Inmaculada Martínez Valpuesta, Pedro Alonso Palicio, Chris Brook
A. Sánchez (Max Planck Institute for Extraterrestrial Physics, Garching); S. Khochfar (Royal Observatory, Edinburgh); I. McCarthy (John Moores University, Liverpool); R. Crain (John Moores University, Liverpool); S. Kay (University of Manchester); Y. Bahé (MPA, Garching); J. Schaye (Leiden Observatory); A, Maccio (NYUAD); A. Di Cintio (AIP); A. Obreja (University Observatory Munich)
How galaxies formed and evolved through cosmic time is one of the key questions of modern astronomy and astrophysics. Cosmological time- and length-scales are so large that the evolution of individual galaxies cannot be directly observed. Only through numerical simulations can one follow the emergence of cosmic structures within the current cosmological paradigm.
The main physical processes in galaxy formation and evolution are gravity, hydrodynamics, gas cooling, star formation, stellar evolution, supernova (SN) and black hole (BH) feedback. These are highly non-linear, thus difficult to describe with analytic models. Moreover, the presence of baryonic matter induces biases that collisionless (“dark matter”) simulations alone cannot reproduce (e.g. van Daalen et al. 2014, MNRAS, 440, 2997; Velliscig et al. 2014, MNRAS, 442, 2641). Semi-analytic models based on these simulations require ad hoc corrections to account for these biases. Hydrodynamical, cosmological simulations are therefore the preferred tool for conducting “controlled experiments” of galaxy formation and evolution.
After three decades of advances in numerical simulations, theorists have only recently been able to reproduce simultaneously the observed properties of the present day galaxy population and the inter-galactic medium (e.g. EAGLE, Schaye et al. 2015, MNRAS, 446, 521; ILLUSTRIS, Vogelsberger et al., 2014, Nature, 509, 177). In particular, the luminosity and mass function of galaxies, the galaxy size- and metallicity-mass relations, and many other properties are now reproduced over a large range of galaxy stellar masses.
Numerical tools are available for investigating the physics of galaxy formation and evolution with unprecedented detail. To date, little effort has been concentrated in studying the properties of the full galaxy population in group and cluster environments. Galaxy groups and clusters are excellent laboratories for studying physical processes, such as mergers, tidal stripping and ram-pressure stripping. It is known these processes shape galaxies at any epoch in cosmic history, but it is not known how, combined, they yield the observed population of cluster galaxies. Moreover, little effort has been put in studying the secular evolution of galaxies with self-consistent models of galaxy formation, and much has to be done to link secular processes to galaxy evolution. Por último, las simulaciones cosmológicas están alcanzando la sofisticación requerida para describir el entorno del Grupo Local en gran detalle. New theoretical results in these fields will be useful for interpreting the data of current and future ground- and space-based galaxy surveys like MANGA, WEAVE, GAIA and EUCLID.
With the completion of the main sample of simulations, the post-processing phase has been started. Dalla Vecchia developed an analysis program to compute luminosities of SSPs and magnitudes of galaxies of ~30 resimulated clusters. The code makes use of the stellar spectra library EMILES, developed at the IAC and recently extended to cover a larger wavelength range.
Within the EUCLID collaboration, a total of 300 cosmological, N-body simulations of a volume representative of the observed universe were performed. The same sample of initial conditions was evolved with different techniques by other members of the collaboration. The comparison of the different techniques will allow to assess their accuracy in the estimation of the covariance matrix, thus the errors in the measurements from large-scale structure surveys.
GALAXY INTERACTIONS IN CLUSTERS
For several decades, it has been known that stellar bars in disc galaxies can be triggered by interactions, or by internal processes such as dynamical instabilities. Martínez-Valpuesta et al. (2017) explore the differences between these two mechanisms using numerical simulations. They used two groups of simulations based on isolated galaxies, one group in which a bar develops naturally, and another group in which the bar could not develop in isolation. The rest of the simulations recreate 1:1 coplanar fly-by interactions computed with the impulse approximation. Compared with equivalent isolated galaxies, they find that bars affected or triggered by interactions: (i) remain in the slow regime for longer, (ii) are boxier in face-on views and (iii) they host kinematically hotter discs. Within this set of simulations, strong differences between retrograde or prograde fly-bys are not seen. They also show that slow interactions can trigger bar formation.