The Fornax3D project: Assembly histories of lenticular galaxies from a combined dynamical and population orbital analysis

Abstract

In order to assess the impact of the environment on the formation and evolution of galaxies, accurate assembly histories of such galaxies are needed. However, these measurements are observationally difficult owing to the diversity of formation paths that lead to the same present-day state of a galaxy. In this work, we apply a powerful new technique in order to observationally derive accurate assembly histories through a self-consistent combined stellar dynamical and population galaxy model. We present this approach for three edge-on lenticular galaxies from the Fornax3D project -FCC 153, FCC 170, and FCC 177 -in order to infer their mass assembly histories individually and in the context of the Fornax cluster. The method was tested on mock data from simulations to quantify its reliability. We find that the galaxies studied here have all been able to form dynamically-cold (intrinsic vertical velocity dispersion σ z 50 km s −1 ) stellar disks after cluster infall. Moreover, the pre-existing (old) high angular momentum components have retained their angular momentum (orbital circularity λ z > 0.8) through to the present day. Comparing the derived assembly histories with a comparable galaxy in a low-density environment -NGC 3115 -we find evidence for cluster-driven suppression of stellar accretion and merging. We measured the intrinsic stellar age-velocity-dispersion relation and find that the shape of the relation is consistent with galaxies in the literature across redshift. There is tentative evidence for enhancement in the luminosity-weighted intrinsic vertical velocity dispersion due to the cluster environment. But importantly, there is an indication that metallicity may be a key driver of this relation. We finally speculate that the cluster environment is responsible for the S0 morphology of these galaxies via the gradual external perturbations, or 'harassment', generated within the cluster.

Diversity of nuclear star cluster formation mechanisms revealed by their star formation histories

“…In Fahrion et al (2019b), we argued that the old age and high metallicity of the NSC in FCC 47 indicates an efficient formation at early times. Similar arguments were made in the detailed analysis of FCC 170 by Pinna et al (2019a) using the same F3D MUSE data which showed that FCC 170 assembled very rapidly and efficiently at early times (see also Poci et al 2021). Their SFH of the central region of FCC 170 is similar to the one presented here.…”

“…Lower-mass edge-on S0 galaxies FCC 153 and FCC 177 are edge-on S0 galaxies like FCC 170, but at significantly lower galaxy mass (see e.g. Pinna et al 2019b;Poci et al 2021 for a detailed analysis using the F3D MUSE data). Pinna et al (2019b) and the Voronoi binned radial profiles presented in this work generally find young ages toward the galaxy centres.…”

“…FCC 170 is an edge-on S0 galaxy with multiple structural components including a thin disk, thick disk, and a X-shaped bulge component (see e.g. Pinna et al 2019a;Poci et al 2021). Modelling this galaxy with imfit is challenging.…”

The Fornax3D project: discovery of ancient massive merger events in the Fornax cluster galaxies NGC 1380 and NGC 1427

“…The merger of NGC 1380 with its most massive satellite occurring ∼ 10 Gyr ago is consistent with this scenario. Two other early-type galaxies in the same clump, NGC 1380A (FCC 177) and NGC 1381 (FCC 170), have also been suggested to have accreted a substantial fraction of stars ∼ 9 Gyr ago (Pinna et al 2019b,a;Poci et al 2021). On the other hand, for NGC 1427 and considering that the merger process could last for 1 − 2 Gyr, the constraint from the stellar age distribution of its hot inner stellar halo does allow the inferred merger event to have started before infall.…”

“…Stellar orbits in the model have been further colored with age and metallicities in a recently-developed population-orbit superposition method (Poci et al 2019;Zhu et al 2020). By fitting the stellar kinematic, age and metallicity maps simultaneously, we have been able to obtain the internal stellar orbit distribution as well as the age and metallicity distributions (Poci et al 2021). With this novel method, chemo-dynamically identification of galactic structures as employed in the Milky Way, has become possible for external galaxies.…”