Prospects for Systematic Planetary Nebulae Detection with the Census of the Local Universe Narrowband Survey

TL;DR

This study evaluates the effectiveness of the CLU narrowband survey in detecting planetary nebulae, achieving high recovery rates and discovering new candidates, thereby enabling a comprehensive catalog covering most of the sky.

Contribution

It demonstrates the high efficiency of the CLU survey in recovering known PNe and identifies new candidates, advancing systematic PN detection over a large sky area.

Findings

Recovered 98% of cataloged PNe in the CLU dataset.

Identified 12 new PN candidates in a 200 deg² region.

Confirmed emission signatures in 4 out of 6 spectroscopically observed candidates.

Abstract

We investigate the efficacy of a systematic planetary nebula (PN) search in the Census of the Local Universe (CLU) narrowband (H$\alpha$) survey that covers a considerably larger sky region of above declination $-20^\circ$ than most previous surveys. Using PNe observed by the Isaac Newton Telescope Photometric H$\alpha$ Survey (IPHAS) as validation, we are able to visually recover 432 out of 441 cataloged PNe (98\%) within the CLU dataset, with 5 sources having unusable CLU images and 4 missed due to limitations of imaging quality. Moreover, the reference PNe are conventionally divided into three PN classes in decreasing order of identification confidence given their spectra and morphologies. We record consistently high recovery rate across all classes: 95\% of True, 71\% of Likely, and 81\% of Possible sources are readily recovered. To further demonstrate the ability of CLU to find new PNe, we undertake a preliminary search of compact PNe within a sub-region of the validation catalog, mainly utilizing the significance of narrow-band colors ($\Sigma$) as a metric for identification. In a $200\,\rm deg^2$ region, we search the CLU source catalog and find 31 PN candidates after automated and visual scrutiny, of which 12 are new sources not appearing in previous studies. As a demonstration of our ongoing follow-up campaign, we present medium-resolution optical spectra of six candidates and notice that four of them show emission signatures characteristic of confirmed PNe. As we refine our selection methods, CLU promises to provide a systematic catalog of PNe spanning $2/3$ of the sky.