Astro 1050     Fri., Nov. 14, 2004
   Today: Chapter 13, Galaxies

Chapter 13: Galaxies
Family of Galaxies
Classification
Properties of Galaxies
Distance; The Hubble Law
Size and Luminosity
Mass (including Dark Matter)
Evolution of Galaxies
Clusters
Mergers

The Hubble Deep Field

The Hubble Ultra Deep Field

“Tuning Fork” Diagram

Types of Galaxies  (pg. 254-255)
Spirals
      Sa                   Sb              Sc
   (large nuclei     
Þ  small nuclei)
(little gas,dust   
Þ lots of gas, dust)
     SBa                SBb            SBc    (as above, with BARS)
Ellipticals
E0  E1 E2 E3 E4 E5 E6 E7
(spherical)               (highly elliptical)
Irregulars

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

Elliptical Galaxy: M87

Irregular Galaxies: Magellanic Clouds

Properties of Galaxies
Distance
Use Cepheid Variables for close objects
Other objects for which Absolute Magnitude is known:
Supernova
Planetary nebula in certain emission lines
Use “Hubble Law” for more distant objects
(Correlation of distance with radial velocity)
Diameter and Luminosity
Obtain from angular size and magnitude, combined with distance
Mass
Rotation curves
Velocity dispersion
90 to 99% of mass is
“dark matter”

The Original Hubble Law

The Hubble Law using galaxies with visible Cepheid variables.

Hubble Law Example
vr = H0 d
  with H0=0.5 (mile/hr)/mile

Hubble Law Example
vr = H0 d
  with H0=0.5 (mile/hr)/mile

Hubble Law Example
vr = H0 d
  with H0=0.5 (mile/hr)/mile

Hubble Law Example using relative vr and relative d

The Hubble Law using secondary distance indicators
Ho = 72 ±8 km/s/Mpc

The Local Group of Galaxies
Galaxies live in clusters
Rich clusters:  thousands of galaxies
Poor clusters:  Fewer than a thousand

The Coma Cluster

Evolution of Galaxies
Galaxies live in clusters
Rich clusters:  thousands of galaxies
Poor clusters:  Few than a thousand
Fundamental difference between stars and galaxies:
Stars live isolated lives:
They are much smaller than distance between them
They virtually never collide
Galaxies are not isolated
They are only slightly smaller than the distances between them
The can (and do) collide, and interact with gas within clusters

Effects of Collisions
Stars pass “through” each other, but orbits around galaxy disrupted
Gas clouds collide
Gas stripped away from stars
Collisions cause bursts of star formation
Ellipticals may be those galaxies which have suffered collisions
Spirals may be those galaxies which have not suffered collisions
Joshua Barnes (Hawaii) and the Space Telescope Science Institude provide a simulation of the Antenna Galaxies: http://imgsrc.stsci.edu/op/pubinfo/pr/1997/34/images/anima.mov

Interacting Galaxies: The Antennae

Interacting Galaxies: Cartwheel

Simulation of the Cartwheel Encounter
From the Space Telescope Science Institute which also provided the Cartwheel image in the textbook:
http://imgsrc.hubblesite.org/hu/discoveries/striking_encounters/graphics/cartwheel.mpg

The Hubble Deep Field

Evidence for “Hierarchical” Galaxy Formation from the Hubble Deep Field

What this might look like
Movie simulation of galaxy formation via assembly of small pieces (courtesy of Space Telescope Science Institute): http://imgsrc.stsci.edu/op/pubinfo/mpeg/galaxies.mpg

Chapter 13: Galaxies
Family of Galaxies
Classification
Properties of Galaxies
Distance; The Hubble Law
Size and Luminosity
Mass (including Dark Matter)
Evolution of Galaxies
Clusters
Mergers