Browsing by Author "Knowles, Kenda"

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    DEVILS/MIGHTEE/GAMA/DINGO: the impact of SFR time-scales on the SFR-radio luminosity correlation
    (Oxford, 2024) Cook, Robin H. W.; Davies, Luke J. M; Knowles, Kenda
    The tight relationship between infrared luminosity ( L TIR ) and 1.4 GHz radio continuum luminosity ( L 1 . 4 GHz ) has proven useful for understanding star formation free from dust obscuration. Infrared emission in star-forming galaxies typically arises from recently formed, dust-enshrouded stars, whereas radio synchrotron emission is expected from subsequent supernovae. By leveraging the wealth of ancillary far -ultra violet –far-infrared photometry from the Deep Extragalactic VIsible Legacy Survey and Galaxy and Mass Assembly surveys, combined with 1.4 GHz observations from the Meer Karoo Array Telescope International GHz Tiered Extragalactic Exploration survey and Deep Investigation of Neutral Gas Origin projects, we investigate the impact of time-scale differences between far -ultraviolet –far-infrared and radio-derived star formation rate (SFR) tracers. We examine how the spectral energy distribution (SED)-derived star formation histories (SFHs) of galaxies can be used to explain discrepancies in these SFR tracers, which are sensitive to different time scales. Galaxies exhibiting an increasing SFH have systematically higher L TIR and SED-derived SFRs than predicted from their 1.4 GHz radio luminosity. This indicates that insufficient time has passed for subsequent supernovae-driven radio emissions to accumulate. We show that backtracking the SFR(t) of galaxies along their SED-derived SFHs to a time several hundred mega years prior to their observed epoch will both linearize the SFR–L 1 . 4 GHz relation and reduce the overall scatter. The minimum scatter in the SFR(t)–L 1 . 4 GHz is reached at 200 –300 Myrprior, consistent with theoretical predictions for the time-scales required to disperse the cosmic ray electrons responsible for the synchrotron emission.
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    The star-formation history of mass-selected galaxies from the VIDEO survey
    (Oxford University Press, 2014) Zwart, Jonathan T.L.; Jarvis, Matt; Deane, Roger P.; Bonfield, David G.; Knowles, Kenda; Madhanpall, Nikhita; Rahmani, Hadi; Smith, Daniel J.B.
    We measure star formation rates (SFRs) and specific SFRs (SSFRs) of Ks-selected galaxies from the VISTA Deep Extragalactic Observations survey by stacking 1.4 GHz Very Large Array data. We split the sample, which spans 0 < z < 3 and stellar masses 108.0 < M*/M < 1011.5, into elliptical, irregular or starburst galaxies based on their spectral energy distributions. We find that SSFR falls with stellar mass, in agreement with the 'downsizing' paradigm. We consider the dependence of the SSFR - mass slope on redshift: for our full and elliptical samples the slope flattens, but for the irregular and starburst samples the slope is independent of redshift. The rate of SSFR evolution reduces slightly with stellar mass for ellipticals, but irregulars and starbursts co-evolve across stellar masses. Our results for SSFR as a function of stellar mass and redshift are in agreement with those derived from other radio-stacking measurements of mass-selected passive and star-forming galaxies, but inconsistent with those generated from semi-analytic models, which tend to underestimate SFRs and SSFRs. There is a need for deeper high-resolution radio surveys such as those from telescopes like the next-generation MeerKAT in order to probe lower masses at earlier times and to permit direct detections, i.e. to study individual galaxies in detail.