2025ApJ...994...94T

We present a resolved study of 877 progenitors of Milky Way Analogs (MWAs) at 0.3 < z < 5, selected with abundance matching in the 10 fields of the Canadian NIRISS Unbiased Cluster Survey. Utilizing 18-21 bands of deep NIRCam, NIRISS, and Hubble Space Telescope photometry, we create resolved stellar mass maps and star formation rate (SFR) maps via spectral energy distribution fitting with Dense Basis. We examine their resolved stellar mass and specific SFR (sSFR) profiles as a function of galactocentric radius and find clear evidence for inside-out mass assembly. The total M_⋆ of the inner 2 kpc regions of the progenitors remains roughly constant (10^9.3–9.4M_⊙) at 2 < z < 5, while the total M_⋆ of the regions beyond 2 kpc increases by 0.8 dex, from 10^7.5M_⊙to 10^8.3M_⊙. Additionally, the sSFRs of the outer regions increase with decreasing redshift, until z ∼ 2. The median Sérsic index of the MWA progenitors stays nearly constant at n ∼ 1 at 2 < z < 5, while the half-mass radii of their stellar mass profiles double. We perform additional morphological measurements on the stellar mass maps via the Gini-M20 plane and asymmetry parameters. They show that the rate of double-peak mergers and disturbances to galaxy structure also increases with redshift, with ∼50% of galaxies at 4 < z < 5 classified as disturbed and ∼20% classified as ongoing mergers. Overall, the early evolution of MWAs is revealed as chaotic, with significant mergers and high SFRs. Mass growth is primarily inside-out and galaxies become more disklike after z = 3.