2020 Fiscal Year Research-status Report
Galactic Outflow Production of Multiphase Gas in the Circumgalactic Medium
| Project/Area Number |
19K03911
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| Research Institution | Shinshu University |
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Principal Investigator |
藤田 あき美 信州大学, 学術研究院工学系, 講師 (50729506)
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| Co-Investigator(Kenkyū-buntansha) |
三澤 透 信州大学, 学術研究院総合人間科学系, 教授 (60513447)
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| Project Period (FY) |
2019-04-01 – 2022-03-31
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| Keywords | circumgalactic medium / galactic outflows / galactic evolution / numerical simulations |
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| Outline of Annual Research Achievements |
Observations at intermediate redshifts reveal the presence of numerous, compact, weak MgII absorbers with near to super-solar metallicities, often surrounded by extended regions that produce CIV and/or OVI absorption, in the circumgalactic medium at large impact parameters from luminous galaxies. Their origin and nature remains unclear. We tested our hypothesis that undetected, satellite dwarf galaxies are responsible for producing some of these weak MgII absorbers, using gas dynamical simulations of galactic outflows from a dwarf galaxy with a halo mass of 5 10^9 Msun, as might be falling into a larger L* halo at z=2. We find that thin, filamentary, weak MgII absorbers (<100 pc) are produced in two stages: 1) when shocked core collapse supernova enriched gas descending in a galactic fountain gets shock compressed by upward flows driven by subsequent SNIIs and cools (phase 1), and later, 2) during an outflow driven by Type Ia supernovae that shocks and sweeps up pervasive SNII-enriched gas, which then cools (phase 2). The MgII absorbers in our simulations are continuously generated by shocks and cooling with ~0.1-0.2 Zsun, but low column density <10^12 cm^-2. They are also surrounded by larger (0.5-1 kpc) CIV absorbers that seem to survive longer. Larger-scale (>1kpc) CIV and OVI clouds are also produced in both expanding and shocked SNII-enriched gas. Observable ion distributions from our models appear well-converged at our standard resolution (12.8pc). Our simulation highlights the possibility of dwarf galactic outflows producing highly enriched multiphase gas.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
In 2020, we published a paper titled, "Origin of Weak MgII and Higher Ionization Absorption Lines in Outflows from Intermediate-Redshift Dwarf Galaxies", in the Astrophysical Journal (Fujita et al. 2020 ApJ 909, 157), based on the analysis of 3D hydrodynamical simulations of galactic outflows in a dwarf halo.
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| Strategy for Future Research Activity |
We will study several cycles of phase 1 & phase 2 formation of clumps and filaments in mass-loaded outflows due to repeated starbursts from a dwarf satellite galaxy embedded in denser, high-pressure gas of its host halo. Thus, we continue to model the effects of repeated SNII & SNIa explosions driving outflows in the same dwarf galaxy at z=2 with halo mass 4 10^9 Msun and R_vir=17.5 kpc, but 1) with repeated starbursts every 200 Myr for 1Gyr, 2) placed in CGM of characteristic haloes expected to collapse from ΛCDM density perturbations as 1-2σ peaks, 3) assuming the dwarf galaxy is moving through the host halo with v=100 km/s and 200 km/s. We will use the adaptive mesh refinement hydrodynamics code ENZO.
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| Causes of Carryover |
Due to corona pandemic, the planned trip to American Museum of Natural History, Center for Computational Astrophysics, and Pennsylvania State University in the USA has been canceled for 2020-2021. The PI, Akimi Fujita, will purchase computers necessary for the analysis of simulations in 2021.
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