February 2-5, 2021

Oral Presentation

A method to constrain black hole models using ratios of line emission

Author(s): Shigeki Inoue (Tsukuba/NAOJ), Hiroshi Matsuo (NAOJ), Naoki Yoshida (Tokyo), Hidenobu Yajima (Tsukuba), Kana Moriwaki (Tokyo)

Presenter: Shigeki Inoue (Tsukuba University / NAOJ)

We study the relationship between galactic quenching process driven by massive black holes (BHs) and relative strength of line emission from star-forming regions in galaxies. BHs are expected to start the quenching process with decreasing densities of their ambient gas by strong feedback effects. Since intensity ratios between a certain pair of line emission are sensitive to local densities, the BH quenching can be imprinted as low values of the line ratios. To demonstrate this, we postprocess the IllustrisTNG and Illustris simulations, which implement drastically different feedback models for massive BHs, by modelling HII regions and computing their line emission of [OIII] 52 and 88 micro-metres. In IllustrisTNG, BH quenching abruptly operates when a BH mass reaches nearly 10^8 solar mass and expels gas around the BHs in star-forming galaxies. We find that the reduced gas densities are reflected as low values of the line ratios measured in these galaxies. In Illustris, on the other hand, since gas densities hardly change with BH mass, the line ratios do not show such a drop at any BH mass. We find that the measurements of the line ratios do not significantly depend on aperture size, which means that observations do not need to resolve the central regions of galaxies. We thus propose that the integrated line ratios can be used to capture the signature of the beginning of the quenching driven by massive BHs.

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