Fundamental relation in isolated galaxies, pairs, and triplets in the local universe

TL;DR

This study establishes fundamental relations for isolated galaxies, pairs, and triplets in the local universe, revealing how interactions influence star formation and metallicity, and proposing nurture-free relations for these systems.

Contribution

It is the first to establish fundamental star formation and metallicity relations specifically for isolated systems in the local universe, considering the effects of interactions.

Findings

Isolated galaxies have lower SFR than main sequence galaxies at fixed stellar mass.

Isolated galaxies exhibit higher metallicity compared to paired and triplet galaxies.

Central and isolated galaxies show similar properties, while satellites have distinct metallicity values.

Abstract

In this work, we establish fundamental relations, for the first time, in isolated systems in the local universe (with 0.005$\leq$z$\leq$0.080), which can give insight into the underlying physics of star-formation. We use a sample of isolated galaxies to explore whether star formation is regulated by smooth secular processes. In addition, galaxies in physically bound isolated pairs and isolated triplets may also interact with each other, where interaction itself may enhance/regulate star-formation and the distribution of gas and metals within galaxies. We made use of published emission line fluxes information from the Sloan Digital Sky Survey (SDSS) to identify SF galaxies in the SDSS-based catalogue of isolated galaxies (SIG), isolated pairs (SIP), and isolated triplets (SIT). We also use this data to derive their aperture-corrected SFR (considering two different methods) and oxygen abundance, 12 + log(O/H), using bright lines calibrations. Stellar masses for SIG, SIP, and SIT galaxies were estimated by fitting their spectral energy distribution on the five SDSS bands. We compared our results with a sample of SF galaxies in the SDSS. We found that, on average, at a fixed stellar mass, the SIG SF galaxies have lower SFR values than Main Sequence (MS) SF galaxies in the SDSS and central galaxies in the SIP and SIT. On average, SIG galaxies have higher 12 + log(O/H) values than galaxies in the SIP, SIT, and comparison sample. When distinguishing between central and satellite galaxies in the SIP and SIT, centrals and SIG galaxies present similar values ($\sim$8.55) while satellites have values close to M33 ($\sim$8.4). Based on our results, we propose a ground level `nurture' free SFR-M$_\star$ and gas metallicity-SFR-M$_\star$ relations for SF galaxies in the local universe.