arXiv subjects

Russ Taylor

Publications and source records attributed to Russ Taylor.

At least 19 recordsLinked to original sources

arXiv2026

SuperMIGHTEE : Spectral Ages of Remnant Radio Galaxy Candidates in the XMM-LSS Field

Remnant radio galaxies, whose lobes are no longer replenished by jets from the active galactic nucleus (AGN), offer key constraints on AGN duty cycles and the timescales of radio jets. We present a spectral-ageing study of 14 candidate remnant radio galaxies in the XMM-LSS field, combining new broad-band data from the MeerKAT MIGHTEE (L-band) and uGMRT superMIGHTEE (band-3 and band-4) surveys with complementary observations from LOFAR, GMRT, and JVLA, covering 144 MHz-1.5 GHz. Spectral modeling confirms 12 sources as genuine remnants, while two are reclassified as active, emphasising the importance of sensitive, multi-frequency coverage for robust remnant identification. Pixel-based spectral age maps yield results (~3-43 Myr) broadly consistent with integrated estimates, revealing relatively short spectral ages (~8-42 Myr). These ages likely reflect enhanced inverse-Compton losses at higher redshifts (0.35 < z < 2.85; median z = 1.25) and possible rapid lobe expansion in low-density environments. The ratios of remnant to total source ages (t_OFF}/t_s) span 0.04-0.83, indicating that the sample traces a broad range of evolutionary stages. Our findings reveal a previously underrepresented population of faint, rapidly fading remnants, suggesting that the remnant phase may be shorter and more dynamic than previously thought. This study highlights the crucial role of MIGHTEE and superMIGHTEE surveys in reliably classifying genuine remnants and provides a framework for constraining AGN life cycles in preparation for forthcoming SKA surveys.

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arXiv2026

Faraday Tomography with the SKA: A New Era of Cosmic Magnetism Studies

The Square Kilometre Array (SKA) represents a significant advancement in radio astronomy, enabling detailed study of cosmic magnetism through Faraday Rotation and Faraday Measurement Synthesis. This chapter provides a comprehensive review of these techniques, tracing their development and illustrating their crucial role in investigating magnetic fields across different cosmic environments. We focus on Array Assembly 4 (AA4), the final deployment stage, featuring 197 dishes (133 SKA, 64 MeerKAT) with 40 km maximum baselines and frequency coverage from 350 MHz to 15.4 GHz (goal: 24 GHz). These capabilities enable high-resolution Faraday tomography of magnetic structures in galaxies, clusters, and the cosmic web. We also highlight the earlier AA* stage with 144 dishes (80 SKA, 64 MeerKAT). Band 1 (350--1050 MHz) offers the finest Faraday depth resolution among the dish bands (full resolution $\sim$2.5 rad m$^{-2}$) with a maximum observable depth around 174,708 rad m$^{-2}$. Other bands (Band 2, Band 5a, Band 5b) enable multi-scale studies, probing larger structures with lower resolution but higher maximum depths. We discuss synergies between Faraday Measurement Synthesis and Image Synthesis techniques, showing how they complement each other in reconstructing magnetic field structures. Simulation results demonstrate the SKA's potential for high-resolution observations. We explore possible enhancements beyond the baseline configuration and synergies with other observatories, emphasizing multi-wavelength astronomy. This chapter aims to provide a thorough account of how the SKA's phased deployment from AA* to AA4 will transform our understanding of cosmic magnetic fields and drive new discoveries in astrophysics.

