Shape and kinematics of elliptical galaxies: evolution due to merging at z ${<}$ 1.5

Abstract

Aims. We investigate the evolution in the shape and kinematics of elliptical galaxies in a cosmological framework. Methods. We identified relaxed, elliptical-like objects (ELOs) at redshifts z = 0, z = 0.5, z = 1 and z = 1.5 within a set of hydrodynamic, self-consistent simulations completed for a concordance cosmological model. Results. The population of elliptical systems that we analysed evolve systematically with time becoming rounder in general by z = 0 and also more velocity dispersion supported. We found that this is due primarily to major dry mergers where only a modest amount of angular momentum is involved in the merger event. Despite the general trend, in a significant number of cases the merger event involves a relatively high amount of specific angular momentum, which causes the system in general to acquire higher rotational support and/or a more oblate shape. These evolutionary patterns persist when we study our systems in projection, in simulating true observations, and thus should be evident in future observations.

Large-scale gas dynamics in the adhesion model: implications for the two-phase massive galaxy formation scenario

“…Galaxy‐like objects of different morphologies (disc‐like, elliptical‐like, irregulars) have been identified in any kinds of simulations. The analyses of their structural and dynamical properties show that they are consistent with observations of the local universe, both for disc‐like (Sáiz et al 2001; Martínez‐Serrano et al 2009) and elliptical‐like objects (Domínguez‐Tenreiro, Sáiz & Serna 2004; Sáiz, Domínguez‐Tenreiro & Serna 2004; Oñorbe et al 2006; Oñorbe et al 2007; González‐García et al 2009). For details on the mass and velocity distributions of the different components, and on the parameters characterizing them, we refer the reader to these publications.…”

“…This can be explained because the POR mass‐scale determines how fast its coalescence length grows on average at PORs of different masses, that is, how fast gaseous mass availability to be accreted is exhausted. During the slow phase of mass assembly, merging is still taking place, the stellar mass bound in massive galaxies increases (González‐García et al, in preparation), and dry mergers (Conselice et al 2003) dominate the mass growth (see for observational information). Thus, the final mass distribution of MGOs, as well as their shapes and kinematical properties, among others, is mostly set by non‐dissipative mergers (González‐García & van Albada 2003; González‐García et al 2009). …”

“…7 7 The merger characteristics have been detected and measured using three‐dimensional visualization techniques, as well as the mass aggregation trees of the objects (for details see González‐García et al 2009). …”

Lagrangian volume deformations around simulated galaxies

“…An object with axis ratio c/a > 0.9 has a nearly spheroidal shape, while one with c/a < 0.9 and T < 0.3 has an oblate triaxial shape. On the other hand, an object with c/a < 0.9 and T > 0.7 has a prolate triaxial shape (González-García et al 2009). …”

Planets, Stars and Stellar Systems

“…Classical bulges can also be spun up by a bar (Saha et al 2011). To further complicate matters, simulations indicate that merger events can result in rotating elliptical galaxies (Naab et al 1999(Naab et al , 2006González-García et al 2009;Hoffman et al 2009), andBekki (2010) has shown that a rotating bulge can also be created by a merger event and is thus not necessarily a sign of a pseudobulge built by secular evolution from disk material as typically assumed. In addition, Qu et al (2011) report on how the rotational delay between old and young stars in the disc of our Galaxy may be a signature of a minor merger event.…”