The evolution of the stellar IMF with HSC strong lenses

2018 Fiscal Year Final Research Report

• Project/Area Number: 17K14250
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Astronomy
• Research Institution: The University of Tokyo
• Principal Investigator: Sonnenfeld Alex 東京大学, カブリ数物連携宇宙研究機構, 特任研究員 (40772827)
• Project Period (FY): 2017-04-01 – 2019-03-31
• Keywords: Galaxies / Strong lensing / Stellar populations

Outline of Final Research Achievements

Galaxy stellar masses are typically obtained by measuring their luminosity and multiplying it by a mass-to-light ratio derived from a model of their stellar population.One of the biggest systematic uncertainties in the determination of this mass-to-light ratio is the stellar initial mass function (IMF).
The stellar IMF can be constrained using strong gravitational lensing. A strong lensing measurement provides the total mass enclosed within the inner regions of a galaxy. By carefully subtracting the dark matter contribution from the total mass, we can obtain the stellar mass,which can then be compared to stellar population models to constrain the IMF.
We studied a sample of 23 strong lenses with data from the Hyper Suprime-Cam survey. We first obtained spectroscopic measurements from the Very Large Telescope, then carried out a statistical study of the stellar IMF of the sample. Our measurement show that the stellar IMF of massive galaxies is not as heavy as previously thought.

Free Research Field

Formation and evolution of massive galaxies

Academic Significance and Societal Importance of the Research Achievements

恒星IMFは一般に銀河質量測定における系統誤差の最も重要な要因の1つと見なされている。これにより、銀河進化や宇宙論研究での理論モデルと数値シミュレーションの比較の精度が制約される。過去10年間で、理論的および観測的側面で恒星IMFに関する研究が数多く行われてきた。これらの努力にもかかわらず、真の恒星IMFとは何か、そしてそれがどのように銀河間で異なるのかについて合意には至っていない。この課題では以前と比較してより少ない仮定で確実な巨大銀河の恒星IMFの新しい測定を提供した。私たちは、新しい観測施設が利用可能になるまでの今後数年間、強い重力レンズ効果による恒星IMFが基準測定値になると期待する。