Detection of infalling hydrogen in transfer between the interacting galaxies NGC 5426 and NGC 5427

TL;DR

This study detects and maps hydrogen gas falling from NGC 5426 onto NGC 5427, revealing details about the infall process, its ionization, and its potential impact on star formation and galactic winds.

Contribution

First direct detection and mapping of infalling hydrogen gas between these interacting galaxies using velocity tagging and Fabry-Perot spectroscopy.

Findings

Infalling gas rate of 10 solar masses per year.

Infalling gas is ionized by escaping Lyman continuum photons.

Infalling gas distribution suggests it is behind the disk of NGC 5427.

Abstract

Using velocity tagging we have detected hydrogen from NGC 5426 falling onto its interacting partner NGC 5427. Our observations, with the GHaFaS Fabry-Perot spectrometer, produced maps of the two galaxies in Halpha surface brightness and radial velocity. We found emission with the range of velocities associated with NGC 5426 along lines of sight apparently emanating from NGC 5427, superposed on the velocity map of the latter. After excluding instrumental effects we assign the anomalous emission to gas pulled from NGC 5426 during its passage close to NGC 5427. Its distribution, more intense between the arms and just outside the disk of NGC 5427, and weak, or absent, in the arms, suggests that the infalling gas is behind the disk., ionized by Lyman continuum photons escaping from NGC 5427. Modeling this, we estimate the distances of these gas clouds- behind the plane: a few hundred pc to a few kpc. We also estimate the mass of the infalling (ionized plus neutral) gas, finding an infall rate of 10 solar masses per year, consistent with the high measured SFR across the disk of NGC 5427 and with the detected circumnuclear galactic wind.