SIMBAD references

The extragalactic distance scale relies heavily on Cepheids. However, it has become clear from observations and pulsation models that the slope and zero point of their P-L relations differ from galaxy to galaxy. This makes the determination of Cepheid distances complex and calls for an independent test of their differences. The test is provided by RR Lyrae star distances of 24 galaxies that calibrate the tip of the red giant branch (TRGB; M^TRGB_I=-4.05), which in turn confirms the adopted Cepheid distances on our 2006 distance scale in 18 cases to within 0.1 mag on average. Relative SN Ia and velocity distances deny a remaining significant metallicity effect of the adopted distances. The new support for these Cepheid distances increases the weight of our previous calibration of the SN Ia luminosity and of the 21 cm line width-luminosity (TF) relation. The value of H₀=62.3 (±5) is confirmed on all scales.