Multiple minor mergers: formation of elliptical galaxies and constraints for the growth of spiral disks

By Frédéric Bournaud, C. Jog, Francoise Combes Aim, CEA-Saclay IISc Bangalore Observatoire de Paris Lerma. 2007

210 citations recorded by the source corpus.

Multiple, sequential mergers are unavoidable in the hierarchical build-up picture of galaxies, in particular for the minor mergers that are frequent and highly likely to have occured several times for most present-day galaxies. However, the effect of repeated minor mergers on galactic structure and evolution has not been studied systematically so far. We present a numerical study of multiple, subsequent, minor galaxy mergers, with various mass ratios ranging from 4:1 to 50:1. The N-body simulations include gas dynamics and star formation. We study the morphological and kinematical properties of the remnants, and show that several so-called “minor” mergers can lead to the formation of elliptical-like galaxies that have global morphological and kinematical properties similar to that observed in real elliptical galaxies. The properties of these systems are compared with those of elliptical galaxies produced by the standard scenario of one single major merger. We thus show that repeated minor mergers can theoretically form elliptical galaxies without major mergers, and can be more frequent than major mergers, in particular at moderate redshift. This process must then have formed some elliptical galaxies seen today, and could in particular explain the high boxiness of massive ellipticals, and some fundamental relations observed in ellipticals. In addition, because repeated minor mergers, even at high mass ratios, destroy disks into spheroids, these results indicate that spiral galaxies cannot have grown only by a succession of minor mergers.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/ef985960ec3fc5e212388b6c91f8c1e72149d307

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Citations in the corpus

A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies. II. Formation of Red Ellipticals (2007, background): “…suggest that ellipticals can instead formwithout a late major merger, in an early, rapid phase of ‘‘clumpy,’’ or minor merging (Kobayashi 2005; Naab et al. 2007; Bournaud et al. 2007) provided that this occurs sufficiently rapidly that the system cannot accrete a disk at an equal or faster pace.”
The CALIFA survey across the Hubble sequence: Spatially resolved stellar population properties in galaxies (2015, unknown): “Califa5_metallicity_v12_8Jun Bournaud et al. 2007).”
Simulations of minor mergers - I. General properties of thick discs (2008, background): “The effects of repeated minor mergers have been considered in, e.g. Bournaud et al. (2007b); Kazantzidis et al. (2007).”
Simulations of binary galaxy mergers and the link with fast rotators, slow rotators, and kinematically distinct cores (2011, background): “Repeated minor mergers may preserve the initial KDC of the initial ETG and heat the external parts of the galaxy (Bournaud et al. 2007; Qu et al. 2010): this could end up with a round slow rotator, but this scenario has not been tested yet.”
The ATLAS3D project - VII. A new look at the morphology of nearby galaxies: the kinematic morphology-density relation (2011, background): “2009; Bois et al. 2010; Hoffman et al. 2010) and large numbers of minor dry mergers (Bournaud et al. 2007) could explain the observed nearly round shape of slow rotators, both inside and outsideV rgo.”
The ATLAS3D project – III. A census of the stellar angular momentum within the effective radius of early‐type galaxies: unveiling the distribution of fast and slow rotators (2011, methodology): “For a disc-like (spiral) galaxy to become a SR, numerical simulations have suggested that it needs to accrete at least half of its stellar mass via mergers (Bournaud et al. 2007; Jesseit et al. 2009; Bois et al. 2010; Bois et al. 2011, hereinafter Paper VI).”
THE DEPENDENCE OF QUENCHING UPON THE INNER STRUCTURE OF GALAXIES AT 0.5 ⩽ z < 0.8 IN THE DEEP2/AEGIS SURVEY (2012, background): “However, it should be noted that minor mergers can create bulges (Bournaud et al. 2007) and do contribute a non-negligible amount (∼ 30”
How do minor mergers promote inside-out growth of ellipticals, transforming the size, density profile and dark matter fraction? (2012, background): “…we aim at assessing the effect of pure collisionless major and minor mergers on the structural evolution for an already existent, observed, high-redshift population of compact and massive galaxies (see e.g. Bournaud et al. (2007) for a discussion on the effect of repeated minor mergers on disks).”
THE MAJORITY OF COMPACT MASSIVE GALAXIES AT z ∼ 2 ARE DISK DOMINATED (2011, background): “To destroy a massive stellar disk, major merging is more efficient, although a sequence of many minor accretion events can have the same effect (Naab et al. 1999; Bournaud et al. 2007).”
THE GREATER IMPACT OF MERGERS ON THE GROWTH OF MASSIVE GALAXIES: IMPLICATIONS FOR MASS ASSEMBLY AND EVOLUTION SINCE z ≃ 1 (2009, background): “If ∼3 such minor mergers have the equivalent morphological impact as one 1:4 merger (Bournaud et al. 2007; Hopkins et al. 2008), minor mergers can account for an additional 2/3 ≈ 70% of the morphological transformations needed to form spheroidals.”
HYDRODYNAMICS OF HIGH-REDSHIFT GALAXY COLLISIONS: FROM GAS-RICH DISKS TO DISPERSION-DOMINATED MERGERS AND COMPACT SPHEROIDS (2010, background): “The timescale for this, given the clump masses and total masses of our models, is typically around 500 Myr (see Bournaud et al. 2007).”
Evolution of magnetic fields in galaxies and future observational tests with the Square Kilometre Array (2008, background): “The SFR during the major merger (<∼2 × 109 yr) was ∼50 times higher than in the case of an isolated galaxy (di Matteo et al. 2007; Bournaud et al. 2007).”
MORPHOLOGICAL QUENCHING OF STAR FORMATION: MAKING EARLY-TYPE GALAXIES RED (2009, background): “The formation of disk galaxies could be explained by a variety of processes, from smooth gas accretion and internal evolution (Elmegreen et al. 2005; Bournaud et al. 2007a; Genzel et al. 2008; Dekel et al. 2009a,b) to the early merging of gas-rich galaxies (Robertson et al. 2006; Springel &…”
THE LUMINOSITY PROFILE AND STRUCTURAL PARAMETERS OF THE ANDROMEDA GALAXY (2011, background): “For instance, whether a galaxy surface density profile closely resembles a pure exponential disk (Freeman 1970) or a de Vaucouleurs profile is either indicative of a quiet recent history (e.g., Toth & Ostriker 1992) or a turbulent past (e.g., Bournaud et al. 2007).”