The resolved star formation history of M51a through successive Bayesian marginalization

TL;DR

This study reconstructs the detailed, space-resolved star formation history of galaxy M51a using pixel-by-pixel spectral fitting and Bayesian methods, revealing its exponential star formation pattern and a major burst around 12 Gyr ago.

Contribution

It introduces a Bayesian successive priors approach to accurately derive the galaxy's star formation history from multi-band photometry, accounting for spatial mass distribution biases.

Findings

Star formation rate increased exponentially for the first 10 Gyr.

A main starburst occurred approximately 12 Gyr ago.

The galaxy's SFH shows an exponential decline after initial growth.

Abstract

We have obtained the time and space-resolved star formation history (SFH) of M51a (NGC 5194) by fitting GALEX, SDSS, and near infrared pixel-by-pixel photometry to a comprehensive library of stellar population synthesis models drawn from the Synthetic Spectral Atlas of Galaxies (SSAG). We fit for each space-resolved element (pixel) an independent model where the SFH is averaged in 137 age bins, each one 100 Myr wide. We used the Bayesian Successive Priors (BSP) algorithm to mitigate the bias in the present-day spatial mass distribution. We test BSP with different prior probability distribution functions (PDFs); this exercise suggests that the best prior PDF is the one concordant with the spatial distribution of the stellar mass as inferred from the near infrared images. We also demonstrate that varying the implicit prior PDF of the SFH in SSAG does not affects the results. By summing the contributions to the global star formation rate of each pixel, at each age bin, we have assembled the resolved star formation history of the whole galaxy. According to these results, the star formation rate of M51a was exponentially increasing for the first 10 Gyr after the Big Bang, and then turned into an exponentially decreasing function until the present day. Superimposed, we find a main burst of star formation at t 11.9 Gyr after the Big Bang.