On the frequency, intensity, and duration of starburst episodes triggered by galaxy interactions and mergers

Abstract

We investigate the intensity enhancement and the duration of starburst episodes triggered by major galaxy interactions and mergers. We analyze two large statistical datasets of numerical simulations. These have been obtained using two independent and different numerical techniques to model baryonic and dark matter evolution that are extensively compared for the first time. One is a Tree-SPH code, the other one is a grid-based N-body sticky-particles code. We show that, at low redshift, galaxy interactions and mergers in general trigger only moderate star formation enhancements. Strong starbursts where the star formation rate is increased by a factor greater than 5 are rare and found only in about 15% of major galaxy interactions and mergers. Merger-driven starbursts are also rather short-lived, with a typical duration of activity of a few 10 8 yr. These conclusions are found to be robust, independent of the numerical techniques and star formation models. At higher redshifts where galaxies contain more gas, gas inflow-induced starbursts are neither stronger nor longer than their local counterparts. In turn, the formation of massive gas clumps, results of local Jeans instability that can occur spontaneously in gas-rich disks or be indirectly favored by galaxy interactions, could play a more important role in determining the duration and intensity of star formation episodes.

Galaxy pairs in the Sloan Digital Sky Survey – VIII. The observational properties of post-merger galaxies

“…The observational data therefore emphasize the conclusion made in the theoretical work of Di Matteo et al (2008), that mergers do not always trigger starbursts.…”

“…Di Matteo et al 2007Matteo et al , 2008Cox et al 2008;Torrey et al 2012). Although the results in Figures 6 and 7 qualitatively support these predictions, the SFRs at coalescence are predicted to frequently exceed the pre-merger phase by a factor of 10 or more.…”

The GalMer database: galaxy mergers in the virtual observatory

“…Other tests are presented in Di Matteo et al (2008a). Smoothed Particle Hydrodynamics (SPH) is a Lagrangian technique in which the gas is partitioned into fluid elements represented by particles, which obey equations of motion similar to the collisionless component, but contain additional terms describing pressure gradients, viscous forces and radiative effects in gas.…”

Galaxy pairs in the SDSS – XIII. The connection between enhanced star formation and molecular gas properties in galaxy mergers

“…The second driver of enhanced star formation in mergers is an increase of the density of molecular gas, which induces a more efficient conversion of gas into stars. Indeed, numerical and hydrodynamical simulations predict that during the merger, gravitational torque decreases the angular momentum of gas which flows towards the galactic centre; the result is a rapid increase of the gas density which finally brings about a burst of nuclear star formation (Mihos & Hernquist 1996;Di Matteo et al 2008;Renaud et al 2014). Besides nuclear starbursts, interactions can also trigger highly efficient star formation across the whole galaxy through several episodes of gas fragmentation in dense clouds induced by gravitational torques, as was shown in high-resolution hydrodynamical simulations (Teyssier et al 2010.…”