Constraining the redshift of reionization using a “modest” array

1. Jonathan Bittner Advisor: Avi Loeb MWA Meeting June 5th 2011 Constraining the redshift of reionization using a “modest” array

2. Global experiments can constrain the redshift of reionization Bowman and Rogers, Nature 2011

3. Generically, the EOR has peak variance when universe is half-ionized 150 kHz 1’ 2’ 300 kHz 4’ 600 kHz 0.6° 1° 1.2 MHz 2° @150kHz @ 1arcmin

4. Why think about this? • A simple constraint to compare to CMB and EDGES • Not an integrated constraint (like CMB), one which actually depends on rate at which reionization proceeded • First detection of cosmological 21-cm signal

5. The excess variance at z_reion can be measured over noise signal total Ratio of signal / noise (z) w/o signal + Signal profile and realization “Effective noise” For tint=500, Δν=2.4 MHz, θw = 1.2º

6. The redshift of reionization can be detected (in principle) with 32T

7. MWA 32T's dense uv-coverage would help overcome many issues Without synthesis With rotation synthesis Judd Bowman, personal communication

8. Foreground subtraction works best at scales with good UV coverage Liu, Tegmark, Zaldarriaga 2008 Bowman, Morales, Hewitt 2009

9. More information at: JCAP04(2011)038 arxiv:1006:5460 Thanks!

10. Dense UV coverage should lessen problem of point-source “frizz” Liu 2008 … the small-scale synthesized beam frizz seen in Figure 1 is largely averaged away when expanding the sky into long-wavelength Fourier modes, whereas the small-scale modes are severely affected. The characteristic scale separating “short" and “long" Fourier modes is determined by the longest baseline radius for which u-v coverage is complete. Bowman 2009 However, after the residual map is transformed back to the Fourier domain, it becomes evident that the polynomial fit has actually done an excellent job of subtracting the foreground contamination from baselines within a radius of u < 500λ, and only a poor job for baselines beyond this radius… where visibility measurements with the MWA become sufficiently sparse that there is no longer complete coverage.

11. We use 21-cm FAST to test this idea • Large cosmological volume (600 Mpc) • Low computational requirements – will run on workstation in < 1 day • Close match to simulations on large scales z=9.25, xHI=0.41

12. We create simulated beams through data cube • Constant comoving width • Gaussian or square top-hat averaging • Random periodic boundary conditions • z=7 to z=15, Δz=0.25 • Vary frequency and beam-width resolution [For illustration only Not a real 3D image]

13. We assume a very modest instrument • 32 tiles, 32x16 dipoles (fixed) • Tile layout as given for MWA 32T by J. Bowman (private communication) • Atot = 460 m² at 158 MHz • Integration: 200-1000 Hours • (about 1000 per year is usable) • Varying: • Beam Width (θw): 4 arcmin to 2.4º • Frequency resolution: 150 KHz to 2.4 MHz θw Furlanetto, Peng, Oh (2006).

14. δTb(z) and xHII in our realization

15. The effective thermal noise is the sampling error in the noise Red line will differ due to finite resolution Excess due to reionization

16. New definitions

17. The peaks occur roughly at xi=0.5 if taken at large scales