DEIMOS Observations

Spectrograph Setup

Spectroscopic observations were completed during June 2020 and 2021. Using Keck/DEIMOS, we used the 600 lines/mm grating blazed at 7500 Å and tilted to a central wavelength of 7200 Å, with the GG455 order-blocking filter employed. This spectroscopic setup provides an approximate spectral coverage of ~ 4500–9900 Å, depending on the slit placement on the particular mask. The spectral resolution (FWHM) for the 600g grating on DEIMOS is ~ 3.5 Å (Weiner 2006), with a dispersion of 0.65 Å per pixel.

Seeing Conditions and Exposure Times

Observing conditions varied throughout the survey. In general, seeing ranged from roughly 0."6 to 1" with variable cloud cover. Each individual exposure was typically ~1800 sec in length, with a minimum of 7 exposures per mask and no dithering applied between exposures.

Observation Issues

One of the chips (CCD5) was inoperative during the 2020 observations and had an elevated level of read noise during the 2021 observations, resulting in decreased sensitivity (or a total loss of spectral coverage) at red wavelengths for approximately ~25% of the slits per mask.