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arXiv2026

A Python-Based Peeling Framework for Radio Interferometry: Application to uGMRT 650MHz Imaging

Modern radio interferometric arrays offer high sensitivity, wide fields of view, and broad frequency coverage, but also pose significant data calibration challenges. Standard direction-independent calibration is insufficient to correct direction-dependent effects, such as ionospheric phase distortions and primary beam variations, which produce strong artifacts around bright sources and limit achievable image dynamic range. Built on standard CASA tasks, we present a Python-based direction-dependent calibration and peeling framework, demonstrated using radio continuum imaging data from the upgraded Giant Metrewave Radio Telescope (uGMRT). The framework efficiently subtracts bright-source models and suppresses their associated direction-dependent artifacts, producing significantly flattened backgrounds and improving image fidelity and faint-source detectability. We further introduce an optimized ``model-restoration'' strategy that mitigates direction-dependent artifacts while preserving the flux densities and morphologies of bright sources that are themselves of scientific interest. For fields containing multiple bright sources, sequential application of the framework systematically reduces background noise, thereby increasing sensitivity and faint-source detectability. The framework is Python-based, CASA-compatible, and can be readily applied to other mid- and low-frequency interferometric arrays. The code is publicly released with this paper.

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arXiv2026

MIGHTEE: Discovery of a triple-double radio galaxy

Triple-double radio galaxies (TDRGs) are amongst the rarest subpopulations of radio galaxies (RGs). They are characterised by three pairs of radio lobes, where each pair of lobes represents an episode of nuclear activity. Such a feature makes them key objects that can be used to constrain the duty cycle of RGs. In this paper, we report the discovery of J022248\m060934, a new TDRG, hosted by a galaxy at a spectroscopic redshift of $z \approx$ 0.94. We have used the MIGHTEE-DR1 data set and MIGHTEE sub-band images as our main data. In total intensity, J022248\m060934 has a bright core and triple-double, edge-brightened-like peaks of radio emission. The polarimetry of the source reveals an inhomogeneous density of the hosting environment which is consistent with the more pronounced bending in its eastern lobes. The spectral index and curvature maps suggest an inverted core and an ultra-steepening of the spectrum towards the outer lobes which reinforce a recurrent nuclear activity. We perform individual spectral age fitting of the components of the source using the JP model and we found a lower limit total age of $\sim$16 Myr. We also derive a short inactive period between the active phases and a rapid duty cycle of 90 per cent for the first cycle of activity. Our spectral ageing analysis suggests that the triple-double structure in TDRGs is not the product of long quiescent periods, as deduced by previous works based on kinematic ages.

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arXiv2025

The superMIGHTEE project: MeerKAT and GMRT Together to Unveil the Deep Radio Sky

An international team of researchers has come together to undertake an ultra-broadband exploration of the deep radio sky. The superMIGHTEE project combines data from the MIGHTEE project, using the precursor Square Kilometre Array (SKA) MeerKAT telescope in South Africa, with observations from the upgraded Giant Metrewave Radio Telescope (uGMRT) in India to produce deep images at several $\mu$Jy sensitivity over a frequency range of 200 MHz--2.5 GHz, with an angular resolution of a few arcseconds. This paper describes the initial superMIGHTEE uGMRT data release, comprising total intensity continuum images covering a total of 9.9 deg$^2$ at 650 MHz and 6.9 deg$^2$ at 400 MHz in the XMM-LSS, COSMOS, and E-CDFS deep fields. The associated radio source catalogs include 27,101 sources at 650 MHz and 10,946 sources at 400 MHz. The redshift distribution of the sources extends to $z\sim4$ with a median value of $z=1$. An overview of the broadband spectra of the sources, in combination with the MeerKAT MIGHTEE 1280 MHz data, reveals a clear change in spectral properties at the transition from an active galactic nuclei-dominated population to a population dominated by star-forming galaxies at flux densities of a few mJy. At higher frequencies, the star-forming galaxy population exhibits an optically thin synchrotron spectral index indicative of energy injection from supernovae. At lower frequencies, the spectra flatten significantly with decreasing flux density, and the fraction of sources with peaked spectra increases. This is the first superMIGHTEE uGMRT data release. Subsequent releases will include spectropolarimetric and spectral line image cubes, as well as images at lower frequencies. The goal of the superMIGHTEE ultra-wideband dataset is to enhance our understanding of the evolution of active galactic nuclei and star-forming galaxies over cosmic time, (abridged).

