1. Observing Cosmic Dawn using the NRO Telescopes
Sangeeta Malhotra &
James Rhoads
4 September 2012
Malhotra & Rhoads

2. Three Pillars for NRO-WFIRST
Decadal survey’s 3 science objectives:
Cosmic Dawn
New Worlds
Physics of the Universe
4 September 2012
Malhotra & Rhoads

3. Three Pillars for NRO-WFIRST
Decadal survey’s 3 science objectives:
Cosmic Dawn
New Worlds: Microlensing; now perhaps direct imaging also.
Physics of the Universe: Dark energy from supernovae, weak lensing, baryon acoustic oscillations
4 September 2012
Malhotra & Rhoads

4. Three Pillars for NRO-WFIRST
Decadal survey’s 3 science objectives:
Cosmic Dawn: Finding the first galaxies, and characterizing reionization with Lyman alpha galaxies.
New Worlds: Microlensing; now perhaps direct imaging also.
Physics of the Universe: Dark energy from supernovae, weak lensing, baryon acoustic oscillations
4 September 2012
Malhotra & Rhoads

5. Why we study reionization
The first time that collapsed structures (stars, black holes) had a global impact on the rest of the universe, and
The last time that a typical baryon did anything exciting.
4 September 2012
Malhotra & Rhoads

6. Ways to Study Reionization
Look for the ionizing sources, estimate Lion, and compare to requirements for (re)ionization
Uncertainties: fesc, clumping, IMF, dust, etc.
Lyman break galaxies with ACS slitless grism redshifts from HST-GRAPES program.
STScI news release STScI ; see also Malhotra et al 2005.
4 September 2012
Malhotra & Rhoads

7. Ways to Study Reionization
Look for the ionizing sources, estimate Lion, and compare to requirements for (re)ionization
Uncertainties: fesc, clumping, IMF, dust, etc.
Look for evidence of neutral gas and/or evidence of free electrons
More direct.
NRO-WFIRST can do both!
Mellema et al, reionization simulation
4 September 2012
Malhotra & Rhoads

8. Cosmological Reionization: Physics behind the Tools
Electron scattering after reionization <=> CMB Polarization
HI 21cm emission before reionization <=> meter-wave radio astronomy
Resonant scattering by HI before reionization <=> Gunn-Peterson test, Lyman alpha based tests, etc.
4 September 2012
Malhotra & Rhoads

9. Lyman- Reionization Tests
Key point:
Lyman- photons scattered in neutral gas.
Lyman- emitting galaxies not seen as compact sources prior to reionization.
4 September 2012
Malhotra & Rhoads

10. Lyman-α in an Ionized IGM
Radiative transfer of Lyman-α and continuum photons in an ionized intergalactic medium.
Ionized IGM
Continuum Photons To
Young starburst
Observer
Lyman α photons
4 September 2012
Malhotra & Rhoads

11. Lyman-α in a Neutral IGM
Radiative transfer of Lyman-α and continuum photons in a neutral intergalactic medium.
Neutral IGM
Continuum Photons To
Young starburst
Observer
(Theory: Miralda-Escude 1998; Miralda-Escude & Rees 1998;
Haiman & Spaans 1999; Loeb & Rybicki 1999;
Observation: Rhoads & Malhotra 2001, Hu et al 2002, Malhotra & Rhoads 2004, Stern et al 2005, Kashikawa et al 2006, Malhotra & Rhoads 2006, Iye et al 2006, Ouchi et al 2010, Hu et al 2010, Kashikawa et al 2011…)
Lyman α photons
4 September 2012
Malhotra & Rhoads

12. Lyman α : Neutral IGM + Ionized Bubble
Continuum Photons
H II
region To
Young starburst
Observer
Lyman α photons
Some flux comes through if the starburst is in a substantial HII region (Madau & Rees 1999; Rhoads & Malhotra 2001; Haiman 2002).
The red wing of the line is less suppressed (Haiman 2002).
Gas motions alter Ly-α radiative transfer (Santos 2004; Dijkstra 2011).
4 September 2012
Malhotra & Rhoads

13. Charting Reionization
Constraints on neutral fraction with redshift.
Abbreviations:
RM01 Rhoads & Malhotra 2001
MR04: Malhotra & Rhoads 2004; St05: Stern et al 2005
Ou10: Ouchi et al 2010; Ka11: Kashikawa et al 2011
Mo11: Mortlock et al 2011, B11: Bolton et al 2011
Sch11:Schenker et al; P11: Pentericci; Ono11: Ono et al
NRO-WFIRST Ly
4 September 2012
Malhotra & Rhoads

