Concept and optical design of the near-infrared integral field unit for SWIMS

Abstract

SWIMS-IFU is an integral field unit for a near-infrared imaging spectrograph SWIMS (Simultaneous-color Wide-field Infrared Multi-object Spectrograph), which is being developed as one of the first-generation instruments for the University of Tokyo Atacama Observatory (TAO) 6.5-m infrared telescope and will be also mounted on the Cassegrain focus of the Subaru telescope in its initial phase (2015-). As SWIMS has a wide wavelength coverage which is implemented by a dichroic mirror placed into the collimated beam which splitting it into blue (0.9-1.4 μm) and red (1.4-2.5 μm) arms, the IFU module enables us to simultaneously obtain spatially resolved entire NIR spectrum from 0.9 to 2.5 μm in a wide-field of view of 14 ′′ x 10.′′4. The concept of the IFU module is easy realization of an integral filed spectroscopy (IFS) mode without modification of an existing spectrograph optics. Our IFU can be installed in a mask storage of SWIMS like other slit mask holders, so we can easily carry out IFS observation by just inserting the IFU module into a focal plane stage. The IFU optics consists of a pre-optics, an image slicer, a pupil mirror array, and a pseudo-slit mirror array. All the components will be aligned on an aluminum frame which has a floor size of < 170mm x 220mm) and a height of <60mm. Compared to existing near-infrared IFU instruments, our IFU has wider field coverage and is more sensitive for extended sources due to its coarser spatial sampling optimized for seeing-limited observations. In this paper, we report the concept and detailed optical design of the SWIMS-IFU.