The Cosmological Distance Ladder – to redshift 1000 First steps on the distance ladder The Copernican revolution The first steps outside the solar system The key modern distance indicator – Cepheid variable stars

The Cosmological Distance Ladder - to redshift 1000 First steps on the distance ladder The Copernican revolution The first steps outside the solar system The key modern distance indicator – Cepheid variable stars www.phwiki.com

The Cosmological Distance Ladder – to redshift 1000 First steps on the distance ladder The Copernican revolution The first steps outside the solar system The key modern distance indicator – Cepheid variable stars

Battersby, Mark, Contributing Editor has reference to this Academic Journal, PHwiki organized this Journal The Cosmological Distance Ladder – to redshift 1000 Michael Rowan-Robinson Imperial College First steps on the distance ladder Aristotle (384-322 BC) – estimated the size of the earth (+ Eratosthenes, Poseidonius, 10%) Hipparcos (2nd C BC) – estimated distance of the moon (59 RE, cf modern value 60.3) Aristotle, by Raphael The Copernican revolution Copernicus (1473-1543) – gave the correct relative distances of the sun in addition to planets (to 5%) – absolute value not determined accurately till the 19th century

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The first steps outside the solar system Bessel 1838 – discovered parallax of nearby star 61 Cyg, its change in apparent direction on the sky due to the earth’s orbit round the sun (the final proof of the Copernican system) The key modern distance indicator – Cepheid variable stars Delta Cephei is the prototype of the Cepheid variable stars, massive stars which pulsate in addition to vary their light output Henrietta Leavitt’s breakthrough In 1912, Henrietta Leavitt, working at the Harvard Observatory, discovered from her studies of Cepheids in the Small Magellanic Cloud that the period of Cepheid variability was related to their lumininosity

The distances of the galaxies In 1924 Edwin Hubble used Leavitt’s discovery to estimate the distance of the Andromeda Nebula. It clearly lay far outside The Milky Way system. The expansion of the universe Three years later, in 1927, he announced, based on distances to 18 galaxies, that the more distant a galaxy, the faster it is moving away from us velocity/distance = constant, Ho (the Hubble law) This is just what would be expected in an exp in addition to ing universe. The Russian mathematician Alex in addition to r Friedmann had shown (1922, 1924) that exp in addition to ing universe models are what would be expected according to Einstein’s General Theory of Relativity, if the universe is homogeneous (everyone sees the same picture) in addition to isotropic (the same in every direction). The history of the Hubble constant Hubble’s estimate of the Ho, the Hubble constant, was 500 km/s/Mpc, which gave an age as long as the universe of only 2 billion years. This was soon shown to be shorter than the age of the earth. From 1927 to 2001 the value of the Hubble constant was a matter of fierce controversy. S in addition to age 1958 >

The cosmological distance ladder This was my 1985 summary of the cosmological distance ladder The cosmological distance ladder In my monograph ‘The Cosmological Distance Ladder’ (Freeman 1985), I set out to underst in addition to the competing estimates of Ho (50 – S in addition to age in addition to Tammann, 100 – de Vaucouleurs), in addition to to reconcile the systematic differences in distance estimates from different methods. With an objective weighting scheme based on quoted errors, in addition to with higher weight as long as purely geometrical distance methods, I concluded that there were systematic errors in the supernova method (too high distances) in addition to in the Tully-Fisher in addition to HII region methods (too low) in addition to that best overall value as long as H0 was Ho = 67 +- 12 km/s/Mpc Implications of the Hubble constant Ho is (velocity/distance) so has the dimensions of (1/time). 1/Ho is the expansion age of the universe (how old the Universe would be if no as long as ces acting) = 15.3 billion yrs For simplest model universe with only gravity acting, age of universe would be 10.2 billion years (gravity slows expansion)

The age of the universe We can use the colours in addition to brightnesses of the stars in globular clusters to estimate the age of our Galaxy ~ 12 billion years Long-lived radioactive isotopes give a similar answer Allowing time as long as our Galaxy to as long as m, the age of the universe is ~ 13 billion years Already a problem as long as L= 0 The Hubble Space Telescope Key Program Following the first HST servicing mission, which fixed the telescope aberration, a large amount of HST observing time was dedicated to measuring Cepheids in distant galaxies, to try to measure the Hubble constant accurately, in addition to to give the different distance methods a secure in addition to consistent calibration. The Key Program soon split into two teams, one led by Wendy Freedman, Jeremy Mould in addition to Rob Kennicutt, the other by Allan S in addition to age in addition to Gustav Tammann. Some of the galaxies studied by HST

HST Key Project strategy Kennicutt et al 1995 The HST Key program final result (1) log V Ho = 72 +- 8 km/s/Mpc (Freedman et al 2001) Any room as long as doubt There is good consistency between the HST Key Program value of Ho in addition to the age of the universe, provided we invoke Einstein’s Cosmological Constant, L (dark energy) Uncertainties in Ho are (1) distance of Large Magellanic Cloud, (2) the adopted Cepheid calibration, (3) corrections as long as dust extinction, (4) corrections as long as metallicity effects, (5) corrections as long as local flow Using the Freedman et al data, my own best estimates as long as these corrections, in addition to the weighting scheme of CDL 1985, I concluded: Ho = 63 +- 6 (Rowan-Robinson 2000, astro-ph/0012026)

