Abundance Gradients and the Formation of the Milky Way

By C. Chiappini, F. Matteucci, D. Romano. 2001

526 citations recorded by the source corpus.

In this paper we adopt a chemical evolution model, which is an improved version of the Chiappini, Matteucci, & Gratton model, assuming two main accretion episodes for the formation of the Galaxy, the first forming the halo and bulge in a short timescale and the second one forming the thin disk, with a timescale that is an increasing function of the Galactocentric distance (being of the order of 7 Gyrs at the solar neighborhood). The present model takes into account in more detail than previously the halo density distribution and explores the effects of a threshold density in the star formation process during both the halo and disk phases. The model also includes the most recent nucleosynthesis prescriptions concerning supernovae of all types, novae, and single stars dying as white dwarfs. In the comparison between model predictions and available data, we have focused our attention on abundance gradients as well as gas, stellar, and star formation rate distributions along the disk, since this kind of model has already proven to be quite successful in reproducing the solar neighborhood characteristics. We suggest that the mechanism for the formation of the halo leaves detectable imprints on the chemical properties of the outer regions of the disk, whereas the evolution of the halo and the inner disk are almost completely disentangled. This is due to the fact that the halo and disk densities are comparable at large Galactocentric distances and therefore the gas lost from the halo can substantially contribute to building up the outer disk. We also show that the existence of a threshold density for the star formation rate, both in the halo and disk phase, is necessary to reproduce the majority of observational data in the solar vicinity and in the whole disk. In particular, a threshold in the star formation implies the occurrence of a gap in the star formation at the halo-disk transition phase, in agreement with recent data. We conclude that a relatively short halo formation timescale (≃0.8 Gyr), in agreement with recent estimates for the age differences among Galactic globular clusters, coupled with an "inside-out" formation of the Galactic disk, where the innermost regions are assumed to have formed much faster than the outermost ones, represents, at the moment, the most likely explanation for the formation of the Milky Way. This scenario allows us to predict abundance gradients and other radial properties of the Galactic disk in very good agreement with observations. Moreover, as a consequence of the adopted "inside-out" scenario for the disk, we predict that the abundance gradients along the Galactic disk must have increased with time and that the average ratios in stars (halo plus disk) slightly decrease going from 4 to 10 kpcs from the Galactic center. We also show that the same ratios increase substantially toward the outermost disk regions and the expected scatter in the stellar ages decreases, because the outermost regions are dominated by halo stars. More observations at large Galactocentric distances are needed to test these predictions.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/13b51e02f7b07cb3f0bdad8c9c28c8d68e529525