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arXiv2025

The Radio Spectral Energy Distribution and Star Formation Calibration in MIGHTEE-COSMOS Highly Star-Forming Galaxies at 1.5 < z < 3.5

Studying the radio spectral energy distribution (SED) of distant galaxies is essential for understanding their assembly and evolution over cosmic time. We present rest-frame radio SEDs of a sample of 160 starburst galaxies at redshifts 1.5 to 3.5 in the COSMOS field, as part of the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) project. MeerKAT observations, combined with archival VLA and GMRT data, allow us to determine the integrated mid-radio (1-10 GHz) continuum (MRC) luminosity and magnetic field strength. A Bayesian method is used to model the SEDs and separate free-free and synchrotron emission. We calibrate the star formation rate (SFR) in radio both directly through SED analysis and indirectly via the infrared-radio correlation (IRRC). With a mean synchrotron spectral index of approximately 0.7, we find that the index flattens with redshift and specific SFR, suggesting that cosmic rays are more energetic in the early universe due to higher star formation activity. The magnetic field strength increases with redshift (B is proportional to (1 + z)^0.7) and with star formation rate (B is proportional to SFR^0.3), indicating a small-scale dynamo as the dominant amplification mechanism. Accounting for SED evolution, the IRRC remains redshift-invariant and does not vary with stellar mass at 1.5 < z < 3.5, though the correlation deviates from linearity. Similarly, we show that SFR estimates based on integrated MRC luminosity are also redshift-invariant.

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arXiv2025

HI Intensity Mapping with the MIGHTEE Survey: First Results of the HI Power Spectrum

We present the first results of the HI intensity mapping power spectrum analysis with the MeerKAT International GigaHertz Tiered Extragalactic Exploration (MIGHTEE) survey. We use data covering $\sim$4 square degrees in the COSMOS field using a frequency range 962.5 MHz to 1008.42 MHz, equivalent to HI emission in $0.4<z<0.48$. The data consists of 15 pointings with a total of 94.2 hours on-source. We verify the suitability of the MIGHTEE data for HI intensity mapping by testing for residual systematics across frequency, baselines and pointings. We also vary the window used for HI signal measurements and find no significant improvement using stringent Fourier mode cuts. Averaging in the power spectrum domain, i.e. using incoherent averaging, we calculate the first upper limits from MIGHTEE on the HI power spectrum at scales 0.5 Mpc$^{-1} \lesssim k \lesssim$ 10 Mpc$^{-1}$. We obtain the best 1$\sigma$ upper limit of 28.6 mK$^{2}$Mpc${^3}$ on $k\sim$2 Mpc$^{-1}$. Our results are consistent with the power spectrum detected with observations in the DEEP2 field with MeerKAT. The data we use here constitutes a small fraction of the MIGHTEE survey and demonstrates that combined analysis of the full MIGHTEE survey can potentially detect the HI power spectrum at $z\lesssim0.5$ in the range 0.1 Mpc$^{-1} \lesssim k \lesssim$ 10 Mpc$^{-1}$ or quasi-linear scales.

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arXiv2024

A Census of the Deep Radio Sky with the VLA I: 10GHz Survey of the GOODS-N field

We present the first high-resolution, high-frequency radio continuum survey that fully maps an extragalactic deep field: the 10GHz 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 10GHz mosaic of the GOODS-field with an average rms noise $\sigma_{\rm n}=671\,\rm nJy\,beam^{-1}$ and angular resolution $\theta_{1/2}=0.22$arcsec across 297$\rm arcmin^2$. To maximize the brightness sensitivity we also produce a low-resolution mosaic with $\theta_{1/2}=1.0$arcsec and $\sigma_{\rm n}=968\,\rm nJy\,beam^{-1}$, from which we derive our master catalog containing 256 radio sources detected with peak signal-to-noise ratio $\geq 5$. 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 10GHz radio source counts in the GOODS-N field agree, in general, with predictions from numerical simulations/models and expectations from 1.4 and 3GHz radio counts.

