Allan Sandage and the distance scale
Abstract
Allan Sandage returned to the distance scale and the calibration of the Hubble constant again and again during his active life, experimenting with different distance indicators. In 1952 his proof of the high luminosity of Cepheids confirmed Baade's revision of the distance scale (H_{0} ~ 250 km s^{1} Mpc^{1}). During the next 25 years, he lowered the value to 75 and 55. Upon the arrival of the Hubble Space Telescope, he observed Cepheids to calibrate the mean luminosity of nearby Type Ia supernovae (SNe Ia) which, used as standard candles, led to the cosmic value of H_{0} = 62.3 +/ 1.3 +/ 5.0 km s^{1} Mpc^{1}. Eventually he turned to the tip of the red giant branch (TRGB) as a very powerful distance indicator. A compilation of 176 TRGB distances yielded a mean, very local value of H_{0} = 62.9 +/ 1.6 km s^{1} Mpc^{1} and shed light on the streaming velocities in the Local Supercluster. Moreover, TRGB distances are now available for six SNe Ia; if their mean luminosity is applied to distant SNe Ia, one obtains H_{0} = 64.6 +/ 1.6 +/ 2.0 km s^{1} Mpc^{1}. The weighted mean of the two independent largescale calibrations yields H_{0} = 64.1 km s^{1} Mpc^{1} within 3.6%.
 Publication:

Advancing the Physics of Cosmic Distances
 Pub Date:
 February 2013
 DOI:
 10.1017/S1743921312021059
 arXiv:
 arXiv:1211.4655
 Bibcode:
 2013IAUS..289...13T
 Keywords:

 cosmological parameters;
 distance scale;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 13 pages, 9 figures, 1 table