The merger rate of galaxies in the Illustris simulation: a comparison with observations and semi-empirical models

By V. Rodriguez-Gomez, Shy Genel, M. Vogelsberger, D. Sijacki, A. Pillepich, L. Sales, P. Torrey, Gregory F. Snyder, D. Nelson, Volker Springel and 2 more. 2015

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We have constructed merger trees for galaxies in the Illustris simulation by directly tracking the baryonic content of subhaloes. These merger trees are used to calculate the galaxy–galaxy merger rate as a function of descendant stellar mass, progenitor stellar mass ratio, and redshift. We demonstrate that the most appropriate definition for the mass ratio of a galaxy–galaxy merger consists in taking both progenitor masses at the time when the secondary progenitor reaches its maximum stellar mass. Additionally, we avoid effects from ‘orphaned’ galaxies by allowing some objects to ‘skip’ a snapshot when finding a descendant, and by only considering mergers which show a well-defined ‘infall’ moment. Adopting these definitions, we obtain well-converged predictions for the galaxy–galaxy merger rate with the following main features, which are qualitatively similar to the halo–halo merger rate except for the last one: a strong correlation with redshift that evolves as ∼(1 + z)^(2.4–2.8), a power law with respect to mass ratio, and an increasing dependence on descendant stellar mass, which steepens significantly for descendant stellar masses greater than ∼2 × 10^(11)M_⊙. These trends are consistent with observational constraints for medium-sized galaxies (M* ≳ 10^(10) M_⊙), but in tension with some recent observations of the close pair fraction for massive galaxies (M* ≳ 10^(11) M_⊙), which report a nearly constant or decreasing evolution with redshift. Finally, we provide a fitting function for the galaxy–galaxy merger rate which is accurate over a wide range of stellar masses, progenitor mass ratios, and redshifts.

Subfields: Astronomy and Astrophysics, Global and Planetary Change

View Paper: https://www.semanticscholar.org/paper/6b9442e0ed8b678d50711e8114f232e2fb61d475

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Citations in the corpus

The size evolution of star-forming and quenched galaxies in the IllustrisTNG simulation (2017, background): “In Section 4, however, we exclude galaxies that experienced a significant SUBFIND-related ‘switch’ where its massive envelope has been temporarily assigned to another galaxy (Behroozi et al. 2015; Rodriguez-Gomez et al. 2015).”
The stellar mass assembly of galaxies in the Illustris simulation: growth by mergers and the spatial distribution of accreted stars (2015, methodology): “To a first approximation, these fractions are independent of stellar mass, in agreement with our findings for the galaxy-galaxy merger rate (Rodriguez-Gomez et al. 2015) and the specific stellar mass accretion rate (Section 3).”
The cosmic baryon cycle and galaxy mass assembly in the FIRE simulations (2016, background): “This is expected given that massive galaxies undergo more frequent mergers (e.g. Rodriguez-Gomez et al. 2015; Wellons et al. 2016).”
The local nanohertz gravitational-wave landscape from supermassive black hole binaries (2017, methodology): “The latter is obtained from the cumulative galaxy-galaxy merger rates from the Illustris cosmological simulation project (Rodriguez-Gomez et al. 2015; Genel et al. 2014).”
Constraining the galaxy–halo connection over the last 13.3 Gyr: star formation histories, galaxy mergers and structural properties (2017, result): “This question has been studied in a number of previous works (Zheng, Coil & Zehavi 2007; Stewart et al. 2009; Hopkins et al. 2010a,b; Zavala et al. 2012; AvilaReese, Zavala & Lacerna 2014; Rodriguez-Gomez et al. 2015, 2016).”
First results from the IllustrisTNG simulations: the stellar mass content of groups and clusters of galaxies (2017, methodology): “The intersection of each curve 4 As initiated and motivated by Rodriguez-Gomez et al. (2015), we follow the common practice in merger analyses to take, for the mass of a merging satellite, its maximum mass at any time along its main progenitor branch, as opposed to its mass at infall or its mass at…”
Massive Black Hole Binary Mergers in Dynamical Galactic Environments (2016, background): “Finally, because binary lifetimes tend to be on the order of the Hubble time while galaxies typically undergo numerous merger events (e.g. Rodriguez-Gomez et al. 2015), subsequent merger events can MNRAS 000, 1–28 (2014) lead to triple MBH systems (see: §4.4) which could be very effective at…”
Supermassive black holes and their feedback effects in the IllustrisTNG simulation (2017, methodology): “…colour coding in this plot shows the fraction of systems that experienced a major merger ( > 1 : 4 in stellar mass ratio2) 2 We measure the merger masses as the stellar mass of the galaxy at the time of maximum mass of the low-mass progenitor (see Rodriguez-Gomez et al. 2015). since redshift z = 4.”
First results from the IllustrisTNG simulations: the galaxy colour bimodality (2017, background): “…star formation, passive red galaxies may grow further in M? down to z = 0 by acquiring new stars through mergers (van Dokkum et al. 1999; Naab et al. 2006), with accreted stellar mass fractions of 50% or higher for galaxies exceeding 1011M (Rodriguez-Gomez et al. 2015; Pillepich et al. 2017).”