14. What can NRO-WFIRST do? Blind slitless search for Lyman alpha:
Sensitive for 7 < z < 15 or so
Redshift range of greatest interest 8-12 or so.
Strawman: 1 sq. degree, ~ hours of integration with grism …
Expect ~ 900 Lyman  galaxies at 8<z<9 per square degree
This could either be an “HDF” level program, or a set of calibration fields re-observed throughout BAO survey.
Round out the numbers for other redshifts during the flight
4 September 2012
Malhotra & Rhoads

15. Lyman- Tests with NRO-WFIRST
Expected numbers in z = 1 bins.
Based on Ouchi 2010 LF at z=6.5.
(Kashikawa et al 11 similar; Hu et al 10 slightly below)
The neutral IGM should truncate this someplace.
4 September 2012
Malhotra & Rhoads

16. Bubbles?
Bubbles of ionized gas in the neutral medium are expected to be 1 pMpc ==> 4’ or so at z ~ 9 ==> fit easily in FoV.
Number of sources per bubble is modest, so we may not map bubbles at the anticipated depth
Reionization signal should come through in clustering statistics.
Furlanetto et al 06, McQuinn et al 07
4 September 2012
Malhotra & Rhoads

17. Bubbles? Figure from Tilvi et al 2009
Mellema et al, reionization simulation
4 September 2012
Malhotra & Rhoads

18. Mapping Ionized and Neutral Gas with Lyman Alpha Galaxies
We can map the distribution of Lyman alpha galaxies over large scales…
This may map out bubbles of ionized gas in the overlap phase of reionization.
4 September 2012
Malhotra & Rhoads

19. Mapping Ionized and Neutral Gas with Lyman Alpha Galaxies
A control sample of Lyman break selected galaxies will be useful (green dots, below).
4 September 2012
Malhotra & Rhoads

20. Equivalent Width Evolution
Identify Lyman Break samples,
Study their Lyman alpha lines.
Do we see a marked decrease in EW [or in p(EW > EW0) ] with increasing z?
See Stark et al 2010, Schenker et al 2011, Ono et al 2011, Pentericci et al 2011.
Issue: the denominator is difficult to measure at present
need N(EW > EW0) / N(total).
N(total) depends on photo-z being well understood
Easy with an NRO-WFIRST (especially if we keep both low- and high-R grisms)
4 September 2012
Malhotra & Rhoads

21. NRO-WFIRST Lyman Break Galaxies
Continuum selection… Y-dropouts (secure!), J-dropouts (less so).
Magnitude should be easy in 1-3 days of observing time.
Very large samples available.
Spec limits: R=75 grism gives AB=25 in 2 hours with s/n=5, and AB=27 in 75 hours
R=600: 2.25 magnitudes worse; don’t count on it for LBG continuum detections at z>7.
4 September 2012
Malhotra & Rhoads

22. LBGs in the Supernova Survey
Assume 0.45 years net integration over 6 sq. degrees and 3 filters.
That is 240 ksec / filter / pixel
Like an HST WFC3-IR survey of 80 orbits/filter, 3 filters, 4300 WFC3-IR fields
I.e. a 1 mega-orbit HST program!
Should get over 105 LBGs at z ~ 8, scaling from Bouwens et al 2011.
So the LBG science becomes “systematic limited” too, in some sense.
4 September 2012
Malhotra & Rhoads

23. LBGs in the Supernova Survey
So the LBG science becomes “systematic limited” too, in some sense.
Y-dropouts: Work well.
Ionizing photon budget at z=8: Uncertainies will be dominated by fesc, etc.
J-dropouts: Need followup to confirm; all we’ll know is a red J-H color.*
If this J-drop followup is not from WFIRST, the ultimate sample size will be much smaller, set by the resources available for confirmation.
* (Of course if NRO-WFIRST can do Ks, the J drops are more secure, and instead it’s the H-drops that need the intensive followup.)
4 September 2012
Malhotra & Rhoads

