2-process Model and Residual Abundance Analysis of the Milky Way Massive Satellites

TL;DR

This study applies the 2-process model to Milky Way and satellite galaxy stars, revealing its effectiveness in characterizing abundance patterns and highlighting systematic differences likely due to gas inflow effects.

Contribution

It demonstrates the 2-process model's ability to accurately fit satellite galaxy abundances and explores the origins of abundance pattern differences between galaxies.

Findings

The model fits satellite galaxy data with small residuals across elements.

Large residuals occur when fitting the Milky Way sample, especially at high metallicity.

Differences in abundance patterns suggest gas inflow influenced the Milky Way's chemical evolution.

Abstract

The ``2-process Model'' is a promising technique for interpreting stellar chemical abundance data from large-scale surveys (e.g., SDSS-IV/V, GALAH), enabling more quantitative empirical studies of differences in chemical enrichment history between galaxies without relying on detailed yield and evolution models. In this work, we fit 2-process model parameters to (1) a luminous giant Milky Way (MW) sample and (2) stars comprising the Sagittarius Dwarf Galaxy (Sgr). We then use these two sets of model parameters to predict the abundances of 14 elements of stars belonging to the MW and in five of its massive satellite galaxies, analyzing the residuals between the predicted and observed abundances. We find that the model fit to (1) results in large residuals (0.1-0.3 dex) for most metallicity-dependent elements in the metal-rich ([Mg/H] $>$ -0.8) stars of the satellite galaxies. However, the model fit to (2) results in small or no residuals for all elements across all satellite galaxies. Therefore, despite the wide variation in [X/Mg]-[Mg/H] abundance patterns of the satellite galaxies, the 2-process framework provides an accurate characterization of their abundance patterns across many elements, but these multi-element patterns are systematically different between the dwarf galaxy satellites and the MW disks. We consider a variety of scenarios for the origin of this difference, highlighting the possibility that a large inflow of pristine gas to the MW disk diluted the metallicity of star-forming gas without changing abundance ratios.