insikt - Astrophysics - # Supernova Remnants and Circumgalactic Medium Absorption

Supernova Ejecta from Runaway Stars as a Potential Source of Super-Virial Absorption in the Circumgalactic Medium

Q: How would the properties of the supernova remnants, such as the explosion energy and progenitor mass, affect the predicted column densities and observational signatures?

The properties of supernova remnants (SNRs), particularly explosion energy and progenitor mass, play a crucial role in determining the predicted column densities and observational signatures of the ejecta. Higher explosion energies typically lead to more energetic shocks, which can significantly enhance the temperature of the shocked ejecta. For instance, in the context of the proposed scenario, an explosion energy of (1.2 \times 10^{51}) erg is considered, which is standard for core-collapse supernovae (CCSNe). This energy influences the dynamics of the SNR, affecting how efficiently the ejecta can mix with the surrounding medium and how much material is heated to super-virial temperatures (≥ (10^7) K). The progenitor mass also directly impacts the amount of material ejected during the supernova event. More massive progenitors tend to lose a significant portion of their mass through stellar winds before the explosion, resulting in a larger ejecta mass. This increased mass can lead to higher column densities of heavy elements, such as oxygen, neon, and silicon, in the shocked ejecta. The mass fraction of these elements, which is influenced by the nucleosynthesis processes during the star's life and the explosion, will also affect the observed abundance ratios in absorption lines. Therefore, the interplay between explosion energy and progenitor mass is critical in shaping the observational signatures, such as the column densities of various ionization states, which can be compared with observations from X-ray spectra of background quasars.

Q: What other observational signatures, beyond absorption lines, could help distinguish the proposed scenario of extra-planar supernova ejecta from a Milky Way-wide hot gas component in the circumgalactic medium?

In addition to absorption lines, several other observational signatures could help differentiate the proposed scenario of extra-planar supernova ejecta from a more uniform Milky Way-wide hot gas component in the circumgalactic medium (CGM). X-ray Emission: The presence of high-energy X-ray emission from the shocked ejecta can be a strong indicator of supernova remnants. The temperature and density of the gas can be inferred from the X-ray spectra, allowing for a comparison with the expected signatures from the supernova scenario. Chemical Composition: The elemental abundance ratios in the X-ray emission or absorption spectra can provide insights into the nucleosynthetic processes at play. The presence of α-elements (like oxygen and silicon) in super-solar ratios would support the idea of enrichment from core-collapse supernovae, distinguishing it from the more uniform composition expected from the CGM. Spatial Distribution: Mapping the spatial distribution of the gas can reveal whether the high-temperature gas is localized around specific supernova remnants or more uniformly distributed across the CGM. A concentrated distribution of high-temperature gas would support the runaway star supernovae hypothesis. Kinematic Signatures: Observations of the velocity structure of the gas can provide clues about its origin. The kinematics of the gas associated with supernova remnants may show distinct patterns, such as outflows or peculiar velocities, that differ from the more isotropic motions expected in the CGM. Time Variability: Monitoring changes in the X-ray or UV emission over time could indicate the dynamic nature of supernova remnants, which may evolve more rapidly than the more stable hot gas in the CGM. By combining these observational signatures with absorption line studies, researchers can build a more comprehensive picture of the origins and properties of the high-temperature gas in the Milky Way's CGM.

Centrala begrepp

Supernova ejecta from runaway stars above the Galactic disk can heat up to super-virial temperatures and produce the observed high column density absorption of highly ionized gas in the circumgalactic medium.

Sammanfattning

The paper proposes a novel explanation for the puzzling detection of large column density absorption lines from highly ionized gas in the circumgalactic medium (CGM) of the Milky Way. The authors suggest that these absorption signatures may not originate from the CGM itself, but rather from supernova (SN) ejecta of runaway stars that explode above the Galactic disk.

Key highlights:

About 20% of massive OB stars (progenitors of core-collapse SNe) are known to be runaway stars that can end up exploding as SNe above the Galactic disk.
The reverse shock in the supernova remnant during the early non-radiative phase can heat the ejecta to temperatures of ≳10^7 K, naturally explaining the observed high column density of ions in the 'super-virial' phase.
The super-solar abundance ratios of ions typical of core-collapse SNe can also be explained by the shocked SN ejecta.
However, SNe from runaway stars have a covering fraction of ≲0.7% and can only explain the observations along limited sightlines.

The authors demonstrate that the column densities along observed lines of sight can be produced by extra-planar SNe if the lines of sight pass through them. This proposal unburdens the need to explain the absorption lines in the context of Milky Way-wide phenomena, which was challenging to reconcile.

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Statistik

The observed column densities of OVIII, NeX, and SiXIV ions towards the quasars IES 1553+113, Mrk 421, and NGC 3783 are:
OVIII: (3.4 ± 1.4) × 10^15, (2.24 ± 0.44) × 10^15, (9.66^+3.90_-3.93) × 10^15 cm^-2
NeX: (15.8 ± 4.6) × 10^15, (2.12^+0.70_-0.66) × 10^15, (15.28 ± 3.37) × 10^15 cm^-2
SiXIV: < 35.26 × 10^15 cm^-2 (for NGC 3783)

Citat

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Viktiga insikter från

Can supernova from runaway stars mimic the signs of absorbing `super-virial' gas?

by Mukesh Singh... på arxiv.org 10-01-2024

https://arxiv.org/pdf/2408.14351.pdf

Can supernova from runaway stars mimic the signs of absorbing `super-virial' gas?

