Spiral Galaxies

Elliptical Galaxies

Irregular Galaxies

Classification of Galaxies

Properties of Galaxies

Spirals Ellipticals IrregularsMass [typical; range]

(solar masses)

1011 ;

109 - 1012

1011.5 ;

106 - 1013

1010 ;

108 - 1011

Size (pc) 104- 105.5 104- 106 103- 105

Color Blue arms,

reddish bulge

reddish bluish

Luminosity 108 - 1010 105 - 1011 107- 109

Stellar Populations Pops I & II Pop II Pop I (Pop II)

Interstellar medium Yes Very little Still some

Rotation Yes (disk) no Not a lot

Fraction 30% 20% 50%

Other galaxy types : Peculiar, Interacting, Ring, Starburst, Dwarf,Luminous Infrared, Active Nuclei, Damped Lyman-alpha

Stephan’s Quintet – Colliding galaxies

The “Anntenae” Galaxies – a case study

Galactic Train Wrecks

Collisional Aftermath

Ring Galaxies – the “splash”

Head-on collisions can produce a “ripple” of star formation that expands outwards.

Galactic Superwinds

The Magellanic

Clouds

Large Magellanic Cloud Small Magellanic Cloud

Southern Hemisphere only

The Galactic Neighborhood

The “Local

Group” of Galaxies

Members of the Local Group

And outward…

Galaxy Clusters

Virgo

Coma

Notice the giant ellipticals at the centers of many clusters.These are an example of “galactic cannibalism”.

Galactic Cannibals – Central CD Ellipticals

At the heart of rich clusters, galaxies pass through the center and are disrupted and collected.

Making a CD galaxy

into the Universe…

Large Scale Structure

On the largest scales (100 million ly) the Universe takes on a “foamy” appearance, with great filaments and walls of galaxies and clusters, surrounding great “voids” that are relatively empty.

Dark Matter - rotation curvesRotation curves imply the mass-to-light ratios of galaxies go up as we look on larger scales: Sun M/L=1, solar neighborhood M/L=3, galaxy M/L=50

Dark Matter – cluster speeds

galaxy clusters M/L=200-500

From average speed of galaxies – the cluster would fly apart

From X-ray gas held in – several million degrees and extensive

What could the dark matter be?

1) Normal but dark matter (“baryonic”) : rocks, white or brown dwarfs?

2) Black holes or neutron stars? Too much metals would have been produced.

Anyway, there is a fundamental reason from the Big Bang this can’t be it…

Dark Matter :gravitational

lensing The mass required to produce the observed lensing is much higher than the luminous mass. This is a direct observation of gravity due to dark matter.

WIMPS and Cold Dark MatterCould dark matter be some kind of new particles which

interact very weakly with matter (like neutrinos do) but massive, and not moving relativistically? Experiments at Berkeley and elsewhere are looking for them (guaranteed Nobel prize!).