Browsing by Author "Deane, Roger P."

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    The preferentially magnified active nucleus in IRAS F10214+4724 - III. VLBI observations of the radio core
    (Oxford University Press, 2013) Deane, Roger P.; Rawlings, S.; Jarvis, Matt; Garrett, M. A.; Heywood, Ian; Klöckner, H. R.; Marshall, P. J.; McKean, J. P.
    We report 1.7GHz very long baseline interferometry (VLBI) observations of IRAS F10214+4724, a lensed z = 2.3 obscured quasar with prodigious star formation. We detect what we argue to be the obscured active nucleus with an effective angular resolution of <50pc at z = 2.3. The S1.7 =210µJy (9σ) detection of this unresolved source is located within the Hubble Space Telescope rest-frame ultraviolet/optical arc, however, 100 mas northwards of the arc centre of curvature. This leads to a source-plane inversion that places the European VLBI Network detection to within milliarcseconds of the modelled cusp caustic, resulting in a very large magnification (μ ∼70), over an order of magnitude larger than the CO (1→0) derived magnification of a spatially resolved Jansky Very Large Array (JVLA) map, using the same lens model. We estimate the quasar bolometric luminosity from a number of independent techniques and with our X-ray modelling find evidence that the AGN may be close to Compton thick, with an intrinsic bolometric luminosity of log10( Lbol, QSO /L ) = 11.34 ± 0.27dex. We make the first black hole mass estimate of IRAS F10214+4724 and find log10(MBH/M ) = 8.36 ± 0.56 which suggests a low black hole accretion rate (λ = ˙M/ ˙ MEdd ∼3±7 2 percent). We find evidence for an MBH/Mspheroid ratio that is one to two orders of magnitude larger than that of submillimetre galaxies (SMGs) at z ∼ 2. At face value, this suggests that IRAS F10214+4724 has undergone a different evolutionary path compared to SMGs at the same epoch. A primary result of this work is the demonstration that emission regions of different sizes and positions can undergo significantly different magnification boosts (>1dex) and therefore distort our view of high-redshift, gravitationally lensed galaxies.
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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.
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    The VLBA candels goods-north survey -i. survey design, processing, data products, and source counts
    (Oxford University Press, 2024) Deane, Roger P.; Jarvis, Matthew J.; Whittam, Imogen H.
    The past decade has seen significant advances in wide-field cm-wave very long baseline interferometry (VLBI), which is timely given the wide-area, synoptic survey-driven strategy of major facilities across the electromagnetic spectrum. While wide-field VLBI poses significant post-processing challenges that can severely curtail its potential scientific yield, man y dev elopments in the km-scale connected-element interferometer sphere are directly applicable to addressing these. Here we present the design, processing, data products, and source counts from a deep (11 μJy beam -1 ), quasi-uniform sensitivity, contiguous wide-field (160 arcmin 2 ) 1.6 GHz VLBI surv e y of the CANDELS GOODS-North field. This is one of the best-studied extragalactic fields at milli-arcsecond resolution and, therefore, is well-suited as a comparative study for our Tera-pixel VLBI image. The derived VLBI source counts show consistency with those measured in the COSMOS field, which broadly traces the AGN population detected in arcsecond-scale radio surv e ys. Ho we ver, there is a distinctive flattening in the S 1.4GHz ∼100-500 μJy flux density range, which suggests a transition in the population of compact faint radio sources, qualitatively consistent with the excess source counts at 15 GHz that is argued to be an unmodelled population of radio cores