MIGHTEE: deep 1.4 GHz source counts and the sky temperature contribution of star-forming galaxies and active galactic nuclei

Abstract

We present deep 1.4 GHz source counts from ∼5 deg2 of the continuum Early Science data release of the MeerKAT International Gigahertz Tiered Extragalactic Exploration (MIGHTEE) survey down to S1.4GHz ∼15 μJy. Using observations over two extragalactic fields (COSMOS and XMM-LSS), we provide a comprehensive investigation into correcting the incompleteness of the raw source counts within the survey to understand the true underlying source count population. We use a variety of simulations that account for: errors in source detection and characterisation, clustering, and variations in the assumed source model used to simulate sources within the field and characterise source count incompleteness. We present these deep source count distributions and use them to investigate the contribution of extragalactic sources to the sky background temperature at 1.4 GHz using a relatively large sky area. We then use the wealth of ancillary data covering a subset of the COSMOS field to investigate the specific contributions from both active galactic nuclei (AGN) and star forming galaxies (SFGs) to the source counts and sky background temperature. We find, similar to previous deep studies, that we are unable to reconcile the sky temperature observed by the ARCADE 2 experiment. We show that AGN provide the majority contribution to the sky temperature contribution from radio sources, but the relative contribution of SFGs rises sharply below 1 mJy, reaching an approximate 15-25 per cent contribution to the total sky background temperature (Tb ∼100 mK) at ∼15 μJy.

The Rapid ASKAP Continuum Survey V: Cataloguing the sky at 1 367.5 MHz and the second data release of RACS-mid

“…The semi-empirical SKA sky model may not be accurate below ∼0.1 mJy (e.g. Smolčić et al 2017a;Hale et al 2023), which is generally below the rms noise in the RACS-mid images. The low flux density limit still allows sources below our detection thresholds to be modelled, but are typically above 0.1 mJy.…”

“…This makes the RACS releases valuable in exploring the radio source counts, which are typically restricted to high sensitivity and small areas (e.g. Vernstrom et al 2016;Smolčić et al 2017a,b;Mandal et al 2021;Matthews et al 2021;Hale et al 2023) or lower sensitivity and wide areas (e.g. White et al 1997;Franzen et al 2021;Matthews et al 2021;Hale et al 2021).…”

The MeerKAT Absorption Line Survey (MALS) Data Release. I. Stokes I Image Catalogs at 1–1.4 GHz

“…A detailed exploration of the abovementioned issues will be presented in future papers involving MALS catalogs from more sensitive wideband images. This will include simulations involving injection of radio sources of known flux densities and sizes in residual images and subjecting these to the same source-finding procedures as used for cataloging to determine completeness as a function of rms and radio source morphology (see, e.g., Bonaldi et al 2021;Shimwell et al 2022;Hale et al 2023). Indeed, wideband images of MALS exhibit large variations in completeness for compact and extended sources (see Figures 7 and 8…”

Constraints on cosmic star formation history via a new modeling of the radio luminosity function of star-forming galaxies

“…In this work, we use the observed source counts from Algera et al (2020a) and Hale et al (2023) to provide an additional constraint in our analysis. The Algera et al (2020a) 3 GHz source counts are measured based on the ultrafaint (reaching a 5σ flux limit of ∼2.7 µJy beam −1 within the center of the 3 GHz image) radio population detected in the Karl G. Jansky Very Large Array COSMOS-XS survey.…”

“…The Algera et al (2020a) 3 GHz source counts are measured based on the ultrafaint (reaching a 5σ flux limit of ∼2.7 µJy beam −1 within the center of the 3 GHz image) radio population detected in the Karl G. Jansky Very Large Array COSMOS-XS survey. The Hale et al (2023) 1.4 GHz source counts are measured based on the continuum early science data release of the MeerKAT International Gigahertz Tiered Extragalactic Exploration (MIGHTEE) survey in the COSMOS and XMM-LSS fields. The MIGHTEE sources were divided into three subsets: SFGs, AGNs, and unclassified sources.…”