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Galactic & Extragalactic Astrophysics - ASTC22

Galactic & Extragalactic Astrophysics - ASTC22. Lecture 2 Stars Hubble sequence Galaxy classification Photometry. The role of star formation. Most star formation occurs in dense star clusters surrounded by H II regions. About 6 new stars per year are born in our Galaxy.

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Galactic & Extragalactic Astrophysics - ASTC22

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  1. Galactic & Extragalactic Astrophysics - ASTC22 Lecture 2 Stars Hubble sequence Galaxy classification Photometry

  2. The role of star formation

  3. Most star formation occurs in dense star clusters surrounded by H II regions About 6 new stars per year are born in our Galaxy

  4. GMCs contain: dark clouds, cores, Bok globules GMC mass / solar mass ~ 105 Oph V380 Ori + NGC1999

  5. Dark clouds L57 Barnard 68

  6. Oph Giant Molecular Cloud, 160 pc away contains numerous dark clouds

  7. H II regions Bright ionized hydrogen clouds, illuminated by type O,B stars

  8. Milky Way (Galaxy)

  9. IRAS all sky survey in the infrared

  10. 8.5 kpc

  11. Can you find the sun?

  12. How does our Galaxy look like from above? Earlier ideas More recent findings

  13. 2 V = GM(r)/r

  14. From BT

  15. From Ch.1 BT

  16. Other galaxiesM 31 Andromeda galaxy (Sb) companions: M 32 (E2) (foreground object) & M 110 (E6p) (below M31) M-object names are from a catalogue by Charles Messier 1740s)

  17. Hubble sequence (tuning fork diagram)

  18. Similar classification applies to other bandpasses (near-IR, in this case) but there’s no guarantee that the morphological type will be the same in the visible (here Hubble sequence is defined) and the other wavelengths. On the contrary, there are sometimes bars and rings which are revealed only in the UV, IR, or radio wavelengths.

  19. Hubble sequence (tuning fork diagram)

  20. De Vaucouleurs galaxy classification extends the Hubble scheme in orthogonal directions, adding more criteria

  21. De Vaucouleurs galaxy classification (cross-section at Hubble type Sb)

  22. Bulk Properties of Galaxies Galaxy Type Spiral /Barred Spiral M=109 to 1011 Msun, L=108 to 1010 Lsun, Diameter=5-250 kpc disk: Population I halo:Population II f=77% (f=Percentage of Observed Galaxies) Elliptical105 to 1013 105 to 1011 1-205 kpcPopulation IIf=20% Irregular108 to 1010 107 to 109 1-10 kpcPopulation If=3%

  23. Some objects in/around galaxies are tiny but almost as bright: supernovae, Active Galactic Nuclei, Quasars (extreme AGNs) a bright supernova

  24. M 104 (Sa)

  25. M81 (Sb)

  26. M 51 (Sc) + NGC 5195 (peculiar SBb?)

  27. Are these colliding or is it just projection effect? Can you say what type they are?

  28. Criteria for distinguishing spirals along the sequence of ‘early-type’ to ‘late-type’: Sa--Sb--Sc 1. Bulge-to-disk light (mass) ratio, size of the bulge (decreases) 2. Prominence of spiral arms, arm-interarm contrast (increases) 3. Visibility and number of population I objects such as: H II regions, OB associations, dark lanes of dust (increases) 4. Pitch angle (openness) of spiral arms (increases)

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