Empirical distribution Si II velocity measurements for the sample of 79 nearby SNe Ia. Top: the histogram of velocities (gray), the best-fitting gamma distribution, with shape parameter a = 4.83 and scale parameter b = 0.54 (blue), and the best-fitting split-normal distribution (Equation (1)) with mode , left-width σ₋ = 0.58, and right-width σ₊ = 1.61, in units of 10³ km s⁻¹ (black). Bottom: the empirical cumulative distribution function of the velocity measurements (red), and the CDFs of the best-fitting distributions.