We present Lightning , a new spectral energy distribution ( SED ) fitting procedure , capable of quickly and reliably recovering star formation history ( SFH ) and extinction parameters .
The SFH is modeled as discrete steps in time .
In this work , we assumed lookback times of 0–10 Myr , 10–100 Myr , 0.1–1 Gyr , 1–5 Gyr , and 5–13.6 Gyr . Lightning consists of a fully vectorized inversion algorithm to determine SFH step intensities and combines this with a grid-based approach to determine three extinction parameters .
We apply our procedure to the extensive FUV-to-FIR photometric data of M51 , convolved to a common spatial resolution and pixel scale , and make the resulting maps publicly available .
We recover , for M51a , a peak star formation rate ( SFR ) between 0.1 and 5 Gyr ago , with much lower star formation activity over the last 100 Myr .
For M51b , we find a declining SFR toward the present day .
In the outskirt regions of M51a , which includes regions between M51a and M51b , we recover a SFR peak between 0.1 and 1 Gyr ago , which corresponds to the effects of the interaction between M51a and M51b .
We utilize our results to ( 1 ) illustrate how UV+IR hybrid SFR laws vary across M51 , and ( 2 ) provide first-order estimates for how the IR luminosity per unit stellar mass varies as a function of the stellar age .
From the latter result , we find that IR emission from dust heated by stars is not always associated with young stars , and that the IR emission from M51b is primarily powered by stars older than 5 Gyr .