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!