1. Cosmology with the 21cm line Gianni Bernardi SKA SA (RARG: O. Smirnov, G. Bernardi, T. Grobler, C. Tasse) Collaborators: (LOFAR-EoR, MWA-EoR, PAPER?) AIMS, August 14th 2013

2. The 21cm line is ideal to study the first billion years Dark Ages: no structures were formed, primordial fluctuations are imprinted in the HI gas Cosmic Dawn: first luminous structures (Pop III stars? Micro quasars?) are formed in the dark matter halos Reionization (EoR): luminous structures (galaxies, AGNs) re- ionize the IGM 3. mK 21 cm line cosmology 4. Courtesy A. Meisinger Evolution of fluctuations 5. Observational specs for 21cm line experiments: Frequency coverage: 30-200 MHz (6 < z < 35) Angular resolution: fluctuations 5 < < 30 arcmin you need a radio interferometer imaging up to < 1 arcmin you need a radio interferometer Sensitivity: mK sensitivity is required to constrain most of the HI models (The VLA @ 74 MHz has an rms sensitivity of 26 K (1 hour)) Challenges: - correction of ionospheric distortions - calibration of time and frequency variable telescope response (beam) - subtraction of bright foregrounds (and their coupling with the instrumental response) 6. Interferometry in 1 slide 7. 2 Antennas 8 Image formation with N antennas 8. 3 Antennas 9 Image formation with N antennas 9. 4 Antennas 10 Image formation with N antennas 10. 5 Antennas 11 Image formation with N antennas 11. 6 Antennas 12 Image formation with N antennas 12. 7 Antennas 13 Image formation with N antennas 13. 8 Antennas 14 Image formation with N antennas 14. 8 Antennas x 6 samples 15 Image formation with N antennas 15. 8 Antennas x 30 samples 16 Image formation with N antennas 16. 8 Antennas x 60 samples 17 Image formation with N antennas 17. 8 Antennas x 120 samples 18 Image formation with N antennas 18. 8 Antennas x 240 samples 19 Image formation with N antennas 19. 8 Antennas x 480 samples 20 Image formation with N antennas 20. 21 21. We live in the era of exploration: current and future 21 cm experiments GMRT LOFAR PAPER MWA HERA - SKA 22. GB et al. 2009 ~2.3 arcmin resolution frequency: ~150 MHz peak flux ~ 2.8 Jy conversion factor: 1mJy/beam=4 K noise: 0.75 mJy/beam The key point to detect the 21cm signal is how well foregrounds can be removed! What do foregrounds look like? 23. GB et al. 2009 Statistical properties of foregrounds * 2noise 180 Y l b C X l X l b N N Power law behavior with best fit amplitude A400= (0.0019 0.0003) K2, and best fit slope I = -2.2 0.3: diffuse Galactic emission Flat power spectrum: residual point sources Power law behavior with best fit amplitude A700= (90 7) (mK)2 and best fit slope Ip = -1.52 0.16: diffuse polarized Galactic emission 24. Statistical properties of foregrounds: the wedge Pober et al. 2013 25. Do we know how to subtract foregrounds? How well? Subtraction of Galactic diffuse emission and extragalactic radio sources: they are supposed to have smooth spectra compared to the 21 cm signal; Bowman, Morales & Hewitt 2009 26. Do we know how to subtract foregrounds? How well? Subtraction of Galactic diffuse emission and extragalactic radio sources: they are supposed to have smooth spectra compared to the 21 cm signal; EoR + FG + noise Eor + noise EoR ~ 5 mK FG ~ 2 K noise ~ 50 mK How well does it work on data? Jelic, .., GB, et al. 2008 27. An interferometer never samples all the Fourier modes PSF sidelobes corruption (k,k); Instrumental frequency response corrupts the foreground frequency smoothness (k); Telescope beams change with frequency and pointing direction (dipoles do not track the sky) and they can be different from each other (k,k); The ionosphere is no longer transparent (time and frequency dependent distortion & refraction) (k,k); RFI corrupts the sky signal (mostly ,k); Real foreground polarized signal can leak into total intensity due to polarized beams a/o imperfect polarization calibration (k); The point is that instrument calibration and foregrounds are coupled foreground properties are corrupted by the instrumental response 28. Sidelobes of bright sources far away from the target field GB et al. 2010 29. Instrumental spectral response Pober et al. 2013 30. 3C197.1: ~6.8 Jy Solutions every 10 sec after averaging the visibilities over ~230 channels rms residual: ~9.8 mJy Calibration accuracy: