Donghui Jeong The Pennsylvania State University

18 August 2014, Cosmic Voids in the Next Generation of Galaxy Surveys @ CCAPP, OSU

HETDEX (Hobby-Eberly Telescope Dark Energy eXperiment)

HETDEX Science Meeting May 2014

Summary

•  There is a lot of overlap between “Telescope”, “VIRUS”, and “DEX” commissioning

•  Definitions will matter –  We don’t want the HETDEX time allocation to be charged for activities

that would be necessary in any case to commission VIRUS –  There are grey areas

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UT Austin Gary Hill (PI)

Karl Gebhardt (PS) Herman Kriel (PM)

John Booth Barbara Castanheira

Taylor Chonis Anita Cochran

Niv Drory Steven Finkelstein

John Good Shardha Jogee David Lambert Hanshin Lee

Phillip McQueen Stephen Odewahn

Dave Perry Chuck Ramiller Richard Savage

Mathew Shethrone Mimi Song Trey Taylor Sarah Tuttle Brian Vattiat

MPE/USM Ralf Bender

Maximilian Fabricius Claus Goessl Ulrich Hopp

Francesco Montesano Ariel Sanchez

Jan Snigula Jochen Weller

!

Penn State *Nishant Agarwal

Niel Brandt Robin Ciardullo Henry Gebhardt Garyl Gronwall Donghui Jeong

Yuexing Li Suvrath Mahadevan

Ana Matkovic Larry Ramsey

Donald Schneider Mike Siegel

Jason Wright

TAMU Darren DePoy Lucas Macri

Jennifer Marshall Casey Papovich

Jean-Philippe Rheault Nicholas Suntzeff

Vy Tran Lifan Wang

!

AIP Luz Marina Cairos Barreto

Roloef de Jong Isabelle Gavignaud

Roger Haynes Carolina Kehrig Andreas Kelz Volker Muller Martin Roth

Matthias Steinmetz Christian Tapken

Lutz Wisotzki

MPA Chi-Ting Chiang Eiichiro Komatsu Philipp Wullstein

!

Other Institutes Lei Hao (SAO)

Carlos Allende Prieto (IAC) Jens Neimeyer (Gottingen)

Wolfram Kollatschny (Gottingen)

Eric Gawiser (Rutgers) Viviana Acquaviva (CUNY)

Povilas Palunas (LCO) Alex Fry (Washington) John Feldmeier (YSU)

Jeremy Murphy (Princeton) Jenny Greene (Princeton)

Guillermo Blanck (Carnegie)

**This list comes from the HETDEX wiki page, which may, unfortunately, miss some of our valuable collaborators/friends.

What is HETDEX?• Hobby-Eberly Telescope Dark Energy Experiment

(HETDEX) is a galaxy survey with unique properties.

• The first blind spectroscopic large-scale structure survey

• We do not pre-select objects; objects are emission-line selected; huge discovery potential

• The first 10 Gpc3-class survey at high z [1.9<z<3.5] with sufficient number density

• The previous big surveys (2dF, SDSS, WiggleZ, etc) were all done at z<1

HETDEX, at a glance• In many ways, HETDEX is a Texas-style experiment:

• Q. How big is a survey telescope? A. 10m

• Q. Whose telescope is that? A. Ours

• Q. How many spectra do you take per one exposure? A. About 35K spectra – at once

• Q. Are you not wasting lots of fibers? A. Yes we are, but so what? Besides, this is the only way you can find anything truly new!

Hobby-Eberly Telescope Dark Energy Experiment (HETDEX)

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Use 10-m HET to map the universe using 0.8M Lyman-alpha emitting galaxies

in z=1.9–3.5

Many, MANY, spectra• HETDEX will use the newly-built integral field unit

spectrographs called “VIRUS*” (Hill et al.)

• We will build and put 78 units on the focal plane

• Each unit has 448 fibers

• Each unit feeds two spectrographs

• Therefore, VIRUS will have 35K fibers in the sky at once (Texas size!)

*VIRUS = Visible Integral-field Replicable Unit Spectrograph

IFUs fabricated at AIP Potsdam

Looong fibers! (Each fiber sees 1.5”)

Put into cables...

One IFU feeds two spec.

448 fibers per IFU

A test IFU being lit

Prime Focus Instrument

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Tracker (“eye balls”)

Tracker (“eye balls”)This is the real one!! (Feb. 24, 2014)

HETDEX Footprint

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Spring Field : 294+126 ☐°

Fall Field: 140+84 ☐°

Total volume = 9 + 4 [Gpc3]

~4000 shots w/ 22’ FoV

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Observed galaxy in the focal plane

~450 fibers with 1.5’’ diameter

A mock field centered around

RA=193, DEC=53 (ΔRA=ΔDec=2°)

~1/5 filling

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east track west track

What do we detect?

