UCLA Infrared Lab

LIGER

A Next Generation Keck AO Instrument
Liger Logo

Liger is a near-infrared integral field spectrograph (IFS) for the W. M. Keck Observatory. It will use the upcoming Keck All-Precision Adaptive optics (KAPA) system on the Keck I telescope with performance and advancements for large format near-infrared detectors. Liger is based largely on the design of IRIS for the forthcoming Thirty Meter Telescope (TMT).    This will minimize costs and fabrication and construction timescales.

The Liger instrument uses the latest near-infrared detectors for an imaging camera that operates simultaneously with an innovative IFS that uses both a slicer and lenslet array for spatial sampling. It will help explore a wide range of science cases including   dark matter substructure, distant galaxies, supermassive black holes, nearby star forming regions, the Galactic Center, and Solar System bodies. It will enable new science by offering enhanced capabilities such as higher spectral resolving power (R∼8000-10000), access to shorter wavelengths (0.84 - 2.4 µm), and larger fields of view compared to any current and future ground- and space-based IFS systems.

Liger is a crucial stepping stone both technologically and scientifically for the next decade in astronomy.

Science Drivers for New Capabilities of Liger

New Capability of Liger Main Science Driver
Extending to higher spectral resolution (R > 8000-10,000) Supermassive and intermediate-mass black hole measurements; high-z galaxy kinematics; planetary and stellar atmospheres and abundance patterns; radial velocity measurements
Extending to visible wavelengths (λ < 1 μm) Dynamics and abundances in a range of systems; solar system bodies; exoplanet metallicities; accretion diagnostics in young stars and planets; low-z galaxies; black hole mass measurements
Larger IFS field of view Crowded field spectroscopy; galactic nuclei; star forming regions; solar system; strong gravitational lens systems
Larger imager field of view Star forming regions; astrometric accuracy for proper motion measurements; Jupiter and Saturn
Parallel imaging Many science cases benefit from parallel imaging to provide astrometric reference and PSF characterization

Liger Subsystem Overview

Liger Layout

Opto-mechanical layout of the Liger imaging camera (green) and the lenslet re-imaging optics (red) and the slicer re-imaging optics (blue). The Keck AO f/15 beam is fed into Liger at the top left. The filter wheel and rotating lyot stop feeds both the imager and integral field spectrograph. There are two pick-off mirrors that can select between the slicer and lenslet IFS modes. The slicer and lenslet IFS share all complex optics like the gratings, common TMA camera, and detector (bottom right). The nominal field of view of the Liger optical system is in the top right with imaging camera (green), two spatial scales slicer IFS (blue), two spatial scales lenslet (red).

Liger Cryostat

Liger Cryostat

A rendering of the octagonal Liger cryostat. The red beam from the Keck Adaptive Optics system enters on the right side. The beam is picked off at two spots on the imaging plane, one for the IFS-Slicer (orange) and one for the IFS-Lenslet (purple). The lower white structure is the existing cart on a solid model of the Keck rail system located at the output port location of Keck AO.

Liger Modes

Capability Mode Spatial Sampling (mas) Field of View (arcseconds) Spectral Resolution (R) Min - Max Wavelengh (μm) Bandpass

Imager
H2RG


10 mas


20.5” x 20.5”


Set by filter


0.84 - 2.4


BB and NB

Lenslet IFS
128x128 spaxels
128x128 spaxels


15 mas
35 mas


1.9” x 1.9”
4.5” x 4.5”


4000
4000


0.84 - 2.4
0.84 - 2.4


5%
5%

Lenslet IFS
16x128 spaxels
16x128 spaxels


15 mas
35 mas


0.2” x 1.9”
0.6” x 4.5”


4000, 8000
4000, 8000


0.84 - 2.4
0.84 - 2.4


5%, 20%
5%, 20%

Slicer IFS
88x45 spaxels
88x45 spaxels


75 mas
150 mas


6.6” x 3.4”
13.2” x 6.8”


4000
4000


0.84 - 2.4
0.84 - 2.4


5%, 20%
5%, 20%

Slicer IFS
44x45 spaxels
44x45 spaxels


75 mas
150 mas


3.3” x 3.4”
6.6” x 6.8”


4000, 8000
4000, 8000


0.84 - 2.4
0.84 - 2.4


5%, 20%, 40%
5%, 20%, 40%

Liger Field of View Compared with OSIRIS

Liger Field of View

IFS observations of a z=2.01 lensed galaxy (SDSS J1206+5142, magnified ~28x by a galaxy group at z=0.42). Liger’s field of view will allow the entire arc and central lens to be observed in one pointing, whereas OSIRIS requires multiple positions even at the largest scale.

Liger Sensitivity

Metallicity gradient (O/H) of the lensed galaxy measured from OSIRIS data in the central R < 1 kpc, where the requisite faint emission lines are detected (Jones et al., 2013). Liger’s slicer field of view and considerably higher sensitivity will map low surface brightness emission lines at larger radii, improving gradient measurements and enabling diagnostics of shocked outflows and active galactic nuclei. Observations of similar lensed quasar systems will enable sensitive probes of dark matter substructure and dark energy, utilizing Liger’s field of view and higher spectral resolution.

Simulated Galactic Center Observations

Simulated Galactic Center Observations

Using Liger (right) compared to OSIRIS (left). Liger’s increased field of view and sensitivity yields a dramatic increase in the number of stars with precise radial velocity measurements (indicated with green circles), including several with short-period orbits (white ellipses).

Liger Technical Team

Name Affiliation Expertise
Maren Cosens UCSD Graduate Student, Opto-mechanical Design and Testing
Michael Fitzgerald UCLA UCLA Co-Lead
Chris Johnson UCLA Systems Manager
Tucker Jones UCSD Project Scientist
Marc Kassis WMKO Instrument WMKO Program Manager
Renate Kupke UCSC UCSC Lead, Optical Design of Imager and IFS
Evan Kress UCLA Mechanical Engineer
James Larkin UCLA UCLA Lead and Co-PI
Jerome Maire UCSD Opto-Mechanical Design, Detector Testing, DRS
Ji-Man Sohn UCLA Software Engineer
Arun Surya UCSD DRS, Readout Processing, Optical Design Characterization
James Wiley UCSD Graduate Student, Opto-Mechanical Design and Testing
Peter Wizinowich WMKO KAPA PI, Liger Performance
Shelley Wright UCSD Principal Investigator (PI)
Andrea Zonca UCSD Software Engineer, DRS Design

Liger Science Team

Name Affiliation Expertise
Maren Cosens UCSD Nearby galaxies and HII regions
Tuan Do UCLA Galactic center; supermassive black holes
Chris Fassnacht UC Davis Cosmology; dark energy and Hubble constant
Deanne Fisher Swinburne Galaxy formation and evolution
Andrea Ghez UCLA  Galactic center
Tucker Jones UC Davis Project Scientist, Galaxy formation and evolution
Jacqueline Keane Hawaii Comets; solar system
Evan Kirby Caltech Nearby galaxies; stellar populations
Quinn Konopacky UCSD Exoplanets; star formation
Jessica Lu UC Berkeley Star formation; nearby galaxies
Naveen Reddy UC Riverside Galaxy formation and evolution
Ryan Sanders UC Davis Galaxy formation and evolution
Karin Sandstrom UCSD Nearby galaxies; interstellar medium
Alice Shapley UCLA Galaxy formation and evolution
Arun Surya UCSD Instrumentation
Tommaso Treu UCLA Cosmology; dark matter substructure
Mike Wong UC Berkeley Solar system; planetary science