English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We present a set of self-consistent chemo-dynamical simulations of MW-typegalaxies formation to study the origin of the bimodality of $\alpha$-elementsin stellar populations. We explore how the bimodality is related to thegeometrically and kinematically defined stellar discs, gas accretion and radialmigration. We find that the two $\alpha$-sequences are formed in quitedifferent physical environments. The high-$\alpha$ sequence is formed earlyfrom a burst of star formation (SF) in a turbulent, compact gaseous disc whichforms a thick disc. The low-$\alpha$ stellar populations is the result ofquiescent SF supported by the slow accretion of enriched gas onto a radiallyextended thin disc. Stellar feedback-driven outflows during the formation ofthe thick disc are responsible for the enrichment of the surrounding gaseoushalo, which subsequently feeds the disc on a longer time-scale. During the thindisc phase, chemical evolution reaches an equilibrium metallicity andabundance, where the stars pile-up. This equilibrium metallicity decreasestowards the outer disc, generating the ridgeline that forms the low-$\alpha$sequence. We identify a second mechanism capable of creating a low-$\alpha$sequence in one of our simulations. Rapid shutdown of the SF, provoked by thefeedback at the end of the thick disc phase, suppresses the chemical enrichmentof the halo gas, which, once accreted onto the star-forming disc, dilutes theISM at the beginning of the thin disc formation. Both mechanisms can operate ina galaxy, but the former is expected to occur when SF efficiency ceases to bedominated by the formation of the thick disc, while the latter can occur in theinner regions. Being the result of the presence of low and high gas densityenvironments, the bimodality is independent of any particular merger history,suggesting that it could be much more widespread than has been claimed.

Bimodality of [\alpha/Fe]-[Fe/H] distributions is a natural outcome of dissipative collapse and disc growth in Milky Way-type galaxies