AzTEC Millimetre Survey of the COSMOS Field - II. Source Count Overdensity and Correlations with Large-Scale Structure

TL;DR

This study identifies a significant over-density of bright sub-millimetre galaxies in a specific COSMOS field region, suggesting lensing effects by large-scale structures rather than direct association with nearby galaxies.

Contribution

It provides new evidence of SMG over-density and spatial correlation with large-scale structure, emphasizing the role of lensing and cosmic variance in SMG observations.

Findings

Over-density of bright SMGs exceeds blank-field expectations.

SMG spatial correlation aligns with lensing by foreground structures.

Weak correlation with weak-lensing maps indicates influence of individual galaxies.

Abstract

We report an over-density of bright sub-millimetre galaxies (SMGs) in the 0.15 sq. deg. AzTEC/COSMOS survey and a spatial correlation between the SMGs and the optical-IR galaxy density at z <~ 1.1. This portion of the COSMOS field shows a ~ 3-sigma over-density of robust SMG detections when compared to a background, or "blankfield", population model that is consistent with SMG surveys of fields with no extragalactic bias. The SMG over-density is most significant in the number of very bright detections (14 sources with measured fluxes S(1.1mm) > 6 mJy), which is entirely incompatible with sample variance within our adopted blank-field number densities and infers an over-density significance of >> 4. We find that the over-density and spatial correlation to optical-IR galaxy density are most consistent with lensing of a background SMG population by foreground mass structures along the line of sight, rather than physical association of the SMGs with the z <~ 1.1 galaxies/clusters. The SMG positions are only weakly correlated with weak-lensing maps, suggesting that the dominant sources of correlation are individual galaxies and the more tenuous structures in the region and not the massive and compact clusters. These results highlight the important roles cosmic variance and large-scale structure can play in the study of SMGs.