HII versus HI in the `green valley' galaxies: direct comparison

TL;DR

This study compares the morphology and kinematics of ionized and neutral hydrogen in green valley galaxies, revealing insights into gas dynamics, feedback processes, and galaxy evolution during transition phases.

Contribution

It provides detailed kinematic analysis of ionized and neutral gas in green valley galaxies, highlighting the role of external gas accretion and feedback in galaxy transition.

Findings

Detection of non-circular gas motions, including AGN-driven outflows.

Observation of global HI+HII gas counter-rotation in one galaxy.

Spatial distribution of ionized gas aligns with HI maps.

Abstract

We study the morphology and kinematics of the ionization state of the gas in four 'green valley' early-type galaxies at different stages of their transition from a 'blue cloud' of star-forming galaxies to the sequence of passive evolution. The previous HI mapping of the considered sample reveals a spatial offset between the cold gas reservoirs and stellar discs depending on the post-starburst age. Consideration of the ionized-gas properties is essential to understand the role of various feedback processes in star formation quenching. We performed long-slit and 3D optical spectroscopic observations at the 6-m Russian telescope and compared the gas and stellar kinematics. Spatial distribution of the ionized gas is in agreement with HI maps; however, the one-order higher angular resolution in the HII velocity fields allows us to study non-circular gas motions in detail, like the AGN-driven outflow in the nucleus of J1117+51. The most intriguing result is the global HI+HII gas counter-rotation relative to the stellar disc in J1237+39. Therefore, in this case all the observed gas in the 'green valley' galaxy was captured from the environment via accretion or minor merging.