The Hobby-Eberly Telescope Dark Energy Experiment Caryl Gronwall, Robin Ciardullo (PSU), Karl Gebhardt, Gary Hill, Eiichiro Komatsu (UT), Niv Drory (UNAM), & the HETDEX Team

HETDEX Consortium University of Texas: MPE/USM: Texas A&M: AIP: Josh Adams Guillermo Blanc John Booth Mark Cornell Taylor Chonis Karl Gebhardt (PS) Jenny Greene Gary Hill (PI) Eiichiro Komatsu Hanshin Lee Phillip MacQueen Jeremy Murphy Steve Odewahn Marc Rafal (PM) 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 Texas A&M: Richard Allen Darren DePoy Steven Finkelstein Jennifer Marshall Casey Papovich Travis Prochaska Nicolas Suntzeff Vy Tran Lifan Wang AIP: Svend Bauer Roelof de Jong Roger Haynes Andreas Kelz Volker Mueller William Rambold Martin Roth Mathias Steinmetz Christian Tapken Lutz Wisotzki Others: Carlos Allende-Prieto (IAC) Viviana Aquaviva (Rutgers) Niv Drory (UNAM) Eric Gawiser (Rutgers) Lei Hao (SHAO) Donghui Jeong (Caltech) Jens Niemeyer (IAG) Povilas Palunas (LCO) Penn State University: Robin Ciardullo Caryl Gronwall Ana Matkovic Larry Ramsey Don Schneider 2

The HETDEX Project HETDEX is a spectroscopic survey to measure the evolution of Dark Energy via the Power Spectrum of Lya Emitters between 1.9 < z < 3.5. The instrument for this project is VIRUS, the Visible Integral-field Replicable Unit Spectrographs. HETDEX is a 3-year Stage III DE experiment, which will begin in Fall 2012. It is extendable to 5 years (Stage IV). Total budget = $37 Million including HET upgrade. Fully funded via private donations, institutions and the NSF.

The Instrument: VIRUS VIRUS is an integral field spectrograph, consisting of 224 1.5″ diameter fibers feeding an R ~ 750 grating covering 3500 Å < l < 5500 Å. This instrument is then cloned. 75 IFUs feed 150 spectrographs to generate 33,600 spectra per observation! 100” 15.6’

VIRUS field layout IFUs layout have a 1/4 fill factor over 22’ diameter field The central gap feeds other instruments (LRS, MRS, HRS) In addition to HETDEX, VIRUS will be observing in parallel with other programs. 100” 15.6’ LRS feed VIRUS IFUs

The HETDEX Survey The HETDEX survey will consist of 20 min exposure time per field, divided into 3 dithers. The (5s) survey limit is about R ~ 22 mag, or Fl ~ 3.5 × 10-17 ergs cm-2 s-1. 10s 5s 3s

The Survey Region HETDEX will survey ~ 300 deg2 with a filling factor of 1 in 5. The primary field is in the north, to take advantage of the HET tracking. There will also be a fall equatorial field -- 28 deg2 of which will be surveyed by Spitzer as part of the SHELA (Spitzer-HETDEX Large Area) survey.

The Survey Region HETDEX will survey ~ 420 deg2 with a filling factor of 1 in 7. The primary field is in the north, to take advantage of the HET’s slow track. A equatorial fall field will also be observed (likely with a higher fill-factor). Spitzer is surveying 28 deg2 of the fall region.

The Spectra HETDEX is a blind spectroscopic survey. Most of the fibers will fall on blank sky. But some will fall on Lya emitters (and other galaxies and stars). A 3 year pilot survey with the prototype IFU spectrograph (VIRUS-P) was completed last year, delivering proof-of-concept, and a database for the development of the software pipeline (CURE). (The latest software release is CURE: Treatment – 2). Adams et al. (2011)

J How Many Spectra??? HETDEX HETDEX will obtain spectra for > 2 million objects. Because the targets are not pre-selected, the density of survey observations is off-scale! HETDEX objects Baldry et al. 2010

The Need for Imaging Many objects will be single emission-line detections. Are they Lya Emitters or foreground [O II] l3727 emitters? Lya emitters at 1.9 < z < 3.5 generally have much larger equivalent width than [O II] emitters at z < 0.5. (Note that w = w0 (1 + z), so the difference is even larger due to redshift boosting.)

The Equivalent Width Cut Spectroscopic follow-up of z = 3.1 Lya emitters in the ECDF-S, (all selected to have EWobs > 80 Å via narrow-band photometry) shows that The brightest object (by far) is an [O II] emitter at z = 0.337 Half of the next 14 brightest objects (and 3 others) are x-ray sources (AGN) All remaining objects are confirmed Lya emitters at z = 3.1

Measuring Equivalent Width HETDEX will classify an object as a Lya emitter if it has a rest-frame equivalent width greater than w0 > 20 Å. So Since the limiting line-flux of HETDEX is known, this defines the required depth for the continuum detection: This is far below the limit of VIRUS. Comparison images are needed to help discriminate [O II] from Lya.

Goals and Timeline The HETDEX survey will begin next fall and take 3 years (1400 hours) to complete. It will Detect Dark Energy at z > 2 Measure curvature to 10-3 Measure H(z=2.8) to 0.9% Measure DA(z=2.8) to 0.9% Slightly improve w0 Greatly improve in w(z) Provide a database for a host of other programs  3s DE detection 5s DE detection  DETF FoM figure-of-merit of 170-250 (x 5 improvement over current experiments.)

Expected Database When completed, the HETDEX database will contain spectra for 4.2 × 108 spectra + additional spectra from parallel-mode observations 0.75 million Lya emitting galaxies between 1.9 < z < 3.5 1 million [O II] l3727 emitting galaxies with z < 0.5 0.4 million other galaxies 0.3 million Milky Way stars down to R ~ 22 2000 rich galaxy clusters (Abell class R > 1) ~104 Quasars (z < 3.5) + 105 AGN A bunch of asteroids, supernovae, intragroup PN, etc. Numbers increase by substantially with parallel observations!

… and many other projects! Additional Science In addition to the measurement of Dark Energy at z > 2, HETDEX will Obtain a measure of non-Gaussianity as good as Planck Generate the best measurement of the total neutrino mass Map out the cosmic web in emission Measure the efficiency of star-formation as a function of environment at z < 0.5 and 1.9 < z < 3.5 Measure the AGN-galaxy correlation function Map out nearby galaxy clusters Probe stellar populations at large galactocentric radii Identify extremely low metallicity stars … and many other projects!

Summary HETDEX will generate huge numbers of spectra in a 300 deg2 region of the northern sky. The experiment will: measure the evolution of Dark Energy to z ~ 3 by measuring the redshifts of 0.75 million Lya emitters with 1.9 < z < 3.5 obtain blue (< 5500 Å) spectra for >1 million other objects HETDEX starts next year, but obtaining complementary imaging is a challenge! http://www.hetdex.org/