| Title | A New Cepheid Distance to the Maser-Host Galaxy NGC 4258 and Its Implications for the Hubble Constant |
| Authors | Macri, L. M.; Stanek, K. Z.; Bersier, D.; Greenhill, L. J.; Reid, M. J. |
| Bibcode | 2006ApJ...652.1133M Search ADS ↗ |
| Abstract | We present initial results from a time series BVI survey of two fields in NGC 4258 using the HST ACS. This galaxy was selected because of its accurate maser-based distance, which is anticipated to have a total uncertainty of ~3%. The goal of the HST observations is to provide an absolute calibration of the Cepheid distance scale and to measure its dependence on chemical abundance (the so-called metallicity effect). We carried out observations of two fields at different galactocentric distances with a mean abundance difference of 0.5 dex. We discovered a total of 281 Cepheids with periods ranging from 4 to 45 days (the duration of our observing window). We determine a Cepheid distance modulus for NGC 4258 (relative to the LMC) of ∆μ0=10.88+/-0.04 (random)+/-0.05 (systematic) mag. Given the published maser distance to the galaxy, this implies μ0(LMC)=18.41+/-0.10r+/-0.13s mag or D(LMC)=48.1+/-2.3r+/-2.9s kpc. We measure a metallicity effect of γ=-0.29+/-0.09r+/-0.05s mag dex-1. We see no evidence for a variation in the slope of the period-luminosity relation as a function of abundance. We estimate a Hubble constant of H0=74+/-3r+/-6s km s-1 Mpc-1 using a recent sample of four well-observed Type Ia SNe and our new calibration of the Cepheid distance scale. It may soon be possible to measure the value of H0 with a total uncertainty of 5%, with consequent improvement in the determination of the equation of state of dark energy. Based on observations with the Advanced Camera for Surveys on board the NASA/ESA Hubble Space Telescope, obtained at STScI, which is operated by AURA, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-9810. |
| Objects | 6 Objects Search NED ↙ |
