- The paper demonstrates that while CCSNe Types II(P), IIb, and Ib exhibit similar Hα luminosities, Type Ic shows a 0.5 dex offset indicating significantly younger environments.
- The methodology employs VLT/MUSE IFU spectroscopy with a fixed 300 pc aperture and robust statistical tests to isolate the star-forming activity at supernova explosion sites.
- Implications highlight that binary interactions largely govern envelope stripping in most CCSNe, whereas Type Ic events suggest a need for more massive or extreme progenitors.
Statistical Environmental Age Study of Core-Collapse Supernovae Using VLT/MUSE IFU Spectroscopy
Introduction
Core-collapse supernovae (CCSNe) are critical endpoints in the evolution of massive stars, significantly influencing galactic chemical feedback, star formation, and multi-messenger phenomena. Understanding the progenitor systems leading to the various CCSN subtypes—specifically Types II(P), IIb, Ib, and Ic—requires disentangling the relative impact of single-star versus binary evolutionary channels, stellar mass, metallicity, and associated environmental parameters. Direct pre-explosion progenitor detections have primarily implicated binary systems in stripped-envelope CCSNe but remain sparse, motivating the further use of spatially resolved environmental studies as a statistical probe of progenitor demographics.
Methodology
A minimally biased sample of 129 CCSNe (z ≤ 0.02) discovered by untargeted, wide-field transient surveys (e.g., ZTF, ATLAS) was assembled, cross-matched with archival VLT/MUSE integral-field spectroscopy to exploit the high spatial resolution and spectral coverage for environmental characterization. Local Hα luminosity was extracted within a fixed 300 pc aperture centered on each explosion site—after extensive corrections for extinction and continuum emission—serving as a direct proxy for local star-forming activity and, statistically, the progenitor population age.
The choice of Hα luminosity over other indices (e.g., Hα equivalent width, NCR-like statistics) provided robustness against dilution by older stellar populations and whole-galaxy star formation gradients, focusing the analysis on the immediate progenitor environment. Bootstrapped resampling and two-sample goodness-of-fit tests (Kolmogorov-Smirnov and Anderson-Darling) were used to quantitatively evaluate type-dependent differences among the local Hα distributions.
Results
The distributions of local Hα luminosity for CCSNe of Types II(P), IIb, and Ib were found to be statistically indistinguishable within stochastic and measurement uncertainties. In contrast, the distribution for Type Ic SNe is systematically offset towards higher Hα luminosity by approximately 0.5 dex, corresponding to significantly younger environments. The Anderson-Darling test shows p-values as low as 0.07 when comparing Ic to the pooled non-Ic sample, rejecting the null hypothesis of identical parent populations at the ∼1.5σ level.
The analysis is robust to division into host metallicity bins and aperture size uncertainties, supported by the use of a uniform physical scale and consideration of progenitor displacement scenarios (e.g., runaways). The results contradict earlier empirical studies that posited a monotonic environmental age sequence (II > IIb > Ib > Ic) strictly tracking the degree of progenitor envelope stripping. Instead, the findings demonstrate that only Type Ic SNe deviate towards systematically younger settings, while Types II(P), IIb, and Ib are drawn from environments of similar age.
Numerical values for the median log(Hα/erg s⁻¹) are:
- II(P): 38.60
- IIb: 38.64
- Ib: 38.47
- Ic: 39.12
Implications and Theoretical Interpretation
The insensitivity of environmental age among Types II(P), IIb, and Ib indicates that the distinction between these classes is predominantly set by binary orbital configuration rather than initial stellar mass, consistent with recent population synthesis models (e.g., POSYDON suite; [Souropanis et al. 2025, (Souropanis et al., 28 Aug 2025)]). These models find that primary stars in binaries comprise the majority of Ib/IIb progenitors, and wide or merging binaries dominate the II(P) channel. The mass range for these events is similar, reinforcing that environmental age (a proxy for initial mass) is a weak predictor within these classes in metal-rich local galaxies.
Type Ic SNe, however, require systematically more massive progenitors and/or extreme binary configurations (high mass ratios, close separations), or extremely efficient post-interaction stellar wind mass loss from the exposed helium star. This observation supports channels in which the complete stripping of both hydrogen and helium envelopes is highly mass-dependent, as predicted in the single- and binary-star regimes. The result also aligns with hybrid mechanisms, such as those advanced by [Fang et al. 2019], in which binary stripping of H is common, but only the most massive systems, with strong winds, lose the remaining He to generate Ic events.
The lack of a continuous environmental age progression across the CCSN subtypes in the local (Z > 0.2 Z_⊙) universe implies that both metallicity and binary interaction must be considered jointly to predict stripped-envelope SN demographics. A strong shift in the mass thresholds for Ib/IIb/Ic production could emerge at lower metallicity, where winds weaken and binary stripping dominates. Furthermore, systematic uncertainties remain in associating local Hα emission with true progenitor mass, given possible contamination, photon leakage, and complex star formation histories; thus, observed age trends, while significant, are likely lower bounds on the true progenitor mass offsets.
Future Directions
Expanding IFU-based studies to higher-redshift and broader metallicity host samples will clarify the interplay between metallicity, mass loss, and binary interaction in CCSN progenitors. Improvements in stellar wind prescriptions, especially for post-interaction helium stars, and more nuanced initial mass functions in population synthesis will refine predicted environmental age separations. Ultimately, future multi-messenger and pre-explosion transient surveys will directly validate or revise the conclusions drawn from environmental statistical proxies.
Conclusion
This work provides conclusive statistical evidence, free from targeted galaxy selection biases, that Type Ic CCSNe preferentially explode in significantly younger, more massive local environments than Types II(P), IIb, or Ib, which themselves do not show significant age differences. The findings imply that mass is a primary determinant only for the complete removal of the progenitor He envelope (Ic SNe), and that the differences between II(P), IIb, Ib largely reflect variations in binary separation rather than initial mass within the local Universe metallicity regime. These results establish a new empirical constraint for massive star/binary evolution models and underscore the value of spatially resolved spectroscopic environmental surveys for probing massive stellar endpoints.
