A Metallicity Dependence on the Occurrence of Core-collapse Supernovae

Pessi, Thallis; Anderson, Joseph P.; Lyman, Joseph D.; Prieto, Jose L.; Galbany, Lluís; Kochanek, Christopher S.; Sánchez, Sebastian F.; Kuncarayakti, Hanindyo

doi:10.3847/2041-8213/acf7c6

The Milky Way Radial Metallicity Gradient as an Equilibrium Phenomenon: Why Old Stars are Metal-Rich

Johnson,

Weinberg,

Blanc

et al. 2024

Preprint

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Metallicities of both gas and stars decline toward large radii in spiral galaxies, a trend known as the radial metallicity gradient. We quantify the evolution of the metallicity gradient in the Milky Way as traced by APOGEE red giants with age estimates from machine learning algorithms. Stars up to ages of \(\sim\)9 Gyr follow a similar relation between metallicity and Galactocentric radius. This constancy challenges current models of Galactic chemical evolution, which typically predict lower metallicities for older stellar populations. Our results favor an _equilibrium scenario_, in which the gas-phase gradient reaches a nearly constant normalization early in the disk lifetime. Using a fiducial choice of parameters, we demonstrate that one possible origin of this behavior is an outflow that more readily ejects gas from the interstellar medium with increasing Galactocentric radius. A direct effect of the outflow is that baryons do not remain in the interstellar medium for long, which causes the ratio of star formation to accretion, \({\dot{\Sigma}}_* / {\dot{\Sigma}}_{\rm in}\), to quickly become constant. This ratio is closely related to the local equilibrium metallicity, since its numerator and denominator set the rates of metal production by stars and hydrogen gained through accretion, respectively. Building in a merger event results in a perturbation that evolves back toward the equilibrium state on \(\sim\)Gyr timescales. Under the equilibrium scenario, the radial metallicity gradient is not a consequence of the inside-out growth of the disk but instead reflects a trend of declining \({\dot{\Sigma}}_* / {\dot{\Sigma}}_{\rm in}\) with increasing Galactocentric radius.

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Galactic Chemical Evolution Models Favor an Extended Type Ia Supernova Delay-time Distribution

Dubay,

Johnson,

Johnson

2024

ApJ

2

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Type Ia supernovae (SNe Ia) produce most of the Fe-peak elements in the Universe and therefore are a crucial ingredient in galactic chemical evolution models. SNe Ia do not explode immediately after star formation, and the delay-time distribution (DTD) has not been definitively determined by supernova surveys or theoretical models. Because the DTD also affects the relationship among age, [Fe/H], and [α/Fe] in chemical evolution models, comparison with observations of stars in the Milky Way is an important consistency check for any proposed DTD. We implement several popular forms of the DTD in combination with multiple star formation histories for the Milky Way in multizone chemical evolution models that include radial stellar migration. We compare our predicted interstellar medium abundance tracks, stellar abundance distributions, and stellar age distributions to the final data release of the Apache Point Observatory Galactic Evolution Experiment. We find that the DTD has the largest effect on the [α/Fe] distribution: a DTD with more prompt SNe Ia produces a stellar abundance distribution that is skewed toward a lower [α/Fe] ratio. While the DTD alone cannot explain the observed bimodality in the [α/Fe] distribution, in combination with an appropriate star formation history it affects the goodness of fit between the predicted and observed high-α sequence. Our model results favor an extended DTD with fewer prompt SNe Ia than the fiducial t −1 power law.

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The Extremely Metal-poor SN 2023ufx: A Local Analog to High-redshift Type II Supernovae

Tucker,

Hinkle,

Angus

et al. 2024

ApJ

0

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We present extensive observations of the Type II supernova (SN II) SN 2023ufx, which is likely the most metal-poor SN II observed to date. It exploded in the outskirts of a low-metallicity (Z host ∼ 0.1 Z ⊙) dwarf (M g = −13.39 ± 0.16 mag, r proj ∼ 1 kpc) galaxy. The explosion is luminous, peaking at M g ≈ −18.5 mag, and shows rapid evolution. The r-band (pseudobolometric) light curve has a shock-cooling phase lasting 20 (17) days followed by a 19 (23) day plateau. The entire optically thick phase lasts only ≈55 days following explosion, indicating that the red supergiant progenitor had a thinned H envelope prior to explosion. The early spectra obtained during the shock-cooling phase show no evidence for narrow emission features and limit the preexplosion mass-loss rate to M ̇ ≲ 10 − 3 M ⊙ yr−1. The photospheric-phase spectra are devoid of prominent metal absorption features, indicating a progenitor metallicity of ≲0.1 Z ⊙. The seminebular (∼60–130 days) spectra reveal weak Fe ii, but other metal species typically observed at these phases (Ti ii, Sc ii, and Ba ii) are conspicuously absent. The late-phase optical and near-infrared spectra also reveal broad (≈104 km s−1) double-peaked Hα, Pβ, and Pγ emission profiles suggestive of a fast outflow launched during the explosion. Outflows are typically attributed to rapidly rotating progenitors, which also prefer metal-poor environments. This is only the second SN II with ≲0.1 Z ⊙ and both exhibit peculiar evolution, suggesting a sizable fraction of metal-poor SNe II have distinct properties compared to nearby metal-enriched SNe II. These observations lay the groundwork for modeling the metal-poor SNe II expected in the early Universe.

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A Metallicity Dependence on the Occurrence of Core-collapse Supernovae

Cited by 3 publications

References 89 publications

The Milky Way Radial Metallicity Gradient as an Equilibrium Phenomenon: Why Old Stars are Metal-Rich

The Milky Way Radial Metallicity Gradient as an Equilibrium Phenomenon: Why Old Stars are Metal-Rich

Galactic Chemical Evolution Models Favor an Extended Type Ia Supernova Delay-time Distribution

The Extremely Metal-poor SN 2023ufx: A Local Analog to High-redshift Type II Supernovae

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