Final Results from theHubble Space TelescopeKey Project to Measure the Hubble Constant

Abstract

We present here the Ðnal results of the Hubble Space T elescope (HST ) Key Project to measure the Hubble constant. We summarize our method, the results, and the uncertainties, tabulate our revised distances, and give the implications of these results for cosmology. Our results are based on a Cepheid calibration of several secondary distance methods applied over the range of about 60È400 Mpc. The analysis presented here beneÐts from a number of recent improvements and reÐnements, including (1) a larger LMC Cepheid sample to deÐne the Ðducial period-luminosity (PL) relations, (2) a more recent HST Wide Field and Planetary Camera 2 (WFPC2) photometric calibration, (3) a correction for Cepheid metallicity, and (4) a correction for incompleteness bias in the observed Cepheid PL samples. We adopt a distance modulus to the LMC (relative to which the more distant galaxies are measured) of mag, or 50 kpc. New, revised distances are given for the 18 spiral galaxies for k 0 (LMC) \ 18.50^0.10 which Cepheids have been discovered as part of the Key Project, as well as for 13 additional galaxies with published Cepheid data. The new calibration results in a Cepheid distance to NGC 4258 in better agreement with the maser distance to this galaxy. Based on these revised Cepheid distances, we Ðnd values (in km s~1 Mpc~1) of (random)^6 (systematic) (Type Ia supernovae),

Pulsating variable stars in the Magellanic Clouds

“…In the latter case, the (Freedman et al 2001) used the slope of the CCs P L relations by Udalski et al (1999a) and a zero-point consistent with an assumed true distance modulus for the LMC of μ LMC =18.5 mag to measure distances to 31 galaxies with distances from 700 kpc to 20 Mpc. These then served to calibrate other, more farreaching secondary distance indicators to determine the Hubble constant in a region of constant Hubble flow (see Freedman et al 2001, but also Saha et al 2001, andTammann et al 2008, for different conclusions on the value of H 0 ).…”

A review of the distance and structure of the Large Magellanic Cloud

“…where µ I and µ V are apparent moduli relative to LMC PL calibrations (Freedman et al 2001). As a check, consider the following application of this method to the Cepheids in the Galaxy.…”

“…Table 2 demonstrates a remarkably high level of consistency. The possibility that a consensus on the LMC distance has been reached seems much more plausible now than it did when Freedman et al (2001) reviewed the literature at the conclusion of the HST key project only two years ago.…”

“…The debate about the distance to the LMC has an epic history full of controversial and dramatic claims, and yet in recent years a standard distance modulus has emerged due primarily to the completion of the Hubble Space Telescope (HST ) key project to measure the Hubble constant (Freedman et al 2001). The standard modulus, µ 0 = 18.5 ± 0.1 mag, yields H 0 = 71 ± 10 km s −1 Mpc −1 (total error) in excellent agreement with that derived from the Wilkinson Microwave Anisotropy Probe: H 0 = 72 ± 5 (Spergel et al 2003), which lends considerable support to its accuracy.…”

Where Does The Dark Matter Begin?

“…The Party line these days is that the Hubble constant is a known quantity based either on local estimates (H 0 = 72 ± 8 km/s/Mpc, Freedman et al 2001) or models of CMB fluctuations assuming a flat universe with a cosmological constant (H 0 = 72 ± 5 km/s/Mpc, Spergel et al 2003). For the purposes of this review, let us assume that the Party is correct and consider its implications.…”