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arXiv2022

A Compressed Sensing Faraday Depth Reconstruction Framework for the MeerKAT MIGHTEE-POL Survey

In this work we present a novel compute framework for reconstructing Faraday depth signals from noisy and incomplete spectro-polarimetric radio datasets. This framework is based on a compressed-sensing approach that addresses a number of outstanding issues in Faraday depth reconstruction in a systematic and scaleable manner. We apply this framework to early-release data from the MeerKAT MIGHTEE polarisation survey.

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arXiv2022

MIGHTEE-HI: the HI Size-Mass relation over the last billion years

We present the observed HI size-mass relation of $204$ galaxies from the MIGHTEE Survey Early Science data. The high sensitivity of MeerKAT allows us to detect galaxies spanning more than 4 orders of magnitude in HI mass, ranging from dwarf galaxies to massive spirals, and including all morphological types. This is the first time the relation has been explored on a blind homogeneous data set which extends over a previously unexplored redshift range of $0 < z < 0.084$, i.e. a period of around one billion years in cosmic time. The sample follows the same tight logarithmic relation derived from previous work, between the diameter ($D_{\rm HI}$) and the mass ($M_{\rm HI}$) of HI discs. We measure a slope of $0.501\pm 0.008$, an intercept of $-3.252^{+0.073}_{-0.074}$, and an observed scatter of $0.057$ dex. For the first time, we quantify the intrinsic scatter of $0.054 \pm 0.003$ dex (${\sim} 10 \%$), which provides a constraint for cosmological simulations of galaxy formation and evolution. We derive the relation as a function of galaxy type and find that their intrinsic scatters and slopes are consistent within the errors. We also calculate the $D_{\rm HI} - M_{\rm HI}$ relation for two redshift bins and do not find any evidence for evolution with redshift. These results suggest that over a period of one billion years in lookback time, galaxy discs have not undergone significant evolution in their gas distribution and mean surface mass density, indicating a lack of dependence on both morphological type and redshift.

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arXiv2021

The Hydrogen Intensity and Real-time Analysis eXperiment: 256-Element Array Status and Overview

The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is a radio interferometer array currently in development, with an initial 256-element array to be deployed at the South African Radio Astronomy Observatory (SARAO) Square Kilometer Array (SKA) site in South Africa. Each of the 6m, $f/0.23$ dishes will be instrumented with dual-polarisation feeds operating over a frequency range of 400-800 MHz. Through intensity mapping of the 21 cm emission line of neutral hydrogen, HIRAX will provide a cosmological survey of the distribution of large-scale structure over the redshift range of $0.775 < z < 2.55$ over $\sim$15,000 square degrees of the southern sky. The statistical power of such a survey is sufficient to produce $\sim$7 percent constraints on the dark energy equation of state parameter when combined with measurements from the Planck satellite. Additionally, HIRAX will provide a highly competitive platform for radio transient and HI absorber science while enabling a multitude of cross-correlation studies. In this paper, we describe the science goals of the experiment, overview of the design and status of the sub-components of the telescope system, and describe the expected performance of the initial 256-element array as well as the planned future expansion to the final, 1024-element array.

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arXiv2021

Direction Dependent Corrections in Polarimetric Radio Imaging III: A-to-Z Solver -- Modeling the full Jones antenna aperture illumination pattern

