Galaxies With a touch of cosmology
Types of Galaxies Spiral Elliptical Irregular
Spiral Galaxies
Spiral Galaxies Disk component where the spiral arms are Interstellar medium Star formation Spheroidal component Bulge central part of galaxy Halo where the oldest stars are located Make up 75-80% of the largest galaxies in the Universe
Features of Spiral Galaxies Rings Bars Spiral Arm Type Grand design well defines spiral arms Flocculent patchy and discontinuous arms Lenticular disk with no arms Bulge size
Elliptical Galaxies
Elliptical Galaxies Only have spheroidal component Sphericity (definitely not a word) varies Little to no star formation Composed mainly of low mass stars Huge range in masses Dwarf ellipticals can be about 10 7 M Sun Giant ellipticals can be about 10 13 M Sun
Irregular Galaxies
Irregular Galaxies Catch-all for everything that is not either a spiral or elliptical galaxy Two basic types: Type I: closely related to spiral galaxies, but their structure is less organized Type II: structure is highly chaotic and typically are gravitationally interacting with another galaxy Lots of star formation More common are large distances
Hubble Classification
Determining Distance
Distance Ladder RADAR bounce radio waves off objects and measure travel time Parallax measure apparent movement of object due to Earth s orbit MS fitting convert apparent magnitudes of cluster stars into absolute magnitudes using theoretical models Standard candles objects that have the same absolute magnitude Cepheids, SNIa Hubble Law use distance dependence of Universal expansion rate
RADAR Radio waves are bounced off of Venus, and with Keper s Laws and a little geometry, the length of one AU can be determined Crucial for using the parallax method
Parallax Best way to determine distance to stars within about 1,000 lyr
MS fitting Use parallax to calibrate Convert apparent magnitudes to absolute m M 5log( d[ pc]) 5 d in parsecs Only good to distances in the Milky Way
Cepheids Evolved massive stars that have internal instabilities Obey a periodluminosity relation Can measure distances up to a few million lyrs
SN Ia All SN Ia have the same luminosity Use Cepheids to calibrate supernovae We can see SN to billions of light years
Velocity of distant objects increases with distance Clear correlation between velocity and distance Line fit to data is Hubble Law v = H 0 d H 0 = 22 km/s/mlyr Hubble Law
Hubble Law Velocity of distant objects increases with distance Clear correlation between velocity and distance Line fit to data is Hubble Law v = H 0 d H 0 = 22 km/s/mlyr
Hubble Law Velocity of distant objects increases with distance Clear correlation between velocity and distance Line fit to data is Hubble Law v = H 0 d H 0 = 22 km/s/mlyr Cosmological redshift makes distant objects appear redder than they are
Galaxy Surveys
Galaxy Formation Start with collapse of protogalactic cloud Type of galaxy depends on: Protogalactic spin faster spinning clouds make spiral galaxies Protogalactic density VIDEO High density clouds cool efficiently fast star formation ellipticals Low density clouds cool inefficiently slow star formation spirals
Giant Elliptical Galaxies Located at the centers of galaxy clusters Always the most massive object in cluster Likely the product of several galaxy mergers Collisions between galaxies would results in lots of star formation Starburst galaxies Star formation would consume all gas, so none is left
Active Galactic Nuclei
Quasars Look like stars through a telescope Extremely distant Have strong visible and radio emission Extremely luminous L ~ 10 12 L Sun ~ 100 L MW Bipolar jets
Other AGN Less Luminous versions of quasars Some AGN change their luminosity in only a few hours Light emitting region can be no more that a few light-hours across L ~ 10 11 10 12 L Sun Visible and radio emission
Radio Galaxies Extremely luminous radio sources L Radio ~ 10 13 L Sun Little to no visible light radiated Observations show radio galaxies and quasars are likely the same type of object view from a different angle Quasars: face on view of accretion disk gives visible light Radio galaxies: edge on view of accretion disk blocks visible light
Power Source Accretion disk around Supermassive Black Hole Up to 10 9 M Sun Radio emission comes from jets of material Visible light comes from super heated central area of accretion disk VIDEO