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SKA 1 Science Requirements The HI Universe from the Dark Ages to Present Day Pulsars for Fundamental Physics

SKA 1 Science Requirements The HI Universe from the Dark Ages to Present Day Pulsars for Fundamental Physics. Science Driver for SKA 1 70-450 MHz AAs: hi- z HI. HI Science (Wilkinson 1991 to Garrett et al. 2010). Direct HI detections to z ~0.2 with WSRT (f~0.01); Verheijen et al (2010).

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SKA 1 Science Requirements The HI Universe from the Dark Ages to Present Day Pulsars for Fundamental Physics

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  1. SKA1 Science RequirementsThe HI Universe from the Dark Ages to Present DayPulsars for Fundamental Physics

  2. Science Driver for SKA1 70-450 MHz AAs: hi-z HI • HI Science (Wilkinson 1991 to Garrett et al. 2010) Direct HI detections to z~0.2 with WSRT (f~0.01); Verheijen et al (2010) Chang et al (2010) Delhaize & Staveley-Smith (2010) Limits on EoR at z~8.5 from GMRT; Paciga et al (2010) Limits on the EoR monopole; Bowman & Rogers (2008)

  3. SKA1 AA leads naturally to SKA2 AA Compared to ~arcmin2 FOV of ALMA SKA1 ~100s deg2 FOV up to ~0.5 GHz Detection and mapping of the EoR SKA2 ~100s deg2 FOV up to ~1.0 GHz Billion Galaxy Redshift Survey to z~2 and fundamental cosmology: outstrips WFIRST/Euclid

  4. Why SKA1 must have AAs with A/Tsys ~2000 m2 K-1 • At z=8.5, HI@150MHz, Tsys~Tsky~500K • Solid curves are for SKA1with A/Tsys=2000 m2 K-1 • Assumes a ‘fully-filled’ core: D= 1 km has a 7’ ‘beam’ • This means we reach S/N>1 regime in reasonable times • If SKA0 does detect EoR, SKA1AA will be needed to map fluctuations (c.f. CMB) • If SKA0 does not directly detect EoR: RFI, ionosphere, polarized foregrounds issues become much more tractable in the S/N>1 regime dn = 0.5 MHz Simulations (Furlanetto et al. 2004) ignores HII regions and z- space distortions, ~agrees with state-of-the-art; e.g. Jelic et al. (2008)

  5. What will precursors and pathfinders tell us? • LOFAR core and MWA512 both have filling factors ~1% in the central 1 km • In even long (1000 hr) exposures they will be working in the S/N<<1 regime • Foregrounds are 104 times brighter and strongly polarized • Ionospheric corrections and RFI excision are challenging (c.f. GMRT) • Based on the difficulty of measuring the auto-correlation signal of HI at z~1 with GBT, with more benign issues, direct EoR detection would be a fantastic achievement • X-correlation can help enormously

  6. Why r = 100 km I: Lya Emitters in the EoR • 2 0 1 • ~20hr exposures with VISTA • Data just taken, candidates identified • Spectroscopic confirmation • underway • 1 1 1 • 1 1 2 • 1 1 0 • VISTA simulations (5% escape fraction; Heywood et al), VISTA data (Jarvis et al) • In SKA0 (e,g. MWA512 and LOFAR) EoR fields (~10-100 deg2), there will be samples for stacking and X-correlation at z~7 (see Jarvis talk) • We will ONLY be able to isolate HI in galaxies if it can be isolated by RESOLUTION • Things will be harder at higher redshifts (earlier epochs), both in finding Lya tracers, and because correlation might be positive or negative! (resolution will be key)

  7. Why n2 = 450 MHz? • z~2 HI. MeerKAT results in ~2014, and first results from SKA1 in ~2018, needs objects to ‘stack’ on: equatorialHETDEX will have ~million of these! • SKA1 + HETDEX cross-correlation uniquely powerful probe of z~2 power spectrum • Options for extending to ‘all sky’ with ~109 galaxies:SKA2 or Euclid/WFIRST

