Browsing by Author "Madhanpall, Nikhita"

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    A large-scale clustering analysis of radio galaxies
    (University of the Western Cape, 2019) Madhanpall, Nikhita; Jarvis, Matt
    The distribution of the visible structure in the Universe is in part dependent on the in uence of the dark matter structure. Measurements of large-scale structure can therefore be related to the dark matter distribution by calculating the galaxy bias b(z), which indicates the extent to which the baryonic matter traces out the underlying dark matter distribution. Radio sources are easily detected out to higher redshifts and are thus an e ective probe of the large-scale structure of the Universe, however very few clustering studies have been carried out at sub-mJy levels, as well as for various radio source types. In this Thesis, I measure the angular two-point correlation function of radio populations using 11,431 sources from a Jansky Very Large Array (JVLA) CnB S1:4 > 440 Jy survey over 100deg2 of the Sloan Digital Sky Survey (SDSS) Southern Equatorial Stripe (Stripe 82), having a resolution of 10 16 arcseconds.
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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.