The Dark Ages and Reionization with 21cm Aaron Parsons

z = 100 to to 70 MHz z = 20 to 5 70 to 240 MHz

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+)

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

k || kxkx kyky

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

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

(Ali et al. 2015)

(Pober et al. 2015)

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

EOR Power Spectrum - Array Sensitivities* ✴ Updated 21 cm Experiment Sensitivites, J. Pober, HERA Memo #3, Table 2 ( Instrument AvoidanceSubtraction DriftTrackDriftTrack PAPER MWA LOFAR (core) HERA HERA MWA SKA1 Low

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

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.

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)

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

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?

Thank You!