Here is an interesting [and important] paper, IMO:(adsbygoogle = window.adsbygoogle || []).push({});

The Hubble Constant: A Summary of the HST Program for the Luminosity Calibration of Type Ia Supernovae by Means of Cepheids

Authors: A. Sandage (1), G.A. Tammann (2), A. Saha (3), B. Reindl (2), F.D. Macchetto (4), N. Panagia (4)

http://www.arxiv.org/abs/astro-ph/0603643

P25

. . . To obtain H0 some assumptions on Omega[M] and Omega[lambda] necessary. The disadvantage of long look-back times for the deermination of H0 becomes most pronounced in case of the Fourier spectrum of the CMB acoustic waves, where a number of free parameters must simultaneously be solved for. The solution for H0 depends therefore on the number of free parameters allowed for and on some priors forced on the data as well as on the observations used. A six-parameter solution of the WMAP data with some priors and additional observational constraints has yielded H0 = 71+4−3 Spergel et al. (2003). This has often been taken as a confirmation of H0 = 72± 8 as obtained from various distance indicators by Freedman et al. (2001), and has led to the opinion that the problem

of H0 has been solved. We disagree. The actual situation has been illustrated by Rebolo et al. (2004) who have used the Very Small Array and WMAP data to derive H0 = 66 ± 7 allowing for twelve free parameters and no priors. Clearly a strong motive to further reduce the systematic error of H0 by conventional means comes from the desire to use the Hubble constant itself as a reliable prior for the interpretation of the CMB spectrum.

A value of H0 = 62.3 corresponds in an Omega[M] = 0.3 and Omega[lambda] = 0.7 universe to an expansion age of 15.1 Gyr, which may be compared with the age of M92 of 13.5 Gyr (VandenBerg et al. 2002) and the Th/Eu age of the Galactic halo of ~15 Gyr (Pagel 2001). Ultra-metal-poor giants yield radioactive ages between 14.2±3.0 to 15.6±4.0 Gyr (Cowan et al. 1999; Westin et al. 2000; Truran et al. 2001; Sneden et al. 2003). A high-weight determination of the U/Th age of the Milky Way gives 14.5 ± 2.5 Gyr (Dauphas 2005). All these values must, of course, still to be increased by the gestation time of the chemical elements.

P26

. . . 7. CONCLUSIONS

(1) The final result of our HST collaboration, ranging over 15 years, is that

H0(cosmic) = 62.3 ± 1.3 (random) ± 5.0 (systematic) (8)

based on 62 SNe Ia with 3000 < vCMB < 20 000 kms−1 and on 10 luminosity-calibrated SNe Ia. All SNe Ia have been corrected for Galactic and internal absorption and are normalized to decline rate #m15 and color (Paper III). The weighted mean luminosities of the 10 calibrators of MB = −19.49, MV = −19.46, and MI = −19.22 (Table 4) are based on metallicity-corrected Cepheid distances (Paper IV) from the new P-L relations of the Galaxy and LMC (Paper I & II). (2) The local value of H0 (300 ∼< v220 < 2000 kms−1) is H0(local) = 60.9 ± 1.3 (random) ± 5.0 (systematic) (9)

from 25 Cepheid and 16 SNe Ia distances, involving a total of 34 di#erent galaxies. Their distances are related to the barycenter of the Local Group and their observed velocities are corrected for a self-consistent Virgocentric infall model with a local infall vector of 220 kms−1.

The local value of H0 is supported by the mean distances and mean velocities hv220i of the Virgo and Fornax cluster (Table 7).

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