PHYS 1830 Lecture 9:

1. PHYS 1830 Lecture 9: HI gas shell in our Milky Way Galaxy. (J. English, J. Stil, & R. Taylor for VGPS.) • Previous Class: • Optical Telescopes • Resolution, Light Gathering Power, Surface Brightness • This Class: Radio Images • Radio Telescopes • Radio Continuum emission • The radio emission line from HI (21 cm Spin Flip Transition) • Multiwavelength observations • Coming up • Adjusting (stretching) Black & White images • Test next Friday Oct 4 in class.

2. TEST! Friday Oct 4th in class for 50 min. • Please check the class website for information (number of questions, kind of questions, topics). • http://www.physics.umanitoba.ca/~english/2013fallphys1830/ then look under “Test Information” and “Term Tests”. • Follow the Oct 4 link. • MONDAY in Allen 514: • Tutorial hour at 3:00 pm

3. What to do for workshop! • Go to website • http://www.physics.umanitoba.ca/~english/2013fallphys1830/bwimaging/

4. Radio Telescopes – Single Dish 64m Parkes, NSW

5. Radio Telescope Arrays: Interferometers summary Recall column VLA Socorro, NM • Angular resolution proportional to λ / Diameter

6. Interferometers summary Recall column Australia Telescope Compact Array

7. Interferometers • Atacama Large Millimetre/submillimetre Array ALMA 2900 m 5000 m

8. Radio Telescope Arrays • A series of radio antenna dishes on a railway track. • Dominion Radio Astrophysical Observatory, Penticton, B.C. • (DRAO)

9. Constructing Colour Images: The W4 Chimney Region in the Milky Way • For images at other wavelengths we do not need to worry about what colour we would see. • Can focus on the physical characteristics. • Optical image by Charles Dyer. • Radio image of neutral hydrogen (H I) gas by English and Taylor for the Canadian Galactic Plane Survey.

10. Constructing Colour Images: The W4 Chimney Region in the Milky Way • Hot gas is expected to escape to high galactic latitudes by flowing through chimneys. • Note the pink ionized hydrogen (H II) gas in the optical image. It sits on the edge of a cavity – a chimney – in the cool neutral hydrogen (H I) gas.

11. J. English Australia Telescope Compact Array J. English Australia Telescope Compact Array Very Large Array (VLA) How do these worK? D. Finley, NRAO/AUI

12. Synthesis Imaging • Antennas are linked to synthesize a large “mirror” as the Earth rotates.

13. Interferometry • The waves arriving at different antennas interfere. • The distance between antennas mean that at a specific time the peaks at one antenna cancel with the troughs at another. There is no signal. • At another time the peaks arriving at one antenna add with the peaks arriving at another antenna. The signal is strong.

14. Interferometry • Distance between antennas and the signal received are mathematically translated into position on sky and brightness. • The larger the distance between antennas the higher the resolution.

15. Interferometry • 12 hour radio synthesis observation. • Westerbork Synthesis Radio Telescope

16. Discussion: • If you wanted to produce high resolution images, where would you place your antennas? • Tight together in a park? • Around the globe? • On earth and in space?

17. Very Long Baseline Interferometry False colour plot of distant quasar. • Right: Using the ground-based telesopes only  resolution ~ 0.002 arcsec • Left: Including the space-based telescope  resolution ~0.0003 arcsec • HST/WFC3  0.13 arcsec in optical

18. Radio Continuum Emission. Nick Strobel 1) Synchrotron radiation is generated when an electron (e-) spirals around a magnetic field line.

19. Radio Continuum Emission. Nick Strobel 2) Thermal radiation is generated when an electron (e-) accelerates near a proton (p+). (The definition of acceleration includes a change in direction.) This process produces "free-free" emission which is also called "bremsstrahlung”.

20. Radio Continuum Example: Cygnus Region – Dominion Radio Astrophysical Observatory (DRAO) and Infrared Astronomical Observatory (IRAS)

21. Supernova remnants are threaded with magnetic fields. Therefore the radio emission assigned red is most likely to be: • Free-free emission • Synchrotron emission Review Question:

22. How does neutral hydrogen emit radiation? Spectral line emission. The Vela Cloud • Hydrogen is the most abundant element in the universe. • Neutral hydrogen, H I, is un-ionized. It has one proton and one electron in the ground state.

23. Spin Flip Transition: Parallel spin Higher energy Anti-parallel spin Lower energy • Electrons can spin in 2 different directions relative to the proton. • Atoms prefer to be in the lowest energy configuration. Therefore the e- flips over.

24. Spin Flip Transition: Parallel spin Higher energy Anti-parallel spin Lower energy • Where does the difference in energy go? • Photon with a wavelength of 21 cm  21 cm spectral line emission. • 21 cm radiation is observable by radio telescopes.

25. Review Question: • Which of the following are true? • Hydrogen atoms can generate emission lines only when the electron changes orbit-like energy levels. • Hydrogen atoms can generate emission lines only when the electron spontaneously flips relative to the proton so that it is in a lower energy orientation. • Hydrogen can generate emission lines by both processes described above.

26. The following images of our Milky Way were not shown in class. However please look at them.

27. Multi-wavelength Data Optical

28. Atomic Neutral Hydrogen H I

29. Radio Continuum 408MHz

30. far infrared

31. Optical

32. Ultraviolet

33. Xray

34. Xray

35. Gamma

36. Gamma