HETDEX Spectrographs R&D for DESpec Jennifer Marshall Texas A&M University

University of Texas: Josh Adams Guillermo Blanc John Booth Mark Cornell Taylor Chonis Karl Gebhardt Jenny Greene Gary Hill Shardha Jogee Eiichiro Komatsu Hanshin Lee Phillip MacQueen Jeremy Murphy Steve Odewahn Marc Rafal Richard Savage Matthew Shetrone Masatoshi Shoji Sarah Tuttle Brian Vattiat MPE/USM: Ralf Bender Maximillian Fabricius Frank Grupp Ulrich Hopp Martin Landriau Ariel Sanchez Jan Snigula Jochen Weller Houri Ziaeepour Penn State University: Robin Ciardullo Caryl Gronwall Ana Matkovic Larry Ramsey Don Schneider AIP: Svend Bauer Roelof de Jong Roger Hanes Andreas Kelz Volker Mueller William Rambold Martin Roth Mathias Steinmetz Christian Tapken Lutz Wisotzki Texas A&M: Richard Allen Darren DePoy Steven Finkelstein Jennifer Marshall Casey Papovich Travis Prochaska Nicolas Suntzeff Vy Tran HETDEX Consortium Other Institutions: Carlos Allende-Prieto (IAC) Viviana Aquaviva (Rutgers) Niv Drory (IAUNAM) Eric Gawiser (Rutgers) Lei Hao (SHAO) Donghui Jeong (CIT) Jens Niemeyer (IAG) Povilas Palunas (LCO) Mike Smith (U Wisconsin)

HETDEX science goals Hobby-Eberly Telescope Dark Energy Experiment –Aims to constrain expansion history over 1.9 < z < 3.5 –Direct detection of dark energy at z~2.5 even if it’s a cosmological constant –0.1% constraint on curvature –Aims to tell if dark energy evolves Measurement of expansion rate and angular diameter distance at z~2.4 to determine if there is any evolution of dark energy Tracers are Ly-α emitting galaxies –Numerous, easily detected with integral field spectrograph

HETDEX observing plan Blind survey with 150+ integral field spectrographs, known as VIRUS –33,600 spectra per exposure –350 – 550 nm –Line flux limit 3.5e-17 and m AB ~ sq. deg. area survey will contain spectroscopy of: –0.8 million LAEs in 9 cubic Gpc volume 1.9 < z < 3.5 –1 million [OII] emitters z < 0.48 –0.4 million other galaxies –0.25 million stars –2000 galaxy clusters –7000 QSOs z < 3.5 –20,000 NVSS radio sources

IFU 448 fibers 50 x 50 sq. arcsec 1.5” fiber dia Observing footprint of the HETDEX Survey HETDEX Survey covers 420 square degrees 22 arcmin field of view 33,600 spectra at a time

HETDEX is comprised of: Major telescope upgrade –Replace entire top end of telescope New instrument, VIRUS –150+ fiber-fed unit spectrographs HETDEX observations Software/data analysis –Data will be public

Telescope improvements Wide Field Upgrade of HET to 22 arcmin FoV and 10 m pupil

Fiber bundles Nine IFUs have been delivered to AIP to qualify vendors and evaluate the production design Murphy et al., 2008, SPIE ; Soukup et al., 2010, SPIE Kelz et al., 2006, SPIE ; IFU output IFU input

VIRUS Visible Integral-field Replicable Unit Spectrograph (VIRUS) –The first highly-replicated instrument in optical astronomy –150+ channel fiber-fed Integral Field Spectrograph placing >33, ” dia fibers on sky – nm coverage and R~700 HET will be transformed into a powerful survey instrument

VIRUS spectrographs Optical design based on VIRUS-P, the prototype spectrograph now in use at McDonald 107” telescope Production design currently being finalized and prototyped

VIRUS spectrographs Simple design –Single reflection spherical collimator –Schmidt camera Two lenses + one spherical mirror –VPH grating High throughput Unit spectrographs packaged in pairs

VIRUS spectrographs 224 spectra per unit spectrograph Data reduction pipeline finalized “VACCINE” at UT “CURE” at MPE

Texas A&M’s role in HETDEX Participate in optical and mechanical design of VIRUS Fabrication and procurement of VIRUS components Assemble VIRUS unit spectrographs Optically align instruments in lab Ship to McDonald

HETDEX+VIRUS specs Wavelength –350 – 550 nm Resolution –R~700 Sensitivity –Line flux limit 3.5e-17 and m AB ~22

Flexibility of VIRUS design VIRUS design is adaptable to almost any fiber-fed spectrograph system –Easy to change resolution, wavelength range, etc. with simple redesigns Has already been used as basis of new spectrograph design –LRS2

LRS2 concept LRS2 will be the first VIRUS adaptation –Consists of two unit pairs, LRS2-B (350 – 650 nm) and LRS2-R (650 – 1100 nm) –R~1800 Work required for LRS2-R: –Replace grating with grism dispersers –Customize optical coatings

DESpec from VIRUS? Same could be done for DESpec –Change grating –Reoptimize coatings –Refractive camera?

Possible DESpec unit spectrograph specs nm coverage using DES 2Kx4K CCD Roughly 4 pixels per resolution element (R~1765 at 775nm; 0.1nm/pixel dispersion) Refractive camera? –Larger detector obscures more light in a reflective design

Possible DESpec unit spectrograph specs Want fibers in focal plane –Assuming ~1 sq. cm per fiber fibers per unit spectrograph Need ~15 unit spectrographs

Estimated cost of DESpec spectrographs Need 15 units for fibers VIRUS unit cost is ~$100K –Without detector systems Total cost for DESpec unit spectrographs after redesign not expected to exceed $200K Total cost: $3M

Work required to design DESpec New optical design for refractive camera Mechanical redesign of camera Mechanical design of instrument mounting scheme on telescope Cooling system redesign

Work required to design DESpec A&M+UT group would need about 2 years of engineering effort for redesign A&M could assemble and test spectrographs in ~2 years –Lots of experience from VIRUS! These are only estimates; will require more careful schedule/planning

Summary VIRUS design could be easily and relatively cheaply adapted to DESpec spectrographs Would need ~15 spectrographs Cost ~$3M 3-4 years of effort in redesign and assembly