Spectroscopic confirmation of hydrogen alpha-selected satellite galaxies

TL;DR

This study validates narrow-band H alpha imaging as an effective method for detecting star-forming satellite galaxies by spectroscopically confirming their velocities and emission lines, showing low contamination from false positives.

Contribution

It provides the first spectroscopic validation of narrow-band H alpha imaging for identifying genuine star-forming satellite galaxies around nearby hosts.

Findings

All observed candidates are confirmed as genuine satellites with similar velocities.

Hydrogen alpha emission is reliably detected in confirmed satellites.

The method shows low false positive rate in satellite detection.

Abstract

We present a spectroscopic test confirming the potential of narrow-band optical imaging as a method for detecting star-forming satellites around nearby galaxies. To date the efficiency of such methods, and particularly the fraction of false detections resulting from its use, has not been tested. In this paper we use optical spectroscopy to verify the nature of objects that are apparently emission-line satellites, taken from imaging presented elsewhere. Observations of 12 probable satellites around 11 host galaxies are presented and used to compare the recession velocities of the host and satellite. This test confirms, in all cases, that there is genuine line emission, that the detected line is hydrogen alpha, and that the satellites have similar recession velocities to their hosts with a maximum difference of ~ 250 km/s, consistent with their being gravitationally bound companions. We conclude that the spectroscopy has confirmed that narrow-band imaging through H alpha filters is a reliable method for detecting genuine, star-forming satellites with low contamination from galaxies seen in projection along the line-of-sight.