The pathfinder Dragonfly Spectral Line Mapper: Pushing the limits for ultra-low surface brightness spectroscopy

TL;DR

The paper presents the development, testing, and sensitivity analysis of the Dragonfly Spectral Line Mapper, a novel ultra-low surface brightness imaging telescope, and discusses future plans for an expanded 120-OTA version.

Contribution

It introduces the pathfinder Dragonfly Spectral Line Mapper with ultranarrow bandpass imaging capabilities and provides a detailed assessment of its sensitivity limits and observational methods.

Findings

Achieved surface brightness limits for ultra-low brightness line emission

Compared instrument sensitivity to other ultra-faint emission observation methods

Outlined plans for a 120-OTA Dragonfly Spectral Line Mapper

Abstract

The pathfinder Dragonfly Spectral Line Mapper is a distributed aperture telescope based off of the Dragonfly Telephoto Array with additional instrumentation (the Dragonfly "Filter-Tilter") to enable ultranarrow bandpass imaging. The pathfinder is composed of three redundant optical tube assemblies (OTAs) which are mounted together to form a single field of view imaging telescope (where the effective aperture diameter increases as the square-root of the number of OTAs). The pathfinder has been on sky from March 2020 to October 2021 equipped with narrowband filters to provide proof-of-concept imaging, surface brightness limit measurements, on sky testing, and observing software development. Here we describe the pathfinder telescope and the sensitivity limits reached along with observing methods. We outline the current limiting factors for reaching ultra-low surface brightnesses and present a comprehensive comparison of instrument sensitivities to low surface brightness line emission and other methods of observing the ultra-faint line emission from diffuse gas. Finally, we touch on plans for the upcoming 120-OTA Dragonfly Spectral Line Mapper, which is currently under construction.