In this third paper of a series describing direction dependent corrections for polarimetric radio imaging, we present the the A-to-Z solver methodology to model the full Jones antenna aperture illumination pattern (AIP) with Zernike polynomials. In order to achieve thermal noise limited imaging with modern radio interferometers, it is necessary to correct for the instrumental effects of the antenna primary beam (PB) as a function of time, frequency, and polarization. The wideband AW projection algorithm enables those corrections provided an accurate model of the AIP is available. We present the A-to-Z solver as a more versatile algorithm for the modeling of the AIP. It employs the orthonormal circular Zernike polynomial basis to model the measured full Jones AIP. These full Jones models are then used to reconstruct the full Mueller AIP repsonse of an antenna, in principle accounting for all the off-axis leakage effects of the primary beam. The A-to-Z solver is general enough to accomodate any interferometer for which holographic measurements exist, we have successfully modelled the AIP of VLA, MeerKAT and ALMA as a demonstration of its versatility. We show that our models capture the PB morphology to high accuracy within the first 1-2 sidelobes, and show the viability of full Mueller gridding and deconvolution for any telescope given high quality holographic measurements.

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arXiv2021

MIGHTEE-HI: Discovery of an HI-rich galaxy group at z = 0.044 with MeerKAT

We present the serendipitous discovery of a galaxy group in the XMM-LSS field with MIGHTEE Early Science observations. Twenty galaxies are detected in HI in this $z\sim0.044$ group, with a $3\sigma$ column density sensitivity of $N_\mathrm{HI} = 1.6\times10^{20}\,\mathrm{cm}^{-2}$. This group has not been previously identified, despite residing in a well-studied extragalactic legacy field. We present spatially-resolved HI total intensity and velocity maps for each of the objects, which reveal environmental influence through disturbed morphologies. The group has a dynamical mass of $\log_{10}(M_\mathrm{dyn}/\mathrm{M}_\odot) = 12.32$, and is unusually gas-rich, with an HI-to-stellar mass ratio of $\log_{10}(f_\mathrm{HI}^\mathrm{*}) = -0.2$, which is 0.7 dex greater than expected. The group's high HI content, spatial, velocity, and identified galaxy type distributions strongly suggest that it is in the early stages of its assembly. The discovery of this galaxy group is an example of the importance of mapping spatially-resolved HI in a wide range of environments, including galaxy groups. This scientific goal has been dramatically enhanced by the high sensitivity, large field-of-view, and wide instantaneous bandwidth of the MeerKAT telescope.

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arXiv2020

HI intensity mapping with the MIGHTEE survey: power spectrum estimates

Intensity mapping (IM) with neutral hydrogen is a promising avenue to probe the large scale structure of the Universe. In this paper, we demonstrate that using the 64-dish MeerKAT radio telescope as a connected interferometer, it is possible to make a statistical detection of HI in the post-reionization Universe. With the MIGHTEE (MeerKAT International GHz Tiered Extragalactic Exploration) survey project observing in the L-band ($856 < \nu < 1712$ MHz, $z < 0.66$), we can achieve the required sensitivity to measure the HI IM power spectrum on quasi-linear scales, which will provide an important complementarity to the single-dish IM MeerKAT observations. We present a purpose-built simulation pipeline that emulates the MIGHTEE observations and forecast the constraints that can be achieved on the HI power spectrum at $z = 0.27$ for $k > 0.3$ $\rm{Mpc}^{-1}$ using the foreground avoidance method. We present the power spectrum estimates with the current simulation on the COSMOS field that includes contributions from HI, noise and point source models constructed from the observed MIGHTEE data. The results from our \textit{visibility} based pipeline are in qualitative agreement to the already available MIGHTEE data. This paper demonstrates that MeerKAT can achieve very high sensitivity to detect HI with the full MIGHTEE survey on quasi-linear scales (signal-to-noise ratio $> 7$ at $k=0.49$ $\rm{Mpc}^{-1}$) which are instrumental in probing cosmological quantities such as the spectral index of fluctuation, constraints on warm dark matter, the quasi-linear redshift space distortions and the measurement of the HI content of the Universe up to $z\sim 0.5$.

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arXiv2018

Large Synoptic Survey Telescope White Paper; The Case for Matching U-band on Deep Drilling Fields

U-band observations with the LSST have yet to be fully optimized in cadence. The straw man survey design is a simple coverage of the medium-deep-fast survey. Here we argue that deep coverage of the four deep drilling fields (XMM-LSS, ECDFS, ELAIS-S1 and COSMOS) has a much higher scientific return, given that these are also the target of the Southern Hemisphere's Square Kilometer Array Pathfinder, the MeerKAT specifically, deep radio observations.

