MOSFIRE

MOSFIRE
Name	MOSFIRE
Type	Near-infrared multi-object spectrograph
Telescope	Keck I telescope
Institution	W. M. Keck Observatory
Detector	HgCdTe 2K×2K array
Wavelength	0.97–2.45 µm
First light	2012
Builders	University of California, Los Angeles; Keck Observatory

MOSFIRE is a near-infrared multi-object spectrograph and imaging instrument mounted on the Keck I telescope at the W. M. Keck Observatory on Mauna Kea. It was developed to provide sensitive spectroscopy and wide-field imaging across the Y, J, H, and K bands for studies of high-redshift galaxies, star formation, and Galactic objects. The instrument combines cryogenic optics, a cryogenic slitmask mechanism, and a large-format HgCdTe detector to enable simultaneous spectroscopy of dozens of targets over the Keck focal plane.

Overview and Purpose

MOSFIRE was designed to address key observational programs in observational cosmology and Galactic astronomy, enabling redshift surveys, emission-line diagnostics, and stellar population studies. Teams from University of California, Los Angeles and partners built the instrument to support projects linked to Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, surveys that follow up targets from Hubble Space Telescope deep fields and candidates from Sloan Digital Sky Survey. Its capability to observe multiple targets simultaneously was driven by demand from researchers working on programs associated with Keck Observatory, California Institute of Technology, and international collaborators.

Design and Instrumentation

The optical design integrates a cryogenic camera, a selectable filter wheel, and a reconfigurable slitmask cassette that operates at cryogenic temperatures. The focal plane uses a 2K×2K HgCdTe array optimized for near-infrared sensitivity, cooled and read out with electronics developed in collaboration with instrumentation groups at UCLA and partner facilities. The configurable slitmask system allows precise placement of slitlets across the Keck I focal plane, enabling spectroscopy of dozens of objects per exposure, a capability sought by teams working on follow-up of targets from Hubble Space Telescope, Spitzer Space Telescope, and photometric catalogs from Subaru Telescope and Canada–France–Hawaii Telescope. The instrument supports low- and medium-resolution grating modes tailored to programs led by researchers associated with University of Arizona, University of California, Berkeley, and other institutions.

Operational Use and Observatories

MOSFIRE is operated at the W. M. Keck Observatory on Mauna Kea and interfaces with observatory scheduling, queue planning, and instrument support teams. Regular users have included guest observers from University of California system campuses, Princeton University, Harvard University, and international groups from Max Planck Society institutes. The instrument has been used in coordinated campaigns alongside facilities such as Atacama Large Millimeter/submillimeter Array, Very Large Telescope, and Subaru Telescope for multiwavelength programs. Observing proposals from programs connected to National Science Foundation grants and institutional time allocation committees make use of MOSFIRE for both large programs and PI-led projects.

Scientific Results and Discoveries

MOSFIRE enabled spectra that measured rest-frame optical emission lines for galaxies at redshifts where such lines are shifted into the near-infrared, supporting studies of star-formation rates, metallicities, and kinematics. Teams using MOSFIRE produced redshift catalogs that complemented surveys from Hubble Space Telescope deep fields, samples selected from Sloan Digital Sky Survey photometry, and candidate lists from Spitzer Space Telescope data. MOSFIRE observations contributed to constraints on the mass-metallicity relation, galaxy assembly histories analyzed in conjunction with data from Chandra X-ray Observatory and Herschel Space Observatory, and studies of reionization-era candidates identified by James Webb Space Telescope precursor programs. Galactic science programs used MOSFIRE for stellar spectroscopy of targets associated with Kepler, Gaia, and cluster studies linked to Hubble Space Telescope photometry. Publications by groups at University of California, Los Angeles, University of California, Santa Cruz, University of Toronto, and others reported kinematic maps and emission-line diagnostics that influenced theoretical modeling efforts at institutions like Institute for Advanced Study and Princeton University.

Calibration, Data Reduction, and Performance

Calibration procedures for MOSFIRE include lamp-based flat fields, arc-lamp wavelength calibration, and telluric standard observations coordinated with observatory calibration plans. Data reduction pipelines developed by teams at UCLA and collaborating institutions produce rectified, sky-subtracted spectra and combine dithered exposures to reach background-limited sensitivity. Performance metrics reported by instrument teams demonstrated system throughput and spectral resolution adequate for detection of faint emission lines in integration times competitive with other near-infrared multi-object spectrographs such as instruments at European Southern Observatory facilities and on Subaru Telescope. The pipeline and user support have been integrated into data archives and analysis workflows used by groups at National Optical Astronomy Observatory partners and university consortia.

Development History and Collaborations

MOSFIRE's development began with proposals and design studies involving faculty and engineering teams at University of California, Los Angeles, funded through grants from agencies including National Science Foundation and institutional support from partner observatories. The project engaged instrument builders, optical designers, and software teams from institutions such as California Institute of Technology and collaborated with the staff of W. M. Keck Observatory for integration and commissioning on Keck I. International collaborators and guest observers from institutions like University of Cambridge, University of Oxford, Max Planck Institute for Astronomy, and National Astronomical Observatory of Japan participated in science verification and early science programs, establishing MOSFIRE as a key facility instrument for near-infrared spectroscopy.

Category:Near-infrared spectrographs