Allan Sandage and the distance scale

Abstract

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 (H0 ∼ 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 H0 = 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 H0 = 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 H0 = 64.6 ± 1.6 ± 2.0 km s −1 Mpc −1 . The weighted mean of the two independent large-scale calibrations yields H0 = 64.1 km s −1 Mpc −1 within 3.6%.

Clustering of Local Group Distances: Publication Bias or Correlated Measurements? VI. Extending to Virgo Cluster Distances

“…Our recommended final value is, in fact, fully consistent with almost all of the weighted average distance moduli to either M87 or the center of the Virgo cluster published since 1990, with the notable exception of the Tammann et al (2000) value, (m − M ) 0 = 31.60 ± 0.09 mag. Jacoby et al (1992) considered seven of the most reliable extragalactic distance tracers-the GCLF, novae, SNe Type Ia, the TFR, the PNLF, SBF, and the D n − σ relation-to derive a weighted average of (m − M ) 0 = 31.02 ± 0.22 mag for the Virgo cluster.…”

“…Note that the error bar associated with the mean Cepheid distance is artificially enhanced by the inclusion of an apparently outlying data point published in December 1998. This latter value, obtained from Tammann et al (2000), 2 is part of a data set of galaxy distances that are commonly referred to as the 'long distance scale. '…”

“…mag, with a Gaussian spread of σ = 0.16 mag (D = 16.2 ± 1.2 Mpc). The equivalent values for the data set without the Tammann et al (2000) measurement are (m − M ) 0 = 31.03 mag and σ = 0.14 mag. None of these tracers suggest any trend as a function of publication date, and hence taking a straight average seems justified, also in view of the relatively small number of data points available.…”

Anchors for the cosmic distance scale: the Cepheids U Sagittarii, CF Cassiopeiae, and CEab Cassiopeiae

“…(1)) matches that derived for LMC and SMC Cepheids (Ngeow et al 2009), but is inconsistent with the slope established for distant solar extragalactic Cepheids associated with known supernova-host galaxies (Majaess 2010;Riess et al 2009). Continued research aimed at reducing uncertainties associated with the Cepheid calibration (e.g., Benedict et al 2007;Gieren et al 2013) and the impact of crowding on remote extragalactic Cepheid photometry may eventually help identify the source behind discrepant values of H 0 cited in the literature (e.g., Riess et al 2011;Freedman et al 2012;Tammann & Reindl 2013;Planck Collaboration 2013).…”

“…The Hubble constant cited by the Planck Collaboration (2013) differs by ∼5% from that determined by the SH 0 ES and Carnegie Hubble projects (Riess et al 2011;Freedman et al 2012), whereby the latter efforts rely partly on Cepheids for determining H 0 (see also Tammann & Reindl 2013, and references therein). The discrepancy is sufficient to hinder efforts to constrain the nature of dark energy (for which σ w ∼ 2σ H 0 , ), and could be linked to a systematic offset in the Cepheid calibration, or unreliable photometry for remote extragalactic Cepheids owing to crowding effects (Mochejska et al 2004;Majaess 2010Majaess , 2011a, see also Table 2 in Riess et al 2011).…”