  At the age of about 1 year, the spectra of most Type Ia supernovae are
dominated by strong forbidden nebular emission lines of FeII and FeIII. Later
observations (at about 2 years) of the nearby SN 2011fe showed an unexpected
shift of ionization to FeI and FeII. Spectra of the very nearby SN Ia 2014J at
an intermediate phase (1 - 1.5 years) that are presented here show a
progressive decline of FeIII emission, while FeI is not yet strong. The
decrease in ionization can be explained if the degree of clumping in the ejecta
increases significantly at ~1.5 years, at least in the Fe-dominated zone.
Models suggest that clumps remain coherent after about one year, behaving like
shrapnel. The high density in the clumps, combined with the decreasing heating
rate, would then cause recombination. These data may witness the phase of
transition from relatively smooth ejecta to the very clumpy morphology that is
typical of SN remnants. The origin of the increased clumping may be the
development of local magnetic fields.
