Local Volume Mapper Instrument

The Local Volume Mapper (LVM) is an SDSS-V survey designed to produce the first contiguous map of ionised gas in the Milky Way and its neighbours. Its spatial resolution is about 0.07 pc in Orion, and drops to about 10 pc in the Magellanic Clouds. The survey’s dedicated hardware is the Local Volume Mapper Instrument (LVM-I). While the survey defines the science goals and observing strategy, LVM-I is the instrument. Together, they turn wide-field spectra into community data products that anyone can download.

The Local Volume Instrument on Robot Ridge at Las Campanas.

LVM Survey At A Glance

• Target area ≈ 2,500 deg² covering the Galactic plane, the Large and Small Magellanic Clouds, and selected nearby galaxies (CONFIRM)
• Spatial resolution < 1 pc in the Milky Way, ≈ 10 pc in the Magellanic Clouds
• Wavelength range 360 – 980 nm, split into three spectrograph channels
• Planned spectra > 55 million over four years
• Sensitivity ~ 1 Rayleigh in H⍺

LVM-I Overview

LVM-I is a fully autonomous facility that combines four small telescopes, an integral-field unit, a fibre system, and three bench spectrographs inside a purpose-built enclosure at Las Campanas Observatory. One telescope gathers science light; the other three record simultaneous calibration data, allowing every exposure to be flux- and sky-corrected.

Telescope Array

• Four custom 16-cm-diameter f/11.4 objectives mounted on precision siderostats
• K-mirror derotators keep position angle fixed
• Dual CMOS acquisition-and-guider cameras on each focal plane maintain sub-arcsecond pointing

This is a cross-section of the telescope solid model from Herbst+ (2024). The telescope array is comprised of four such units.

Integral Field Unit and Fiber System

• Four separate IFUs: one 0.5-degree science IFU with 1,801 fibres and three smaller IFUs (60 + 59 + 12 fibres) for calibration
• Hexagonally packed 35-arcsec spaxels deliver contiguous coverage across the science field
• An 18.5-metre fibre run feeds a distributor that routes fibres to the spectrographs while minimising blue losses

The LVM-I fiber system undergoing splicing by the team at AAO (credit: David Robertson). Three slits are shown on the bottom (fed by blue cables), and the four IFUs are terminated on the left hand side (fed by grey cables).
A solid model showing the routing of fibers from the back of the telescopes to the spectrographs. (Credit: Tobias Feger, AAO)

Spectrographs

  • Three DESI-heritage spectrographs covering 360 – 980 nm at R ≈ 4,000
  • Thermally controlled to a fraction of a degree C.
  • Nine STA 4850 CCDs held at –100 °C by automated liquid-nitrogen coolers
All three LVM Spectrographs in their thermal enclosure (Image Credit: Nick Konidaris)

Control and Autonomy

  • Robotically scheduled via Python/RabbitMQ control software
  • Weather-sensing, emergency shut-offs, and daily LN₂ fills are fully automated
  • Typical clear-night open-shutter fraction exceeds 90 percent
  • Extensive safety features are built into the LVM software and operational plan

Status

LVM-I achieved first light at Las Campanas in April of 2023, and has been collecting science data nightly since 18 July 2023.

The LVM-Instrument during sunset. (Image Credit: Nick Konidaris)
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