1	Astr 5460 Wed., Oct. 22, 2003 Today: Overview of Milky Way and Galaxies, part 2 of the course
2	The Milky Way (during the Leonid Meteor Shower) Milky Way made of many faint stars Bands of dark dust visible too Many types of objects (eg. O, B stars, Hydrogen clouds) concentrated along plane of Milky Way
3	The Importance of Cosmic Dust
4	The Structure of our Galaxy The Disk Component Stars, gas, and dust The spiral arms Size: Luminous Diameter ~ 25 kpc Thickness 300 pc – 1 kpc O stars and dust 30 pc Sunlike stars greater The Spherical Component Old Stars, but little gas or dust The Halo Globular clusters Isolated old stars red dwarfs, giants, white dwarfs The Nuclear Bulge
5	Just How Did We Figure This Out???
6	To sort out size, structure, kinematics, other basic properties, we need: Bright objects visible at large distances Objects above or below the plane – so as not obscured by gas, dust Ways to measure distances to those objects -- KEY Ways to see material other than stars Gas, dust, ???, total (dark) mass distribution Ways to map motion of objects in our Galaxy Examples of other Galaxies
7	The Andromeda Galaxy
8	M51: The Whirlpool Galaxy
9	Galaxies Basic Properties. Classifications Luminosity Functions Galaxy Masses Elliptical Galaxies Spiral Galaxies Correlations with Types
10	“Tuning Fork” Diagram
11	Spiral types The nuclear bulge is population II (old stars) So the Sa – Sc sequence is consistent with little gas Þ more gas
12	Elliptical Galaxy: M87 (OK, actually a cD, but similar)
13	Irregular Galaxies: Magellanic Clouds
14	Frequency of Galaxy Types
15	Frequency of Galaxy Types
16	Frequency of Galaxy Types
17	The Local Group of Galaxies Galaxies live in clusters (Chapter 25) Rich clusters: thousands of galaxies Poor clusters: Fewer than a thousand
18	Interacting Galaxies: The Antennae
19	Interacting Galaxies: Cartwheel
20	For Next Time Start in on the details, our own Milky Way, covered in the textbook Chapter 22. A new assignment involving analytic problems, galaxy spectra (stellar synthesis population models), and some new IRAF tasks (we’ll meet in my lab part of the hour). Complete all oral exams by Monday.
21	The Nucleus of the Galaxy Likely Black hole High velocities Large energy generation At a=275 AU P=2.8 yr Þ 2.7 million solar masses Radio image of Sgr A about 3 pc across, with model of surrounding disk
22	A movie of stars at the core www.mpe.mpg.de/www_ir/GC Very cool, new, and worth a look! This is the best evidence to date for a massive black hole at the Galactic core. Now essentially “proven.”