Chemical Signature Indicating A Lack of Massive Stars in Dwarf Galaxies

TL;DR

This paper investigates the unique chemical signatures in dwarf galaxies, linking them to a deficiency of very massive stars and proposing a different initial mass function as a key factor in their evolution.

Contribution

It provides a detailed model explaining the chemical enrichment history of dwarf galaxies and connects elemental abundance patterns to the absence of massive stars.

Findings

Enhanced s-process elements indicate fewer massive stars.

Low alpha/Fe ratios suggest a different initial mass function.

Model explains chemical evolution in the Fornax dwarf galaxy.

Abstract

Growing evidence supports an unusual elemental feature appearing in nearby dwarf galaxies, especially dwarf spheroidals (dSphs), indicating a key process of galaxy evolution that is different from that of the Galaxy. In addition to the well-known deficiency of alpha-elements in dSphs, recent observations have clearly shown that s-process elements (Ba) are significantly enhanced relative to Fe, alpha-, and r-process elements. This enhancement occurs in some dSphs as well as in the Large Magellanic Cloud, but is unseen in the Galaxy. Here we report that this feature is evidence of the lack of very massive stars (> 25 solar mass) as predicted in the low star formation rate environment, and we conclude that the unique elemental feature of dwarf galaxies including a low-alpha/Fe ratio in some low-metallicity stars is, at least in some part, characterized by a different form of the initial mass function. We present a detailed model for the Fornax dSph galaxy and discuss its complex chemical enrichment history together with the nucleosynthesis site of the light s-process element Y.