Setting the normalcy level of HI properties in isolated galaxies

TL;DR

This study analyzes the HI properties of ~800 isolated galaxies to establish a baseline for normalcy, revealing that most have symmetric HI disks and that asymmetries are less common than in denser environments, informing galaxy evolution models.

Contribution

It provides a large, well-defined sample of isolated galaxies' HI data, revisiting assumptions about HI disk perturbations and establishing a low asymmetry baseline for the local universe.

Findings

Most isolated galaxies have symmetric HI disks.

Isolated galaxies show ~20% fewer asymmetric HI profiles than field samples.

A small percentage of galaxies exhibit large HI asymmetries, linked to specific mechanisms.

Abstract

Studying the atomic gas (HI) properties of the most isolated galaxies is essential to quantify the effect that the environment exerts on this sensitive component of the interstellar medium. We observed and compiled HI data for a well defined sample of ~ 800 galaxies in the Catalog of Isolated Galaxies, as part of the AMIGA project (Analysis of the ISM in Isolated GAlaxies, http://amiga.iaa.es), which enlarges considerably previous samples used to quantify the HI deficiency in galaxies located in denser environments. By studying the shape of 182 HI profiles, we revisited the usually accepted result that, independently of the environment, more than half of the galaxies present a perturbed HI disk. In isolated galaxies this would certainly be a striking result if these are supposed to be the most relaxed systems, and has implications in the relaxation time scales of HI disks and the nature of the most frequent perturbing mechanisms in galaxies. Our sample likely exhibits the lowest HI asymmetry level in the local Universe. We found that other field samples present an excess of ~ 20% more asymmetric HI profiles than that in CIG. Still a small percentage of galaxies in our sample present large asymmetries. Follow-up high resolution VLA maps give insight into the origin of such asymmetries.