Browsing by Author "Delhaize, Jacinta"

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    Open Access
    Searching for AGN-associated HI-21cm absorption with the MIGHTEE survey
    (2026) Charlton, Kathleen; Delhaize, Jacinta
    We present a targeted search for AGN-associated 21-cm HI absorption in the COSMOS field up to z = 0.48, using HI and continuum data from the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE). MIGHTEE is a galaxy evolution survey with the SKA precursor telescope MeerKAT. The MIGHTEE data has a high spectral resolution of 26.1 kHz (→ 8 km s→1) and has excellent sensitivity, allowing us to probe HI absorption against continuum fluxes down to S1.28 GHz → 40 μJy beam→1, far fainter than previously possible. Our primary goal is to identify inflows and outflows of gas associated with the radio galaxy itself, to examine the interplay between gas, AGN fuelling, AGN feedback, and the impact of these on star formation and overall evolution of the host galaxies. We search for absorption against 111 radio AGN previously identified in the MIGHTEE Early Science field using the automated linefinder flashfinder. Using the linefinder, we identify 12 spectra as having potential spectral lines. We confirm four candidates using the Mahalanobis Distance, a multivariate generalisation of the Z-score which quantifies the o!set between a data point and a reference distribution. We report HI absorption detections against three resolved continuum sources: J100028.27 +024103.3, J100043.19 +014607.8 and J100131.14+022924.6, as well as against one unre- solved continuum source J095927.25+014634.8. With large velocity o!sets from the back- ground hosts and full width half maxima below 200 km s→1, it is likely that we are probing gas in the outer intergalactic medium, rather than close to the supermassive black hole. We employ the extensive multi-wavelength information in the COSMOS field to examine the HI detections as well as the host galaxy properties and environments. We detect two absorbers against the resolved radio galaxy J100028.27+024103.3, hosted by the BCG of cluster WHLJ100028.3 +024103. We suggest that the HI is stripped gas from nearby galaxy zCOSMOS 84586, which if confirmed would make it the highest redshift detection of HI cluster dynamics ever observed. The absorbing HI associated with J100043.19+014607.8, J100131.14+022924.6 and J095927.25+014634.8 is inferred to be part of large-scale HI disks or gas shells in the outer halo. The detections display a range of peak optical depths 0.19+0.04 →0.04 % < ωpeak < 81+10 →11 %. We find that J095927.25+014634.8 is the lowest luminosity radio source with detected HI in absorption at a distance greater than z > 0.1 to date. These results help us probe the current limitations of low-luminosity HI absorption studies and look to what will be achieved with the SKA.
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    Open Access
    The automated detection and multiwavelength properties of LADUMA HI galaxies
    (2025) Stockenstroom, Leyya; Delhaize, Jacinta; Jarvis, Matt
    In this study, we investigate the neutral atomic hydrogen (HI) and star formation history (SFH) properties of 104 low redshift (0 < zHI < 0.088) galaxies from the Looking At the Distant Universe with the MeerKAT Array (LADUMA) survey. LADUMA is a deep and narrow HI emission survey underway with the MeerKAT telescope. We perform automated source finding over the low redshift Early Science LADUMA data cube using the SoFiA-2 algorithm. The source finding mask created in this work will be used to clean the first public data release of the LADUMA data cubes, which will be outlined in an upcoming paper. We present the confirmed SoFiA-2 detections of HI and compare the results to those produced by manual and semi-automated methods of source finding. We find generally good agreement between the methods, suggesting that SoFiA-2 will be an efficient and effective method on subsequent LADUMA data cubes. Additionally, we perform spectral energy distribution (SED) fitting to far-ultraviolet (FUV) to far-infrared (FIR) multiband photometry of our HI sample, thereby determining their stellar masses (M∗), star formation rates (SFRs), and star formation histories (SFHs). We explore the relationship between galaxies' HI and star formation history properties (HI-SFH). To do this, we examine the lookback time of peak star formation (τpeak) versus the HI mass to stellar mass fraction (MHI /M∗) and the peak star formation rate versus MHI /M∗. The latter is investigated here for the first time, to the best of our knowledge. Our findings reveal a strong anti-correlation between MHI /M∗ and SFRpeak of our HI sample, with τpeak decreasing as MHI /M∗ increases. This suggests that galaxies with lower MHI /M∗ have previously undergone more aggressive periods of star formation than galaxies with higher MHI /M∗. Additionally, galaxies with higher MHI /M∗ exhibit rising star formation rates at the time of observation and are likely to reach their peak star formation rate in future stages of their evolution. These findings serve as a low redshift pilot study, which can be applied to and compared with similar source finding and HI-SFH studies in upcoming higher redshift data from the LADUMA survey.