Galaxy And Mass Assembly (GAMA): the effect of close interactions on star formation in galaxies

Abstract

The modification of star formation (SF) in galaxy interactions is a complex process, with SF observed to be both enhanced in major mergers and suppressed in minor pair interactions. Such changes likely to arise on short timescales and be directly related to the galaxy-galaxy interaction time. Here we investigate the link between dynamical phase and direct measures of SF on different timescales for pair galaxies, targeting numerous star-formation rate (SFR) indicators and comparing to pair separation, individual galaxy mass and pair mass ratio. We split our sample into the higher (primary) and lower (secondary) mass galaxies in each pair and find that SF is indeed enhanced in all primary galaxies but suppressed in secondaries of minor mergers. We find that changes in SF of primaries is consistent in both major and minor mergers, suggesting that SF in the more massive galaxy is agnostic to pair mass ratio.We also find that SF is enhanced/suppressed more strongly for short-time duration SFR indicators (e.g. Hα), highlighting recent changes to SF in these galaxies, which are likely to be induced by the interaction. We propose a scenario where the lower mass galaxy has its SF suppressed by gas heating or stripping, while the higher mass galaxy has its SF enhanced, potentially by tidal gas turbulence and shocks. This is consistent with the seemingly contradictory observations for both SF suppression and enhancement in close pairs.

Galaxy And Mass Assembly (GAMA): Gas Fueling of Spiral Galaxies in the Local Universe. I. The Effect of the Group Environment on Star Formation in Spiral Galaxies

“…10 M e , in line with the results of the dedicated investigation of star formation in close pairs presented by Davies et al (2015).…”

“…In using the galaxies in our samples as test particles and their SFR as a probe of gas fueling, it is essential to exclude close pairs of galaxies, as the effects of galaxy-galaxy interactions are known to boost the rate at which galaxies convert their ISM into stars (e.g., Barton et al 2000;Robotham et al 2013;Davies et al 2015). Although these galaxy-galaxy interactions, which are likely to be present in close pairs, are an important and interesting aspect of galaxy evolution in the group environment, they will be superimposed on the galaxy-IHM effects, which are the focus of this work.…”

“…In addition to ensuring that the relation between ISM and star formation is as consistent as possible over the range of environments for the galaxies considered, controlling for galaxy morphology also aids in isolating the effects of galaxy-IHM interactions from those of galaxy-galaxy interactions, which may severely impact the SFR of galaxies (e.g., Robotham et al 2014;Alatalo et al 2015;Davies et al 2015;Bitsakis et al 2016). As major galaxy-galaxy interactions can strongly perturb disk galaxies and lead to a morphological transformation, focusing on disk-dominated galaxies ensures that no major merger has taken place, effectively enabling us, in combination with the deselection of close pairs of galaxies based on the G3C, to isolate the effects of galaxy-IHM interactions.…”

The third data release of the Kilo-Degree Survey and associated data products

“…This is supplemented by redshift samples not used by Hildebrandt et al (2017), i.e. GAMA-II data 11 (Liske et al 2015); 2dFLenS measurements (Blake et al 2016); SDSS-DR13 galaxy spectroscopy (SDSS Collaboration et al 2016); additional redshifts in the COSMOS field from the "GAMA G10" analysis (Davies et al 2015); and extra redshifts in the CDFS field from the ACES survey (Cooper et al 2012). After combining all these datasets and removing duplicates we have over 300 000 sources detected also by KiDS that are used for training and tests of the photometric redshift accuracy.…”

Connecting optical and X-ray tracers of galaxy cluster relaxation

“…Galaxy interactions, such as mergers and impulsive highspeed encounters, can drive gas to the central regions and induce star-burst events which may exhaust a galaxies gas reserves (e.g. Mihos & Hernquist 1994a,b;Ellison et al 2008;Davies et al 2015). These interactions can also influence galaxy morphology through the growth of a strong bulge component, and the end products of major mergers tend to be bulge dominated galaxies with classical de Vaucouleurs profiles (e.g.…”