Astr 5460     Wed., Oct. 22, 2003

	Today: Overview of Milky Way and Galaxies, part 2 of the course

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

The Importance of Cosmic Dust

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

Just How Did We Figure This Out???

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

The Andromeda Galaxy

M51:  The Whirlpool Galaxy

Galaxies

	Basic Properties.
		Classifications
		Luminosity Functions
		Galaxy Masses
		Elliptical Galaxies
		Spiral Galaxies
		Correlations with Types

“Tuning Fork” Diagram

Spiral types

	The nuclear bulge is population II  (old stars)
	So the Sa – Sc sequence is consistent with  little gas Þ more gas

Elliptical Galaxy: M87
(OK, actually a cD, but similar)

Irregular Galaxies: Magellanic Clouds

Frequency of Galaxy Types

Frequency of Galaxy Types

Frequency of Galaxy Types

The Local Group of Galaxies

	Galaxies live in clusters (Chapter 25)
		Rich clusters:  thousands of galaxies
		Poor clusters:  Fewer than a thousand

Interacting Galaxies: The Antennae

Interacting Galaxies: Cartwheel

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.

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

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.”