Spectroscopic follow-up of a sub-set of the Gaia/IPHAS catalogue of H\alpha-excess sources

TL;DR

This study combines position-based and CMD-based methods to identify Hα-excess sources, using spectroscopic follow-up to validate the effectiveness of the novel approach in detecting faint and rare emission line objects.

Contribution

The paper introduces a combined selection technique for Hα emitters and validates it through spectroscopic follow-up, revealing sources missed by traditional methods.

Findings

15 out of 70 confirmed Hα emitters were identified only by CMD-based selection.

Spectroscopic follow-up confirms the effectiveness of the combined selection method.

Distribution analysis supports classification of emission sources in large surveys.

Abstract

State-of-the-art techniques to identify H\alpha emission line sources in narrow-band photometric surveys consist of searching for H\alpha excess with reference to nearby objects in the sky (position-based selection). However, while this approach usually yields very few spurious detections, it may fail to select intrinsically faint and/or rare H\alpha-excess sources. In order to obtain a more complete representation of the heterogeneous emission line populations, we recently developed a technique to find outliers relative to nearby objects in the colour-magnitude diagram (CMD-based selection). By combining position-based and CMD-based selections, we built an updated catalogue of H\alpha-excess candidates in the northern Galactic Plane. Here we present spectroscopic follow-up observations and classification of 114 objects from this catalogue, that enable us to test our novel selection method. Out of the 70 spectroscopically confirmed H\alpha emitters in our sample, 15 were identified only by the CMD-based selection, and would have been thus missed by the classic position-based technique. In addition, we explore the distribution of our spectroscopically confirmed emitters in the Gaia CMD. This information can support the classification of emission line sources in large surveys, such as the upcoming WEAVE and 4MOST, especially if augmented with the introduction of other colours.