16 Galaxies Island Universes

16 Copyright – FORS1 VLTI, European Southern Observatory

16 Hubble Tuning Fork

16 Ellipticals

16 Huge No gas. No dust. No young stars. Nothing but old stars. –Random orbits.

16 M 87 Copyright – Anglo-Australian Telescope Board Copyright - HST

16 Hubble Tuning Fork

16 Copyright – Adam Block, KPNO

16 Spirals

16 Like Milky Way. Disks and bulge. Young stars and old. Gas and dust. Stars forming. Stars dying. M81 and M82 – Copyright R. Gendler

16 M63 Copyright – S. Miyazaki, Suburu

16 NGC1365 Copyright – VLT

16 M31 The Andromeda Galaxy Copyright – Jason Ware Copyright – S. Miyazaki, Suburu

16 M33 – Copyright NOAO

16 M51 - Copyright HST John P. Gleason

16 NGC 4314

16 NGC 891 – Copyright J.C. Barentine, NOAO NGC 891 – Copyright WIYN

16 Sombrero Galaxy – Copyright P. Barthel VLT M10 – copyright Credner and Kohle

16 NGC 4526

16 Irregulars

16 Distance to Near Galaxies Need a standard candle. If there is something in a galaxy which has a known luminosity we can determine a distance. Several candidates: –Variable stars –Supernovae –“Brightest” stars

16 M3 Variables in Clusters Copyright – K. Stanek (Harvard)

16 Variable Stars For RR Lyrae stars: –Average luminosity is a standard candle –Always ~ 100 x Sun For Cepheid variables: –Pulsation period is proportional to average luminosity –Observe the period  find the luminosity Good to 15 Mpc!

16 Nearby Galaxies Cepheids Period Luminosity  M v Know m v Get Distance

16 For Cepheid in M100 P = 20 days. From P-L: L = x Sun M sun = 5, so M Cep = -5 m = 20 m – M = 25 So 25/5 = 5 = log(d/10pc) How log works: –What is 100 = 10 x ? –Same as saying 2 = log(100) So 5 = log(d/10pc) d/10pc = D = 1,000,000 pc How it works

16 The Local Group

16 Groups

16 The Virgo Cluster

16 Clusters

16 Concept Test A standard candle can be any object (or class of object) that: a.Always has the same luminosity. b.Has some means of knowing its luminosity without first needing to know its distance. c.Can vary in brightness (as long as it always has the same average luminosity). d.Has a known absolute magnitude. e.Always gives off the same amount of energy, regardless of distance from us.

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16 NGC 1316 – Copyright VLT

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16 Distant Galaxies Can’t see individual stars. Supernovae rare. Can use nearby galaxies to get distances to further galaxies. Distance ladder: –Parallax  nearby stars –Nearby stars  H-R diagram –H-R diagram  distant stars (variables) –Variable stars  nearby galaxies –Nearby galaxies  Hubble’s Law

16 21cm Radiation Neutral hydrogen (HI) gives off light, = 21cm. Milky Way HI emission – Copyright J. Dickey

16 Extragalactic HI Observe HI in other galaxies. Measure wavelength of 21 cm radiation. Doppler Shift: Get velocity away from us.

16 Hubble’s Law Measure the velocity of every galaxy. Nearly all are redshifted. Use Cepheids to measure distances to nearby galaxies. Result: The faster it’s moving, the farther away it is. H o = 71 km/s/Mpc

16 Map the Universe v = H o D If you know H o : 71 km/s/Mpc Measure v Get D Find: Voids Walls Clusters

Mpc 70 Mpc

16 Concept Test Imagine that Cepheid variables were more luminous than previously thought. As a result, Hubble’s constant would be: a.Smaller than previously thought. b.Larger than previously thought. c.Unchanged since we aren’t changing either the velocity or position of the galaxy. d.None of the above.

16 Limits to Hubble’s Law Negative velocity? Galaxy pairs? Clusters? Orbits?

16 Homework #16 For Friday Read: Bennett Ch 22.1 – 22.4 Do Ch22: –Problems: 9, 12