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[论文解读] The Scale of Stellar Yields: Implications of the Measured Mean Iron Yield of Core Collapse Supernovae

David H. Weinberg, Emily J. Griffith|arXiv (Cornell University)|Sep 11, 2023
Gamma-ray bursts and supernovae被引用 4
一句话总结

本文利用Rodriguez等人（2023年）对核心坍缩超新星（CCSN）平均铁产量的最新实测结果，$\bar{y}_{\rm Fe}^{\rm cc} = 0.058 \pm 0.007\,M_\odot$，通过假设低金属丰度恒星中观测到的$[\alpha/{\rm Fe}]$平台反映了CCSN的真实产量比，推断$\alpha$-元素产量的绝对尺度。研究发现，氧和镁的产量与太阳值一致，支持Sukhbold等人（2016年）提出的模型，即在$M < 40\,M_\odot$的前身星中形成黑洞，且暗示银河系外流强度低于以往假设，从而减少了为匹配观测到的金属丰度和元素模式而对强风的需求。

ABSTRACT

The scale of alpha-element yields is difficult to predict from theory because of uncertainties in massive star evolution, supernova physics, and black hole formation, and it is difficult to constrain empirically because the impact of higher yields can be compensated by greater metal loss in galactic winds. We use a recent measurement of the mean iron yield of core collapse supernovae (CCSN) by Rodriguez et al. (RMN23), $\bar{y}_{ m Fe}^{ m cc} =0.058 \pm 0.007 M_\odot$, to infer the scale of alpha-element yields by assuming that the plateau of [alpha/Fe] abundance ratios observed in low metallicity stars represents the yield ratio of CCSN. For a Kroupa IMF and a plateau at [alpha/Fe]=0.45, we find that the population-averaged yields of O and Mg per unit mass of star formation are about equal to the mass fractions of these elements in the sun. The inferred O and Fe yields agree with predictions of the Sukhbold et al. (2016) CCSN models assuming their Z9.6+N20 neutrino-driven engine, a scenario in which many progenitors with $M&lt;40M_\odot$ implode to black holes rather than exploding. The yields are lower than assumed in some models of galactic chemical evolution (GCE) and the galaxy mass-metallicity relation, reducing the level of outflows needed to match observed abundances. For straightforward assumptions, we find that one-zone GCE models with mass-loading factor $η\approx 0.6$ evolve to solar metallicity at late times. By requiring that models reach [alpha/Fe]=0 at late times, and assuming a mean Fe yield of $0.7M_\odot$ per Type Ia supernova, we infer a Hubble-time integrated SNIa rate of $1.1 imes 10^{-3} M_\odot^{-1}$, compatible with estimates from supernova surveys. The RMN23 measurement provides one of the few empirical anchors for the absolute scale of nucleosynthetic yields, with wide-ranging implications for stellar and galactic astrophysics.

研究动机与目标

  • 利用实测约束确定核心坍缩超新星中$\alpha$-元素核合成产量的绝对尺度。
  • 解决星系化学演化（GCE）模型中产量不确定性与星系外流效率之间的长期退化问题。
  • 检验低金属丰度恒星中观测到的$[\alpha/{\rm Fe}]$平台是否真实反映了CCSN的$\alpha$-元素与铁的产量比。
  • 评估推断出的产量与理论模型的一致性，特别是涉及大质量恒星中黑洞形成的相关模型。
  • 评估其对星系质量-金属丰度关系及宇宙金属预算的影响。

