Conceptual design of IR multi-IFU spectrograph with MOAO

To study properties of cold dark matter (CDM), which can only be observed through its gravitational interaction with galaxies, spatially resolved spectra at least to the K-band are desirable. We started designing a spectrograph which observes multiple targets spatially resolved in a telescope field of view fed with multi-object adaptive optics (MOAO). The current design either places field lenses on the telescope field of view to image the pupil onto steering mirrors, or uses a single set of field lens to deliver beams to pick-off arms. The steering mirror on the pupil image tilts and selects a sub-field from each of the telescope field of view physically split by the field lenses. This allows cheaper and more robust construction of a method to select the target fields with a limitation in selections of the target fields. On the other hand, the pick-off arm implementation allows more flexibility in assigning targets to fields of the integral field units (IFUs) especially when targets are clustered. The IFU arranges spatial elements of each of sub-field of view to be fed into the spectrograph. If enough pixels are afforded, using microlens arrays, which image pupils of spatial elements onto the object plane of the spectrograph is ideal in robustness. Otherwise, an image slicer is to be located to arrange the sub-field of view onto the entrance slit. The instrument should be built as modules to allow expeditious scientific results.