Far beyond stacking: Fully bayesian constraints on sub-microJy radio source populations over the XMM-LSS-VIDEO field

Abstract

Measuring radio source counts is critical for characterizing new extragalactic populations, brings a wealth of science within reach and will inform forecasts for SKA and its pathfinders. Yet there is currently great debate (and few measurements) about the behaviour of the 1.4-GHz counts in the microJy regime. One way to push the counts to these levels is via 'stacking', the covariance of a map with a catalogue at higher resolution and (often) a different wavelength. For the first time, we cast stacking in a fully bayesian framework, applying it to (i) the SKADS simulation and (ii) VLA data stacked at the positions of sources from the VIDEO survey. In the former case, the algorithm recovers the counts correctly when applied to the catalogue, but is biased high when confusion comes into play. This needs to be accounted for in the analysis of data from any relatively-low-resolution SKA pathfinders. For the latter case, the observed radio source counts remain flat below the 5-sigma level of 85 microJy as far as 40 microJy, then fall off earlier than the flux hinted at by the SKADS simulations and a recent P(D) analysis (which is the only other measurement from the literature at these flux-density levels, itself extrapolated in frequency). Division into galaxy type via spectral-energy distribution reveals that normal spiral galaxies dominate the counts at these fluxes.

14 pages, 11 figures, 5 tables, submitted to MNRAS

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• MIGHTEE: Deep 1.4 GHz Source Counts and the Sky Temperature Contribution of Star Forming Galaxies and Active Galactic Nuclei
• Constraints on submicrojansky radio number counts based on evolving VLA-COSMOS luminosity functions
• The Second Radio Synchrotron Background Workshop: Conference Summary and Report
• Optimising commensality of radio continuum and spectral line observations in the era of the SKA
• Measuring the HI mass function below the detection threshold
• The optically-selected 1.4-GHz quasar luminosity function below 1 mJy
• The LOFAR Two-metre Sky Survey: Deep Fields Data Release 2. I. The ELAIS-N1 field
• A deep radio view of the evolution of the cosmic star-formation rate density from a stellar-mass selected sample in VLA-COSMOS
• The MOSDEF Survey: Calibrating the relationship between H$\alpha$ star-formation rate and radio continuum luminosity at $1.4<z<2.6$