Recent star formation history of Galactic disc

Given a set of isochrones and a Kroupa (2001) initial mass function, we sample b({tau},|{vec}x, {vec}{alpha}) to maximise the likelihood of the data n(M_K_|{vec}x, {vec}{alpha}), accounting for the selection function. This results in a set of mono-age stellar density maps across a sizeable portion of the Galactic disc. These maps show that some, but not all, spiral arms are reflected in overdensities of stars younger than 500Myr.

The maps of the youngest stars (<10Myr) trace major star forming regions. The maps at all ages exhibit an outward density gradient and distinct spiral-like spatial structure, which is qualitatively similar on large scales among the five age bins. When summing over the maps' area and extrapolating to the whole disc, we find an effective star-formation rate over the last 10Myr of ~3.3M_{sun}_/yr, higher than previously published estimates that had not accounted for unresolved binaries.

Remarkably, our stellar age distribution implies that the star-formation rate has been three times lower throughout most of the last Gyr, having risen distinctly only in the very recent past. Finally we use TNG50 simulations to explore how justified the common identification of local age distribution with global star formation history is: we find that the global star-formation rate at a given radius in Milky-Way-like galaxies is approximated within a factor of ~1.5 by the young age distribution within a 6kpcx6kpc area near R_{sun}_.