On the radial abundance gradients in disks of irregular galaxies

TL;DR

This study investigates the distribution of chemical abundances across irregular galaxy disks, revealing a correlation between surface brightness profiles and abundance gradients, challenging previous assumptions about irregular galaxies.

Contribution

It provides the first detailed analysis linking surface brightness profiles to radial abundance gradients in irregular galaxies.

Findings

Flat inner surface brightness profiles correspond to shallow abundance gradients.

Steep inner profiles are associated with steeper abundance gradients.

Irregular galaxies can exhibit significant radial abundance gradients, contrary to prior beliefs.

Abstract

We determine the radial abundance distributions across the disks of fourteen irregular galaxies of the types Sm and Im (morphological T types T = 9 and T =10) as traced by their HII regions. The oxygen and nitrogen abundances in HII regions are estimated through the Te method or/and with the counterpart method (C method). Moreover, we examine the correspondence between the radial abundance gradient and the surface brightness profile. We find that irregular galaxies with a flat inner profile (flat or outwardly increasing surface brightness in the central region) show shallow (if any) radial abundance gradients. On the other hand, irregular galaxies with a steep inner profile (with or without a bulge or central star cluster) usually show rather steep radial abundance gradients. This is in contrast to the widely held belief that irregular galaxies do not usually show a radial abundance gradient.