1. Galaxies and Cosmology 5 points, vt-2007 Teacher: Göran Östlin Lecture 3

2. Practical info Language? English or Swedish? Registration Who am I, who are you? Assistants: Jens, Teresa and Michael Course book: Jones & Lambourne + extra material (handed out + www). The book is up to date and comprehensive, but a bit ”easy” Course www-page continously updated http://www.astro.su.se/utbildning/kurser/vt2007/ai1420/ Lectures L1-L12 Exercise sessions 1-4 3 Hand in exercises -> bonus points (max 3x2) on exam 2 Laboratory exercises (mandatory): Get 1 bonus point on the exam if OK before (hand in latest 5/6). Tenta/Exam, max 30 points G (18 points) or VG (24)

3. Hydrostatic equilibrium: Sound cross time Free fall time Collapse if Star formation

4. Stars are born in dusty molecular clouds Dust allows the gas to cool Jeans mass for typical molecular clouds 10 4 -10 5 solar masses Contraction leads to decreasing M jeans and fragmentation Star formation is collective => populations

5. R136 cluster of young stars

6. IMF: initial mass function Young massive stars in R136 (Massey & Hunter)

7. IMF: Salpeter (1955): Massey & Hunter confirmedSalpeter Slope for young masssive stars

8. Unveiling the IMF in the solar neighbourhood is more complex due to the presence of many stellar generations

9. IMF of the Pleiades young star cluster Simple = Single Stellar Population (SSP)

10. Herzsprung-Russel / Colour-Magnitude Diagram (HR diagram / CMD) Not SSP

11. Nearest stars Brightest stars

12. Iso-chrones Positions of stars of given age = SSP RGB more sensitive to metallicity than age Metal-rich Metal-poor

13. observed CMDs for two ”simple/single stellar populations”

14. Globular cluster CMDs

16. Parallax & parsecs For example, a star that has a parallax of say 1 arc second will be at a distance of:

17. The Milky Way Galaxy a.k.a. the Galaxy (galaxias kyklos) NB this is a painting, not a photograph

18. Milky Way Galaxy Appearance, size, morphology –Disk, bulge, halo Constituents: –Stars of various populations –Gas (cold, warm, hot) and dust = ISM –Dark matter Dynamics Evolution and recycling Galactic centre

19. The local group, a photo montage

23. Artist’s impresseion The Milky Way Galaxy Galaxy = MW galaxy = others

24. Milky way look alike

25. NGC 891 MW (COBE)

26. Equatorial vs Galactic coordinates

27. Extent of optical emission (starlight) vs 21cm (neutral gas) In Milky Way and other spiral galaxies 21 cm spin flip transition of neutral Hydrogen (H I ) (see box 1.3, page 30)

29. Nearest stars Brightest stars Nearest stars dominated by low luminosity brighest stars dominated by high because these are most commonlumionsity as we can see them far away

30. Pleiades young star cluster Horsehead nebula in Orion Pop I = young Stars in the disk

31. Globular cluster (population II) on the order of a million stars, gravitationally bound

32. X-ray binaries in globular cluster ”47 Tuc”

33. Colour distribution of halo and disk stars - Age vs Metallicity

34. Metal-rich Globular Clusters (near the plane) Metal-poor Globular Clusters (in the halo)

35. Vertical distribution of stars Disks have exponential light distribution: I = surface brightness, h = scale length (height) Thin (h z = 300 pc) vs Thick (h z = 1 kpc) Disk Thick disk older, hence no A-stars

36. Disks have exponential light distribution: I = surface brightness, intensity (flux per angular area) h = scale length (height) Surface photometry NB surface brightness independent of distance - Flux per angular area - Luminosity per metric area

37. Radial distribution of neutral atomic (H I ) and molecular (H 2 ) gas in the Milky Way Galaxy H 2 has no ’dipole moment’ and therefore no suitably observable transitions at typical ISM cloud temperatures, but the CO molecule can be used as tracer (see Box 1.4 on page 33 in JL)

38. PropertyPopulation IIntermediatePopulation II OrbitsCircularElongatedVery elliptical Shapespiral armsdiskspherical/halo Thickness(pc) 1204002000 Metals (%) 3-40.4-20.4 or less Mass (M sun )2x10 9 5x10 10 2x10 10 Age (yr)10 8 10 9 10 10 Typical objectsOpen clusters, Sun Globular clusters HII regions, RR Lyrae stars Stellar populations in MW Population III ? Zero metallicity

39. Chemical composition of star clusters in MW

40. High lattitude neutral hydrogen