Djupare frågor

How would the properties of the supernova remnants, such as the explosion energy and progenitor mass, affect the predicted column densities and observational signatures?

The properties of supernova remnants (SNRs), particularly explosion energy and progenitor mass, play a crucial role in determining the predicted column densities and observational signatures of the ejecta. Higher explosion energies typically lead to more energetic shocks, which can significantly enhance the temperature of the shocked ejecta. For instance, in the context of the proposed scenario, an explosion energy of (1.2 \times 10^{51}) erg is considered, which is standard for core-collapse supernovae (CCSNe). This energy influences the dynamics of the SNR, affecting how efficiently the ejecta can mix with the surrounding medium and how much material is heated to super-virial temperatures (≥ (10^7) K).
The progenitor mass also directly impacts the amount of material ejected during the supernova event. More massive progenitors tend to lose a significant portion of their mass through stellar winds before the explosion, resulting in a larger ejecta mass. This increased mass can lead to higher column densities of heavy elements, such as oxygen, neon, and silicon, in the shocked ejecta. The mass fraction of these elements, which is influenced by the nucleosynthesis processes during the star's life and the explosion, will also affect the observed abundance ratios in absorption lines. Therefore, the interplay between explosion energy and progenitor mass is critical in shaping the observational signatures, such as the column densities of various ionization states, which can be compared with observations from X-ray spectra of background quasars.

What other observational signatures, beyond absorption lines, could help distinguish the proposed scenario of extra-planar supernova ejecta from a Milky Way-wide hot gas component in the circumgalactic medium?

In addition to absorption lines, several other observational signatures could help differentiate the proposed scenario of extra-planar supernova ejecta from a more uniform Milky Way-wide hot gas component in the circumgalactic medium (CGM).

X-ray Emission: The presence of high-energy X-ray emission from the shocked ejecta can be a strong indicator of supernova remnants. The temperature and density of the gas can be inferred from the X-ray spectra, allowing for a comparison with the expected signatures from the supernova scenario.

Chemical Composition: The elemental abundance ratios in the X-ray emission or absorption spectra can provide insights into the nucleosynthetic processes at play. The presence of α-elements (like oxygen and silicon) in super-solar ratios would support the idea of enrichment from core-collapse supernovae, distinguishing it from the more uniform composition expected from the CGM.

Spatial Distribution: Mapping the spatial distribution of the gas can reveal whether the high-temperature gas is localized around specific supernova remnants or more uniformly distributed across the CGM. A concentrated distribution of high-temperature gas would support the runaway star supernovae hypothesis.

Kinematic Signatures: Observations of the velocity structure of the gas can provide clues about its origin. The kinematics of the gas associated with supernova remnants may show distinct patterns, such as outflows or peculiar velocities, that differ from the more isotropic motions expected in the CGM.

Time Variability: Monitoring changes in the X-ray or UV emission over time could indicate the dynamic nature of supernova remnants, which may evolve more rapidly than the more stable hot gas in the CGM.

By combining these observational signatures with absorption line studies, researchers can build a more comprehensive picture of the origins and properties of the high-temperature gas in the Milky Way's CGM.

Could the proposed scenario of runaway star supernovae have broader implications for understanding the energetics and chemical enrichment of the circumgalactic and intergalactic media in galaxies?

Yes, the proposed scenario of runaway star supernovae has significant implications for our understanding of the energetics and chemical enrichment of both the circumgalactic medium (CGM) and the intergalactic medium (IGM) in galaxies.

Energetics: The energy released during supernova explosions contributes to the overall energy budget of the CGM and IGM. Runaway stars, which can explode outside the Galactic plane, may inject energy into the CGM in a more localized manner, potentially leading to the formation of bubbles or cavities in the surrounding gas. This localized energy input can influence the thermal and dynamical state of the CGM, affecting its ability to retain or lose gas.

Chemical Enrichment: Supernovae are key contributors to the chemical enrichment of the universe. The ejecta from runaway star supernovae, which are rich in heavy elements synthesized during the stellar lifecycle, can enhance the metallicity of the CGM and IGM. This enrichment is crucial for understanding the evolution of galaxies, as it affects star formation rates and the cooling processes in the gas.

Feedback Mechanisms: The feedback from supernovae can regulate star formation in galaxies. The energy and material ejected by supernovae can drive galactic winds, which may expel gas from the galaxy or mix it with the surrounding medium. This process can influence the cycle of gas inflow and outflow, impacting the overall evolution of galaxies.

Galaxy Formation and Evolution: Understanding the role of runaway star supernovae in the CGM can provide insights into the processes that govern galaxy formation and evolution. The interplay between supernova feedback, gas dynamics, and chemical enrichment is fundamental to models of galaxy evolution.

Intergalactic Medium Dynamics: The implications extend to the IGM, where enriched material from supernovae can contribute to the overall metallicity of the universe. This can affect the formation of structures in the IGM and the properties of the cosmic web.

In summary, the scenario of runaway star supernovae not only offers a novel explanation for observed phenomena in the Milky Way but also enriches our understanding of broader astrophysical processes that shape the universe.