Browsing by Author "Whittam, Imogen"

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    MIGHTEE: a first look at MIGHTEE quasars
    (Oxford University Press, 2025) Whittam, Imogen; White, Sarah; Delvecchio, Ivan
    In this work, we study a robust, Ks-band complete, spectroscopically confirmed sample of 104 unobscured (Type-1) quasars within the COSMOS and XMM–LSS fields of the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey, at 0.60 < zspec < 3.41. The quasars are selected via gJKs colour-space and, with 1.3-GHz flux-densities reaching rms ≈ 3.0 μJy beam−1, we find a radio-loudness fraction of 5 per cent. Thanks to the deep, multiwavelength data sets that are available over these fields, the properties of radio-loud and radio-quiet quasars can be studied in a statistically robust way, with the emphasis of this work being on the active-galactic-nuclei (AGNs)-related and star-formation-related contributions to the total radio emission. We employ multiple star-formation-rate estimates for the analysis so that our results can be compared more easily with others in the literature, and find that the fraction of sources that have their radio emission dominated by the AGN crucially depends on the SFR estimate that is derived from the radio luminosity. When redshift dependence is not taken into account, a larger fraction of sources is classed as having their radio emission dominated by the AGN. When redshift dependence is considered, a larger fraction of our sample is tentatively classed as ‘starbursts’. We also find that the fraction of (possible) starbursts increases with redshift, and provide multiple suggestions for this trend.
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    Mightee: Deep 1.4 ghz source counts and the sky temperature contribution of star-forming galaxies and active galactic nuclei
    (Oxford University Press, 2023) Hale, Catherine; Whittam, Imogen; Jarvis, Matt
    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 survey down to S1.4GHz ∼15 μ Jy. 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 characterization, clustering, and variations in the assumed source model used to simulate sources within the field and characterize source count incompleteness.