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Citations in the corpus

CHARACTERIZING THE CIRCUMGALACTIC MEDIUM OF NEARBY GALAXIES WITH HST/COS AND HST/STIS ABSORPTION-LINE SPECTROSCOPY (2012, background): “Nevertheless, this study offers tantalizing preliminary evidence for the detection of low-metallicity gas accretion required by Galactic chemical evolution models (Larson 1972; Chiappini et al. 2001, Section 5.2).”
Europium production: neutron star mergers versus core-collapse supernovae (2013, methodology): “This model is an updated version of the Chiappini et al. (1997, 2001) two-infall model, where it is assumed that the inner halo and part of the thick disc formed by means of a gas accretion episode independently from the thin disc, which formed by means of another gas accretion episode on a much…”
Stellar Abundance and Galactic Chemical Evolution through LAMOST Spectroscopic Survey (2006, background): “Simple chemical evolution models assume gas infall as the main ingredients (e.g. Chiappini et al. 1997, 2001; Goswami & Prantzos 2000; Hou et al. 2000; Francois et al. 2004).”
Quantifying the uncertainties of chemical evolution studies II. Stellar yields (2010, methodology): “A thorough discussion of the adopted formalism and basic equations can be found elsewhere (Chiappini et al. 1997, 2001).”
Estimating stellar birth radii and the time evolution of Milky Way’s ISM metallicity gradient (2018, methodology): “Depending on the initial conditions, the Galactic disk could have started forming with a flat radial [Fe/H] gradient (Chiappini et al. 2001; Cescutti et al. 2007).”
Reconstructing the star formation history of the Milky Way disc(s) from chemical abundances (2014, background): “Chiappini et al. (1997, 2001) therefore, favor a rapidly formed thick disc, while Fenner & Gibson (2003) interpret their thick disc as a thickened thin disc (Wyse 2001).”
Oxygen, carbon and nitrogen evolution in galaxies (2002, background): “…for Mg, Si, Ca and S show that for [Fe/H] < −1.0 the [α/Fe] ratio is almost constant, defining a plateau, whereas for oxygen there seems to be a slight increase of the [O/Fe] ratio with decreasing metallicity (see Chiappini et al. 2001 for a discussion on this particular point - hereafter CMR2001).”
Numerical simulation of a possible origin of the positive radial metallicity gradient of the thick disk (2013, methodology): “…supernova feedback, metal enrichment and metal-dependent radiative cooling (derived with MAPPINGSIII: Sutherland & Dopita 1 Also, for the reader interested in analytical arguments, we refer them to the previous literature (e.g. Chiappini et al. 2001; Renda et al. 2005; Marcon-Uchida et al. 2010).”
Distances to Galactic High-Velocity Clouds. I. Cohen Stream, Complex GCP, Cloud g1 (2007, background): “Indirect evidence for infalling gas is provided by two arguments (Chiappini et al. 2001).”
Radial migration in disc galaxies — I. Transient spiral structure and dynamics (2011, background): “For the past thirty years, an implicit assumption has been made in such modeling: stars remain in the same part of the disk forever (e.g. Tinsley 1975; Matteucci & Francois 1989; Boissier & Prantzos 1999; Chiappini et al. 2001).”
Origin and structure of the Galactic disc(s) (2009, background): “By the fact that the timescale of SNIa-enrichment does not vary with radius either, the ISM trajectories tend to be nearly aligned.”
EXTRAGALACTIC CHEMICAL ABUNDANCES: DO H ii REGIONS AND YOUNG STARS TELL THE SAME STORY? THE CASE OF THE SPIRAL GALAXY NGC 300 (2009, background): “…necessary observational constraints to the parameters that drive models of the chemical evolution of galaxies, such as the radial dependence of accretion and star formation rate in galactic disks (Matteucci & Francois 1989; Boissier & Prantzos 1999; Chiappini et al. 2001; Colavitti et al. 2008).”
Gaseous Galaxy Halos (2012, background): “…of the long-lived stars in the Galactic disk indicate the vast majority of the incoming fuel should be low metallicity, and therefore feedback material cannot be the dominant fuel at all redshifts (Chiappini et al., 2001; Larson, 1972; Fenner & Gibson, 2003; Sommer-Larsen et al., 2003).”
METALLICITY GRADIENTS IN THE MILKY WAY DISK AS OBSERVED BY THE SEGUE SURVEY (2011, background): “Thus, observations of the radial metallicity gradient of the disk are crucial to constraining chemical evolution models (e.g., Chiappini et al. 2001; Cescutti et al. 2007; Magrini et al. 2009).”
Chemical evolution with radial mixing (2008, methodology): “An important difference between our models and those of Chiappini et al. (2001) is that in our models the SFR is a smooth function of time and the bimodality in [α/Fe ] is achieved without a dip in the SFR. Chiappinin et al. (1997) give for the inner and outer parts of their models the radial…”
Metallicity gradients in local field star-forming galaxies: insights on inflows, outflows, and the coevolution of gas, stars and metals (2015, background): “While the details vary from model to model, typical assumptions of inside-outdisk growth, no radial matter exchange, and closed-box chemicalevolution can successfully reproduce the current gradients in local galaxies (e.g.,Chiappini et al. 2001; Fu et al. 2009).”