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Galaxies and Cosmology

Galaxies and Cosmology. 5 points, vt-2007 Teacher: Göran Östlin Lecture 3. Practical info. Language? English or Swedish? Registration Who am I, who are you? Assistants: Jens, Teresa and Michael

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Galaxies and Cosmology

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

  4. Stars are born in dusty molecular clouds Dust allows the gas to cool Jeans mass for typical molecular clouds 104-105 solar masses Contraction leads to decreasing Mjeans and fragmentation Star formation is collective => populations

  5. R136 cluster of young stars

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

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

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

  14. Globular cluster CMDs

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

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

  17. 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

  18. The local group, a photo montage

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

  20. Milky way look alike

  21. MW (COBE) NGC 891

  22. Equatorial vs Galactic coordinates

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

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

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

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

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

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

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

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

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

  32. Radial distribution of neutral atomic (HI) and molecular (H2) gas in the Milky Way Galaxy H2 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)

  33. Stellar populations in MW Property Population I Intermediate Population II Orbits Circular Elongated Very elliptical Shape spiral arms disk spherical/halo Thickness(pc) 120 400 2000 Metals (%) 3-4 0.4-2 0.4 or less Mass (Msun) 2x1095x10102x1010 Age (yr) 1081091010 Typical objects Open clusters, Sun Globular clusters HII regions, RR Lyrae stars Population III ? Zero metallicity

  34. Chemical composition of star clusters in MW

  35. High lattitude neutral hydrogen

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