Prof. Matt Jarvis

Abstract:

Context . Ly α emitters (LAEs) are galaxies with strong Ly α emission, tracing early star formation and ionizing radiation. Their connection to active galactic nuclei (AGNs) is key to understanding the mechanisms behind (extended) Ly α emission. Aims . For this study, we measured the fraction of LAEs identified as radio-emitting AGNs ( f AGN,radio ) and the fraction of radio sources that exhibit Ly α emission ( f Ly α ) to investigate the connection of radio AGN activity to Ly α emission at 1.88 < z < 3.52. Methods . We identified 928 sources that were detected in both the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) and the LOw Frequency ARray (LOFAR) surveys. These matches were drawn from 55 109 spectroscopically confirmed LAEs and 27 625 radio sources. Results . After applying completeness corrections, we obtain f AGN,radio = 1.77 ± 0.04% and f Ly α = 18.15 ± 0.14% (for Ly α fluxes above 3×10 −17 erg s −1 cm −2 and radio flux densities above 0.1 mJy at 144 MHz). The fraction f AGN,radio increases from 0.4 ± 0.1% at log 10 L Lyα,ergs −1 ≈ 42.6 to 9.7 ± 1.3% at log 10 L Lyα,ergs −1 ≈ 44.5. The fraction f Lyα rises from 0.7 ± 0.1% at log 10 L 150,WHz −1 ≈ 24.6 to 55.8 ± 14.5% for log 10 L 150,WHz −1 ≈ 28.3. ‘LAEs with radio AGNs’ and ‘optical AGNs with Ly α emission’ exhibit similar radio luminosity distributions above the AGN threshold ( L 150MHz > 10 23.9 W Hz −1 ), though optical AGNs show systematically higher Ly α luminosities. We find no statistically significant correlations of Ly α luminosity with both radio luminosity and a low-frequency spectral index, suggesting that Ly α emission is regulated by gas properties rather than jet power alone. We also find a positive correlation between the full width at half maximum (FWHM) and luminosity of the Ly α line, suggesting that more luminous sources have broader lines, potentially due to enhanced outflows or velocity dispersions. However, we find no correlation between FWHM and radio size, indicating minimal direct jet-gas interaction in these systems. Conclusions . Our results show that most Ly α emission at 1.88 < z < 3.52 is powered by star formation, with radio AGN activity confined to a small luminous subset (1.77 ± 0.04%). While luminous systems preferentially host radio AGNs, the lack of correlation between Ly α and radio luminosities in individual sources indicates that Ly α emission is governed primarily by host galaxy gas properties rather than direct AGN jet coupling.

Abstract:

Abstract The rotation velocities of disc galaxies trace dark matter halo structure, providing direct constraints on the galaxy–halo connection. We construct a Bayesian forward model to connect the dark matter halo population predicted by ΛCDM with an observed sample of disc galaxies (SPARC) through their maximum rotation velocities. Our approach combines a subhalo abundance matching scheme (accounting for assembly bias) with a parameterised halo response to galaxy formation. When assuming no correlation between selection in the SPARC survey and halo properties, reproducing the observed velocities requires strong halo expansion, low abundance matching scatter and a halo proxy that strongly suppresses the stellar masses in satellite haloes. This is in clear tension with independent clustering constraints. Allowing for SPARC-like galaxies to preferentially populate low Vmax haloes at fixed virial mass greatly improves the goodness-of-fit and resolves these tensions: the preferred halo response shifts to mild contraction, the abundance matching scatter constraint relaxes to σSHAM < 0.30 dex at 1σ and the proxy becomes consistent with clustering. However, the inferred selection threshold is extreme, implying that SPARC galaxies occupy the lowest ~15 per cent of the Vmax, halo distribution at fixed Mvir. Moreover, even with selection, the inferred scatter remains in statistical disagreement with the low-mass clustering constraints, which are most representative of the SPARC galaxies in our sample. Our analysis highlights the advantage of augmenting clustering-based constraints on the galaxy–halo connection with kinematics and suggests a possible tension using current data.

Abstract:

Abstract Radio continuum surveys provide samples of active galactic nuclei (AGN) and star forming galaxies (SFGs) to high redshifts, free of biases due to dust obscuration. However, radio detected sources require multi-wavelength counterparts to understand their intrinsic properties (e.g. redshift, stellar mass) and to study the evolution of star formation and AGN activity. In this work we present host galaxy counterparts for the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey continuum Data Release 1 in regions with the best ancillary data (totalling 7.5 sq. deg). We combine statistical cross-matching and visual inspection to identify Ks-band selected host galaxies, and additionally combine multiple radio components into single physical objects, where needed. This results in a combined radio catalogue of ~66 000 sources, with host counterparts and redshifts identified for ~95 per cent of sources in the COSMOS field, ~91 per cent in XMM-LSS and ~90 per cent in CDFS-DEEP. This includes a significant fraction of sources with spectroscopic redshifts within the COSMOS field (~50 per cent), with ~30 and ~20 per cent in the XMM-LSS and CDFS-DEEP fields respectively. Using the cross-matched catalogue, we make an initial identification of radio-excess and star forming galaxies based on comparisons of the radio luminosities to host star formation rates. Using this split as a proxy for radio loud AGN or SFGs, we present expectations for the redshift distributions of these sources, finding broad agreement with those from deep radio luminosity functions and simulated catalogues.

Abstract:

Abstract 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 (tOFF/ts) 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.

Abstract:

We present a catalogue of H i sources extracted from the MIGHTEE survey data cubes covering the COSMOS field. The catalogue contains 293 sources in the redshift range of . In addition to H i masses and velocity widths, the catalogue includes optical through near-infrared photometry and inferred stellar masses and star-formation rates. The quantity of sources in the H i catalogue acquired through untargeted source finding is greatly influenced by the source finding methods used. This study therefore also provides a well-characterized expected completeness of the detected sample of galaxies based on their properties, informing of any detection biases, inferred through a comparative study of different source finding algorithms. We have tested the performance of widely-used source finders: pybdsf, profound, and sofia, along with new source finder leshi, focusing exclusively on H i source detection rather than source characterization in the first instance. The source finders were tested by injecting a sample of simulated galaxies divided into narrow bins of mass, inclination and distance into a MeerKAT data cube. The results inform the source finding strategies for the MeerKAT International GigaHertz Tiered Extragalactic Exploration (MIGHTEE) survey, as well as upcoming SKAO surveys.