1. Measuring the Gas in Galaxies in the Distant Past Philip Lah Too late. Here comes the SKA.

2. Who am I? I am astronomer with a joint appointment at the: National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, India and the Research School of Astronomy & Astrophysics, Mount Stromlo Observatory, Australian National University I use both radio and optical telescopes for my research

3. Atmospheric Transmission Atmospheric Opacity 0 % 50 % 100 % 1 nm 1 μm 1 mm 1 m 1 km Wavelength → ← Frequency radio optical infrared gamma rays, X-rays & ultraviolet

4. Hydrogen Gas in the Universe

5. Hydrogen 76% by mass of the baryons – normal matter (that is not the weird stuff – Dark Matter) Neutral Atomic Hydrogen Gas produces emission at a wavelength of 21 cm

6. Hydrogen Gas in the Universe Hydrogen 76% by mass of the baryons – normal matter (that is not the weird stuff – Dark Matter) Neutral Atomic Hydrogen Gas (HI) produces emission at a wavelength of 21 cm

7. 21 cm Atmospheric Transmission Atmospheric Opacity 0 % 50 % 100 % 1 nm 1 μm 1 mm 1 m 1 km Wavelength → ← Frequency radio optical infrared gamma rays, X-rays & ultraviolet

8. HI 21-cm Emission From Galaxies

9. Galaxy M33: optical

10. Galaxy M33: HI 21-cm emission

11. Galaxy M33: optical and HI

12. Galaxy M33: optical

13. Why Study Neutral Atomic Hydrogen Gas?

14. HI Gas and Star Formation neutral atomic hydrogen gas cloud (HI) molecular gas cloud (H 2 ) star formation

15. Redshift, Observing the Past

17. The Expanding Universe

18. Hubble`s Law redshift velocity related to distance distance related to age (due to light travel time)

19. Hubble`s Law redshift velocity related to distance distance related to age (due to light travel time)

20. 21 cm Atmospheric Transmission Atmospheric Opacity 0 % 50 % 100 % 1 nm 1 μm 1 mm 1 m 1 km Wavelength → ← Frequency radio optical infrared gamma rays, X-rays & ultraviolet redshifted

21. The History of Star Formation in the Universe

22. Star Formation Rate Density

23. ~10 times current rate

24. The Amount of HI Gas in the Universe

25. HI Gas Density

26. ~2 times current density

27. HI Gas Density

28. region where I have been working

29. Current Observations

30. Giant Metrewave Radio Telescope

32. Coadding HI signals

33. RA DEC Radio Data Cube Frequency HI redshift

34. Coadding HI signals RA DEC Radio Data Cube Frequency HI redshift positions of optical galaxies

35. Coadding HI signals frequency flux

36. Coadding HI signals frequency flux z2 z1 z3 z1, z2 & z3 optical redshifts of galaxies

37. Coadding HI signals velocity z1 z2 z3 flux z1, z2 & z3 optical redshifts of galaxies

38. Coadding HI signals velocity z1 z2 z3 flux velocity Coadded HI signal z1, z2 & z3 optical redshifts of galaxies

39. My Current Best Observation

40. HI blue outside x-ray gas blue galaxies surrounding the core of a large galaxy cluster galaxies observed as they were 4 billion years ago coadding signal from 94 galaxies

41. HI blue outside x-ray gas blue galaxies surrounding the core of a large galaxy cluster galaxies observed as they were 4 billion years ago coadding signal from 94 galaxies

42. Future Observations

43. The SKA and Me SKA`s collecting area 20  GMRT`s collecting area SKA better receivers SKA larger field of view SKA better RFI environment

44. The SKA and Me my current research looking at galaxies 3 to 4 billion years ago – SKA directly detect HI signal originally SKA proposed to detect HI gas from 8 billion years ago stacking with SKA ~12.7 billion years ago, the era of first galaxies SKA fully operational 2024

45. The SKA pathfinders

46. MeerKAT South African SKA pathfinder 13.5 m diameter dishes 64 dishes finished 2014 (2018)

47. ASKAP 12 m diameter dishes 30 dishes focal plane array finished 2013