Describing the Nonuniversal Galaxy Merger Timescales in IllustrisTNG: Effects of Host Halo Mass, Baryons, and Sample Selection

Abstract

Galaxy merger timescales are crucial for understanding and modeling galaxy formation in our hierarchically structured Universe. However, previous studies have reported widely varying dependencies of merger timescales on initial orbital parameters and mass ratio at the first crossing of $r_{\mathrm{vir}}$. Using IllustrisTNG simulations, we find that these dependencies vary with host halo mass, suggesting that discrepancies in prior studies may arise from differences in the systems analyzed. Specifically, in low-mass halos, merger timescales show a stronger dependence on initial orbital parameters, while in high-mass halos, this dependence weakens. To account for these variations, we present a fitting formula that incorporates host mass dependence, achieving a logarithmic scatter smaller than 0.15 dex. Comparing dark matter-only and baryonic simulations, we observe similar merger timescales for circular orbits but notable differences for radial orbits. In halos with $M_{\mathrm{host}}<10^{12.5}{h}^{-1}{M}_{\odot }$, mergers in dark matter-only runs take longer than in baryonic runs, whereas the trend reverses in more massive halos. We attribute these differences to the competing effects of tidal disruption by central galaxy disks and the resistance of baryonic satellites to tidal stripping. Finally, we extend our model to predict merger timescales from any starting radius within the halo. By fitting the extended model to the entire infall sample, we find that using only the merger sample can underestimate merger timescales, particularly for low mass ratios. Our model provides a valuable tool for improving semi-analytical and empirical models of galaxy formation.

arXiv comment21 pages, 17 figures. Accepted for Publication in ApJ. Models summarized in Table 1

References in corpus (57)

• Planck 2015 results. XIII. Cosmological parameters
• A Universal Density Profile from Hierarchical Clustering
• Populating a cluster of galaxies - I. Results at z=0
• E pur si muove: Galiliean-invariant cosmological hydrodynamical simulations on a moving mesh
• Statistical Properties of X-ray Clusters: Analytic and Numerical Comparisons
• Simulating Galaxy Formation with the IllustrisTNG Model
• Hierarchical Galaxy Formation
• A Unified, Merger-Driven Model for the Origin of Starbursts, Quasars, the Cosmic X-Ray Background, Supermassive Black Holes and Galaxy Spheroids
• First results from the IllustrisTNG simulations: matter and galaxy clustering
• First results from the IllustrisTNG simulations: the stellar mass content of groups and clusters of galaxies
• The hierarchical formation of the brightest cluster galaxies
• First results from the IllustrisTNG simulations: the galaxy color bimodality
• First results from the IllustrisTNG simulations: A tale of two elements -- chemical evolution of magnesium and europium
• Simulating galaxy formation with black hole driven thermal and kinetic feedback
• Concentrations of Dark Halos from their Assembly Histories
• From dwarf spheroidals to cDs: Simulating the galaxy population in a LCDM cosmology
• First results from the IllustrisTNG simulations: radio haloes and magnetic fields
• Triaxial Modeling of Halo Density Profiles with High-resolution N-body Simulations
• The merger rate of galaxies in the Illustris Simulation: a comparison with observations and semi-empirical models
• Galaxy formation in the Planck Cosmology - I. Matching the observed evolution of star formation rates, colours and stellar masses
• Accurate universal models for the mass accretion histories and concentrations of dark matter halos
• The stellar mass assembly of galaxies in the Illustris simulation: growth by mergers and the spatial distribution of accreted stars
• Dynamical Friction and Galaxy Merging Timescales
• Density Profiles of Dark Matter Halo are not Universal
• The Growth and Structure of Dark Matter Haloes
• Not so lumpy after all: modeling the depletion of dark matter subhalos by Milky Way-like galaxies
• Sinking Satellites and the Heating of Galaxy Discs
• The Assembly of Galaxies in a Hierarchically Clustering Universe
• Disruption of Dark Matter Substructure: Fact or Fiction?
• Dark Matter Substructure in Numerical Simulations: A Tale of Discreteness Noise, Runaway Instabilities, and Artificial Disruption
• A fitting formula for the merger timescale of galaxies in hierarchical clustering
• Density Profiles of Cold Dark Matter Substructure: Implications for the Missing Satellites Problem
• The Dynamics of Sinking Satellites Around Disk Galaxies: A Poor Man's Alternative to High-Resolution Numerical Simulations
• Galactic Angular Momentum in the Illustris Simulation: Feedback and the Hubble Sequence
• On the Life and Death of Satellite Haloes
• Dynamical friction and the evolution of satellites in virialized halos: the theory of linear response
• A calibration of the relation between the abundance of close galaxy pairs and the rate of galaxy mergers
• Ghostly Tributaries to the Milky Way: Charting the Halo's Stellar Streams with the Gaia DR2 catalogue
• What determines satellite galaxy disruption?
• A unified model for the spatial and mass distribution of subhaloes
• A profile in FIRE: resolving the radial distributions of satellite galaxies in the Local Group with simulations
• Galaxy Merger Rates up to z $\sim$ 3 using a Bayesian Deep Learning Model $-$ A Major-Merger classifier using IllustrisTNG Simulation data
• On the nature of the ring-like structure in the outer Galactic disk
• Orbital parameters of infalling satellite haloes in the hierarchical $\Lambda$CDM model
• Galaxy Evolution in all Five CANDELS Fields and IllustrisTNG: Morphological, Structural, and the Major Merger Evolution to $z\sim 3$
• CosmicGrowth Simulations---Cosmological simulations for structure growth studies
• Modelling Galaxy Merger Timescales and Tidal Destruction
• A scaling relation between merger rate of galaxies and their close pair count
• Tidal Stripping in the Adiabatic Limit
• Major mergers between dark matter haloes -- II. Profile and concentration changes
• Tidal evolution of cored and cuspy dark matter halos
• Major mergers between dark matter haloes -- I. Predictions for size, shape, and spin
• Tracking the orbit of unresolved subhalos for semi-analytic models
• A universal model for the evolution of tidally stripped systems
• Accurate Measurement of the Lensing Magnification by BOSS CMASS Galaxies and Its Implications for Cosmology and Dark Matter
• Halo Growth and Merger Rates as a Cosmological Test
• Extracting Galaxy Merger Timescales II: A new fitting formula

Cited by in corpus (1)

• Abundance and phase-space distribution of subhalos in cosmological N-body simulations: testing numerical convergence and correction methods