Abstract
We present an updated version of the multicolor light-curve shape method to measure distances to Type Ia supernovae (SNe Ia), incorporating new procedures for K-correction and extinction corrections. We also develop a simple model to disentangle intrinsic color variations and reddening by dust and expand the method to incorporate U-band light curves and to more easily accommodate prior constraints on any of the model parameters. We apply this method to 133 nearby SNe Ia, including 95 objects in the Hubble flow (cz ≥ 2500 km s-1), which give an intrinsic dispersion of less than 7% in distance. The Hubble flow sample, which is of critical importance to all cosmological uses of SNe Ia, is the largest ever presented with homogeneous distances. We find that the Hubble flow SNe with H0dSN ≥ 7400 km s-1 yield an expansion rate that is 6.5% ± 1.8% lower than the rate determined from SNe within that distance, and this can have a large effect on measurements of the dark energy equation of state with SNe Ia. Peculiar velocities of SN Ia host galaxies in the rest frame of the Local Group are consistent with the dipole measured in the cosmic microwave background. Direct fits of SNe Ia that are significantly reddened by dust in their host galaxies suggest that their mean extinction law may be described by RV 2.7, but optical colors alone provide weak constraints on RV.
Highlights
The cosmological applications of type Ia supernovae (SN Ia) result from precise distances to these calibrated candles
The first of these was introduced by Phillips (1993), who noted that the parameter ∆m15(B), the amount by which a SN Ia declined in the B-band during the first fifteen days after maximum light, was well correlated with SN Ia intrinsic luminosity
Constructing a Hubble diagram of nearby SN Ia (Hubble 1929; Kirshner 2004) requires a Hubble flow sample, for which the measured recession velocities are dominated by the cosmological redshift
Summary
The cosmological applications of type Ia supernovae (SN Ia) result from precise distances to these calibrated candles. A number of methods have been developed to measure calibrated distances from SN Ia multicolor light curves, with each enjoying a similar level of success The first of these was introduced by Phillips (1993), who noted that the parameter ∆m15(B), the amount by which a SN Ia declined in the B-band during the first fifteen days after maximum light, was well correlated with SN Ia intrinsic luminosity. Riess et al (1998a) updated the training set, using reliable distances measured by the Hubble Law in favor of other methods, added a quadratic (∆2) term to create the template light curves, and included the effects of covariance in the model The application of this version of MLCS to nearby SN Ia and the Hubble Constant is given by Jha et al (1999a). Krisciunas, personal communication; (41) Krisciunas et al 2003; (42) Leonard et al 2005; (43) Szaboet al. 2003; (44) Benetti et al 2004; (45) Li et al 2003; (46) Pignata et al 2004
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