제목: What Dense Spectroscopic Surveys and Cosmological Simulations Reveal About Clusters: The Velocity Dispersion Function​

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​​​​​​​​​​​​​​​​​​연사: Prof. Ju-bee Sohn (서울대학교)​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

장소: 과학관 B103호​​

Abstract:

Dense spectroscopy and cosmological simulations are two fundamental tools for advancing astrophysics in the coming decades. In this talk, I will highlight one application of these tools in studying galaxy clusters: the velocity dispersion function. The central stellar velocity dispersion serves as a key observable linking galaxies to their dark matter subhalos. We derive the velocity dispersion function for ~10 massive clusters in the local universe and compare it to that of field galaxies. Our results reveal a significant excess of galaxies with velocity dispersions above 250 km/s in cluster environments, indicating the efficient formation of massive galaxies in dense regions. To provide theoretical context, we examine velocity dispersion functions in cosmological simulations, including IllustrisTNG, EAGLE, and HorizonRun 5. Notably, all simulated galaxies exhibit significantly lower velocity dispersions (by ~70%) at fixed stellar mass compared to observations. This offset persists across most simulations, except in cases where AGN feedback is absent. However, simulations without AGN feedback fail to reproduce the observed shape of the velocity dispersion function. Since cosmological simulations are not explicitly calibrated to match observed velocity dispersions, stellar velocity dispersion serves as a crucial benchmark for testing galaxy formation models across different environments. Upcoming and ongoing spectroscopic surveys—including DESI, 4MOST, and PFS—will provide unprecedented datasets, making the velocity dispersion function a vital tool for understanding the connection between galaxies and their dark matter subhalos.​