Using the Near Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST) we have spatially resolved 56 galaxies at redshifts 1 < z < 6 in the Hubble Ultra Deep Field. What is unique about this program (PID 2123, PI=Kassin) is the micro-shutter assembly (MSA) was used in “slitlet stepping mode” which essentially turned the MSA into a multi-object IFU. Slitlet stepping exploits the multiplex and sensitivity advantages of the MSA to carry out a survey in a vastly shorter time than a large IFU sample would require. We present the software which was developed to create the spectral cubes for these galaxies.

The NIRSpec MSA consists of four quadrants of 365 × 171 shutters that can be individually opened and closed to create the spectral slit configurations for this multi-object spectroscopy mode. MSA slitlets are one or more open shutters, adjacent in the cross-dispersion (spatial) direction, that form a longer “slitlet.” Combing the multiple open shutters and slitlet-stepping across the galaxies can efficiently obtain spatially resolved spectroscopy of several galaxies at the same time. Depending on the galaxy size, 1 to 8 unique slitlets are designed to cover the entire galaxy.

MSA “slitlet-stepping” is not presently an official JWST supported mode. Regardless, in Cycle 1, this mode has been used, albeit in different manners, by GO2123 and GO2132, demonstrating its viability. Here we present the MSA cube building software developed for GO2123, also known as GARDEN: Galaxies at All Redshifts Deciphered and Explained with the NIRSpec MSA. GARDEN has observed 56 galaxies at redshifts between 1 and 5 with specialized MSA stepping configurations depending on their morphologies and non-functioning shutters. We present a specialized set of software routines to create IFU-like data cubes for these galaxies. The slitlet-stepping cube building software is general and can be used on other NIRSpec MSA “slitlet-stepping” programs to take calibrated 2-D images and produces 3-D spectral cubes.