Decoupled gas kinematics in isolated early-type disc galaxies

TL;DR

This study investigates the gas kinematics in isolated early-type disc galaxies, revealing that a significant fraction exhibit decoupled ionized gas components likely acquired through external accretion, with implications for galaxy evolution.

Contribution

It provides new observational evidence of decoupled gas kinematics and suggests external accretion as the source, contrasting with internal or primordial origins.

Findings

58% of galaxies have decoupled ionized gas components

Most decoupled gas shows counterrotation relative to stars

Ionized gas has subsolar metallicity, indicating external accretion

Abstract

We have studied a sample of completely isolated galaxies by means of long-slit spectroscopy at the 6-m telescope. We have found that 7 of 12 (58 +/- 14 %) galaxies have revealed a presence of large-scale ionized-gas component which angular momentum is mostly differ from stellar one: 5 of 7 (71 +/- 17 %) show a visible counterrottation. The diagnostic diagram demonstrates a wide range of gas excitation mechanism. We have estimated the gas oxygen abundance in the cases where excitation mechanism by young stars dominates and have found that ionized gas has a subsolar metallicity. We concluded that cold-gas accretion from primordial cosmological filaments is unlikely for these objects, while external accretion from dwarf gas-rich satellites is more suitable.