Radio source stacking and the infrared / radio correlation at microJy flux densities

TL;DR

This study uses source stacking to analyze the infrared/radio correlation at microJy flux densities, revealing regional variations but no significant evolution over specific flux ranges.

Contribution

It compares stacking methods and demonstrates that stacked images can lose information, applying the technique to new wavelength data and revealing regional differences.

Findings

Variation in correlation strength between regions

No significant evolution over 24-um flux range

No significant evolution over 70-um flux range

Abstract

We investigate the infrared / radio correlation using the technique of source stacking, in order to probe the average properties of radio sources that are too faint to be detected individually. We compare the two methods used in the literature to stack sources, and demonstrate that the creation of stacked images leads to a loss of information. We stack infrared sources in the Spitzer extragalactic First Look Survey (xFLS) field, and the three northern Spitzer Wide-area Infrared Extragalactic survey (SWIRE) fields, using radio surveys created at 610 MHz and 1.4 GHz, and find a variation in the absolute strength of the correlation between the xFLS and SWIRE regions, but no evidence for significant evolution in the correlation over the 24-um flux density range 150 uJy - 2 mJy. We carry out the first radio source stacking experiment using 70-um-selected galaxies, and find no evidence for significant evolution over the 70-um flux density range 10 mJy - 100 mJy.