The far-infrared (FIR) spectral region is unique in that it enables studies of the thermal dust continuum emission and key atomic and molecular cooling lines, revealing the nature of the cool, dense universe, hidden from view at UV, optical, or even near-infrared wavelengths. Over the past two decades, the Infrared Space Observatory, Spitzer Space Telescope, Herschel Space Observatory, and Planck showed in unprecedented detail the intricate interactions between stars and the surrounding interstellar medium of the Milky Way and external galaxies. They refined our understanding of star formation as a function of cosmic time.
Herschel produced unparalleled wide-field images of the dust continuum emission in nearby molecular clouds, revealing a remarkable, filamentary structure of the dense galactic interstellar medium. These beautiful images lack, however, the velocity information that is needed to understand fully the three-dimensional motions of the molecular gas within this complex filamentary network. The new FIR facilities, notably SOFIA, as well as the future ultra-long duration balloon and space missions, such as Galactic/Extragalactic ULDB Spectroscopic Terahertz Observatory (GUSTO) and the Origins Space Telescope (OST), will soon be able to fill this gap, building upon the remarkable successes of the past and focusing on the unique aspects of the FIR.
The upGREAT instrument on SOFIA currently covers the 1.9-2.5 THz band, which includes the fine structure line of ionized carbon [CII], with 14 spatial pixels, and the 4.745 THz line of atomic oxygen [OI] with 7 pixels. This allows spectroscopic imaging of galactic star forming regions and nearby galaxies. However, much larger heterodyne arrays, of order 128 spatial pixels, offering an order of magnitude increase in the mapping speed, are currently under consideration for the fourth generation SOFIA facility instruments call in 2018.
GUSTO is an ultra-long duration balloon mission recently selected by NASA that will study the life cycle of interstellar gas in our Milky Way galaxy on much larger angular scales than those currently accessible to SOFIA, including the complex dynamics and gas flow in the vicinity of the center of our galaxy. Equipped with spectroscopic arrays to observe the atomic fine structure lines of carbon [CII], oxygen [OI], and nitrogen [NII], GUSTO will provide the spectral and spatial information needed to untangle the complexities of the interstellar medium, and map out large sections of the plane of the Milky Way and the Large Magellanic Cloud. The mission is targeted for launch in 2021 from McMurdo, Antarctica, and is expected to stay in the air between 100 to 170 days, depending on weather conditions. LERMA is participating in scientific preparation of GUSTO by developing a grid of PDR models that will be used to interpret the observations. The GUSTO precursor, STO-2, successfully flew in December of 2016.
Looking further into the future, OST is a NASA FIR mission concept currently being prepared for presentation to the US Decadal Survey in 2019. The quest to understand water transport from molecular clouds to protoplanetary disks, and the formation of planets like Earth is a particularly compelling mission goal, which cannot be addressed using SOFIA or balloon platforms. This requires a space FIR facility with enhanced measurement capabilities relative to those of Herschel, offering substantial gains in sensitivity, angular resolution, and improved spectroscopic capabilities. LERMA is currently leading a study of a European large-format Heterodyne Receiver for OST (HERO).
The goal of the proposed symposium is to review the current FIR spectroscopic imaging capabilities, discuss the most compelling science cases, as well as the technical capabilities of the future missions currently under consideration, notably GUSTO and OST. Over the years, LERMA has maintained very close scientific and technical collaborations with the NASA Jet Propulsion Laboratory in Pasadena. The proposed symposium will be a celebration of the distinguished scientific career of one of the long-term LERMA collaborators, Dr. Paul Goldsmith of JPL/Caltech.
Dr. Goldsmith is one of the founding fathers of molecular astrophysics—the active field that uses molecular and atomic spectral lines as tracers of the physical conditions in the dense, neutral ISM. Specific examples of his accomplishments include the seminal work on the thermal balance of dense clouds (Goldsmith and Langer 1978), as well as his life-long work on the physical structure of dense cores, including the early work on the velocity field (turbulent motions, rotation, molecular outflows), density and temperature distribution (collisional excitation, infrared pumping), clumping, and the gas-to-dust ratio. The large-scale molecular survey of the Taurus Molecular Cloud (Goldsmith et al. 2008), revealing the relation between the magnetic field geometry and large-scale gas morphology, is another more recent example, as is the theoretical and observational work on the chemistry of molecular clouds, including the life-long search for molecular oxygen that finally came to fruition with Herschel’s detection of submillimeter O2 emission in Orion KL and Ophiuchi A. Dr. Goldsmith has been the NASA Project Scientist for Herschel/HIFI and is currently the Project Scientist for GUSTO.
The symposium will consist of three half-day sessions (1.5 days), including about 8 invited talks plus attendee contributed oral and poster presentations, with plenty of time allocated for informal discussions. It will take place in the Fall of 2018, following the workshop Oxygen in the Universe, funded by the Institute of Advanced Studies at the University of Cergy-Pontoise. We expect participation of about 75 international scientists.
SOC :
Darek Lis (LERMA), Maryvonne Gerin (LERMA), Edith Falgarone (LERMA ; TBC), Edwin Bergin (U. Michigan), William Langer (JPL/Caltech), Jan Tauber (ESA)
Budget estimate :
Conference dinner at the Cassini room : 75 x 80€ = 6000€
Lunch for participants from outside Paris Observatory : 60 x 11€ = 660€
Three coffee breaks : 75 x 12€ = 900€
Travel assistance for 10 young participants within Europe : 10 x 500€ = 5000€
Total : 12,560€