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Uncover galaxies’ past merger events through a population-orbit superposition method
报告题目:Uncover galaxies’ past merger events through a population-orbit superposition method
报 告  人:Ling Zhu 朱玲 (Shanghai Astronomical Observatory)
报告时间:2021-09-16 16:00:00

Abstract: Driven by gravity, galaxies are expected to continuously grow through the merging of smaller systems. To derive their past merger history is challenging, as the accreted stars disperse quickly. The details of the merger history of galaxies beyond the local group have so far remained hidden. Here I will show you how we discover the ancient, massive merger events in Fornax cluster galaxies. By applying a recently developed population-orbital superposition model to each galaxy, we fit its surface brightness as well as stellar kinematic, age, and metallicity maps from VLT/MUSE IFU data, and obtain the stellar orbits, age and metallicity distributions of this galaxy. We apply the method to 19 ETGs in Fornax 3d surveys and found two of them, NGC1380 and NGC1427, have massive inner stellar halo component made of highly radial orbits. By comparing to analogues from the cosmological galaxy simulation TNG50 and EAGLE, we find that the formation of the inner stellar halo of NGC1380 and NGC1427 requires a merger with a massive satellite galaxy with stellar mass of ~4e10 M_sun and ~1.4e10M_sun, respectively.  The merger time of NGC 1380 should be ~10 Gyr constrained by the stellar age distribution of its cold disk. These massive merger events are the first major merger events found in normal phase-mixed galaxies beyond the local volume. Our chemo-dynamical method, when applied to extended deep IFU data and in combination with cosmological galaxy simulations, can quantitatively unravel the merger history of a large number of nearby galaxies.