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The Milky Way

The Milky Way. Nucleus Bulge Bar Disk Halo. Thick Disk. Thin Disk. Thick = 2 – 3 kpc Thin = .6 - .8 kpc Where it drops by a factor of e (2.72). Latitude (b), Longitude (l). +b. l=90. l=0. l=270. l=180. l=180. -b. Ecliptic. Radio – 74 cm. Radio - 21 cm. Infrared. Near IR.

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The Milky Way

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  1. The Milky Way Nucleus Bulge Bar Disk Halo

  2. Thick Disk Thin Disk Thick = 2 – 3 kpc Thin = .6 - .8 kpc Where it drops by a factor of e (2.72)

  3. Latitude (b), Longitude (l) +b l=90 l=0 l=270 l=180 l=180 -b

  4. Ecliptic

  5. Radio – 74 cm

  6. Radio - 21 cm

  7. Infrared

  8. Near IR

  9. Visible

  10. UV

  11. X-ray

  12. Gamma-rays

  13. Disk • Variations with distance from mid-plane • Star density (decreases out) • [Fe/H] (decreases out) • Age (increases out) • z-velocity (increases outward) • Thin/Thick disk correlate with Populations

  14. Thin disk • Population I, solar+ [Fe/H] • Spiral Arms (500 pc thick) • Outside of spirals, stellar density lower • Sun is in between arms, above midplane • How do we know this? • How do we find spiral arms?

  15. 2 kpc

  16. Surveying the Galaxy • Finding Disk, Spirals • Look for gas • H I for the disk • CO, GMCs for the Spiral arms • Other objects associated with spiral structure • What do you actually see? • What is actually measured?

  17. Observe gas along a line of sight • Measure radial velocities • NOT DISTANCES! • Need to assume a velocity pattern - rotation curve • Need to know Sun’s velocity, distance

  18. Disk Sections • Based upon how they move, and material concentration • Within 3 kpc of center, Bulge (<3kpc) • From 3 kpc to solar distance (3-7.5 kpc) • Beyond solar distance (>7 kpc) • Best velocity/material maps based on • H I • CO – also indicate amount of H2

  19. H I map • Near l=0º, very little H I < 3 kpc (vel high, but not strong) • “Horns” at l=30º, vel=150 km/s • Curve not symmetric, galaxy is warped • Rotation curve of galaxy is relatively flat

  20. CO Map • Not as spread out in velocity as H I • “Horns” at l=25, vel = 130 km/s – due to “molecular ring” • Assymetric • Rotation curve of galaxy is relatively flat • H I 3x greater than CO in 3 kpc<R<solar distance • Very little CO beyond solar distance

  21. H I Map “Fingers of God”

  22. Overall gas distribution • Molecular gas (CO) peaks at ~4 kpc • Within 3 kpc much less gas • Almost all CO within solar circle • Less than half of H I in solar circle • H I remains high from 3 kpc<R<solar circle • At solar circle (½ density thickness) • CO thickness = 50 pc • H I thickness = 100 pc

  23. Beyond solar circle • Severe warping apparent (>15 kpc) • R=24 kpc, warp = 4 kpc • H I peaks at 12-15 kpc • H I density drops strongly after 16 kpc

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