Lecture 19: Normal Galaxies- Galaxies in the 'Hood

"Won't you be my neighbor?"

Mr. Rogers

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    • Date: April 11, 1995
    Reading Assignment: pp. 543-553

    Description : morphology and distance determination to galaxies in our local group

    Objectives

  • be able to describe and apply the Hubble classification scheme
  • be able to compare elliptical and spiral galaxies
  • be able to describe irregular galaxies and how they differ form elliptical and spiral galaxies
  • be able to define and describe the Tully-Fisher relationship
  • be able to describe the size and contents of our local group

    • Lecture Outline

    Slide # 1: Normal Galaxies - Galaxies in the 'Hood Slide # 2: Today's Lecture (GRAPHICS)

  • our Galaxy
  • a normal spiral galaxy
  • galaxy morphology
  • spirals, ellipticals, and irregulars
  • the Distance Ladder
  • Tully-Fisher relationship
  • the Local Group
    • Slide # 3: The View from Earth (GRAPHICS)
  • the Milky Way is a faint band of stars that circle sky
    • Slide # 4: The Curtis-Shapley Debate (GRAPHICS)
  • what is the size of our galaxy?
  • what is the nature of spiral nebula?
    • Slide # 5: Cepheid Variables
  • very high luminosity stars
  • found in globular clusters
  • by measuring the period, you can find the luminosity
  • from the luminosity and the brightness, you can calculate the distance
    • Slide # 6: Our Galaxy (GRAPHICS)
  • side view
    • Slide # 7: Spiral Arms
  • HI gas in our Galaxy is distributed in spiral arms
  • arms connect to the bulge
  • most young stars are also in these arms
  • regions of on-going star formation
    • Slide # 8: Disk Orbits (GRAPHICS)
  • top view
    • Slide # 9: Halo and Bulge Orbits (GRAPHICS)
  • everything orbits around the nucleus
  • random orientations and shapes
    • Slide # 10: Results (GRAPHICS)
  • a rotation curve
    • Slide # 11: Results
  • the mass of the Galaxy is about 1011 times the mass of the Sun
  • there is much more mass that the stars, dust, and gas we observe
  • some mass is NOT detected in any electromagnetic wavelength
    • Slide # 12: Dark Matter
  • matter detected because of its gravity
  • has no electromagnetic emission that we have detected
  • over 90% of our Galaxy is composed of Dark matter
  • also called the "Missing Mass"
    • Slide # 13: Are all Galaxies Spirals?
  • No!
  • Some have completely different shapes!
    • Slide # 14: Catalogs of Galaxies
  • astronomers began collecting photographs of galaxies
  • classification schemes were invented to understand these images
    • Slide # 15: The Hubble Classification Scheme
  • spirals
  • barred spirals
  • ellipticals
  • irregulars
    • Slide # 16: Spirals
  • similar to our Galaxy
  • has a bulge, disk, spirals arms, and halo
  • has circular orbits in the disk
  • random orbits in the halo and bulge
  • young stars found in the spiral arms
    • Slide # 17: Spiral Galaxies (GRAPHICS)
  • side view
    • Slide # 18: Spiral Arms (GRAPHICS)
  • top view (M51)
    • Slide # 19: Disk and Bulge (GRAPHICS)
  • m104
    • Slide # 20: 2.5 Meter Telescope (GRAPHICS)
  • M96
    • Slide # 21: HST Image
  • M96
    • Slide # 22: Constellation Corner (GRAPHICS)
  • Constellation De Jour
    • Slide # 23: Scorpius (GRAPHICS)
  • July 4 - 11pm - South - 4.0
    • Slide # 24: Scorpius (GRAPHICS)
  • July 4 - 11pm - South - 4.0
    • Slide # 25: Scorpius (GRAPHICS)
  • July 4 - 11pm - South - 4.0
    • Slide # 26: Scorpius (GRAPHICS)
  • July 4 - 11pm - 4.0 - S
    • Slide # 27: Scorpius (GRAPHICS)
  • July 4 - 11pm - 4.0 - S
    • Slide # 28: Barred Spirals
  • similar to normal Spirals
  • has disk, spiral arms, and halo
  • also has a disk-shaped bulge
  • bulge is replaced by "bar" of stars
  • stars are in circular orbits in the disk
  • random orbits in the halo
  • young stars found in the spiral arms
    • Slide # 29: Spiral Arms (GRAPHICS)
  • top view (M51)
    • Slide # 30: A Barred Spiral (GRAPHICS)
  • NGC 1365
    • Slide # 31: A Barred Spiral (GRAPHICS)
  • M91
    • Slide # 32: S0 Galaxies
  • has a bulge and disk
