Transcript Galaxies
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 107 MSun – Giant ellipticals can be about 1013 MSun 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 5 log(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 Hubble Law • Velocity of distant objects increases with distance • Clear correlation between velocity and distance • Line fit to data is Hubble Law • v = H0d • H0 = 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 = H0d • H0 = 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 = H0d Cosmological redshift makes • H0 = 22 km/s/Mlyr 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 • High density clouds cool efficiently fast star formation ellipticals • Low density clouds cool inefficiently slow star formation spirals • VIDEO 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 ~ 1012 LSun ~ 100 LMW • 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 ~ 1011 – 1012 LSun • Visible and radio emission Radio Galaxies • Extremely luminous radio sources – LRadio ~ 1013 LSun – 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 109 MSun • Radio emission comes from jets of material • Visible light comes from super heated central area of accretion disk • VIDEO