Page 1 of 1

[1004.1856] The Hubble Constant

Posted: April 15 2010
by Syksy Rasanen
This is a nice review of the determination of [tex]H_0[/tex], with an emphasis on methods independent of the cosmological model. The updated HST value is given as [tex]73\pm2\pm4[/tex] km/s/Mpc, with values from other methods in the same range. (To be contrasted with 0806.3018, which gives [tex]62\pm1\pm4[/tex] km/s/Mpc, from SNIae, Cepheids and the tip of the red giant branch.)

Cepheids remain an important calibrator for the distance scale, and there is still controversy about metallicity corrections (partly explaining the discrepant numbers mentioned above). One of the improvements reported here is changing the calibration from Cepheids in the Large Magellanic Cloud to Cepheids in our own galaxy. Since the metallicity of these Cepheids is closer to the galaxies where the supernovae used for the determination of [tex]H_0[/tex] reside, this should make the corrections smaller. The authors in fact write that this changes the metallicity corrections from a systematic error to a statistical error, which will decrease as more Cepheids are observed.

There is also a short review on the age of the universe, where I found the CMB discussion to be a bit misleading, because the dependence on the cosmological model is not mentioned (apart from the assumption of spatial flatness).