  • no spiral arms
  • no new star formation
  • almost no gas
    • Slide # 33: Elliptical Galaxies
  • no disk or spiral arms
  • all stars in "random orbits"
  • no young stars
  • no gas or on-going star formation
  • may be very large or very small
  • giant and dwarf sizes
  • a million to a trillion stars
  • kiloparsec to megaparsec sizes
  • range from circular to elongated
    • Slide # 34: A Giant Elliptical (GRAPHICS)
  • M87
    • Slide # 35: Irregular Galaxies
  • no spiral structure or disk
  • not elliptical in shape
  • does not fit the normal catagories
  • may have very high rates of star formation
    • Slide # 36: Irregular Galaxy (GRAPHICS)
  • Large Magellanic Cloud
    • Slide # 37: Irregular Galaxy (GRAPHICS)
  • NGC 1313
    • Slide # 38: Hubble Types (GRAPHICS)
  • Hubble classification scheme
    • Slide # 39: Galaxy Sizes (GRAPHICS)
  • spirals and ellipticals
    • Slide # 40: Star Formation and Galaxies
  • spirals and barred spirals have moderate rates of star formation
  • ellipticals and S0's have essentially no on-going star formation
  • irregulars have variable amounts of star formation
  • may be very high or very low
    • Slide # 41: Evolution of Galaxies
  • do spirals evolve from ellipticals?
  • do spirals arms and bulges change?
  • what are irregular galaxies?
    • Slide # 42: Galaxy Evolution
  • it appears that some or perhaps most ellipticals form when spiral galaxies mer
  • spirals seem to form directly from giant intergalactic gas clouds
    • Slide # 43: Formation of Spirals (GRAPHICS)
  • halo objects and bulge form from subfragmentation
    • Slide # 44: Spiral Formation (GRAPHICS)
  • remaining gas collapses into disk and then spiral arms begin to form
    • Slide # 45: Formation of Ellipticals
  • collision of spirals creates a galaxy with random orbits-- an elliptical
  • galaxy collisions are relatively common
  • about 5% of galaxies are currently interacting with their neighbors
    • Slide # 46: The Distance Ladder
  • to measure the distance to galaxies, you need to use several steps
  • you cannot measure distances to galaxies directly
    • Slide # 47: Radar
  • it is possible to bounce radio signals off the surface of Venus, Mars, and Mer
  • since the speed of light is constant, the time proportional to distance
  • allows us to accurately measure the size of the solar system
    • Slide # 48: Direct Parallax (GRAPHICS)
  • determine the distance to nearby stars using trigonometry
    • Slide # 49: Spectroscopic Parallax
  • absolute magnitude is related to stars spectral class
  • by comparing absolute and apparent magnitude, you can calculate distance
  • not a real parallax, but uses a "standard candle"
    • Slide # 50: Standard Candles
  • used in many stages of the distance ladder
  • assumes that something has a known absolute magnitude
    • Slide # 51: Cepheid Variables
  • bright variable stars
  • period of pulsation is related to absolute magnitude
  • a bright standard candle which is easy to identify
  • can be used for globular clusters and nearby galaxies
    • Slide # 52: Type Ia Supernova Explosions
  • very bright explosions
  • can be identified from spectra and light curve
  • luminosity, so they work as a standard candle
    • Slide # 53: The Tully-Fisher Relationship
  • the rotation speed of galaxies is related to its total mass
  • the mass is related to its luminosity
  • so--- the rotation speed of galaxies is related to its luminosity
  • galaxies can be used as "standard candles"
    • Slide # 54: Measuring the Rotation Speed (GRAPHICS)
  • the Doppler Shift
    • Slide # 55: The Tully-Fisher Relationship
  • spiral galaxies
  • to about 200 Mpc distance
    • Slide # 56: The Distance Ladder
  • radar
  • parallax
  • spectroscopic parallax
  • Cepheid variables
  • type I supernova, Tully-Fisher
    • Slide # 57: Clusters of Galaxies (GRAPHICS)
  • center of the Virgo Cluster
    • Slide # 58: A New Debate
  • what is the nature of Gamma-Ray bursts
  • are they inside or outside our Galaxy?
  • A Debate on April 22 at the Natural Hisotry Museum
  • Lamb vs Paczynski