Did the Milky Way just light up? The recent star formation history of the Galactic disc

[Abridged] We map the stellar age distribution ($\lesssim 1$ Gyr) across a 6kpc$\,\times\,$6kpc area of Galactic disc to constrain our Galaxy's recent star-formation history. Our modelling draws on sample Zari et al. (2021) that encompasses all presumed OBA stars ($\sim 500,000$ sources) with $G<16$. To be less sensitive reddening, we do not forward model detailed CMD these stars, but instead K-band absolute magnitude distribution, $n(M_K)$, among $M_K<0$ and $T_{\mathrm{eff}} > 7000$K at certain positions $\vec{x}$ in as step function five bins, $b(\tau~|~\vec{x}, \vec{\alpha})$, logarithmically-spaced from $\tau = 5$ Myr Gyr. Given set isochrones Kroupa (2001) initial mass function, $b(\tau\,|\,\vec{x}, \vec{\alpha})$ maximize likelihood data, accounting for selection function. This results mono-age density maps sizeable portion disc. These show some, all, spiral arms are reflected overdensities younger than 500 Myr. The youngest ($<10$ Myr) trace major star forming regions. ages exhibit an outward gradient distinct spiral-like spatial structure, which is qualitatively similar large scales intervals. When summing over maps' extrapolating whole disc, find effective rate last 10 $\approx 3.3 \mathrm{M_{\odot}/yr}$, higher previously published estimates. Remarkably, implies has been three times lower throughout most Gyr, having risen distinctly only very past.