GBT 21 cm intensity mapping collaboration

Academia Sinica (Tzu-Ching Chang, Victor Yu-wei Liao)Beijing (Xuelei Chen, Yi-Chao Li)Carnegie Mellon University (Aravind Natarajan, Jeff Peterson, Tabitha Voytek)CITA/UToronto (Nidhi Banavar, Liviu Calin, Adam Lewis, Kiyo Masui, Ue-Li Pen, Richard Shaw, Eric Switzer)McGill (Kevin Bandura)

ARAA review article May 2010 (Morales and Wyithe) comparing to z ~ 10:

Two months later:

IM: now and thenz ~1 ~10

Science goal BAO EoR

Signal (mK) 0.1 10

Thermal noise (K) 30 300

Foreground spatial fluctuation (K)

0.1 10

Angular scale ~10’+ (non-linear scale)

~10’- (bubble scale)

First proposed 2007 1970’s?

First detected 2010 >2012

Strategy single dish Interferometers

RFI

Liu and Tegmark 2011

The real data

Signal-only simulations

20 Mpc

ΩHI = 10-3

Relaxed quadratic estimation

Most general: Inverse covariance, down-weight foreground in both angle and frequency.

Imperfect spectral baseline – need non-parametric removal: SVD on cross maps

Liu & Tegmark MNRAS, Volume 419, Issue 4, pp. 3491-3504.Projecting (idempotent) LOS modes is “good enough” vs. optimal downweighting.

These suggest that our method is slightly sub-optimal (in theory), but ideal in practice because we use the covariance of the real data!

SVD eigenvalues

Modes falling off rapidly: few DOF to describe most of the foregrounds.

Mode number (sorted)

Eig

enva

lue

Real data, cleaned

(25 modes removed here.)

Cross-pairs: GBT power

( *

(

)

)*×

Map A

Weight B

Map B

Weight A

Cross-pairs: WiggleZ crosspower

( *

(

)

)*×

Map A

Selection function

Galaxy catalog

Weight A

Preliminary

Fisher-matrix predictions

Conclusions• End-to-end demonstration: calibration, ionosphere,

point sources, galaxy, spectral response, etc. No show stoppers. Lessons learned for EoR.

• Foreground subtraction under control: ready for z~1 21cm intensity mapping.

• Consistent autonomous 21cm maps and power spectra.

• Proposal for GBT 0.5<z<1 BAO survey using new ASIAA 9 pixel receiver array starting 2013.

• Retires major risk for CHIME!