| 研究実績の概要 |
In the nearby universe, there is a close relationship between the mass of a galaxy and the mass of its central supermassive black hole thus indicating that the formation of the two are linked. The mechanism that controls the connection between the two is currently not understood. To resolve this issue, we measured the masses in stars of 32 galaxies hosting supermassive black holes at earlier times in the history of our universe with near-infrared (NIR) imaging from the Hubble Space Telescope (HST) and spectroscopy from Subaru Telescope. In FY2018, we acquired all HST observations and carried out the full analysis of the required data. This involved the modification of available analysis tools to separate the NIR emission from Active Galactic Nucleus (AGN) from that of its host galaxy using the HST images. This procedure required an accurate characterization of the spatial resolution of the observations through 2D empirical modeling of the point-spread function (PSF). To achieve this, we used observations of stars in the field-of-view of each HST observation that resulted in a library of 70 stars to assess the shape of the PSF. The emission from our target galaxies was split into the unresolved emission indicative the AGN while the more extended emission is indicative of the underlying host galaxy. The stellar mass of the host galaxies was measured for all targets. This is the first time that such measurements have been made on a well understood sample at high redshifts. We fit our observations with stellar population models to infer their masses in stars.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
3: やや遅れている
理由
In FY2018, we needed to build a library of all stars in the field-of-view of each HST observation and develop a method to decide which ones should be used in the analysis of each target. From our initial analysis of the point-spread function of stars in the field-of-view of each target Active Galactic Nucleus, the number of stars (~3-4) in each field was insufficient to characterize the point spread function to be used to decompose the AGN and host galaxy emission in that specific field. The solution was to build a library of 2-D models to all stars in the 32 HST observations in hand. The optimal point-spread function model to apply for each AGN was determined out of this full list. A point-spread function library has been successfully generated and incorporated into the analysis. The extra work delayed the analysis by three months. In subsequent fiscal years, no further delays occurred.
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| 今後の研究の推進方策 |
In FY 2019, the primary activity was the write up of the results as a peer-reviewed paper (Ding, Silverman et al.) based on our finding that the mass relation between supermassive black holes and their host galaxies at 1<z<2 is similar to that in the local universe thus indicating a co-evolution scenario. We also completed a study (Ding, Treu, Silverman et al.) that compared the observational data to theoretical models of black hole and galaxy evolution using hydrodynamic and semi-empirical cosmological simulations available to our team (N. Menci; Rome, T. Di Matteo; Carnegie Mellon). At the time of writing this report, this work has been accepted and is in press. A third study on the sizes of the host galaxies has been published (Silverman et al.) which shows that AGN hosts have intermediate sizes relative to the overall galaxy population thus shedding light on the link between black hole and bulge growth. In FY2020, we plan to construct a comparison sample of lower redshift (z<1) quasars identified from the Sloan Digital Sky Survey that have optical imaging from the Subaru Telescope Strategic Survey Program. This provides a direct comparison on the black hole to host mass relation across a wide range of cosmic time and links directly the local and high redshift measurements. Preliminary results are available but will reach maturity in FY2020. In addition, we plan to compare the structural properties of galaxies including their sizes, light profiles and other features such as rings and spiral arms using the Subaru HSC imaging of SDSS quasars.
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