1. The Dark Ages and Reionization with 21cm Aaron Parsons

2. z = 100 to 20 15 to 70 MHz z = 20 to 5 70 to 240 MHz

3. Why 21cm Cosmology Line Emission Optically thin Observable even into Dark Ages Directly probes redshift evolution Sensitive to Ly-α: Wouthuysen Field Effect X-ray/DM: Heating UV: Ionization Integrated measure of galactic properties includes low-mass tails bubble size breaks some degeneracies Complementary to CMB optical probes of galaxies other potential lines (e.g. CO, C+)

4. The (21cm) Frequency Axis CMB 21cm Measurements vs. frequency

5. k || kxkx kyky

6. First Generation Image-domain model subtraction not yet generating competitive limits LOFAR rumor: limits approaching PAPER-64 at low k samples many modes pairs well with auxiliary science data and processing intensive still resort to filtering/mode projection at the end

7. First Generation Visibility (delay-domain) filtering relies on spectrally smooth responses and short baselines labor saving devices: drift-scanning, redundancy limiting for auxiliary science

8. (Ali et al. 2015)

9. (Pober et al. 2015)

10. Second Generation Hydrogen Epoch of Reionization Array $2.1M under MSIP1 + external support = HERA-37 invited to apply to MSIP2 for HERA-352 based off of PAPER approach augments with US MWA team imaging

14. EOR Power Spectrum - Array Sensitivities* ✴ Updated 21 cm Experiment Sensitivites, J. Pober, HERA Memo #3, Table 2 (http://reionization.org/memos)reionization.org/memos Instrument AvoidanceSubtraction DriftTrackDriftTrack PAPER 1281.56-4.46- MWA 1280.660.862.503.15 LOFAR (core)0.701.907.4812.22 HERA 375.67-15.46- HERA 33138.75-111.69- MWA 2562.402.818.289.64 SKA1 Low21.2326.92139.07115.13

15. HERA Timeline 20152016201720182019202020212022 HERA-19 HERA- 37 HERA-61 HERA-127 HERA-331 SKA-Low Early Science MSIP2 proposal MSIP2 funding 2020 decadal MSIP2 ends HERA-III?

16. After HERA? What does the science demand? cross-correlations (CO, C+, EE, Ly-α, WFIRST) cosmology (more k-space inside wedge) higher order statistics & model fitting Bottom line: “imaging” (at some level) traditional synthesis imaging? Probably not.

17. Option 0 Dedicated “21cm only” Array extend HERA no viable omnibus funding line through NSF instead $2-3M/yr incremental packages cut corners Pros: incrementally fundable keeps the US 21cm community going Cons: no community growth leadership easily lost no other science supported hard to plan (always one proposal away from bust)

18. Option 1 US-led “21cm+” facility 2010 Decadal’s “HERA-III” at MREFC level (~$150M) auxiliary science: FRB, planetary B fields, ionosphere, …? NRAO managed Pros: continued US leadership in this area instrument design driven by 21cm reionization science other low-frequency science Cons: tricky funding pathway community organization

19. Option 2 SKA-Low Pros: leveraged international investment Cons: SKA-Low is not currently well coupled to 21cm efforts current schedule & design not compatible with 21cm science how much opportunity for US leadership?

20. Thank You!