GMACS: The Wide-Field, Multi-Object
Spectrograph for the
Giant Magellan Telescope
Jennifer Marshall
Texas A&M University
http://kicp-workshops.uchicago.edu/decam-nfc2018/
First Generation Instruments
Instrument / Mode Capabilitiesλ Range,
μmResolution Field of View
G-CLEF / NS, GLAO Optical High Resolution
Spectrograph / PRV0.35 – 0.95 20 – 100K
7 x 0.7,1.2”
fibers
GMACS / NS, GLAO Wide-Field Optical Multi-
Object Spectrograph0.36 – 1.0
1,500 – 4,000
(10K w/
MANIFEST)
40-60 arcmin2
GMTIFS / LTAO,
NGSAONIR AO-fed IFS / Imager 0.9 – 2.5 5,000 & 10,000 10 / 400 arcsec2
GMTNIRS / NGSAO,
LTAO
JHKLM AO-fed High
Resolution Spectrograph1.2 – 5.0 50K, 100K 1.2” long-slit
MANIFEST* / NS,
GLAO
Facility Robotic Fiber
Feed0.36 – 1.0 20’ diameter
International GMACS team
• D.L. DePoy, J. L. Marshall, Casey
Papovich, Travis Prochaska, Luke
Schmidt, Erika Cook (Texas A&M)
• Cynthia Froning (UT-Austin)
• Soojong Pak, Tae-Geun Ji, Hye-In
Lee, (Kyung Hee University, Korea)
• Claudia Mendes de Oliveira, Rafael
Ribeiro, Daniel Faes, Aline Souza,
Mario Almeida (Sao Paolo, Brazil)
• Damien Jones (Australia)
• Keith Taylor (California)
• (Paul Scowen, ASU)
• With contributions from
– Steve Shectman,
Carnegie Observatories
– GMACS Science Forum
– GMT SAC
– GMT staff
– MANIFEST Team,
Australia
• Matthew Colless
• Jon Lawrence
– Many others
GMACS science goals
• General use spectrograph– Performance optimized for
faint targets
– Exploits GMT’s large collecting area and wide field
• Follow up objects identified by DES/LSST– GMACS will be able to take
a spectrum of any object imaged by LSST
– Goal: spectrum of any LSST alert within ~1 hour
GMACS Science DriversScience Case constraints
Time-domain science High rel. precision/repeatability/efficiency; large simultaneous
wavelength coverage
Brown dwarf/exoplanet
atmospheres (weather)
5’ FOV, blueward of JWST wavelength coverage. High stability for
transit spectroscopy.
Star/Star Cluster ages <2 Å resolution at Li 6708Å for age measurements; blue coverage
(Ca HK)
YSO accretion rates simultaneous coverage of Balmer lines/break (365-656 nm)
Dwarf Galaxy dynamics Coverage of CaT (850 nm, R~5000); 3 km/s velocity precision, high
stability. 20’ FOV preferable
Stellar Abundances R~5000, blue/red wavelength coverage (370-540 nm; CaT 850 nm)
Redshift surveys
(LSST, DES follow-up)
High multiplexing, slitlength requirement: source density will be
~50-60 arcmin-2. FOV as large as possible. Large simultaneous
wavelength coverage to improve efficiency.
Galaxy assembly,
IGM/CGM studies
R~3000 and redder wavelength coverage for absorption line
studies of z > 1 galaxies.