• λ=350–550nm with the resolving power of R~700 down to a flux sensitivity of a few x 10–17 erg/cm2/s (continuum AB mag~22) gives us:

• ~0.8M Lyman-alpha emitting galaxies at 1.9<z<3.5

• 1/10 of them would be AGNs

• ~2M [OII] emitting galaxies

• ...and lots of other stuff (like white dwarfs)

One way to impress you

• So far, about ~1000 Lyman-alpha emitting galaxies have been discovered over the last decade

• These are interesting objects – relatively low-mass, low-dust, star-forming galaxies

• We will detect that many Lyman-alpha emitting galaxies within the first 2 hours of the HETDEX survey

Yes, we do detect LAEs!

• We have been using the Mitchell spectrograph on the 2.7-m Harlan Smith telescope over 111 nights, detecting 105 LAEs in 1.9<z<3.8 over 169 arcmin2.

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We also detect others• We have detected 397 emission-line galaxies over 169

arcmin2 from the HETDEX Pilot Survey on 2.7-m.

• Among these, 105 are LAEs; and the majority of the other objects are [OII] emitters at z<0.56.

• We discriminate between them using the Equivalent-Width (EW) cut at the rest-frame 20 angstroms (assuming LAEs).

• LAEs have larger EWs. With imaging data going down to ~25 mag in g or r, this cut eliminates ~99% of [OII] interlopers. We can do science with [OII] too!

What can HETDEX do?• Primary goal: to detect the influence of dark energy on the

expansion rate at z~2 directly, even if it is a cosmological constant

• Use both Baryon Acoustic Oscillation and the full shape and anisotropy (more later)

• Supernova cannot reach z>2: a new territory

• In addition, we can address many other cosmological and astrophysical issues.

Other “Prime” Goals• Is the observable universe really flat?

• We can improve upon the current limit on Ωcurvature by a factor of 10 – to reach Ωcurvature ~ 10–3 level.

• How large is the neutrino mass?

• We can detect the neutrino mass if the total mass is greater than about 0.13 eV (3σ) [currently σΣmν ~ 0.1eV, Beutler+2014]

• The absolute lower limit to the total mass from neutrino experiments is the total mass > 0.05 eV. Not so far away!

Other “Prime” Goals• Is inflation responsible to generate seed fluctuation?

• We can measure primordial non-Gaussianity better than the Planck satellite with ΔfNL = 3.65!

• What is the shape of primordial power spectrum?

• Combining to Planck, HETDEX will measure Δns=0.025!

• By detecting ns at two different scales, we can also measure Δαs=0.05.

“Sub-prime” Goals

• Being the first blind spectroscopic survey, HETDEX is expected to find unexpected objects.

• Also, we expect to have an unbiased catalog of white dwarfs; metal-poor stars; distant clusters of galaxies; etc

Voids in HETDEX LAEs

• Two challenges to detect voids in HETDEX

• Gaps between IFU spectrographs (dictated by pattern)

• ~1 Mpc/h gap for each ~2 Mpc/h

• A hole at the center of size 5 x 7 Mpc2/h2

• Smaller density fluctuations at high redshifts (1.9 < z < 3.5)

• D(z=[1.9~3.5]) ~ 1/[2.3~3.5] x D(z=0) ➔ Need 3 x more significance than local universe

Voids in HETDEX OIIS

• It may be better to consider OII-3727 emitters

• Gaps between IFU spectrographs (dictated by pattern)

• ~0.3 Mpc/h gap for each ~0.6 Mpc/h

• A hole at the center of size 1.5 x 3.5 Mpc2/h2

• Larger number density 2 Million objects over 0.4 Gpc3

• nOII ~ 0.015 [Mpc/h]-3 (c.f. nLAEs ~ 2x10-4 [Mpc/h]-3)

Conclusion

• HETDEX will start the main survey in the next year (Fall 2015)

• HETDEX is the first blind spectroscopic survey with a large (~10 Gpc3) volume

• We expect to detect ~0.8M Lyman-alpha emitting galaxies to map the large-scale structure in an unexplored territory of z=1.9–3.5

• Target: detection of dark energy at 1.9<z<3.5

• also measure the neutrino mass; curvature; primordial power spectrum, non-Gaussianity, and (possibly) detect Cosmic Voids!