2019 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 / numerical simulations |
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| Outline of Annual Research Achievements |
Observations 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 CGM at large impact parameters from luminous galaxies. Thus, we run gas dynamical simulations of galactic outflows from a dwarf satellite galaxy, which is expected to arise in a larger L* halo at z=2, and study the gas interaction in the halo to test our hypothesis that invisible, satellite dwarf galaxies are responsible for producing such weak MgII absorbers. We find that thin, filamentary weak MgII absorbers are produced in two phases: when 1) SNII enriched eventually loses energy to descend toward expanding SNII enriched gas and gets shocked to cool (phase 1), and later, 2) an outflow driven by SNIa shocks and sweeps pervading SNII enriched gas, which then cools (phase 2). These MgII absorbers are <100 pc in size with ~10-20% of solar metallicity, and are continuously generated by shocks and cooling. They are also surrounded by larger CIV absorbers (0.5-1 kpc) in the presence of the UV metagalactic radiation at high redshift. Covering fractions are >50% for higher ion clouds, but ~3-6%, much less than the observed estimate (~30%) for MgII clouds, probably because our simulation is limited to a single, instantaneous starburst in a small box out of which a substantial amount of metal-enriched gas leaves. Our simulation nonetheless highlights a possibility of galactic outflows producing multiphase gas, and future, more general simulation can estimate their global importance.
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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 2019, we finished running 3D hydrodynamical simulations of galactic outflows in a dwarf halo at redshift z=2 with a halo mass of 5E9 Msolar and a virial radius f 17.5 kpc by modeling a single, instantaneous starburst of 1E6 Msolar with Z=0.001 Zsolar, and we are currently writing a paper to be submitted to the Astrophysical Journal. Our plan was to have a face-to-face meeting in March 2020 to go over the simulation results and our draft for the paper at American Museum of Natural History, Center for Computational Astrophysics, and Pennsylvania State University in the USA, but due to corona pandemic, our communication has been slow and we are still working on the draft with international collaborators.
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| Strategy for Future Research Activity |
We continue to model the effects of repeated SN explosions driving outflows based on our superbubble model in the same dwarf halo studied in the previous year, however, we model 1) repeated starbursts every 100 Myr, 2) for 1 Gyr, 3) in a much larger grid. 1) With a more realistic treatment of star formation, we expect that repeated SNII driven outflows and SNIa driven outflows will continuously shock gas which then cools to produce more clumps and filaments. We will test the effects of repeated phase 1 and phase 2 formation for MgII clouds in galactic outflows. 2) With continuous star formation for 1 Gyr, we expect such MgII clouds to have near to super-solar metallicities with significant iron enrichment. The high metallicity and high iron contents of low-ionization absorbers have never been studied in numerical simulations. 3) In a larger grid that covers the entire dwarf halo and beyond, we expect radiatively cooling, metal-enriched gas to fill the dwarf halo and produce more MgII clouds with a higher covering fraction and higher CIV and OVI column densities. As a next step, we are also running “zoom-in” simulations with a higher resolution on MgII clouds to study the size, distribution, and the fate of weak MgII clouds.
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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 was canceled. The PI, Akimi Fujita, will visit those institutions as well as Columbia University in 2020, when possible, to present our results at their institutional meetings.
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Research Products
(4 results)
