Browsing by Author "Taylor, A. R."

Now showing 1 - 6 of 6
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    Cosmic evolution of star-forming galaxies to z 1.8 in the faint low-frequency radio source population
    (Oxford University Press, 2019) Ocran, E. F.; Taylor, A. R.; Vaccari, M.
    We study the properties of star-forming galaxies selected at 610 MHz with the GMRT in a survey covering ∼1.86 deg2 down to a noise of ∼7.1 μJy beam−1. These were identified by combining multiple classification diagnostics: optical, X-ray, infrared, and radio data. Of the 1685 SFGs from the GMRT sample, 496 have spectroscopic redshifts whereas 1189 have photometric redshifts. We find that the IRRC of star-forming galaxies, quantified by the infrared-to-1.4 GHz radio luminosity ratio qIR⁠, decreases with increasing redshift: qIR=2.86±0.04(1+z)−0.20±0.02 out to z ∼ 1.8. We use the V/Vmax statistic to quantify the evolution of the comoving space density of the SFG sample. Averaged over luminosity our results indicate ⟨V/Vmax⟩ to be 0.51±0.06⁠, which is consistent with no evolution in overall space density. However, we find V/Vmax to be a function of radio luminosity, indicating strong luminosity evolution with redshift.
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    Deep GMRT 610 MHz observations of the ELAIS N1 field: Catalogue and source counts
    (Oxford University Press, 2019) Taylor, A. R.; Ocran, E. F.; Vaccari, M.
    This is the first of a series of papers based on sensitive 610 MHz observations of the ELAIS N1 field, using the Giant Metrewave Radio Telescope. We describe the observations, processing and source catalogue extraction from a deep image with area of 1.86 deg2 and minimum noise of ∼7.1 μJy beam−1. We compile a catalogue of 4290 sources with flux densities in the range of 28.9 μJy– 0.503 Jy and derive the Euclidean-normalized differential source counts for sources with flux densities brighter than 35.5μJy⁠.
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    The evolution of the low-frequency radio AGN population to z 1.5 in the ELAIS N1 field
    (Oxford University Press, 2021) Ocran, E. F.; Taylor, A. R.; Vaccari, M.
    We study the cosmic evolution of radio sources out to z ≃ 1.5 using a GMRT 610 MHz survey covering ∼1.86 deg2 of the ELAIS N1 field with a minimum/median rms noise 7.1/19.5 μJy beam−1 and an angular resolution of 6 arcsec. We classify sources as star forming galaxies (SFGs), radio-quiet (RQ) and radio-loud (RL) Active Galactic Nuclei (AGNs) using a combination of multiwavelength diagnostics and find evidence in support of the radio emission in SFGs and RQ AGN arising from star formation, rather than AGN-related processes. At high luminosities, however, both SFGs and RQ AGN display a radio excess when comparing radio and infrared star formation rates.
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    J1615+5452: a remnant radio galaxy in the ELAIS-N1 field
    (Oxford University Press, 2020) Taylor, A. R.; Randriamanakoto, Z.; Ishwara-Chandra, C. H.
    We report the discovery of a remnant radio active galactic nucleus (AGN) J1615+5452 in the field of ELAIS-N1. GMRT continuum observations at 150, 325, and 610 MHz combined with archival data from the 1.4 GHz NVSS survey were used to derive the radio spectrum of the source. At a redshift z ∼ 0.33, J1615+5452 has a linear size of ∼100 kpc and spectral indices ranging between α1400610<−1.5 and α325150=−0.61±0.12⁠. While the source has a diffuse radio emission at low frequencies, we do not find evidence of core, jets, or hotspots in the 1.4 GHz VLA data of ∼5 arcsec angular resolution.
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    The optical polarization of the blazar PKS 2155–304 during an optical flare in 2010
    (Oxford University Press, 2020) Taylor, A. R.; Peceur, N. W.; Kraan-Korteweg, R. C.
    An analysis is presented of the optical polarimetric and multicolour photometric (BVRJ) behaviour of the blazar PKS 2155–304 during an outburst in 2010. This flare develops over roughly 117 d, with a flux doubling time τ ∼ 11 d, which increases from blue to red wavelengths. The polarization angle is initially aligned with the jet axis but rotates by roughly 90° as the flare grows. Two distinct states are evident at low and high fluxes. Below 18 mJy, the polarization angle takes on a wide range of values, without any clear relation to the flux. In contrast, there is a positive correlation between the polarization angle and flux above 18 mJy.
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    A wide-area GMRT 610-MHz survey of ELAIS N1 field
    (Oxford University Press, 2020) Taylor, A. R.; Ishwara-Chandra, C. H.; Green, D. A.
    In this paper, we present a wide-area 610-MHz survey of the ELAIS N1 field with the GMRT, covering an area of 12.8 deg2 at a resolution of 6 arcsec and with an rms noise of ∼40 μJy beam−1. This is equivalent to ∼20 μJy beam−1 rms noise at 1.4 GHz for a spectral index of −0.75. The primary goal of the survey was to study the polarized sky at sub-mJy flux densities at < GHz frequencies, alongwith a range of other science goals such as investigations into the nature of the low-frequency μJy source populations and alignments of radio jets. A total of 6400 sources were found in this region, the vast majority of them compact.