# Measuring Star-Formation Histories, Distances, and Metallicities with Pixel Color-Magnitude Diagrams I: Model Definition and Mock Tests

## TL;DR

This paper introduces an advanced GPU-accelerated pixel color-magnitude diagram technique for accurately measuring star formation histories, metallicities, distances, and dust properties of galaxies, even in semi-resolved regimes, with high precision.

## Contribution

The paper presents a new Python package, pcmdpy, with improved physical modeling and computational speed, enabling detailed stellar population analysis of galaxies up to 100 Mpc away.

## Key findings

- The method can recover SFH, metallicity, distance, and dust extinction from mock data.
- GPU acceleration makes the analysis roughly 7 times faster.
- The technique is effective for galaxies within 10 Mpc and applicable up to 100 Mpc.

## Abstract

We present a comprehensive study of the applications of the pixel color-magnitude diagram (pCMD) technique for measuring star formation histories (SFHs) and other stellar population parameters of galaxies, and demonstrate that the technique can also constrain distances. SFHs have previously been measured through either the modeling of resolved-star CMDs or of integrated-light SEDs, yet neither approach can easily be applied to galaxies in the "semi-resolved regime". The pCMD technique has previously been shown to have the potential to measure stellar populations and star formation histories in semi-resolved galaxies. Here we present Pixel Color-Magnitude Diagrams with Python (pcmdpy), a GPU-accelerated package that makes significant computational improvements to the original code and including more realistic physical models. These advances include the simultaneous fitting of distance, modeling a Gaussian metallicity-distribution function, and an observationally-motivated dust model. GPU-acceleration allows these more realistic models to be fit roughly 7x faster than the simpler models in the original code. We present results from a suite of mock tests, showing that with proper model assumptions, the code can simultaneously recover SFH, [Fe/H], distance, and dust extinction. Our results suggest the code, applied to observations with HST-like resolution, should constrain these properties with high precision within 10 Mpc and can be applied to systems out to as far as 100 Mpc. pCMDs open a new window to studying the stellar populations of many galaxies that cannot be readily studied through other means.