1. Galactic coordinates in celestial equator plane NCP in galactic plane
galactic equator tilted ~ 63 1/2 deg to CE
galactic center is toward Sagitarrius
RA~18h, Dec ~ -29deg

2. Makeup of Milky Way Galaxy
Stars - Disk (O, B stars, SG, young to old open clusters)
Halo & Bulge (RR Lyr, globular clusters, MACHOs)
Gas - some in disk, hot gas in halo
Dust - in disk [results in reddening E(B-V), Av]

3. DUST m-M = -5 + 5 log d + A E(B-V) = (B-V)observed - (B-V)normal
Av ~ 3 E(B-V) [~ 1 mag/kpc roughly]
Find E(B-V) from:
spectral type of star and observed B-V
H / H ratio [normal = 3]
HI maps NH/E(B-V) = 5x1021 atoms/cm2/mag
2200Å bump

4. Extinction =
A()/E(B-V) 10 4
Wavelength (Å)

5. Stellar Populations z(pc) Age (109yrs) Z Distr Examples
Extreme Pop I < patchy O,B,SG, open clusters
Older Pop I patchy sun, A stars
*************************************************************************************
Disk Pop II smooth planetaries, RR Lyr
Intermed Pop II smooth long P var
Halo Pop II > smooth globular clusters

6. Interstellar Gas optical absorption lines CaI, CaII, NaI
HII regions (recombination around hot star) T~10,000K, density ~ 5000 ions/m3
HI gas (21 cm) T~100K, density ~106 atoms/m3
molecular clouds (radio) H2, OH, NH3 T~10K, density ~109 mol/m3
X-rays (hot coronal gas) T~ 106K, density < 104 particles/m3

7. Counting Stars D= #stars/unit volume
Local luminosity function: #stars/unit V with given Mv
total sky = 4 steradians = 41,253 sq deg
for solid angle , area =  r2
dV =  r2 dr
N(r) = D(r)dV=  Dr2dr = 1/3 Dr3 
log r = (m-M+5)/5 = 0.2 m + const (for given M)
r = 10(0.2m+c) and N(r) = 10(0.6m+c)
since = 4, expect 4xmore at m+1 than m dr
r2 r
not observed

9. Finding the mass of the Milky Way
Kepler’s law using sun’s orbit (P=250 million yrs, v=250 km/s, a=8kpc)
mMW + msun = 42a3/GP2 ~ 1011M
Halo mass: MACHOs, high vel stars
Rotation curve: M = rv2/G

11. The Galactic Center (Sgr A*)
Evidence for a Supermassive BH at the center:
stationary (located at dynamic center of MW)
energetic X-ray source
small size (radio shows smaller than solar system)
no visible object at opt nor IR from Keck images
motions of nearby stars (1000’s of km/s) imply 3 million M
How does Supermassive BH form?
stars in center are < 1000AU apart (200,000AU near sun)
SN chain reaction could produce many stellar BHs
collisions between BHs cause monster supermassive BH

12. Galaxy Evolution
Top Down: large concentration of matter (1015M) fragment into galaxies of 1012M
Bottom up: small structures merge into galaxies, then clusters
globulars formed ~ 13 billion yrs ago
collapse to disk
star formation continued in disk
collisions with dwarf galaxies add to halo
in ~ 5 billion yrs, collision with Andromeda could cause burst of star formation, uses up gas & dust and turns MW into an elliptical galaxy

13. Review of Astr 322- the Contents of the Milky Way
Structure
Disk Bulge Halo
Pop I Pop II Pop II
Stars Gas & Dust Dark Matter
Hot, cold; Av, E(B-V) MACHOs + ?
Motion
Disk - LSR
Halo - high v, elliptical
Viewing geometry
Single (sun), binary, clusters (open, globular)
Horizon (alt, azimuth)
Celestial (RA, Dec)
Galactice (b, l)
Properties (d, T, L, Mv, spectra, mass, radius)
Evolution - low mass (T Tauri, MS, giant, planetary, WD)
- high mass (MS, SG, SN, pulsar or BH)
Variables - geometric, eruptive, pulsating
Instrumentation:
Telescopes (refractors, reflectors)
CCDs, spectrographs, Space