The SDSS-V Local Volume Mapper Instrument

We describe the Sloan Digital Sky Survey Local Volume Mapper Instrument (LVM-I) construction, testing, and initial performance. The facility is designed to produce the first integral map of thousands of degrees of the Southern sky. The map will cover spectra from bluer than [O II] to 980 nm with a dispersion of over R = ∆λ/λ > 4, 000 at Hα wavelength. Each spaxel will have a pitch of ∼35^′′, and the survey will be conducted using four integral field units (IFUs) with an instantaneous field of view of 530 arcmin². The LVM facility is designed to achieve the required sub-Rayleigh spectroscopy over large sky areas with outstanding spectrophotometric accuracy and precision. LVM-I is designed to produce this unique dataset using four siderostats on commercial mounts. The four beams are fed into 16-cm-diameter f/11.4 apochromatic objectives, and the sky is derotated with K mirrors. These telescopes produce an image of the field onto both guider cameras and a lenslet array. The array reimages the field at f/3.7 onto 107-micron-diameter fibers. Blue throughput is maximized with a short 18.5-m fiber run from the IFUs to the spectrographs. The fibers are reconfigured inside a splicing box to distribute the fibers from the four telescopes to three spectrographs. The spectrographs are near-copies of the Dark Energy Survey three-band f/1.7 spectrographs, which deliver sharp images over the entire chromatic range. Nine STA charge-coupled devices (CCDs), cooled with liquid-nitrogen dewars, are used for the survey. The LVMI is controlled with custom Python software and distributed over various computers using power-over-ethernet networking. The system is housed in a custom enclosure with a roll-off roof to grant access to the sky. The enclosure allows all four telescopes to point all over the sky and measure the transmissivity of the atmosphere and the sky background. Some of the first-light data products are highlighted here.