Present-day nitrogen isotopic ratio in the solar neighbourhood compared to Galactic Chemical Evolution models predictions. Shaded areas: ALMA measurements of the CN/C¹⁵N and HCN/HC¹⁵N ratios in TW Hya and MWC 480 respectively. Symbols: directly measured ratios (i.e. not using double-isotopic ratios) in the present-day solar neighbourhood at r_G = 8.5(10) kpc (references are provided in Table D.1). Black curves: GCE model predictions Romano & Matteucci (2003) scaled to a PSN ratio of ℛ_⊙ = 441, with ¹⁵N as a primary (full line, their model 2) or secondary product (dashed lines, their models 3s an 3n). Blue curve: GCE model 2 including a 2 kpc outward Sun migration (see the text for details). The weighted average isotopic ratios in comets of 144(3) (see also Fig. A.1) and of 111(19), from H¹³CN/HC¹⁵N observations in 5 disks (Guzmán et al. 2017), are also indicated.