Browsing by Author "Taylor, Russ"

Now showing 1 - 4 of 4
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    A census of the deep radio sky with the vla. i. 10 ghz survey of the goods-n field
    (American Astronomical Society, 2024) Jiménez-Andrade, Eric Faustino; Taylor, Russ; Murphy, Eric
    We present the first high-resolution, high-frequency radio continuum survey that fully maps an extragalactic deep field: the 10 GHz survey of the Great Observatories Origins Deep Survey-North (GOODS-N) field. This is a Large Program of the Karl G. Jansky Very Large Array that allocated 380 hours of observations using the X-band (8 − 12 GHz) receivers, leading to a 10 GHz mosaic of the GOODS-field with an average rms noise σn = 671 nJy beam−1 and angular resolution θ1/2 = 0. ′′22 across 297 arcmin2 . To maximize the brightness sensitivity we also produce a low-resolution mosaic with θ1/2 = 1. ′′0 and σn = 968 nJy beam−1 , from which we derive our master catalog containing 256 radio sources detected with peak signal-to-noise ratio ≥ 5. Radio source size and flux density estimates from the high-resolution mosaic are provided in the master catalog as well. The total fraction of spurious sources in the catalog is 0.75%. Monte Carlo simulations are performed to derive completeness corrections of the catalog. We find that the 10 GHz radio source counts in the GOODS-N field agree, in general, with predictions from numerical simulations/models and expectations from 1.4 and 3 GHz radio counts.
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    Big data research infrastructure collaboration toward the SKA (BRICSKA)
    (Academia Brasileira de Ciencias, 2021) Taylor, Russ; Porto, Fabio; Cui, Chenzhou
    Astronomy is entering an era of mega-data that will render conventional research methods as well as data and visual analytics tools ineffective. The Square Kilometre Array (SKA) drives one of the most significant big data challenges of the next decades. South Africa, China and India are partners in the global SKA collaboration and host recently completed, next generation radio astronomy facilities. South Africa, Brazil, China and India are involved in the Large Synoptic Survey Telescope (LSST), which represents a complementary mega-data challenge, vastly increasing the current data volume of optical surveys, and providing critical multi-wavelength data set for SKA analytics. Russian researchers are also engaged in radio astronomy and multi-wavelength, multi-messenger projects driving increasing volumes of observational data.
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    The nature of the microjy source population
    (University of the Western Cape, 2015) Ocran Emmanuel Francis; Taylor, Russ; Vaccari, Mattia
    The study of the faint radio universe and of its properties has recently become a very active field of research not only because of the much improved capabilities of the SKA pathfinders but also because of the need to better plan for SKA surveys. These new facilities will map large areas of the sky to unprecedented depths and transform radio astronomy into the leading technique for investigating the complex processes which govern the formation and evolution of galaxies. This thesis combines multi-wavelength techniques, highly relevant to future deep radio surveys, to study the properties of faint radio sources. The nature of the faint radio sources is presented, over a large GMRT survey area of an area of 1.2 deg2 comprising 2800 sources. Utilising multi-wavelength data we have matched 85% of the radio population to Spitzer/IRAC and obtained a redshift estimate for 63%. The redshift associations are a combination of photometric and spectroscopic redshift estimates. This study investigates several multi-wavelength diagnostics used to identify AGN, using radio, infrared, optical and x-ray data . This analysis shows that various diagnostics (from the radio through the X-ray ones) select fairly different types of AGNs, with an evidence of a disagreement in the number of AGNs selected by each individual diagnostics. For the sources with redshift we use a classification scheme based on radio luminosity, x-ray emission, BOSS/SDSS spectroscopy, IRAC colors satisfying the Donley criterion, and MIPS 24ɥm radio-loud AGN criteria to separate them into AGNs and SFGs. On the basis of this classification, we find that at least 12.5% of the sources with redshifts are AGNs while the remaining 87.5% are adopted as SFGs. We explore the nature of the classified sources through the far-infrared radio correlation. We measure a median qIR value of 2:45± 0:01 for the SFGs and qIR value of 2:27 ± 0:05 for the AGNs. The decrease in the median value of qIR for the AGNs is a result of the additional AGN component to radio emission for the AGN-powered sources and find tentative evidence of an evolution of the qIR with redshift.
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    The jet paths of radio active galactic nuclei and their cluster weather
    (EDP Sciences, 2025) Taylor, Russ; Vardoulaki, Eleni; Backöfer, Vincent
    We studied bent radio sources within X-ray galaxy groups in the COSMOS and XMM-LSS fields. The radio data were obtained from the MeerKAT International GHz Tiered Extragalactic Explorations data release 1 (MIGHTEE-DR1) at 1.2-1.3 GHz, with angular resolutions of 8.9″ and 5″, and median noise levels of rmsmed ∼= 3.5 and 5.5 μJy/beam. Bent radio active galactic nuclei (AGN) were identified through visual inspection. Our analysis included 19 bent radio AGN in the COSMOS field and 17 in the XMM-LSS field that lie within X-ray galaxy groups (2 × 1013 ≲ M200c/M⊙ ≤ 3×1014). We investigated the relationship between their bending angle (BA) - the angle formed by the jets or lobes of two-sided radio sources associated with AGN - and the properties of their host galaxies and large-scale environment probed by the X-ray galaxy groups. Our key findings are: (a) In the XMM-LSS field, we observed a strong correlation between the linear projected size of the bent AGN, the group halo mass, and the projected distance from the group centre. This trend, consistent with previous studies, was not detected in the COSMOS sample. (b) The BA is a function of environmental density, with the type of medium playing a significant role. Additionally, at z ≤ 0.5 we found a higher number of bent sources (BA ≤ 160°) compared to higher redshifts (z ∼ 1), by a factor of >1.5. This trend aligns with magneto-hydrodynamic simulations, which suggest that denser environments and longer interaction times at lower redshifts contribute to this effect. A comparison with the literature suggests that jet bending in galaxy groups within the redshift range 0.1 < z < 1.2 is primarily driven by ram pressure exerted on the jets, which occurs during quiescent phases of AGN activity. This study underscores the role of environmental interactions in shaping the morphology of radio AGN within galaxy groups, providing insights into the interplay between large-scale structure and AGN physics.