SPICA: the next observatory class infrared space astronomy mission

Over the last 40 years enormous advances have been made in infrared astronomy. Virtually all of these can be traced to the use of space-based telescopes, which avoid the deleterious effects of the earth’s atmosphere, and continued improvements in detector sensitivity and instrument design. Since its initial and modest contributions to previous infrared space astronomy missions, starting with ISO through to Herschel, Canada has grown in stature and is now recognized as a partner of choice by leading space agencies and scientific consortia embarking on the next generation of IR space astronomy missions. This white paper reviews the history of Canada’s contributions to IR space astronomy missions and presents the case for Canadian participation in the ESA-JAXA SPICA mission, which has been selected as one of three finalists for ESA’s fifth medium class mission, M5. Observations at far-infrared (FIR) wavelengths are optimal, not only for exploring galaxy formation in the farthest reaches of the Universe, but also star formation in our own Galaxy. Indeed, the study of cold and/or enshrouded systems can only be observed in the FIR. In essence, this provides the rationale for all space astronomy missions from IRAS through to Herschel. By any measure, Herschel was an outstanding success. It has caused astronomers to re-examine their theories of star formation and provided our first large scale view of distant star forming galaxies. With the SPICA telescope actively cooled to ~8 K, the lower thermal background will enable sensitivities two to three orders of magnitude better than Herschel’s! This sensitivity increase will allow SPICA not only to label photons by their wavelength over a volume of the Universe somewhere between one and ten thousand times greater than observed with Herschel, but also, and for the first time, allow it to label photons by their polarization in our Galaxy. Together these improvements augur major advances in the field. The SPICA instrument suite consists of three independent instruments: SAFARI – a FIR spectrometer; SMI – a mid-Infrared camera and spectrometer; and B-BOP - a FIR imaging polarimeter. The key features of each instrument are presented. Canadian scientific, technical and strategic leadership in the SPICA mission is well established. As a founding member of the SPICA/SAFARI consortium, Canada not only has much greater visibility and influence on the project, but also has the opportunity to contribute high-profile flight hardware to the mission. One of the primary tasks of the initial CSA-funded SPICA SAFARI Study was to identify and leverage Canadian signature technologies to establish a potential role for Canada in SPICA. As a result of the work undertaken over the last decade, Canada has the opportunity to deliver the high-resolution spectrometer component of the SAFARI instrument; one of three critical components of SAFARI which lies at its very heart. It is key to two of the main science drivers of the mission: i) galaxy evolution through spectral measurements of galaxies at high-redshift, and; ii) disk evolution by disentangling the line and continuum components of emission from spectral measurements of disks. Both of these fields of study are areas of excellence in Canadian astronomy. Several members of the team have a wealth of experience from science exploitation of Herschel data, some playing leading roles in Herschel key projects and many have been involved in developing the science cases for SPICA. All stand ready to assume leadership roles once the mission is selected by ESA and receives mission funding from the CSA. The impact on Canadian science, in terms of return on investment by the involvement of Canadian astronomers in science exploitation with SPICA through access to the guaranteed time will be over twice that of Herschel, which was one of, if not the, highest ROI of any CSA-funded space astronomy missions. Over the last decade Canada will have invested over $5M to establish a leading role in SPICA and as a result is now positioned to build the mission critical, high-resolution spectrometer for what will be the leading infrared observatory of the next decade if it is selected by ESA in 2021. At that time, Canada will have to make a decision on whether it will sign up for the mission. This point will be the last off-ramp for any nation in the SPICA consortium. Perhaps the greatest risk at an agency level is to diminish the trust that ESA has in the CSA as a dependable partner after staying the course for over a decade. ESA will hold the Mission Selection Review, to pick the winner of the three M5 finalists in April 2021. Programmatically, a letter will be required before this date (early 2021) from the CSA to ESA effectively stating that if ESA chooses SPICA, Canada is committed to the project. Securing mission funding requires approval from the Treasury Board of Canada. A strong statement of endorsement for SPICA in the LRP is a necessary prerequisite.White paper identifier W04