On the triggering of extreme starburst events in low-metallicity galaxies: a deep search for companions of Green Peas

Abstract

Green pea galaxies are starbursting, low-mass galaxies that are good analogues to star-forming galaxies in the early universe. We perform a survey of 23 Green Peas using the MUSE Integral Field Unit spectrograph on the VLT to search for companion galaxies. The survey reaches an average point-source depth of $\sim 10^{-18}$ erg cm${}^{-2}$ s${}^{-1}$ for emission lines. The MUSE field of view allows us to probe a 1$\times$1 arcmin${}^2$ field around these galaxies and to search their surroundings for faint companions that could have interacted with them and induced their starburst episodes. We search for companions using a variety of methods including template matching to emission and absorption line spectra. When restricting the search to the same physical area (R = 78 kpc) for all galaxies, we find that the fraction of green pea galaxies with companions is $0.11_{-0.05}^{+0.07}$. We define a control sample of star-forming galaxies with the same stellar masses and redshifts as the green peas, but consistent with the star-formation main sequence. We find that green pea galaxies are as likely to have companions as the control sample; for which the fraction of objects with companions is $0.08_{-0.03}^{+0.05}$. Given that we do not find statistical evidence for an elevated companion fraction in the green peas in this study, we argue that the ``companions" are likely unrelated to the bursts in these galaxies.

Accepted for publication in the Astrophysical Journal