24. LBGs in the Supernova Survey
What if the supernova survey is run “DESTINY” style, using an R=75 grism for the whole effort?
Supernova monitoring -- should be workable; like DESTINY w. a bigger mirror.
Binning it up to fake a broad band light curve: cost is about 1.6 mag of light curve depth.
Comparable to the gain by going from 1.2 to 2.4m, for point sources.
Spinoff science: Excellent LBG survey: (spectroscopic conf. of every LBG down to L*)
Interesting for high-EW Lyman- too.
IFU vs Grism: SNe * 1000 sec --> 1.9 Msec
Grism: R=75, 1.5 hours, get to AB=24.8 at s/n=5 per res element or so.
4 September 2012
Malhotra & Rhoads

25. Quasars: How faint? How many?
At least comparable to Euclid
Euclid: ~ 50 QSO at z>8 according to the Red Book,
Euclid and SDT-WFIRST: 1300 at z>7 and 22 at z>10 according to WFIRST SDT final report.
Ought to be 3x better than that!
Followup desirable to learn about reionization.
Should look more at the QSO game: What can be done with 10 quasars at z=9, or 50 at z=8? Is R=600 good enough to get any reionization science out of them?
4 September 2012
Malhotra & Rhoads

26. GRB Afterglow Spectra? GRB afterglows have clean power law spectra,
Look for the Ly damping wing of neutral IGM (see Totani et al 2006; Mesinger & Furlanetto 2008).
Want R ~ spectroscopy.
The “BAO” grism would suffice… s/n ~ 6 at AB=21 in 300 sec.
An IFU could be even better, if R is enough.
Operational Issues:
Response time?
Field of Regard?
Scientific issues:
Sample size in 5-10 year NRO-WFIRST mission lifetime? (Depends on sources of triggers.)
4 September 2012
Malhotra & Rhoads

27. Say, can you see O? WFIRST at 1.3m, cold mirror: zmax = 2.7
NRO-WFIRST, 2.4m, warmer: zmax = 2.0
The Fix: Use [OIII] lines as well as H lines for BAO.
1.2 < z[OIII] < 3.0 for 1.1 <  < 2.0m.
The larger aperture should balance somewhat weaker lines out to z=2.7 …
And the [OIII] line is not much weaker than H.
4 September 2012
Malhotra & Rhoads

28. H, [OIII], [OII]
Empirical number-flux relation from PEARS slitless spectrscopic survey, drawn from fig. 4 of Pirzkal et al 2012.
[OIII] sample just 2x fainter than H sample, despite greater distance.
[OII] another 2x fainter.
Based on 1100 lines in 900 galaxies.
Pirzkal et al fig. 4
4 September 2012
Malhotra & Rhoads

29. H, [OIII], [OII]
Luminosity functions from PEARS slitless spectrscopic survey, drawn from fig. 7-9 of Pirzkal et al 2012.
Full completeness simulations folded into the derivation of LF from number-flux relation.
Uncorrected for redshift evolution.
Pirzkal et al fig. 7, 8, 9
4 September 2012
Malhotra & Rhoads

30. Say, you can see O!
Predicted [OIII] number counts for both NRO-WFIRST and Euclid, compared to other BAO studies.
[OIII]: Based on Pirzkal et al [OIII] LF, adjusted for cosmic SFRD evolution
Other stuff: Straight from the Euclid Red Book (Laureijs et al).
4 September 2012
Malhotra & Rhoads

31. GO Programs for Cosmic Dawn
Many possibilities.
Ultra-deep field - imaging
Ultra-deep field - grism
High-z object search in/around lensing clusters
Coordinated mapping with 21cm EoR experiments
4 September 2012
Malhotra & Rhoads

32. NRO, without presuming WFIRST
We win big if we have enough IR pixels behind a 2.4m mirror and deployed in a sensible configuration-- whether that configuration is exactly WFIRST or not.
Tunable bandpass imaging?
Microshutter / micromirror arrays?
A  for “ErinCam” NRO-WFIRST design is 20x JWST NIRCAM, 36x JWST NIRISS.
With a microshutter array, could we get comparable gains over JWST NIRSPEC?
K band …???
Filter wheels: Let’s have two (or more) wheels, in sequence.
4 September 2012
Malhotra & Rhoads

33. Conclusions:
An NRO-WFIRST telescope can advance the Decadal Survey’s goal of studying Cosmic Dawn:
Using capabilities that complement JWST
And that cannot be approached by other facilities, present or planned.
Key points:
Lyman  galaxies from a deep survey of a few sq. deg with R=600 slitless spectra.
Quasars from the wide area surveys
LBGs from deep surveys, followed up with spectra if possible.
Reward: A detailed chronicle of reionization and galaxy formation up to z ~ 12.
4 September 2012
Malhotra & Rhoads