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Whirlwind Tour of the Universe, Part 2A: Normal (& Active Galaxies

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Whirlwind Tour of the Universe, Part 2A: Normal (& Active Galaxies Whirlwind Tour of the Universe, Part 2a: Normal (& Active Galaxies & Hubble Law) Goals: 1. Overview of Galaxy Types and Properties 2. Methods of Study The Backstory: Messier •Looking for Halley’s Comet Found “cometary nebulae” that • Charles Messier were not moving (1730-1817) ? Messier’s Sketch of Andromeda The Backstory: The Great Debate April 26, 1920 - “The Scale of the Universe” Harlow Shapley vs. Heber Curtis • Milky Way was the • Milky Way was one of entire Universe many galaxies in a vast universe • spiral nebulae were • spiral nebulae were clouds of gas in MW enormously distant No Clear Resolution The Resolution: Edwin Hubble (1889-1953) • Noticed individual stars in Andromeda (Messier 31) • Measured the distance using known bright variable stars (Cepheid Variables) • Result was MUCH farther than expected, placing it well beyond the Milky Way Conclusive evidence for a “universe of galaxies” The Backstory: Hubble’s Tuning Fork Diagram (1936) Hubble divided galaxies into different “classes” based on their appearance - First study of galaxy morphologies (Evolutionary Sequence?) Galaxy Morphologies Hubble Ultra Deep Field Galaxy Morphologies Virgo Galaxy Cluster Original HDF (close up) Galaxy Toolkit: Morphologies (Hubble’s Tuning Fork Diagram) Morphological Classifications: •Ellipticals •Spiral and Barred Spiral •Lenticular (S0) •Irregular Elliptical Galaxies (E0-E7) Text Classified according to their eccentricity: •E0 is spherical, E7 is most eccentric •En where n = 10(a-b)/a - what are a & b? Elliptical Galaxies (E0-E7) Text Classified according to their eccentricity: •E0 is spherical, E7 is most eccentric •En where n = 10(a-b)/a - what are a & b? No info on 3-D morphology! Types of Elliptical Galaxies 12 13 Giant Ellipticals - few Mpc across, 10 /10 M⊙ 6 Dwarf Ellipticals (dE) - as small as 1 kpc, 10 M⊙ Dwarf Spheroidal (dSph) - Very low stellar density and surface brightness Trends: • low gas content (1% of total mass in ISM) • no current star formation (weak dust emission) NGC 205 • no O/B stars (similar to mw halo - color?) • Unlike halo stars, metal abundances of these stars are high (2x solar) • Slow rotation/random velocities - geometry? • Luminosity concentrated at center Leo I dSph Galaxy Toolkit: Metallicity/Surface Brightness Surface Brightness: Brightness distribution of a galaxy (or any 2 extended source) measured in magnitudes/arcsec (µI, µB, µR, etc.) Results in isophotes Luminosity Profiles: Luminosity per unit area Metallicity: Abundance of elements other than H/He (relative to solar) Spiral Galaxies (Sa-Sc) Classified according to tightness of spiral arms and size of nuclear bulge •Sa - tightest spirals and largest bulges •Sc - loosest and smallest Sizes - R = 10 to 30 kpc 7 11 Masses - M = 10 to 10 Msun Milky Way - Between Sb/Sc (Sb or Sbc)...BARRED Barred Spiral Galaxies (SBa - SBc) •Contain a linear feature of nearly uniform brightness centered on nucleus •Subclasses follow those of spirals with subtypes a b and c Spiral Galaxies - Types Grand Design Spiral - well defined spiral structure (like MW) Flocculent - less organized spiral design Trends: • Lots of gas & dust (ISM) • O and B stars - ongoing Star Formation!! • Young - metallicity? • Disk/Bulge geometry - rotation? • Sharp Luminosity profiles... NGC 4414 Lenticular Galaxies (S0) •Smooth, central brightness concentration (bulge similar to E) surrounded by a large region of less steeply declining brightness (similar to a disk) •No spiral arm structure but some contain dust and gas •Originally thought to be transition objects between Sa and E but typical S0 is 1-2 mags fainter than typical Sa, E (van den Bergh 1998) Irregular Galaxies (Irr I, Irr II) NGC 4485-Irr II M82-Irr II Irr I •Small galaxies with no morphological symmetry •Lots of young, blue stars and interstellar material •Two major subtypes: •Irr I: spiral-like but no defined arms, bright knots with O,B stars •Irr II: smooth but with dust lanes and gas filaments (e.g. M82) - explosive Starburst Galaxies - M82 (Cigar - Irr2) Starburst Galaxies - M82 (Cigar - Irr2) •supergalactic wind of ionized gas powered by the energy released in the starburst! Starburst Galaxies - M82 (Cigar - Irr2) •supergalactic wind of ionized gas powered by the energy released in the starburst! Star Formation in Galaxies 30 Dorado (Tarentula Nebula) in LMC Star Formation in Galaxies 30 Dorado (Tarentula HII image of LMC Nebula) in LMC Dark Cloud - CO emission shows complex of GMCs (~20) extending in arc over 600pc FIR shows embedded regions where dust is heated by SF! Star Formation in Galaxies 30 Dorado (Tarentula HII image of LMC Nebula) in LMC Dark Cloud - CO emission shows complex of GMCs (~20) extending in arc over 600pc FIR shows embedded regions where dust is heated by SF! N11 - Ring of clouds (Orion anyone??) Star forming regions in LMC are very similar to those in MW!.
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