  8. HETDEX with VIRUS on HET 100” 15.6’ 1.5” fiber dia Spring field approx 10 x scale Net fill factor in survey is 1/7 (60 sq. deg in 420) • Blind survey with 150+ VIRUS • 33,600 spectra per exposure • 350 – 550 nm • Survey begins 2012 • 0.8 million LAEs in 9 Gpc3 volume 1.9 < z < 3.5 • >1 million [OII] emitters z < 0.48 • First detection of dark energy at z>2 IFU 448 fibers 50 x 50 sq. arcsec Fall field equatorial Slide from Gary Hill (Texas)

  9. New Technique: “Intensity Mapping” • ~10,000 optical galaxies from DEEP2 over ~1 deg2: ‘drift scan’ with the GBT • Good RFI conditions essential • z=0.53 to z= 1.12 driven by frequency range of GBT (f=0.01): much longer in z than on sky • 15’ (13 Mpc) beam so sums emission on large scales: s >> expected for effective exposure time ~0.5 hr in each of ~8 ‘pointings’ • Intensity Map (autocorrelation) is upper limit to HI signal • ‘X-correlation’ (stacking) reduces systematic error, and provides ~SKA sensitivity • Detection at z~0.8 exactly as predicted by SKADS simulations (great news for SKA!), but suggests X-correlation is essential in the S/N<1 regime: and still misses HI not clustered with tracers s~4 mK ~4s detection at 0.15 mK Chang et al (2010)

  10. Why n1= 70 MHz? • Below 151 MHz (z=8.5 HI) • Tsky ~500 (n / 151)-2.7 K • Since signals remain at the 10-100 mK level, progress into the dark ages probably requires much larger (SKA2) collecting area, and may require even longer integrations • But Lya coupling from first stars produce strong fluctuations • ~10 km2 would give A/Tsys ~ ~250 • New semi-numerical simulations extend to z~25 over ~1 Gpc3 • P(k) at z~20! • Signatures of First stars! Santos et al (2010) Santos et al (2010) z~20 Lya coupling X-ray heating

  11. Why dishes? • Beyond Einstein: from GR to Quantum Gravity • Detect Gravitational Waves • Study supranuclear matter Out of the Galactic Plane, surveys yield may benefit from SKA1 AAs but only if they reach ~450 MHz (Smits et al. 2010). Needs 1.5-3 GHz in Plane to combat interstellar scattering. Timing demands this 1.5-3 GHz band. Must have a southern facility with A/Tsys ~1000 m2 K-1, e.g.3xeVLA or MeerKAT, comparable to Arecibo or FAST in the north.

  12. CO Emitters in the EoR and SKA Red: 5s • Simulations by Ian Heywood: and real eVLA data at z~6 (Carilli) looks very similar • SKA0 (MeerKAT) potentially - dependent on dish efficiency at ~15 GHz: z~7 CO(1-0) - world-beating: ~5-times faster than the VLA (largely) due to smaller dishes • Heywood et al awarded 6000 MeerKAT hours for this experiment • Stacking experiments fine, but to cover ~10-100 deg2 (MWA512/LOFAR) EoR patches, and get ~10-100k tracers (at z~8.5) would require new instruments (e.g SKA1 dishes with ~10-times MeerKAT mapping speed), and to isolate contribution due to variance in galaxies still needs SKA1 RESOLUTION

  13. Concluding Remarks • In SKA0-2 we are fortunate to have an iconic project with the credibility to ask for €0.35B soon, and an additional €1.2B by ~2020: this phasing helps SKA stay global given different international funding situations but success requires global coherence to give confidence to funders, and to optimally solve the remaining challenges • SKA0 (e.g. MWA512 or LOFAR) could detect EoR fluctuations, but will most likely need to use X-correlation techniques to do so: Lya and CO tracers both look promising • Direct detection of the EOR (via auto-correlation) may need the S/N>1 regime, and hence strongly motivates an SKA1 with A/Tsys ~2000 m2 K-1, and a high-filling-factor core (irrespective of SKA0 results) • r=100 km, giving ~arcsec resolution for SKA1 AAs, is needed to isolate HI variance due to galaxies from HI in IGM • Up to 450 MHz AA capability with SKA1 can measure P(k) at z~2 leading to transformational cosmology with SKA2 with mid-frequency AAs • Down to ~70 MHz capability can probe the z~20 dark ages (first stars)! • Dishes needed for pulsar key science driver, and may significantly aid EoR studies

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