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
Ž 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 Ž 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.”