The NGC7771+NGC7770 Minor Merger: Harassing the Little One?

TL;DR

This study uses optical spectroscopy and imaging to show that in a 10:1 stellar mass ratio minor merger, the smaller galaxy undergoes a galaxy-wide starburst and gas stripping, while the larger galaxy remains unaffected.

Contribution

It provides observational evidence that minor mergers can induce significant star formation and gas stripping in the satellite galaxy, challenging previous models predicting minimal impact.

Findings

NGC7770 is experiencing a galaxy-wide starburst.

Gas filaments in NGC7770 are likely stripped and shock-excited.

The primary galaxy NGC7771 shows no significant star formation enhancement.

Abstract

Numerical simulations of minor mergers, typically having mass ratios greater than 3:1, predict little enhancement in the global star formation activity. However, these models also predict that the satellite galaxy is more susceptible to the effects of the interaction than the primary. We use optical integral field spectroscopy and deep optical imaging to study the NGC7771+NGC7770 interacting system (~10:1 stellar mass ratio) to test these predictions. We find that the satellite galaxy NGC7770 is currently experiencing a galaxy-wide starburst with most of the optical light being from young and post-starburst stellar populations(<1Gyr). This galaxy lies off of the local star-forming sequence for composite galaxies with an enhanced integrated specific star formation rate. We also detect in the outskirts of NGC7770 Halpha emitting gas filaments. This gas appears to have been stripped from one of the two galaxies and is being excited by shocks. All these results are consistent with a minor-merger induced episode(s) of star formation in NGC7770 after the first close passage. Such effects are not observed on the primary galaxy NGC7771.