Properties of Galaxies
during Reionization
Very red coverage (>900 nm for Ly-α at z > 6.5), higher resolution
and high multiplexing/FOV helpful (~0.5-1 source/arcmin2)
Technical requirements
High throughput across wide wavelength range
Maintain compatibility with MANIFEST fiber positioner
2.73m
(9.0ft)
2.73m
(9.0ft)
Weight:
5500 kg
(12100
lb)5.23m
(17.2ft)
GMACS design concept
Design choices
• Gregorian slit mask-fed– Maximum throughput
• Refractive optics– Maximum throughput
• No folds of convenience– Maximum throughput
– Large instrument
• Two channels– Maximum throughput
– Simultaneous wavelength coverage in low resolution mode
• VPH gratings– Maximum throughput
– Adjustable camera-collimator angle 2.73m
(9.0ft)
2.73m
(9.0ft)
Weight:
5500 kg
(12100
lb)5.23m
(17.2ft)
• Transmissive design
• Panchromatic collimator– Beam ~270mm
– 7.4’ diameter field of view
• Dichroic to split beam– Blue- and red-optimized
cameras
– Articulated arms for VPH grating use
• Detector format: 8k x 12k, 15μm pixels
• Image quality linked to MANIFEST integration– Goal: 80% EE at 0.15 arcsec
Optical design
Blue camera optical design
Blue camera+panchromatic collimator
Optomechanical
design
• Structural elements– Interface to telescope
– Flexure compensation
• Numerous ~300mm class lenses– Lens barrels and cells
design
• Mechanisms– Slit mask interchange
– Camera/collimator angle articulation
– Grating/filter selector
– Shutter
– Flexure compensation
Collimator
Dichroic
Grating
& Filter
Blue Camera
Red Camera
Grating
& Filter
CaF2
CaF2PSK
3
PSK
3
PSK
3
FPL5
1
FPL5
1Silica
SilicaShutt
er
LN2
Dewar
1378mm
450mm
2 x 3
Array of
4k2 CCDs
MANIFEST coordination
• Ultimately GMACS will be used with MANIFEST fiber feed
• Allows multi-object observations over full corrected 20 arcminute diameter field (~300 arcmin2 field)
• Re-mapping of slit to allow higher resolution – GMACS resolution up to
R~15000
– Higher resolution means more objects fit in focal plane
• Better ability to observe transients in real time with repositionable fibers
MANIFEST fibers positioned with Starbugs:
GMACS design
Many more details in
2016 (and soon 2018)
SPIE papers:
instrumentation.tamu.edu
GMACS Science DriversScience Case constraints
Time-domain science High rel. precision/repeatability/efficiency; large simultaneous
wavelength coverage
Brown dwarf/exoplanet
atmospheres (weather)
5’ FOV, blueward of JWST wavelength coverage. High stability for
transit spectroscopy.
Star/Star Cluster ages <2 Å resolution at Li 6708Å for age measurements; blue coverage
(Ca HK)
YSO accretion rates simultaneous coverage of Balmer lines/break (365-656 nm)
Dwarf Galaxy dynamics Coverage of CaT (850 nm, R~5000); 3 km/s velocity precision, high
stability. 20’ FOV preferable
Stellar Abundances R~5000, blue/red wavelength coverage (370-540 nm; CaT 850 nm)
Redshift surveys
(LSST, DES follow-up)
High multiplexing, slitlength requirement: source density will be
~50-60 arcmin-2. FOV as large as possible. Large simultaneous
wavelength coverage to improve efficiency.
Galaxy assembly,
IGM/CGM studies
R~3000 and redder wavelength coverage for absorption line
studies of z > 1 galaxies.
Properties of Galaxies
during Reionization
Very red coverage (>900 nm for Ly-α at z > 6.5), higher resolution
and high multiplexing/FOV helpful (~0.5-1 source/arcmin2)
GMACS Science DriversScience Case constraints
Time-domain science High rel. precision/repeatability/efficiency; large simultaneous
wavelength coverage
Brown dwarf/exoplanet
atmospheres (weather)
5’ FOV, blueward of JWST wavelength coverage. High stability for
transit spectroscopy.
Star/Star Cluster ages <2 Å resolution at Li 6708Å for age measurements; blue coverage
(Ca HK)
YSO accretion rates simultaneous coverage of Balmer lines/break (365-656 nm)
Dwarf Galaxy dynamics Coverage of CaT (850 nm, R~5000); 3 km/s velocity precision, high
stability. 20’ FOV preferable
Stellar Abundances R~5000, blue/red wavelength coverage (370-540 nm; CaT 850 nm)
Redshift surveys
(LSST, DES follow-up)
High multiplexing, slitlength requirement: source density will be
~50-60 arcmin-2. FOV as large as possible. Large simultaneous
wavelength coverage to improve efficiency.
Galaxy assembly,
IGM/CGM studies
R~3000 and redder wavelength coverage for absorption line
studies of z > 1 galaxies.
Properties of Galaxies
during Reionization
Very red coverage (>900 nm for Ly-α at z > 6.5), higher resolution
and high multiplexing/FOV helpful (~0.5-1 source/arcmin2)
GMACS will be able to take a spectrum
of any object imaged by LSST
SnowPAC2018: Roadmaps to
Wide Field Southern Spectroscopic Surveys
In the landscape of future LSST (even DES) spectroscopic followup, there is a lot missing:
• Aperture
• Hemisphere
• The future
The future of wide field survey spectroscopy, adapted from
Jeff Newman. Disclaimer: dates are rough and preliminary.
GMACS science:
Thinking outside the box
With ~100 nights, GMACS can
• Fully map Milky Way halo by measuring velocities and rough metallicities of all stars in known halo substructures (UFDs, streams, etc.)
• Spectroscopically train photometric redshifts to enhance DETF FOM (Newman Method)
• Measure the mass of the neutrino by measuring galaxy power spectrum at z > 2.5
With rapid response capability, GMACS
• Is uniquely able to followup any LSST faint transient
• Can acquire transient observations at the same time as primary science observations
Possibilities are numerous, but only with appropriate coordination between partners/users
Thank you!