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NGC 1380 Ling Zhu Email: [email protected] Collaborators: Glenn Van De Ven, Ryan Leaman, Annalisa Pillepich, the Fornax3d Team, the Illustris TNG50 Team

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NGC 1380 Ling Zhu Email: Lzhu@Shao.Ac.Cn Collaborators: Glenn Van De Ven, Ryan Leaman, Annalisa Pillepich, the Fornax3d Team, the Illustris TNG50 Team Discovery of an ancient massive merger in the Fornax cluster galaxy NGC 1380 Ling Zhu Email: [email protected] Collaborators: Glenn Van de Ven, Ryan leaman, Annalisa Pillepich, the Fornax3D team, the Illustris TNG50 team. NGC 1380 + progenitor satellite We discover an ancient, massive merger event in the lenticular galaxy NGC 1380 in %& (3×10 !⊙) the Fornax cluster. By applying a recently developed population- orBital superposition model1 to NGC 1380’s surface Brightness as well as stellar kinematic, ] ⊙ 10%& age, and metallicity maps from VLT/MUSE IFU data, we oBtain the stellar orBits, ! age and metallicity distriButions of this galaxy. The highly radial orBits which make up an inner stellar halo are ∼ 13 Gyr old with metallicity Z/Z⊙ ∼ 1.2 and comprise 10 a stellar mass of M∗,halo(r<2Re)∼3.410 M⊙. By comparing to analogues from the 10' Andromeda cosmological galaxy simulation TNG50, we find that the formation of the inner %& Milky Way + M32p (2×10 !⊙) ( + Gaia-Enceladus (4×10 !⊙) stellar halo of NGC 1380 requires a merger with a massive satellite galaxy with [ Mass of Merger 10 stellar mass of ∼ 3 10 M⊙ that occurred roughly ∼ 10 Gyr ago. The massive merger in NGC 1380 is the first major merger event found in a normal phase-mixed 10( galaxy Beyond the Local Volume, and it is the oldest and most massive one identified in nearBy galaxies so far. Our chemo-dynamical method, when applied to 2 Billion years ago 10 Billion years ago extended deep IFU data and in comBination with cosmological galaxy simulations, Time of Merger can quantitatively unravel the merger history of a large numBer of nearBy galaxies. The most massive merger events in the only three galaxies that have been uncovered. With a progenitor mass of ∼ 3 10 10 M⊙ and accretion time of ~10 Gyrs ago, the merger we discovered in NGC 1380 is the most massive and oldest major merger discovered in nearby galaxies so far. (a) NGC 1380 Disk Warm component Inner stellar halo Bulge (b) Data Model ) 9:;<= $ / Fig.2. The model in phase-space of radius r vs. Circularity %. Panel (a): probability density of orbits in the model, ] ⊙ 787 Panel (b): age and Panel (c): metallicity distribution. We separate theThe mergergalaxy starts into 4 components based on the # 6 (a) () ( model.TNG50 The inner 468590 stellar halo is a dynamical hot component, which is radially extended,The oldmerger and ends metal-poor. 10 [ ∗ log # : 1.24 0.9 Redshift z SB (b) Inner stellar halo is product of an massive merger Main progenitor From minor mergers st before the Merger From main progenitor From the 1 satellite Insitu during the merger Insitu after the merger at z < 0.9 The galaxy at z=0 [km/s] ] . + + + + = ckpc Z [ X [ckpc] X [kpc] X [kpc] X [kpc] X [kpc] X [kpc] X [kpc] Disk " ! [km/s] Warm σ Inner + + + + = stellar halo Circularity Bulge r [ckpc] r [kpc] r [kpc] r [kpc] r [kpc] r [kpc] r [kpc] , h Fig.3. A NGC 1380-analogues from the cosmological simulation TNG50. This galaxy has experienced a massive merger at z~1. Before the merger, this galaxy has rarely inner stellar halo component, while at z=0, it has an 10 inner stellar halo mass of 3.3 10 M⊙, 90 percent of which is product of the merger. + h NGC 1380 ] Gyr [ t Merger ending time Log 10 ⊙ ( prob Z / ) Z NGC 1380 Y[arcsec] Y[arcsec] Y[arcsec] Y[arcsec] Y[arcsec] Y[arcsec] Y[arcsec] Y[arcsec] Y[arcsec] Y[arcsec] Y[arcsec] Y[arcsec] Y[arcsec] Y[arcsec] X [arcsec] X [arcsec] Fig.4. We select all the galaxies with similar stellar mass and Fig.1. NGC 1380 is a lenticular galaxy in the Fornax cluster, it was oBserved By size of NGC 1380 from TNG50, and find a strong correlation Fig.5. Based on the model, we find a transition from non- MUSE/VLT with 3 pointings as shown in Panel (a). Panel (b): the left column between the inner stellar halo mass and the stellar mass of disk dominating to disk dominating orbits at t~10 Gyr. is the data derived from the oBservations. The right column is a best-fitting its most massive satellite ever accreted. Only after the merger, a dynamical cold disk could form 10 from our population-orbit superposition model. Our model fit the surface With M∗,halo(r<2Re)∼3.410 M⊙ for NGC 1380, we infer a and persist. The last massive merger of NGC 1380 should 10 brightness, kinematic maps, and age, metallicity maps simultaneously. stellar mass of ~ ∼ 3 10 M⊙ for its most massive satellite. be ended before t~10 Gyr..
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