提出的方法

  • 作者将Rodriguez等人（2023年）提供的核心坍缩超新星平均铁产量实测值$\bar{y}_{\rm Fe}^{\rm cc} = 0.058 \pm 0.007\,M_\odot$作为产量缩放的固定锚点。
  • 假设低金属丰度恒星中观测到的$[\alpha/{\rm Fe}]_{\rm cc} = 0.45$平台真实反映了CCSN对$\alpha$-元素与铁的产量比。
  • 利用Kroupa（2001年）初始质量函数，推断氧和镁相对于其太阳丰度的群体平均产量。
  • 在时间独立外流效率$\eta = \dot{M}_{\rm out}/\dot{M}_*$和Ia型超新星延迟时间分布（DTD）的假设下，应用单区星系化学演化（GCE）模型。
  • 使用具有双参数恒星形成历史（SFH）的GCE解析解，模拟$[\alpha/{\rm Fe}]$和$[\rm Fe/H]$的演化。
  • 通过与原初氘氢比（D/H）的一致性进行检验，并根据$[\alpha/{\rm Fe}]$在晚期趋于0的要求，推断宇宙时空中Ia型超新星的总累积率。
Figure 1: Distribution of APOGEE disk and halo stars in $[\alpha/{\rm Fe}]$ - $[{\rm Fe/H}]$ for the $\alpha$ -elements O (left), Mg (middle), or Si (right). Above $[{\rm Fe/H}]=-0.8$ stars are randomly downsampled by a factor of 10; the transition to full sampling produces the edge at $[{\rm Fe/H}]
Figure 1: Distribution of APOGEE disk and halo stars in $[\alpha/{\rm Fe}]$ - $[{\rm Fe/H}]$ for the $\alpha$ -elements O (left), Mg (middle), or Si (right). Above $[{\rm Fe/H}]=-0.8$ stars are randomly downsampled by a factor of 10; the transition to full sampling produces the edge at $[{\rm Fe/H}]

实验结果

研究问题

  • RQ1在实测铁产量约束下，核心坍缩超新星的$\alpha$-元素产量的绝对尺度是什么？
  • RQ2推断出的产量与大质量恒星核合成及黑洞形成理论模型相比如何？
  • RQ3在新的铁产量约束下，为重现观测到的金属丰度和元素模式，需要多大程度的星系外流？
  • RQ4低金属丰度恒星中观测到的$[\alpha/{\rm Fe}]$平台是否可被视为CCSN真实产量比？
  • RQ5为匹配银河系中观测到的$[\alpha/{\rm Fe}]$演化，所需的宇宙时空中Ia型超新星总累积率是多少？

主要发现

  • 核心坍缩超新星的氧和镁群体平均产量为$\log y_{\rm O}^{\rm cc}/Z_{{\rm O},\odot} = \log y_{\rm Mg}^{\rm cc}/Z_{{\rm Mg},\odot} = -0.01 \pm 0.1$，表明其与太阳丰度基本相等。
  • 推断出的产量与Sukhbold等人（2016年）的CCSN模型一致，该模型假设采用Z9.6+N20中微子驱动引擎，预测在$M < 40\,M_\odot$前身星中形成黑洞。
  • 采用外流效率$\eta \approx 0.6$的单区GCE模型可在晚期重现太阳金属丰度，表明其所需的外流强度低于某些以往GCE模型的假设。
  • 模型预测的星际介质D/H比值约为原初值的70%，在2σ水平上与观测估计一致。
  • 为使$[\alpha/{\rm Fe}] \approx 0$在晚期达到，推断出的宇宙时空中Ia型超新星总累积率为$1.1 \times 10^{-3}\,M_\odot^{-1}$，与超新星巡天估计一致。
  • RMN23铁产量测量为恒星产量的绝对尺度提供了关键实测锚点，对恒星演化、星系形成及宇宙金属预算具有广泛影响。
Figure 2: Left: Continuous explosion landscapes for a range of $e_{0}$ values ( $0.035-0.07$ and All Explode) as a function of progenitor ZAMS mass. Horizontal lines indicate the masses where successful explosions occur. Lines are colored by $e_{0}$ , with low values of $e_{0}$ in yellow and high va
Figure 2: Left: Continuous explosion landscapes for a range of $e_{0}$ values ( $0.035-0.07$ and All Explode) as a function of progenitor ZAMS mass. Horizontal lines indicate the masses where successful explosions occur. Lines are colored by $e_{0}$ , with low values of $e_{0}$ in yellow and high va

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