an indication that the gas reservoir responsible for the star formation changes either in mass or properties, before the star formation is affected. We also noticed that galaxies with the lowest cold-molecular-gas-to-stellar-mass ratios are preferentially either in the cluster core or in overdensities away from the cluster, confirming the existence of a pre-processing in overdensities surrounding the cluster. But active galaxies inside or close to the cluster, do not always have depleted CO reservoir. This thesis opens up new prospects on the study of the cold gas content of galaxies at intermediate redshift. It showed the necessity to observe galaxies that are in a transition regime between star forming and passive, in order to understand how star formation is suppressed around clusters. Those results could be extended to much larger samples, with the help of the upcoming new generation of instruments such as the Square Kilometer Array.

EPFL2021

Cold gas in the cosmic web around galaxy clusters

Damien Louis Alexandre Spérone-Longin

EPFL2021