Exploring the links between star formation and minor companions around isolated galaxies

TL;DR

This study investigates the relationship between star formation activity and the presence of minor companions around isolated galaxies, finding a small but statistically significant excess of companions around actively star-forming galaxies.

Contribution

It provides observational evidence linking minor companions to increased star formation in isolated galaxies, using SDSS data and statistical analysis.

Findings

Star-forming galaxies are more likely to have minor companions than quiescent ones.

Approximately 16% of star-forming galaxies have companions within 60 kpc, compared to 11% of quiescent galaxies.

The difference in satellite counts is statistically significant up to 100 h$^{-1}$ kpc.

Abstract

Previous studies have shown that galaxies with minor companions exhibit an elevated star formation rate. We reverse this inquiry, constructing a volume-limited sample of \simL\star (Mr \leq -19.5 + 5 log h) galaxies from the Sloan Digital Sky Survey that are isolated with respect to other luminous galaxies. Cosmological simulations suggest that 99.8% of these galaxies are alone in their dark matter haloes with respect to other luminous galaxies. We search the area around these galaxies for photometric companions. Matching strongly star forming (EW(H{\alpha})\geq 35 \AA) and quiescent (EW(H{\alpha})< 35 \AA) samples for stellar mass and redshift using a Monte Carlo resampling technique, we demonstrate that rapidly star-forming galaxies are more likely to have photometric companions than other galaxies. The effect is relatively small; about 11% of quiescent, isolated galaxies have minor photometric companions at radii \leq 60 kpc h$^{-1}$ kpc while about 16% of strongly star-forming ones do. Though small, the cumulative difference in satellite counts between strongly star-forming and quiescent galaxies is highly statistically significant (PKS = 1.350 \times10$^{-3}$) out to to radii of \sim 100 h$^{-1}$ kpc. We discuss explanations for this excess, including the possibility that \sim 5% of strongly star-forming galaxies have star formation that is causally related to the presence of a minor companion.