Spectral mapping reconstruction of extended sources

Three-dimensional spectroscopy of extended sources is typically performed with dedicated integral field spectrographs. We describe a method of reconstructing full spectral cubes, with two spatial and one spectral dimension, from rastered spectral mapping observations employing a single slit in a traditional slit spectrograph. When the background and image characteristics are stable, as is often achieved in space, the use of traditional long slits for integral field spectroscopy can substantially reduce instrument complexity over dedicated integral field designs, without loss of mapping efficiency - particularly compelling when a long-slit mode for single unresolved source follow-up is separately required. We detail a custom flux-conserving cube reconstruction algorithm, discuss issues of extended-source flux calibration, and describe CUBISM, a tool that implements these methods for spectral maps obtained with the Spitzer Space Telescope's Infrared Spectrograph.