1. The Milky Way
Nucleus
Bulge
Bar
Disk
Halo

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

3. Latitude (b), Longitude (l)

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. Outside of spirals, stellar density lower
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

19. 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

20. 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

21. 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

22. H I Map
“Fingers of God”

23. 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

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