# ADF22: Blind detections of [CII] line emitters shown to be spurious

## TL;DR

This study re-examines two candidate [CII] emitters at high redshift using deeper ALMA observations, finds neither candidate, and reveals a higher-than-expected rate of spurious detections in previous blind surveys.

## Contribution

It provides evidence that blind [CII] emitter detections at z ~ 6 may be unreliable, highlighting the need for follow-up observations to confirm high-redshift galaxy candidates.

## Key findings

- Neither candidate was confirmed in deeper observations.
- The contamination rate of initial detections is higher than previously estimated.
- The cause of spurious detections remains under investigation.

## Abstract

We report Atacama Large Millimetre/submillimeter Array (ALMA) Cycle-5 follow-up observations of two candidate [CII] emitters at z ~ 6 in the ALMA deep field in SSA22 (ADF22). The candidates were detected blindly in a Cycle-2 ALMA survey covering ~ 5 square arcmins, with a single tuning, along with two CO lines associated with galaxies at lower redshifts. Various tests suggested at least one of the two > 6-sigma [CII] candidates should be robust (Hayatsu et al. 2017). Nevertheless, our new, deeper observations recover neither candidate, demonstrating a higher contamination rate than expected. The cause of the spurious detections is under investigation but at present it remains unclarified.