Are Milky-Way-like galaxies like the Milky Way? A view from SDSS-IV/MaNGA

TL;DR

This study compares Milky Way analogues from SDSS-IV/MaNGA to the actual Milky Way, revealing diverse evolutionary histories and structural differences among similar galaxies through spectral modeling of their chemical and star formation properties.

Contribution

It introduces a semi-analytic spectral fitting method to analyze spatially-resolved chemical evolution in Milky Way-like galaxies, highlighting their varied formation histories.

Findings

Some MW analogues closely match the Milky Way's properties.

Galaxies divide into self-similar and centrally-quenched categories.

Centrally-quenched galaxies formed stars earlier.

Abstract

In this paper, we place the Milky Way (MW) in the context of similar-looking galaxies in terms of their star-formation and chemical evolution histories. We select a sample of 138 Milky-Way analogues (MWAs) from the SDSS-IV/MaNGA survey based on their masses, Hubble types, and bulge-to-total ratios. To compare their chemical properties to the detailed spatially-resolved information available for the MW, we use a semi-analytic spectral fitting approach, which fits a self-consistent chemical-evolution and star-formation model directly to the MaNGA spectra. We model the galaxies' inner and outer regions assuming that some of the material lost in stellar winds falls inwards. We also incorporate chemical enrichment from type II and Ia supernovae to follow the alpha-element abundance at different metallicities and locations. We find some MWAs where the stellar properties closely reproduce the distribution of age, metallicity, and alpha enhancement at both small and large radii in the MW. In these systems, the match is driven by the longer timescale for star formation in the outer parts, and the inflow of enriched material to the central parts. However, other MWAs have very different histories. These divide into two categories: self-similar galaxies where the inner and outer parts evolve identically; and centrally-quenched galaxies where there is very little evidence of late-time central star formation driven by material accreted from the outer regions. We find that, although selected to be comparable, there are subtle morphological differences between galaxies in these different classes, and that the centrally-quenched galaxies formed their stars systematically earlier.