MOSFIRE, the multi-object spectrometer for infra-red exploration at the Keck Observatory

Abstract

This paper describes the as-built performance of MOSFIRE, the multi-object spectrometer and imager for the Cassegrain focus of the 10-m Keck 1 telescope. MOSFIRE provides near-infrared (0.97 to 2.41 m) multi-object spectroscopy over a 6.1' x 6.1' field of view with a resolving power of R~3,500 for a 0.7" (0.508 mm) slit (2.9 pixels in the dispersion direction), or imaging over a field of view of ~6.9' diameter with ~0.18" per pixel sampling. A single diffraction grating can be set at two fixed angles, and order-sorting filters provide spectra that cover the K, H, J or Y bands by selecting 3 rd , 4 th , 5 th or 6 th order respectively. A folding flat following the field lens is equipped with piezo transducers to provide tip/tilt control for flexure compensation at the <0.1 pixel level. Instead of fabricated focal plane masks requiring frequent cryo-cycling of the instrument, MOSFIRE is equipped with a cryogenic Configurable Slit Unit (CSU) developed in collaboration with the Swiss Center for Electronics and Microtechnology (CSEM). Under remote control the CSU can form masks containing up to 46 slits with ~0.007-0.014 precision. Reconfiguration time is < 6 minutes. Slits are formed by moving opposable bars from both sides of the focal plane. An individual slit has a length of 7.0" but bar positions can be aligned to make longer slits in increments of 7.5. When masking bars are retracted from the field of view and the grating is changed to a mirror, MOSFIRE becomes a wide-field imager. The detector is a 2K x 2K H2-RG HgCdTe array from Teledyne Imaging Sensors with low dark current and low noise. Results from integration and commissioning are presented.

Spectroscopic detection of C iv λ1548 in a galaxy atz = 7.045: implications for the ionizing spectra of reionization-era galaxies

“…Near-infrared spectroscopic observations of Abell 1703 were carried out with MOSFIRE (McLean et al 2010(McLean et al , 2012 on the Keck-I Telescope on April 11, 2014 UT. The spectroscopic observations were taken using the YJ grating with the J-band filter, which has a resolution of R=3318 and covers a wavelength range of λ=1.15-1.35µm.…”

“…Recently Stark et al (2014a) reported tentative CIII] detections in two galaxies with previously confirmed redshifts (z = 6.029 and z = 7.213) from Lyα. Here we build on this progress with an exploration of the strength of high ionization emission features (CIVλλ1548,1551 and He IIλ1640) in a small sample of z 7 UV-selected galaxies using the MOSFIRE (McLean et al 2012) spectrograph on the Keck I tele- scope. We report the detection of strong nebular CIVλ1548 emission in the spectrum of A1703-zd6, a spectroscopically confirmed galaxy at z = 7.045.…”

A HIGH FRACTION OF Lyα EMITTERS AMONG GALAXIES WITH EXTREME EMISSION LINE RATIOS AT z ∼ 2*

“…The parent sample for this work consists of 315 galaxies in the redshift range 1.95 z 2.65 for which measurements (or upper McLean et al 2010McLean et al , 2012 on the Keck I telescope. An earlier version of this parent sample, with 219 galaxies, was described in detail by Steidel et al (2014), and we refer the reader to that paper for details of the MOSFIRE observations and data reduction.…”

A concept for seeing-limited near-IR spectroscopy on the Giant Magellan Telescope

“…This is only a factor of ∼ 2 larger than FIRE on Magellan, and it is considerably smaller than many multi-object cryogenic spectrographs on 6-10 meter telescopes today. 31,32 Since SuperFIRE is a single-object spectrograph, such a comparison does not imply that these instruments address identical science. It simply illustrates that fabrication, installation, and telemetry for dewars of this size are within current capabilities.…”