The Distance to NGC 1316 (Fornax A) From Observations of Four Type Ia
  Supernovae
  The giant elliptical galaxy NGC 1316 (Fornax A) is a well-studied member of
the Fornax Cluster and a prolific producer of Type Ia supernovae, having hosted
four observed events since 1980. Here we present detailed optical and
near-infrared light curves of the spectroscopically normal SN 2006dd. These
data are used, along with previously published photometry of the normal SN
1980N and SN 1981D, and the fast-declining, low-luminosity SN 2006mr, to
compute independent estimates of the host reddening for each supernova, and the
distance to NGC 1316. From the three normal supernovae, we find a distance of
17.8 +/- 0.3 (random) +/- 0.3 (systematic) Mpc for Ho = 72. Distance moduli
derived from the "EBV" and Tripp methods give values that are mutually
consistent to 4 -- 8%. Moreover, the weighted means of the distance moduli for
these three SNe for three methods agree to within 3%. This consistency is
encouraging and supports the premise that Type Ia supernovae are reliable
distance indicators at the 5% precision level or better. On the other hand, the
two methods used to estimate the distance of the fast-declining SN 2006mr both
yield a distance to NGC 1316 which is 25-30% larger. This disparity casts doubt
on the suitability of fast-declining events for estimating extragalactic
distances. Modest-to-negligible host galaxy reddening values are derived for
all four supernovae. Nevertheless, two of them (SN 2006dd and SN 2006mr) show
strong NaID interstellar lines in the host galaxy system. The strength of this
absorption is completely inconsistent with the small reddening values derived
from the supernova light curves if the gas in NGC 1316 is typical of that found
in the interstellar medium of the Milky Way. In addition, the equivalent width
of the NaID lines in SN 2006dd appear to have weakened significantly some
100-150 days after explosion.
