Browsing by Author "Jarvis, Matthew J."

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    MIGHTEE-HI: deep spectral line observations of the COSMOS field
    (Oxford University Press, 2024) Heywood I; Jarvis, Matthew J. ; Ponomareva, A.A
    The MIGHTEE survey utilizes the South African MeerKAT radio telescope to observe four extragalactic deep fields, with the aim of advancing our understanding of the formation and evolution of galaxies across cosmic time. MIGHTEE’s frequency coverage encompasses the HI line to a redshift of z ≃ 0.58, and OH megamasers to z ≃ 0.9. We present the MIGHTEE-HI imaging products for the COSMOS field, using a total of 94.2 h on-target and a close-packed mosaic of 15 individual pointings. The spectral imaging covers two broad, relatively interference-free regions (960–1150 and 1290–1520 MHz) within MeerKAT’s L-band, with up to 26 kHz spectral resolution (5.5 km s−1 at z = 0). The median noise in the highest spectral resolution data is 74 μJy beam−1, corresponding to a 5σHI mass limit of 108.5 M☉ for a 300 km s−1 line at z = 0.07. The mosaics cover >4 deg2, provided at multiple angular resolution / sensitivity pairings, with an angular resolution for HI at z = 0 of 12 arcsec. We describe the spectral line processing workflow that will be the basis for future MIGHTEE-HI products, and validation of, and some early results from, the spectral imaging of the COSMOS field. We find no evidence for line emission at the position of the z = 0.376 HI line reported from the CHILES survey at a >94 per cent confidence level, placing a 3σ upper limit of 8.1 × 109 M☉ on MHI for this galaxy. A public data release accompanies this article.
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    MIGHTEE-Hi: The relation between the Hi gas in galaxies and the cosmic web
    (Oxford University Press, 2022) Tudorache, Madalina N.; Jarvis, Matthew J.; Heywood, Ian
    We study the 3D axis of rotation (3D spin) of 77 Hi galaxies from the MIGHTEE-Hi Early Science observations, and its relation to the filaments of the cosmic web. For this Hi-selected sample, the alignment between the spin axis and the closest filament (|cos 𝜓|) is higher for galaxies closer to the filaments, with h|cos 𝜓|i = 0.66 ± 0.04 for galaxies < 5 Mpc from their closest filament compared to h|cos 𝜓|i = 0.37±0.08 for galaxies at 5 < 𝑑 < 10 Mpc. We find that galaxies with a low Hi-to-stellar mass ratio (log10 (𝑀HI/𝑀★) < 0.11) are more aligned with their closest filaments, with h|cos 𝜓|i = 0.58 ± 0.04; whilst galaxies with (log10 (𝑀HI/𝑀★) > 0.11) tend to be mis-aligned, with h|cos 𝜓|i = 0.44 ± 0.04. We find tentative evidence that the spin axis of Hi-selected galaxies tend to be aligned with associated filaments (𝑑 < 10 Mpc), but this depends on the gas fractions. Galaxies that have accumulated more stellar mass compared to their gas mass tend towards stronger alignment.
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    The star formation rates of QSOs
    (Royal Astronomical Society, 2022) Symeonidis, Myrto; Maddox, Natasha; Jarvis, Matthew J.
    We examine the far-IR properties of a sample of 5391 optically selected QSOs in the 0.5 < z < 2.65 redshift range down to log [νLν,2500(erg/s)] > 44.7, using SPIRE data from Herschel-ATLAS. We split the sample in a grid of 74 luminosity-redshift bins and compute the average optical–infrared spectral energy distribution (SED) in each bin. By normalising an intrinsic AGN template to the AGN optical power (at 5100˚A) we decompose the total infrared emission (LIR; 8—1000µm) into an AGN (LIR,AGN) and star-forming component (LIR,SF). We find that the AGN contribution to LIR increases as a function of AGN power which manifests as a reduction of the ‘far-IR bump’ in the average QSO SEDs. We note that LIR,SF does not correlate with AGN power; the mean star formation rates (SFRs) of AGN host galaxies are a function of redshift only and they range from ∼6 M⊙/yr at z ∼ 0 to a plateau of . 200 M⊙/yr at z ∼ 2.6.
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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