Distance of LMC mo = 18.5+-0.1 (d = 50 kpc, +-10%) – a fundamental limitation of local estimates of Ho perhaps Gaia will resolve this Type Ia supernova In 1998 two teams announced that using Type Ia supernovae as st in addition to ard c in addition to les implied that L > 0 (Schmidt et al 1998, Garnevich et al 1998, Riess et al 1998, Perlmutter et al 1999) There were issues with (1) treatment of extinction by dust, (2) consistency of treatment of correlation of decline rate with luminosity (Liebundgut 2001, Rowan-Robinson 2002). I also raised two other issues: (3) inconsistencies with earlier supernova data, (4) inappropriate use of supernovae not observed be as long as e maximum Joint HST Key Project in addition to SN team found Ho = 68 +- 5 (Gibson et al 1999) supernova issues data is clearly excellent, but this is not a geometric distance method new HST-ACS observations of Cepheids in galaxies with well-observed Type Ia supernovae gives Ho = 73 +- 6 (Riess et al 2005) – but based on LMC, with 10% distance uncertainty inconsistencies with earlier results can be attributed to photographic data issue of luminosity-decline rate relation addressed by Jha et al (2007) (see also new approach by Wang et al 2005, Nobili et al 2005) still some unresolved inconsistencies in derivation of extinction (can only be resolved by use of more photometric b in addition to s)

supernovae 2007 Latest data from Riess et al (2007) – clear support as long as consensus L model (cf also Astier et al 2005, SN Legacy Survey) consensus HST key program found Ho = 72 +- 8 (Freedman et al 2001) WMAP (year 1) found Ho = 72 +- 5 (Spergel et al 2003) (year 3) Ho = 73 +- 3 (Spergel et al 2007) new HST-ACS observations of Cepheids in galaxies with well-observed Type Ia supernovae gives Ho = 73 +- 6 (Riess et al 2005) so have consensus as long as H0=73, Wm=0.25, WL=0.75, age of universe 13.7 billion years History of the universe

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The HST Key program final result (2) new study of Cepheid P-L relation (Tammann et al 2003) difference between P-L relation in Galaxy in addition to LMC (S in addition to age et al 2005) new calibration using Baade-Wesselink method (so no LMC distance error) new discussion of extinction in supernovae Ho = 62 +- 5 km/s/Mpc (S in addition to age et al 2007) Hubble diagram as long as 62 supernovae other work on Ho Feast review (2007, ‘From IRAS to Herschel/Planck’): new HST Cepheid distances (Benedict et al 2007) revised Hipparcos parallaxes (van Leeuwen et al 2007) – revise S in addition to age’s Ho to 69.6 NGC4258 Cepheids (Macri et al 2006), consistency with maser distance gravitational lens time delay: 68+- 10 (Oguri 2007) 72+-10 (Saha et al 2006) Sunyaev-Zeldovich method as long as clusters: 66+-14 (Jones et al 2005) 76+-10 (Bonamente et al 05) CMB fluctuations in addition to Ho Boomerang in addition to Maxima, as long as flat universe, H0 = 75+-10 (Jaffe et al 2001) WMAP first year results: 72 +- 5 (Spergel et al 2003) include also SLOAN large-scale structure data: 68 +- 10 (Tegmark et al 2004) include Sloan large-scale structure + baryonic acoustic oscillation data: 65 +- 4.5 (Eisenstein et al 2005), WMAP 3-year results: 73 +- 3 (Spergel et al 2007) with LSS, BAO 69-72

Primordial density spectrum power-law assumption Spergel et al (2004) show that with power-law spectrum, but no restriction to flat models, can get wide range of fits just to WMAP3 CMB data can see that priors on Ho or assumption of flatness as long as ce us towards WL = 0.75 consensus model however dropping assumption of power-law opens up possibilities even further (Blanchard et al 2003) Blanchard et al (2003) model Blanchard et al (2003) showed that if we relax the assumption of a power-law primordial density spectrum (to a broken power-law) we can fit the CMB fluctuation spectrum just as well as the consensus model with a L=0, W0=1 (Einstein de Sitter) model, provided Ho = 46 can get consistency with large-scale structure data if Wn ~ 0.2 (mixed dark matter) however, inconsistent with supernova data in addition to H0=46 is 3-s from the direct estimates Shafieloo in addition to Souradeep (2007) deconvolve primordial density spectrum from CMB fluctuations in addition to show L=0, W0=1, H0=50, model is actually better fit than consensus model galaxy baryon acoustic peak SDSS (Eistenstein et al 2005) in addition to 2dFGRS (Cole et al 2005) have claimed to detect baryon acoustic oscillation (BAO) peak on scale ~ 150 Mpc in the galaxy correlation function Blanchard et al (2006) admit this is fatal as long as their L=0 model, if confirmed BAO plus CMB first Doppler peak is the ultimate geometrical measurement of Ho

conclusions local direct estimates of H0 = 62-72 +- 10% CMB estimates = 65-73 +- 4% (generally assuming flat universe, power-law spectrum, negligible Wn, w=-1) baryonic acoustic peak plus CMB first Doppler peak is the ultimate geometrical measurement of Ho precision measurements of H0 (say to 1%) could tell us that we need new physics beyond St in addition to ard Model. accurate distance to LMC (Gaia) Baade-Wesselink methods as long as Cepheids in addition to supernovae, multi-l photometry to control extinction in addition to metallicity

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