HETDEX Spectrographs R&D for DESpec

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

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

3. 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

4. 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 mAB~22 • 420 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

5. 100” Observing footprint of the HETDEX Survey 1.5” fiber dia 22 arcmin field of view 33,600 spectra at a time IFU 448 fibers 50 x 50 sq. arcsec HETDEX Survey covers 420square degrees

6. 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

7. Fiber bundles Nine IFUs have been delivered to AIP to qualify vendors and evaluate the production design IFU input IFU output Kelz et al., 2006, SPIE 6273-121; Murphy et al., 2008, SPIE 7018-104; Soukup et al., 2010, SPIE 7735-180

8. VIRUS • Visible Integral-field Replicable Unit Spectrograph (VIRUS) • The first highly-replicated instrument in optical astronomy • 150+ channel fiber-fed Integral Field Spectrograph placing >33,000 1.5” dia fibers on sky • 350-550 nm coverage and R~700 • HET will be transformed into a powerful survey instrument

9. 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

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

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

12. 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

13. HETDEX+VIRUS specs • Wavelength • 350 – 550 nm • Resolution • R~700 • Sensitivity • Line flux limit 3.5e-17 and mAB~22

14. 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

15. 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

16. DESpec from VIRUS? • Same could be done for DESpec • Change grating • Reoptimize coatings • Refractive camera?

17. Possible DESpec unit spectrograph specs • 550-1000nm coverage using DES 2Kx4K CCD • Roughly 4 pixels per resolution element (R~1765 at 775nm; 0.1nm/pixeldispersion) • Refractive camera? • Larger detector obscures more light in a reflective design

18. Possible DESpec unit spectrograph specs • Want 3000-4000 fibers in focal plane • Assuming ~1 sq. cm per fiber • 200-250 fibers per unit spectrograph • Need ~15 unit spectrographs

19. Estimated cost of DESpec spectrographs • Need 15 units for 3000-4000 fibers • VIRUS unit cost is ~$100K • Without detector systems • Total cost for DESpecunit spectrographs after redesign not expected to exceed $200K • Total cost: $3M

20. 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

21. 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

22. 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