Interstellar Na I and Ca II absorption in the spectrum of the recent supernova in NGC 4321

Using the supernova as a background continuum source, we have observed interstellar Na I and Ca II absorption at the redshift of the galaxy NGC 4321. Weak galactic Ca II K lines are also detected. The column densities for gas in NGC4321 are N(Na I) = $$4.4_{-1.0}^{+4.3}\,\times\,{10}^{12}\,\text{cm}^{-2}$$ and N(Ca II) = $$7.4_{-2.0}^{+9.6}\,\times\,{10}^{12}\,\text{cm}^{-2}$$, and the velocity width is b = $$15_{-6}^{+11}\,\text{km}\,\text{s}^{-1}$$ (1 σ errors). The resulting Ca II/Na I ratio (~ 1.7) suggests that the bulk of the absorbing material occurs in the plane rather than in the halo of NGC 4321. The sodium column density predicts that E (B–V) = $$0.13_{-0.02}^{+0.06}$$ for the intervening material.