A single galaxy with its millions or billions of stars is only a very small spot in the observable universe. Galaxies & AGN’s (Chapter 13) Hercules Cluster taken by Victor Andersen at Kitt Peak National Observatory

Student Learning Objectives Classify and compare galaxy types. Identify properties of galaxies.

The Hubble eXtreme Deep Field (2012) combines all previous observations of the Hubble Ultra Deep Field Every dot is a galaxy!

The Hubble eXtreme Deep Field Combining over 2000 images of the same small spot of sky Taken over almost 10 years Made up of a total of 22 days of exposure time 50 days of observing time

How are galaxies classified?  Galaxies are classified according to their appearance.  Spiral Galaxies have 2 or more “arms”, a nucleus, and a halo.  S-type  Young and old stars  Gas and dust in disk  Bright spiral arms Spiral Barred-Spiral Elliptical Irregular

Grand Spiral Galaxy NGC 1232 APOD 2012 January 7

 Spiral arms follow the rotation of the galaxy. Our sister galaxy The Andromeda Galaxy Shows how Andromeda may have developed spiral arms

 Barred-Spiral Galaxies have a bar structure between the nucleus and spiral arms.  SB-type  SAB type (intermediate)  Bars may develop in spirals over time. Barred Spiral Galaxy NGC 6217 APOD/NASA

 Elliptical Galaxies have a smooth, round/elliptical shape.  Mostly old stars  No cool gas or dust to form new stars  Stars concentrated at the center  Random stellar orbits Elliptical Galaxy M87 APOD

 Elliptical galaxies are classified by apparent shape. E0E7 SphericalVery Elliptical No FlatteningVery Flattened M89 E0M32 E2NGC 4621 E7 Sloan Digital Survey

 Irregular Galaxies are a non-uniform spattering of stars and ISM.  50% of total mass is ISM APOD

Practice 1)Classify each galaxy. 2)What type of galaxy is the Milky Way?

How are properties of distant galaxies measured?  Galaxies are traveling away from each other as space expands.  Wavelengths are stretched.   leads to distance (Doppler effect)

Hubble Law  The Hubble Law is evidence that the universe is expanding. Redshift  Velocity  Distance Example: v = 200 km/s v = Hd

Practice 1) If a Galaxy A is receding at 600 km/s, how far away is it? 2) Would Galaxy B, which is receding at 700 km/s, be closer or more distant than Galaxy A? 3) If the Hubble constant has ± 2.5 units of error, what does that mean for measured distances to galaxies?

Mass  Galaxy rotation curves lead to mass

NASA image  Gravitational lensing may lead to mass

Dark Matter  The only way dark matter can be detected is by mapping its gravitational affects.  MACHOs (brown dwarfs and/or small, dense chunks of heavy elements)  WIMPs (exotic particles - not normal matter)

What are active galactic nuclei?  Active Galactic Nuclei are objects that have an extremely powerful energy source at the center of the galaxy. Seyfert Galaxies Small spiral galaxies with hot gas in the nucleus APOD Seyfert Galaxy NGC 7742

Radio Galaxies Elliptical galaxies with strong radio emission Plasma Jets from Radio Galaxy Hercules A (APOD)

Quasar Quasi-stellar objects (star-like) The Einstein Cross Gravitational Lens (APOD)

Practice 1)What powers an AGN? What makes it active? 2)What two things are indicated by the fact that quasars are only found in the most distant galaxies?

The Unified Model  All AGN’s share many of the same properties. High velocity jets & Extreme energy output  AGNs may be the same type of object, viewed from different angles with respect to our line of sight

Practice Match the AGN with the line of sight Radio Seyfert Quasar Face on Side-view Edge-on

Are galaxies found alone in space or in clusters?  Galaxies are usually part of a cluster.  Each galaxy has its own orbit within the cluster.  Galaxy clusters are bound together by mutual gravity.

HCG 87: A Small Group of Galaxies (APOD) Poor Cluster

Virgo Cluster Galaxies (APOD) Rich Cluster

The Virgo Cluster An estimated 2,000 galaxies are in this galaxy cluster Image Credit Atlas of the Universe

Practice Is the Local Group a rich or poor cluster?

Superclusters  Superclusters are clusters of galaxy clusters.  Superclusters are not bound together by gravity.

What happens when galaxies collide?  Gravitational attractions within galaxy clusters lead to collisions. The Milky Way & Andromeda  Shape distortion  Mergers  Bursts of star formation  Black hole object growth  Spiral arm structure