Submm/mm Galaxy Counterpart Identification Using a Characteristic Density Distribution

TL;DR

This paper introduces a new IRAC color-based method for identifying submm/mm galaxy counterparts, improving accuracy over previous techniques and applicable regardless of radio detection, especially effective with moderate beamsizes.

Contribution

The paper develops a non-parametric IRAC color-color characteristic density distribution method combined with likelihood ratios for counterpart identification, reducing radio bias and enhancing accuracy.

Findings

Identifies ~85% of SMG counterparts with ~18" beamsize.

Achieves 33-49% identification rates with larger beamsizes.

Demonstrates improvement over positional-only methods using simulations.

Abstract

We present a new submm/mm galaxy counterpart identification technique which builds on the use of Spitzer IRAC colors as discriminators between likely counterparts and the general IRAC galaxy population. Using 102 radio- and SMA-confirmed counterparts to AzTEC sources across three fields (GOODS-N, GOODS-S, and COSMOS), we develop a non-parametric IRAC color-color characteristic density distribution (CDD), which, when combined with positional uncertainty information via likelihood ratios, allows us to rank all potential IRAC counterparts around SMGs and calculate the significance of each ranking via the reliability factor. We report all robust and tentative radio counterparts to SMGs, the first such list available for AzTEC/COSMOS, as well as the highest ranked IRAC counterparts for all AzTEC SMGs in these fields as determined by our technique. We demonstrate that the technique is free of radio bias and thus applicable regardless of radio detections. For observations made with a moderate beamsize (~18"), this technique identifies ~85 per cent of SMG counterparts. For much larger beamsizes (>30"), we report identification rates of 33-49 per cent. Using simulations, we demonstrate that this technique is an improvement over using positional information alone for observations with facilities such as AzTEC on the LMT and SCUBA-2 on JCMT.