Galaxy pairs in the Sloan Digital Sky Survey - VI. The orbital extent of enhanced star formation in interacting galaxies

TL;DR

This study analyzes how galaxy interactions influence star formation, finding significant enhancement up to 150 kpc separation, with the strongest effects at less than 20 kpc, based on SDSS data and simulations.

Contribution

It introduces a new method to distinguish environmental effects and demonstrates that star formation enhancement occurs at wider separations than previously thought.

Findings

Star formation enhancement extends up to ~150 kpc separation.

Strongest enhancements are at <20 kpc, especially in close pairs.

Wider separation pairs also show significant star formation activity.

Abstract

We use pair and environmental classifications of ~ 211,000 star-forming galaxies from the Sloan Digital Sky Survey, along with a suite of merger simulations, to investigate the enhancement of star formation as a function of separation in galaxy pairs. Using a new technique for distinguishing between the influence of nearby neighbours and larger scale environment, we find a clear enhancement in star formation out to projected separations of ~ 150 kpc, beyond which there is no net enhancement. We find the strongest enhancements at the smallest separations (especially < 20 kpc), consistent with earlier work. Similar trends are seen in the simulations, which indicate that the strongest enhancements are produced in highly disturbed systems approaching final coalescence, whereas the more modest enhancements seen at wider separations are the result of starburst activity triggered at first pericentre passage, which persists as the galaxies move to larger separations. The absence of any net enhancement beyond 150 kpc provides reassurance that the detected enhancements are due to galaxy-galaxy interactions, rather than larger scale environmental effects or potential pair selection biases. A rough census indicates that 66 per cent of the enhanced star formation in our pair sample occurs at separations > 30 kpc. We conclude that significant interaction-induced star formation is not restricted to merger remnants or galaxies with close companions; instead, a larger population of wider separation pairs exhibit enhanced star formation due to recent close encounters.