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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

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Galaxies

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  1. Galaxies With a touch of cosmology

  2. Types of Galaxies • Spiral • Elliptical • Irregular

  3. Spiral Galaxies

  4. 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

  5. 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

  6. Elliptical Galaxies

  7. 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

  8. Irregular Galaxies

  9. 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

  10. Hubble Classification

  11. Determining Distance

  12. 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

  13. 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

  14. Parallax • Best way to determine distance to stars within about 1,000 lyr

  15. MS fitting • Use parallax to calibrate • Convert apparent magnitudes to absolute • d in parsecs • Only good to distances in the Milky Way

  16. Cepheids • Evolved massive stars that have internal instabilities • Obey a period-luminosity relation • Can measure distances up to a few million lyrs

  17. SN Ia • All SN Ia have the same luminosity • Use Cepheids to calibrate supernovae • We can see SN to billions of light years

  18. 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

  19. 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

  20. 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 Cosmological redshift makes distant objects appear redder than they are

  21. Galaxy Surveys

  22. 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

  23. 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 Giant Elliptical Galaxies

  24. Active Galactic Nuclei

  25. Look like stars through a telescope Extremely distant Have strong visible and radio emission Extremely luminous L ~ 1012 LSun ~ 100 LMW Bipolar jets Quasars

  26. 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

  27. 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

  28. 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

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