SPICA/SAFARI will provide the next step in Far-Infrared Astronomical research capabilities after the Herschel/HIFI mission. To minimise the background noise level, the mirror of this joint European-Japanese space telescope will be cooled to close to absolute zero (-273 °C).
As a result, the detectors are no longer ‘blinded' by the thermal radiation coming from the mirror itself, allowing the ultra sensitive SPICA instruments to detect infrared sources more than two orders of magnitude weaker than would have been possible for Herschel.
After launch, around 2030, SPICA (SPace IR telescope for Cosmology and Astrophysics) will be the most sensitive telescope in mid- and far-infrared. This enables astronomers to investigate, for example, how the first galaxies were formed and how the formation of galaxies evolved over cosmic time. Over the last years, a large Japanese/European consortium of scientists and technicians have developed SPICA and its instruments from the initial ideas into a mission concept that can be implemented within the financial constraints posed by the participating agencies.
On behalf of the SPICA consortium, SRON submitted a proposal late 2016, in response to ESA's call for a medium-size mission opportunity (M5). By the end of 2017 ESA is expected to select three missions to be studied further under this call. Following selection into the M5, starting early 2018, the SPICA and SAFARI teams willsignificantly step up their activities in establishing a full detailed design of the mission and instruments.
SAFARI, by far the largest SPICA instrument and a key element of the space observatory, is being developed under the leadership of SRON. SAFARI is a far infrared spectrometer, which uses the latest generation of ultrasensitive Transition Edge Sensors - SRON key technology - to be able to fully profit from the extremely low background of the cold mirror. Thus SAFARI will allow astronomers not only to search for the far infrared signal of the first and oldest galaxies, but also for ice and water vapor in protoplanetary disks.
Understanding the origin and evolution of galaxies, stars, planets and life itself is a fundamental objective of astronomy. Although impressive advances have been made, our knowledge of how the first galaxies and stars formed, and how they evolved into what we see around us today, is still far from complete. A major reason for this is that the birth and much of the growth of galaxies, stars and planets occurs in regions that are hidden by a thick blanket of dust – virtually inaccessible to the optical instruments that have been the main tools of the trade since the invention of the telescope. In the infrared, it is possible to penetrate this obscuring dust and access a vast array of spectral diagnostics both in the local universe and at high redshift.
IR spectroscopy in the range 12-230 µm with SPICA, will reveal the physical processes that govern the formation and evolution of galaxies and black holes over cosmic time. With its 2.5-m telescope actively-cooled to below 8 K, the observatory will allow the first direct spectroscopic determination, in the mid-IR rest-frame, of both the star-formation rate and black hole accretion rate histories of galaxies, reaching lookback times of 12 Gyr, for large statistically significant samples.
Densities, temperatures, radiation fields and gas-phase metallicities will be directly measured in dust-obscured galaxies and active galactic nuclei (AGN), sampling a large range in mass and luminosity, from faint local dwarf galaxies to luminous quasars in the distant Universe. AGN and starburst feedback and feeding mechanisms in distant galaxies will be uncovered through detailed measurements of molecular and atomic line profiles. SPICA's large-area deep spectrophotometric surveys will provide mid-IR spectra and continuum fluxes for unbiased samples of tens of thousands of galaxies, out to redshifts of z~6.
Furthermore, SPICA spectroscopy will have the potential to uncover the most luminous galaxies in the first few hundred million years of the Universe, through their characteristic dust and molecular hydrogen features.
By providing access to the mid- and far InfraRed wavelength domain, SPICA bridges the gap where ‘astronomy is blind’, between ALMA in the submillimetre domain, the James Webb Space Telescope (JWST) and the new generation of extremely large telescopes (ELTs) at shorter wavelengths.
A second key objective of SPICA is to further the understanding of the formation and evolution of planetary systems. Planet formation is deeply linked to the evolution of the circumstellar gas reservoir, which can be uniquely traced in planet-forming systems with far-IR observations of the HD molecule. SPICA will characterize the warm gas disc mass down to the gas dispersal stage. Thanks to SPICA's mid-IR high spectral resolution capabilities, the gas dispersal in planet forming systems will be measured using a unique set of molecular/atomic and ionised gas tracers.
Furthermore, SPICA will uniquely probe multiple phases of water (warm and cold vapour, and ice), which cannot be observed from Earth, through the entire planet forming reservoir. The study of water, throughout the evolution of planet forming systems, will also help us understand the emergence of water in the Solar System and its delivery to the still-forming Earth.
SPICA will furthermore, for the first time, resolve the far-infrared polarization, and therefore the magnetic field, of galactic filaments which play a critical role at the onset of the star-formation process. Additionally, the spectroscopic capabilities of SPICA will shed light on the nature of the turbulent gas and the way in which the compression energy is dissipated through filament and core assembly, providing the experimental basis to advance theories of star formation within molecular clouds.
SPICA's two spectroscopic instruments, SAFARI, a joint European-Canadian-US contribution, and SMI from Japan, together provide several modes of operation. SAFARI provides low (R~300) to medium (R up to 11000) resolution spectroscopic capabilities at a uniquely high sensitivity of a few times 10-20 Wm-2 (5σ, 10hr) instantaneously covering the full 35 to 230 μm range. In the 12-18μm mid-infrared SMI provides a high-resolution R~28000 spectroscopy mode, as well as a medium resolution (R~150-1500) capability from 17 to 35 μm. Additionally, SMI provides 10’×12’ wide field imaging in the mid-infrared at 34 μm and POL delivers imaging polarimetry in the far infrared. The third instrument, BiBoP, provides a small field sensitive polarimetric capability for three bands at 110, 220 and 350 μm.
The SPICA telescope design and manufacture builds directly on the legacy of Herschel, enhancing the mission’s reliability. SRON has been the lead of the SAFARI project, largely based on SRON's experience in building complex space instruments, and its prominent role in the development of sensitive infrared detectors. Gaining maximum benefit from the low infrared emission of SPICA’s cooled mirror, requires the use of detectors that are several orders of magnitude more sensitive than those of Herschel.
SAFARI is a very different instrument from HIFI. HIFI 'sees' just a small part of the nearby universe but with a very high spectral resolution. SAFARI is a thousand-fold more sensitive infrared camera with about 4000 pixels that can instantaneously take fingerprints of the very far away cosmos over a large range of different wavelengths.