2013 Fiscal Year Research-status Report
宇宙に於けるエネルギー収支の型録化と交互作用の試驗II
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23540288
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| Research Institution | The University of Tokyo |
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Principal Investigator |
福来 正孝 東京大学, カブリ数物連携宇宙研究機構, 特任教授 (40100820)
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| Keywords | cosmic energy inventory / cosmic dust / MgII absorbers / damped Lyman alpha |
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| Research Abstract |
In the course of building the cosmic energy inventory, we realised that the Galaxy is not the Island Universe: it is not quite an isolated object, nor a closed entity, even if we take the sphere of the virial radius enclosing the galaxy. Many components are leaked substantially from the virial sphere to intergalactic space. This is noted specifically for dark matter and dust, which are made somehow observationally accessible. Our technique to observe them in the intergalactic space resorts to passive means using a bright object behind as a beacon. It rests on the technique of stacking images over a large number of galaxies, with which we can measure the effect that is smaller by 1/10 to 1/100, or even less, than is accessible with direct measurements. With this way we detect the components located outside galaxies, which otherwise cannot be detected. When those inferred to exist beyond the virial sphere are taken into account, the inventory closes. We have applied this to the Mg II clouds (2012) and to Lyman alpha clouds (2014). Interpretation of this work requires the clarification of physical properties of dust. This was the work carried out and published this year. We inferred that the size distribution of intersteller dust is universal, obeying the power law with index approximately -3.5 and with a cutoff at some maximum size at a few tenths of microns. This contrasts to our knowledge to date, mainly from the work of Draine and others. This may hint the dynamics of the dust formation, not only is useful to interpret our results for quasar-line absorbers.
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| Current Status of Research Progress |
Current Status of Research Progress
3: Progress in research has been slightly delayed.
Reason
The delay I report here is relative to the schedule initially set. The reason is that I found something unexpected after I started this project. I thought, as most of people do, that intergalactic space is vacuum, all materials being thoroughly confined in galaxies or at least within their gravitational spheres (virial spheres) centred on galaxies. In the course of building the inventory and examining the consistency among its entries, I found that this is not the case. Many components seem to be leaked out from galaxies, and intergalactic space is not empty. This compels that I must study circumgalactic astrophysics first.
From the viewpoint of research schedule, this might be counted as a negative element, but, in fact, I should take this to be a great advantage from the study for the inventory. This enabled us to find what has been missed over years, giving a chance to reconsider it. So far, wherever I did the counting including the intergalactic component, the inventory seems to close, verifying the presence of the leaked component. This may be a detour, but is a necessary one and it enriched the work for cosmic energy inventory.
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| Strategy for Future Research Activity |
I will study circumgalactic physics more, as much as I could with the present knowledge. I have just resumed to make the full energy inventory, but I may have to work in advance for the part concerning relativistic components. For this work I expect some help by a young astrophysicist I found at Institute for Advanced Study.
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| Expenditure Plans for the Next FY Research Funding |
An important part of this work has been done in collaboration with Brice Menard of Johns Hopkins University. I could take the opportunity to finalise the project (about damped Lyman alpha absorbers) when I have visited Institute for Advanced Study in Princeton, to which I invited him to come (with the US money). This enabled me to save the remaining amount of the FY2013 funding.
I want to reserve this money to support visitors needed for my research (including Brice Menard again), which happens from time to time. I need stimulating and technical discussions from time to time, since the subject covers a wide range of astrophysics.
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