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

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

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

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 dr r2 r not observed

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

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 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

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