Surrogate modelling the Baryonic Universe I: The colour of star formation

Understand

The spectral energy distribution of a galaxy emerges from the complex interplay of many physical ingredients, including its star formation history (SFH), metallicity evolution, and dust properties.

• Using GALAXPY, a new galaxy spectral prediction tool, and SFHs predicted by the empirical model UNIVERSEMACHINE and the cosmological hydrodynamical simulation IllustrisTNG, we isolate the influence of SFH on optical and near-infrared colours from 3200 to 10800 \r{A} at z=0.
• By carrying out a principal component analysis, we show that physically-motivated SFH variations modify galaxy colours along a single direction in colour space: the SFH-direction.
• We find that the projection of a galaxy's present-day colours onto the SFH-direction is almost completely regulated by the fraction of stellar mass that the galaxy formed over the last billion years.