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arXiv2017

MeerKLASS: MeerKAT Large Area Synoptic Survey

We discuss the ground-breaking science that will be possible with a wide area survey, using the MeerKAT telescope, known as MeerKLASS (MeerKAT Large Area Synoptic Survey). The current specifications of MeerKAT make it a great fit for science applications that require large survey speeds but not necessarily high angular resolutions. In particular, for cosmology, a large survey over $\sim 4,000 \, {\rm deg}^2$ for $\sim 4,000$ hours will potentially provide the first ever measurements of the baryon acoustic oscillations using the 21cm intensity mapping technique, with enough accuracy to impose constraints on the nature of dark energy. The combination with multi-wavelength data will give unique additional information, such as exquisite constraints on primordial non-Gaussianity using the multi-tracer technique, as well as a better handle on foregrounds and systematics. Such a wide survey with MeerKAT is also a great match for HI galaxy studies, providing unrivalled statistics in the pre-SKA era for galaxies resolved in the HI emission line beyond local structures at z > 0.01. It will also produce a large continuum galaxy sample down to a depth of about 5\,$\mu$Jy in L-band, which is quite unique over such large areas and will allow studies of the large-scale structure of the Universe out to high redshifts, complementing the galaxy HI survey to form a transformational multi-wavelength approach to study galaxy dynamics and evolution. Finally, the same survey will supply unique information for a range of other science applications, including a large statistical investigation of galaxy clusters as well as produce a rotation measure map across a huge swathe of the sky. The MeerKLASS survey will be a crucial step on the road to using SKA1-MID for cosmological applications and other commensal surveys, as described in the top priority SKA key science projects (abridged).

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arXiv2017

A High Resolution Survey of the Galactic Plane at 408 MHz

The interstellar medium is a complex 'ecosystem' with gas constituents in the atomic, molecular, and ionized states, dust, magnetic fields, and relativistic particles. The Canadian Galactic Plane Survey has imaged these constituents with angular resolution of the order of arcminutes. This paper presents radio continuum data at 408 MHz over the area 52 degrees < longitude < 193 degrees, -6.5 degrees < latitude < 8.5 degrees, with an extension to latitude = 21 degrees in the range 97 degrees < longitude < 120 degrees, with angular resolution 2.8' x 2.8' cosec(declination). Observations were made with the Synthesis Telescope at the Dominion Radio Astrophysical Observatory as part of the Canadian Galactic Plane Survey. The calibration of the survey using existing radio source catalogs is described. The accuracy of 408-MHz flux densities from the data is 6%. Information on large structures has been incorporated into the data using the single-antenna survey of Haslam (1982). The paper presents the data, describes how it can be accessed electronically, and gives examples of applications of the data to ISM research.

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arXiv2017

The Optical Polarization Variability of PKS 2155-304: Correlations at Low and High Energies

Gamma-ray emitting blazars have been the targets of many recent or ongoing monitoring programmes. The resulting multi-wavelength data archives are ideal for studying the quiescent and variable behaviour of the blazar PKS 2155-304. Here, observations of the optical polarization of the source between 2009 and 2014 (> 5 years) are presented, together with overlapping radio, photometric and gamma-ray measurements. During this time the source displayed significant variability at all wavelengths, with several prominent flares seen for the optical and gamma-ray intensity. These flares are typically associated with large rotations (>80{\deg}) in the polarization angle, during which the polarization angle appears to be oriented parallel to the position angle of the spatially resolved radio jet. Our aim is to determine if these large polarization angle rotations are correlated to the multi-wavelength outbursts seen in PKS 2155-304 in order to examine how changes in the polarization angle (and its orientation relative to the jet) relate to changes in the spectral energy distribution of the source.

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