The chemical evolution of the Milky Way in the Gaia era Valeria - - PowerPoint PPT Presentation

The chemical evolution

• f the Milky Way

in the Gaia era

Valeria Grisoni PhD student University of Trieste In collaboration with:

• F. Matteucci and E. Spitoni

Warsaw 2018, September 7th

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AMBRE data (Mikolaitis et al. 2017) show that in the abundance patterns of the α-elements there are two distinct sequences corresponding to thick and thin disc stars, and also a further metal-rich high-α MRHA population. THICK MRHA THIN

Observational data

Observed [Mg/Fe] vs. [Fe/H] from Mikolaitis et al. (2017), where

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• Initial conditions
• Gas flows
• The stellar birthrate function:

SFRxIMF

• The stellar yields

Basic ingredients

• f chemical evolution models

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Basic equations

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Chemical evolution models

In Grisoni et al. (2017; 2018), we model the thick and thin disc evolution by adopting two different chemical evolution approaches: i) a revisited two-infall approach (Chiappini et

• al. 1997; Romano et al. 2010) applied to the

thick and thin discs; ii) a new parallel approach, where thin and thick discs start forming at the same time. Basic parameters: timescales of the formation and star formation efficiencies in the two discs.

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Temporal evolution of the star formation rate for the two-infall model (left) and the parallel model (right).

Results of Grisoni et al. (2017): i) star formation history

Thick disc Thin disc Gap Thick disc Thin disc

Two-infall Parallel

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Observed and predicted [Mg/Fe] vs. [Fe/H] for the two-infall model (upper panel) and the parallel model (lower panel).

ii) abundance patterns

Thick disc Thin disc Gap Thick disc Thin disc

Two-infall Parallel

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Observed and predicted [Mg/Fe] vs. [Fe/H] for the two-infall model at various Galactocentric radii (inside-out scenario). The only way to interpret the MRHA stars in terms of the two-infall model is by assuming radial migration, i.e. stars moving from other Galactocentric radii.

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iii) metallicity distribution function

MDFs observed and predicted by the two-infall model (upper panels) and by the parallel model (lower panels).

THICK MRHA THIN THIN THICK+MRHA

N/Ntot N/Ntot N/Ntot N/Ntot [Fe/H] [Fe/H] [Fe/H] [Fe/H]

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Results of Grisoni et al. (2018)

[Mg/Fe] vs [Fe/H] at various Galactocentric distances observed by APOGEE (Hayden et al. 2015) and predicted by the models of Grisoni et al. (2018).

[Fe/H] [Mg/Fe]

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Results of Spitoni et al. (2018)

Upper panel: [α/Fe] vs [Fe/H] predicted by the parallel model (Spitoni et al. 2018) compared with APOKASC data by Silva Aguirre et al. (2018). Middle panel: [α/Fe] vs age predicted by parallel model and compared with APOKASC data. Lower panel: parallel model results, in which the observational errors have been taken into account.

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Results of Spitoni et al. (2018)

Upper panel: [α/Fe] vs [Fe/H] predicted by the two-infall model (Spitoni et al. 2018) compared with APOKASC data by Silva Aguirre et al. (2018). Middle panel: [α/Fe] vs age predicted by the two-infall model and compared with APOKASC data. Lower panel: two-infall model results, in which the observational errors have been taken into account.

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Results of Spitoni et al. (2018)

[α/Fe] vs [Fe/H] at different age ranges,

• bserved by Silva

Aguirre et al. (2018) and predicted by the two- infall model taking into account the

• bservational errors on

age and metallicity by Spitoni et al. (2018).

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Summary and conclusions

In Grisoni et al (2017; 2018) we studied the formation and evolution of the Milky Way thick and thin discs and compared

• ur results with recent data (AMBRE and APOGEE). We

adopted two different approaches: i) a two-infall approach applied to thick and thin discs. This approach seems the best to reproduce the abundance patterns as well as the ages of stars. The metal-rich alpha- enhanced stars, in this framework, can be interpreted as stars migrated from the inner regions; ii) a parallel approach. While this approach could explain the metal rich alpha-enhanced stars, it seems less suitable for reproducing the stellar ages, as provided by asteroseismology (Spitoni et al. 2018).