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

University of Texas: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

Penn State University:Robin Ciardullo

Caryl Gronwall

Ana Matkovic

Larry Ramsey

Don Schneider

AIP:Svend Bauer

Roelof de Jong

Roger Haynes

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

Lifan Wang

HETDEX Consortium

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)

The HETDEX ProjectHETDEX is a spectroscopic survey to measure the evolution of Dark Energy via the Power Spectrum of Ly 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.

100”

15.6’

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

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 feedVIRUS IFUs

The HETDEX Survey

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

3

5

10

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 ~ 300 deg2 with a filling factor of 1 in 5. The primary field is in the north, to take advantage of the HET tracking.

HETDEX is a blind spectroscopic survey. Most of the fibers will fall on blank sky. But some will fall on Ly emitters (and other galaxies and stars).

The Spectra

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)

JJ

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

ob

ject

s

Baldry et al. 2010

Many objects will be single emission-line detections. Are they Ly Emitters or foreground [O II] 3727 emitters?

The Need for Imaging

Ly 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.)

Measuring Equivalent Width

HETDEX will classify an object as a Ly emitter if it has a rest-frame equivalent width greater than w0 > 20 Å. So

€

FlineFcont

> (1+ z) w0

Since the limiting line-flux of HETDEX is known, this defines the required depth for the continuum detection:

€

mAB = 25.09 − 2.5logFline

3.5 ×10−17ergs cm-2s-1

⎛

⎝ ⎜

⎞

⎠ ⎟+ 2.5log

w0

20Å

⎛

⎝ ⎜

⎞

⎠ ⎟− 2.5log

λ

4750Å

⎛

⎝ ⎜

⎞

⎠ ⎟

This is far below the limit of VIRUS. Comparison images are needed to help discriminate [O II] from Ly

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

3 DE detection

5 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 Ly emitting galaxies between 1.9 < z < 3.5

•1 million [O II] 3727 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!

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 Ly 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/