Cosmic Distance Determinations Radar (works for inner solar system) Parallax D(pc) = 1 p(arcsec) GAIA satellite (2013) 20 micro-arcsec resolution! Thus D < 10 kpc Beyond Parallax: Standard Candles Use measured flux and known luminosity of object. r L d = 4 F
Spectroscopic Parallax For each individual star, determine location on HR diagram using spectrum and luminosity class (determined from line widths) Use on a cluster of stars to reduce uncertainties D < 10-50 kpc
Cepheid variables are pulsating variable stars (similar to the RR Lyraes) due to a dynamical instability (between radiation pressure and gravity). Oscillation period correlated to luminosity D < 25 Mpc Cepheid Variables https://universe-review.ca/r02-07-candle.htm
http://astrowww.phys.uvic.ca/~lff/research.html
Cepheids in Andromeda Edwin Hubble used 100-inch telescope on Mount Wilson Found a cepheid in Andromeda nebula Proved that Andromeda was a whole galaxy completely separate from the Milky Way. 770 kpc away Firm evidence for the island universes hypothesis The Andromeda galaxy (M31)
Cepheids in the Virgo galaxy cluster with Hubble Space Telescope (16 Mpc away )
Planetary Nebula For a particular galaxy, determine the number of PN as function of apparent magnitude (flux) of O III (5007 A). Fit to planetary nebula luminosity function (PNLF) based on statistical distribution in terms of absolute magnitude (luminosity)
White Dwarf Supernova Most luminous standard candle
High-Z Supernova z = 1.71 10 Billion light years away! http://newscenter.lbl.gov/2013/01/09/scp0401-farthest-yet/ https://arxiv.org/abs/1205.3494
Structure of Galaxy Distribution Milky Way is one of roughly 30 galaxies in the local group. 2 spirals 1 small spiral 2 ellipticals 13 irregulars 14 dwarf ellipticals 90% of mass is due to M31 and Milky Way diameter about 10 million ly
Nearby Clusters Other nearby clusters are also poor: Sculptor group (d=1.8 Mpc): 6 spiral galaxies M81 group (d=3.1 Mpc): 8 spiral galaxies Centaurus (d=3.5 Mpc): 17 spiral galaxies M101 (d=7.7 Mpc): 5 spiral galaxies Roughly 20 small groups within 15 Mpc Nearest Rich Clusters: Virgo (d = 16 Mpc): 250 large galaxies, 2,000 small galaxies, size = 3 Mpc; M87 in center (which has a mass 3 x 10 13 M solar )
Virgo Cluster
Coma Cluster
Structure of Galaxy Distribution Coma Cluster (d=100 Mpc): Roughly 10,000 galaxies; Most galaxies are ellipticals One of the largest clusters known: 7 Mpc across Mass roughly 7 x 10 14 M Solar Superclusters: Clusters of clusters Combined mass of 10 15 M solar Size roughly 40 Mpc 100 Mpc Milky Way in Local supercluster (Virgo supercluster) Voids Size roughly 50 Mpc
http://www.atlasoftheuniverse.com/superc/com.html
Hubble s Law z = 0 = 0 1 1929: Hubble discovered that all far-away galaxies are redshifted : The redshift is proportional to the distance to the galaxy
Interpretation was that the redshifts are due to Doppler shifts z = s For small redshifts, z v/c 1+v/c 1 v/c Hubble s Law: Recession velocity is proportional to distance to galaxy v = H 0 d 1
z = / emit = obs / emit 1= s (1 + v/c) (1 v/c) 1 Note that the relationship between velocity and redshift is not linear for relativistic velocities.
Peculiar Velocities Galaxies are moving due to gravitational interactions with other galaxies. Without peculiar velocities, we could easily measure Hubble s constant using nearby galaxies. Typical peculiar velocities are Thus velocities due to Hubble s law dominate when H 0 d >> 100 km/s, or d >> 1 Mpc. v p 100 km/s
Hubble s Constant Lots of research went into determining H 0 H 0 = 74 ± 3 km/s/mpc https://www.cfa.harvard.edu/~dfabricant/huchra/hubble/
New way to get distance! v = H 0 d d = cz H 0 =4 10 3 74 km/s/mpc H 0 z Mpc
Supercluster Distribution
2dF Survey 1997-2002 Anglo-Australian Observatory 221,414 galaxies with reliable redshifts 1500 square degrees
6dF Galaxy Survey 136,304 spectra, 110,256 redshifts (southern sky) 10 times the sky area of the 2dF UK Schmidt Telescope Multi-object fibre spectograph 2001-2006
Sloan Digital Sky Survey Dedicated 2.5 m telescope at Apache Point (New Mexico) 2000 present 500 million photometric observations; over 3 million spectra 35% sky coverage