Constraining the redshift of reionization using a “modest” array

Jonathan Bittner

Advisor: Avi LoebMWA Meeting June 5th 2011

Bowman and Rogers, Nature 2011

Global experiments can constrain the redshift of reionization

Generically, the EOR has peak variance when universe is half-ionized

1’2’

4’

0.6° 1°

2°

150 kHz300 kHz

1.2 MHz

600 kHz

@150kHz @ 1arcmin

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

The excess variance at z_reion can be measured over noise

+

total

w/osignal

Ratio of signal / noise (z)

Signal profile and realization

“Effective noise”

signal

For tint=500, Δν=2.4 MHz, θw = 1.2º

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

MWA 32T's dense uv-coverage would help overcome many issues

Without synthesis With rotation synthesis

Judd Bowman, personal communication

Foreground subtraction works best at scales with good UV coverage

Liu, Tegmark, Zaldarriaga 2008 Bowman, Morales, Hewitt 2009

Thanks!

More information at:

JCAP04(2011)038

arxiv:1006:5460

Dense UV coverage should lessen problem of point-source “frizz”

… 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.

Liu 2008

Bowman 2009

However, after the residual map is transformed back to the Fourierdomain, 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.

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

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 onlyNot a real 3D image]

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

Furlanetto, Peng, Oh (2006).

θw

δTb(z) and xHII in our realization

The effective thermal noise is the sampling error in the noise

Red line will differ due to finite resolution

Excess due to reionization

New definitions

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