1. Seeing the universe through redshifted 21-cm radiation Somnath Bharadwaj Physics & CTS IIT Kharagpur

2. Collaborators Shiv K Sethi Biman Nath T Roy Choudhury Jayaram Chengalur Saiyad Ali Jayanti Prasad Tapomoy Guha Sarkar Kanan Datta Suman Majumdar Sanjay Pandey Abhik Ghosh NCRA,TIFR RRI BITS,Pilani JU Stockholm IUCAA LBSC,Gonda Tarun D Saini IISc Biswajit Pandey

3. The Expanding Universe

4. Redshift – distance - time z3z3 z1z1 z2z2 Observer

5. Neutral Hydrogen - HI Ground state 21 cm radiation

6. Constituents of the Universe Baryons 75 % Hydrogen 25% Helium

7. Cosmic Microwave Background Radiation (CMBR) T=2.725 K Observer

8. HI Evolution

9. z > 1000 T  =2.725 K (1+z) Hydrogen is ionized at z>1,000 Recombination – HI formed for first time at z=1,000

10. CMBR anisotropies Universe ionized and opaque at z >1000 Nearly isotropic  T ~ 10 micro K WMAP NASA T=2.725 K Z=1000

11. HI Evolution Dark Age HI seen in absorption against CMBR

12. HI Evolution HI seen in emission Epoch of Reionization

13. HI Evolution Post-Reionization HI seen in emision

14. Evolution of the Universe

15. Structure Formation Z=1000 Z=0

16. Rionization 15 >z > 6 Photoionization First Luminous Objects z~30

17. Simulation Majumdar, Bharadwaj& Roy Choudhury 2012,MNRAS, Submitted

18. What do we observe? Fluctuations in 21-cm radiation with frequency ad angle on sky

19. The Dark Matter Power Spectrum

20. Mini-Summary ● Redshifted 21-cm radiation fluctuates with frequency and angle on sky ● Observations can be used to study: – Universe at z ~ 50 (Dark Age) – only possible probe – Formation of the first luinous objects – Reionization – Structure formation after reionization

21. Our Efforts Started With

22. GMRT Giant Meter-wave Radio Telescope

23. Radio Interferometric Array Frequency MHz1532353256101420 z8.35.03.41.30 32 MHz bands with 128 separate channels GMRT 30 antennas 45 diameter

24. No! Have we observed the cosmological 21-cm radiation?

25. Predicted Signal z=10, x=0.5 10 arc-minutes mK Datta, Roy Choudhury & Bharadwaj 2007, 387,767

26. Haslam Map - 408 MHz All-Sky Survey ) ≈ 4 0 Angular scales (off-galactic) Synchrotron Radiation 180K – 70,000K at 150 MHz

27. GMRT Observations Ghosh, Prasad, Bharadwaj, Ali & Chengalur 2012, MNRAS, In Press FIELD I

28. 14 hrs GMRT Observations RA 01 36 46 DEC 41 24 23 Ali, Bharadwaj & Chengalur 2008,MNRAS,385,2166 FIELD IV

29. Measured C ℓ Ghosh, Prasad, Bharadwaj, Ali & Chengalur 2012, MNRAS, In Press

30. Foregrounds Point SourcesDiffuse Removal is Biggest Challenge

31. GMRT Observations Ghosh, Prasad, Bharadwaj, Ali & Chengalur 2012, MNRAS, In Press FIELD I Point Source Dominated

32. Low resolution Residual Map. Taper @ |U|=170 Diffuse Structure Appearing On the Map on Scales > 10 arcmin The brightest structures in this map are at 5 σ level compared to the local rms value ~ 23.5 mJy/Beam.

33. The brightest structures in this map are at 10 σ level compared to the local rms value ~ 35 mJy/Beam. Taper @ |U|=100

34. Angular Power spectrum :  The power spectrum of the Diffuse emission was fitted by a power-law down to ℓ = 800 ( θ ≈ 10'):

35. Currently working on ● Theoretical Predictions of Expected 21-cm Signal ● Detection Strategies ● Quantify and Remove Foregrounds

37. Thank You

38. Concluding Remarks ● Probe Dark Ages, First Luminous Objects, reionization, post- reionization ● Potential Probe of Dark Energy ● Challenge Foregrounds, RFI