NCP

galactic equator tilted ~ 63 1/2 deg to CE

galactic center is toward Sagitarrius

RA~18h, Dec ~ -29deg

Galactic coordinates

in galactic plane

in celestial equator plane

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]

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

0

0

00 0 0

Wavelength (Å)

Extinction =

A()/E(B-V)

0

4

10

Stellar Populations

z(pc) Age (109yrs) Z Distr Examples

Extreme Pop I 120 <0.1 0.04 patchy O,B,SG, open clusters

Older Pop I 160 0.1-10 0.03 patchy sun, A stars

*************************************************************************************

Disk Pop II 400 3-10 0.02 smooth planetaries, RR Lyr

Intermed Pop II 700 10 0.01 smooth long P var

Halo Pop II 2000 >10 0.003 smooth globular clusters

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

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 100.6 = 4, expect 4xmore at m+1 than m

not observed

rr2

dr

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 = 42a3/GP2 ~ 1011M

Halo mass: MACHOs, high vel stars

Rotation curve: M = rv2/G

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

Galaxy Evolution

• Top Down: large concentration of matter (1015M) fragment into galaxies of 1012M

• Bottom up: small structures merge into galaxies, then clusters

1) globulars formed ~ 13 billion yrs ago

2) collapse to disk

3) star formation continued in disk

4) collisions with dwarf galaxies add to halo

5) in ~ 5 billion yrs, collision with Andromeda could cause burst of star formation, uses up gas & dust and turns MW into an elliptical galaxy

Review of Astr 322- the Contents of the Milky Way

Content Structure

Motion

Viewing geometry

Instrumentation:

Disk Bulge Halo

Pop I Pop II Pop II

Disk - LSR

Halo - high v, elliptical

Horizon (alt, azimuth)

Celestial (RA, Dec)

Galactice (b, l)

Telescopes (refractors, reflectors)

CCDs, spectrographs, Space

Stars Gas & Dust Dark Matter

Hot, cold; Av, E(B-V) MACHOs + ?

Single (sun), binary, clusters (open, globular)

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