PFS – SuMIRe

The Prime Focus Spectrograph (PFS) of the Subaru Measurement of Images and Redshifts (SuMIRe) project has been endorsed by Japanese community as one of the main future instruments of the Subaru 8.2-meter telescope at Mauna Kea, Hawaii. This optical/near-infrared multi-fiber spectrograph targets cosmology with galaxy surveys, Galactic archaeology, and studies of galaxy/AGN evolution.

Taking advantage of Subaru’s wide field of view, which is further extended with the recently completed Wide Field Corrector, PFS will enable us to carry out multi-fiber spectroscopy of 2400 targets within 1.3 degree diameter. A microlens is attached at each fiber entrance for F-ratio transformation into a larger one so that difficulties of spectrograph design are eased. Fibers are accurately placed onto target positions by positioners, each of which consists of two stages of piezo-electric rotary motors, through iterations by using back-illuminated fiber position measurements with a wide-field metrology camera. Fibers then carry light to a set of four identical fast-Schmidt spectrographs with three color arms each : the wavelength ranges from 0.38 um to 1.3 um will be simultaneously observed with an average resolving power of 3000.

Before and during the era of extremely large telescopes, PFS will provide the unique capability of obtaining spectra of 2400 cosmological/astrophysical targets simultaneously with an 8-10 meter class telescope.

The PFS collaboration, led by IPMU, consists of USP/LNA in Brazil, Caltech/JPL, Princeton, & JHU in USA, LAM (CNRS/AMU) in France, ASIAA in Taiwan, and NAOJ/Subaru.

LAM’s work on the Subaru PFS concentrates on two major items, the Spectrograph System and the Data Reduction Pipeline.

The Spectrograph System (SpS) is composed of four identical Spectrograph Modules (SM -see one SM in the picture below) fed by 600 fibers each. Each module incorporates three channels covering the wavelength ranges 0.38-0.65µm (“Blue”), 0.63-0.97µm (“Red”), and 0.94-1.26µm (“NIR”) respectively ; with resolving power which progresses fairly smoothly from about 2200 in the blue to about 5000 in the infrared. The Red channel includes an exchange mechanism for the dispersive component, allowing for a “medium resolution” observing mode (with a resolving power greater than 5000).
Figure 1 shows the different components of one spectrograph module. All spectrograph opto-mechanical components are mounted on a 2.4×1.9m carbon fiber optical bench. All elements (except for the cryostats) will be baffled to prevent for the external stray light and dust to enter.

The Spectrograph System will be installed in an environment-controlled room (Spectrograph Clean Room) at the IR4 floor of the SUBARU telescope atop the summit of Mauna Kea (Hawaii). The spectrograph system is modular in its design to allow for Assembly, Integration and Tests (AI&T) and for its safe transport up to the summit.

To minimize integration and test activities at the summit, each one of the four Spectrograph Modules will be firstly fully integrated and validated at LAM (France) before it is shipped to Hawaii.

In parallel to these SpS activities, the software team will design and develop a full data reduction pipeline able to handle the 2400 spectra, reduce them and perform the analysis on the 1D spectra.