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Constraints on the Galactic Chemical Evolution of $^3\rm{He}$

Miqaela K. Weller, David H. Weinberg

Abstract

We examine the galactic chemical evolution (GCE) of $^3\rm{He}$ in one-zone and multi-zone models, with particular attention to the stellar yields and GCE parameters that can reproduce both the protosolar $^3\rm{He}$ abundance and recent gas-phase $^3\rm{He}/^4\rm{He}$ measurements in the Orion nebula. Published stellar models indicate negligible net $^3\rm{He}$ production by massive stars, while the predicted yields from asymptotic giant branch (AGB) stars are metallicity-dependent and span a range of $\sim 2.5$ depending on the extra mixing processes incorporated in the stellar models. The dominant contribution to $^3\rm{He}$ production comes from $1-2\ M_\odot$ stars, making $^3\rm{He}$ evolution slow compared to other AGB elements and to Fe enrichment from Type Ia supernovae. We constrain our GCE models to reproduce the observed [O/H] in the interstellar medium, and our fiducial models adopt an empirically motivated IMF-averaged oxygen yield $y_{\rm O} \approx 1.2\ Z_{\rm O, \odot}$. Even with the lowest of the AGB $^3\rm{He}$ yields, based on stellar models with rotational and thermohaline mixing, our GCE models tend to overpredict the protosolar and Orion $^3\rm{He}$ abundances; they require a slow onset of star formation and low star formation efficiency to come close to the observed values. With a higher oxygen yield, calibration to observed [O/H] implies stronger outflows, making it easier to reproduce the observed $^3\rm{He}$. Alternatively, the true $^3\rm{He}$ yield could be lower than that predicted by existing stellar models, suggesting that mixing in red giants is not yet fully captured. Future $^3\rm{He}$ measurements that probe higher metallicity environments could help distinguish these possibilities.

Constraints on the Galactic Chemical Evolution of $^3\rm{He}$

Abstract

We examine the galactic chemical evolution (GCE) of in one-zone and multi-zone models, with particular attention to the stellar yields and GCE parameters that can reproduce both the protosolar abundance and recent gas-phase measurements in the Orion nebula. Published stellar models indicate negligible net production by massive stars, while the predicted yields from asymptotic giant branch (AGB) stars are metallicity-dependent and span a range of depending on the extra mixing processes incorporated in the stellar models. The dominant contribution to production comes from stars, making evolution slow compared to other AGB elements and to Fe enrichment from Type Ia supernovae. We constrain our GCE models to reproduce the observed [O/H] in the interstellar medium, and our fiducial models adopt an empirically motivated IMF-averaged oxygen yield . Even with the lowest of the AGB yields, based on stellar models with rotational and thermohaline mixing, our GCE models tend to overpredict the protosolar and Orion abundances; they require a slow onset of star formation and low star formation efficiency to come close to the observed values. With a higher oxygen yield, calibration to observed [O/H] implies stronger outflows, making it easier to reproduce the observed . Alternatively, the true yield could be lower than that predicted by existing stellar models, suggesting that mixing in red giants is not yet fully captured. Future measurements that probe higher metallicity environments could help distinguish these possibilities.

Paper Structure

This paper contains 13 sections, 11 equations, 12 figures.

Table of Contents

  1. Introduction
  2. Theoretical Yield Calculations
  3. CCSN and Massive Star Winds
  4. AGB Stars
  5. Summary
  6. One-zone Galactic Chemical Evolution
  7. The Impact of Outflows and Star Formation Efficiency
  8. The Impact of Star Formation History and Oxygen Yield Normalization
  9. Two Infall Models
  10. Summary
  11. Multi-zone Galactic Chemical Evolution
  12. Conclusions
  13. Analytic Solutions

Figures (12)

  • Figure 1: Fractional net $^3\rm{He}$ yields of massive stars as a function of stellar mass, based on the stellar evolution and supernova models of LC18, S16, and NKT13. Consistent color-coding is used between panels to denote similar metallicities reported by the different studies. Black points (AllExp) in the S16 panel show calculations with forced explosions of all progenitors as described by Griffith21. Gray open circles (note that this is for [M/H] = 0 as well) show the original S16 results for their N20 central engine, where many progenitors collapse to black holes. Points below the dotted lines represent a net sink of $^3\rm{He}$, meaning that the star consumed more $^3\rm{He}$ than it produced.
  • Figure 2: Fractional net $^3\rm{He}$ yields from Lagarde2011 for models with no mixing and models that include extra mixing processes (i.e., thermohaline and rotational mixing) as a function of mass and metallicity. If the yield at 8 $M_{\odot}$ is not reported, we adopt the yield at 6 $M_{\odot}$ in lieu of linearly extrapolating. Like with Figure \ref{['fig: ccnet']}, the black dotted line denotes zero $^3\rm{He}$ production and we have again displayed metallicities with similar colors for ease of comparison.
  • Figure 3: Production of $^3\rm{He}$ from AGB stars only as a function of time for a population of stars born at $t = 0$. The markers indicate the time at which 50% of the total $^3\rm{He}$ has been produced. This value is larger for the standard yield cases as 1 -- 2 $M_{\odot}$ stars dominate the production.
  • Figure 4: Net IMF-averaged yields of massive stars (solid and markers) and AGB stars (dashed). The yields from massive stars are slightly negative and negligible compared to yields from AGB stars. Our preferred yield set, L11 Therm. + Rot., increases with metallicity by a factor of $\sim2$ over our metallicity range.
  • Figure 5: $Y_3$ as a function of time for one-zone models with exponentially declining SFH, for three different combinations of SFE timescale $\tau_{*}$, SFH decline timescale $\tau_{\mathrm{SFH}}$, and outflow efficiency $\eta$. Dotted curves in the upper panels show analytic solutions with the $^3\rm{He}$ yield computed for the metallicity at time $t$ (left) or time $t - t_{\rm dep}$ (right). Lower panels show residuals between analytic and numerical solutions.
  • ...and 7 more figures