Chapter 20 Galaxies

 

What is this? Spectra 

 

There are many galaxies.  The Hubble Deep Field zoom

               Also Hubble Deep Field South and Ultra Deep Field

 

Classified by appearance

         Spirals  1 2 3 Sombrero   ir   warped disk

       Barred Spirals 1 2

         Ellipticals  Giant (M87)  dwarf

         Irregulars  Large and Small Magellanic Clouds

 

Hubble ‘tuning fork’

 

Clusters of Galaxies

         Groups  We are in the Local Group

         Rich clusters

 

Properties of galaxies

 

How do you find the distance?

Standard candles

         Cepheids M100  period luminosity relation   a

         Supernovae  white dwarf supernovae

Main sequence fitting   a

Tully-Fisher relation    a

Hubble’s Law

         Distant galaxies are redshifted   large distances only

 

         d = v/H0

 

H0 is the Hubble constant is 22km/sec/Mly

        

All this needs to be calibrated – The Distance Chain

 

Explanation of Hubble’s Law    The universe is expanding.

         model

 

Finite speed of light means we look back into the earlier universe

         Lookback time

         Cosmological horizon – since the universe has a beginning

 

Masses of galaxies from rotation curves

Brightness from distance and photometry