The science case and data processing strategy for the Thinned Aperture Light Collector (TALC): a project for a 20m far-infrared space telescope

Abstract

The future of far-infrared observations rests on our capacity to reach sub-arcsecond angular resolution around 100 µm, in order to achieve a significant advance with respect to our current capabilities. Furthermore, by reaching this angular resolution we can bridge the gap between capacities offered by the JWST in the near infrared and those allowed by ALMA in the submillimeter, and thus benefit from similar resolving capacities over the whole wavelength range where interstellar dust radiates and where key atomic and molecular transitions are found.In an accompanying paper, 1 we present a concept of a deployable annular telescope, named TALC for Thinned Aperture Light Collector, reaching 20 m in diameter. Being annular, this telescope features a main beam width equivalent to that of a 27 m telescope, i.e. an angular resolution of 0.92" at 100 µm. In this paper we focus on the science case of such a telescope as well on the aspects of unconventional data processing that come with this unconventional optical configuration.The principal science cases of TALC revolve around its imaging capacities, that allow resolving the Kuiper belt in extra-solar planetary systems, or the filamentary scale in star forming clouds all the way to the Galactic Center, or the Narrow Line Region in Active Galactic Nuclei of the Local Group, or breaking the confusion limit to resolve the Cosmic Infrared Background. Equipping this telescope with detectors capable of imaging polarimetry offers as well the extremely interesting perspective to study the influence of the magnetic field in structuring the interstellar medium.We will then present simulations of the optical performance of such a telescope. The main feature of an annular telescope is the small amount of energy contained in the main beam, around 30% for the studied configuration, and the presence of bright diffraction rings. Using simulated point spread functions for realistic broad-band filters, we study the observing performance of TALC in typical situations, i.e a field of point sources, and fields with emission power at every physical scales, taken to represent an extragalactic deep field observation and an interstellar medium observation. We investigate different inversion techniques to try and recover the information present in the input field. We show that techniques combining a forward modeling of the observation process and a reconstruction algorithm exploiting the concept of sparsity (i.e. related to the more general field of compressed sensing) represent a promising avenue to reach the angular resolution promised by the main beam of TALC.

Bringing high spatial resolution to the far-infrared

“…Because of the missing central part of the single dish, the main lobe concentrates only ∼30% of the beam, which would be extremely detrimental to the effective spatial resolution promised by a 20 m outer diameter (1.2 at 100 μm). However, modern data processing techniques show that it is possible to recover close to the optimal spatial resolution in a wide variety of astrophysical imaging science cases (see [102]).…”

Epistémologie du modèle

“…Les lentilles, les tracés sismographiques, les solutions colorées, encore à portée de la perception humaine, ont été remplacés par des capteurs, pour la plupart numériques, dont les données récoltées ne sont elles-mêmes intelligibles qu'à travers de nouvelles médiations, souvent complexes. Ces médiations successives ne sont évidemment pas neutres et posent de réelles problématiques épistémologiques aux équipes qui les emploient Sauvage et al (2014). Que ce soit dans l'infiniment petit avec les microscopes à balayage électronique, ou les télescopes comme Herschel 3 , les images données à voir sont de pures constructions relevant davantage de la vue d'artiste que d'une quelconque réalité.…”

Dynamic stabilization of thin aperture light collector space telescope using active rods

“…Toward this purpose, the thin aperture light collector (TALC) project is currently under study by a European consortium. [2][3][4] The general structure of the TALC is one of a bicycle wheel. The diameter of the annular mirror of the TALC is 20 m after deployment.…”