Ian Heywood

Abstract:

In MeerKAT observations pointed at a Galactic X-ray binary located on the Galactic plane, we serendipitously discovered a radio nebula with cometary-like morphology. The feature, which we named 'the Mini Mouse' based on its similarity with the previously discovered 'Mouse' nebula, points back towards the previously unidentified candidate supernova remnant G45.24+0.18. We observed the location of the Mini Mouse with MeerKAT in two different observations, and we localized with arcsecond precision the 138-ms radio pulsar PSR J1914+1054g, recently discovered by the FAST telescope, to a position consistent with the head of the nebula. We confirm a dispersion measure of about 418 pc cm-3 corresponding to a distance between 7.8 and 8.8 kpc based on models of the electron distribution. Using our accurate localization and two period measurements spaced 90 d apart, we calculate a period derivative of (2.7 ± 0.3) × 10 -14 s s-1. We derive a characteristic age of approximately 82 kyr and a spin-down luminosity of 4 × 1035 erg s-1. For a pulsar age comparable with the characteristic age, we find that the projected velocity of the neutron star is between 320 and 360 km s-1 if it was born at the location of the supernova remnant. The size of the proposed remnant appears small if compared with the pulsar characteristic age; however, the relatively high density of the environment near the Galactic plane could explain a suppressed expansion rate and thus a smaller remnant.

Abstract:

The newest generation of radio telescopes is able to survey large areas with high sensitivity and cadence, producing data volumes that require new methods to better understand the transient sky. Here, we describe the results from the first citizen science project dedicated to commensal radio transients, using data from the MeerKAT telescope with weekly cadence. Bursts from Space: MeerKAT was launched late in 2021 and received ∼89 000 classifications from over 1000 volunteers in 3 months. Our volunteers discovered 142 new variable sources which, along with the known transients in our fields, allowed us to estimate that at least 2.1 per cent of radio sources are varying at 1.28 GHz at the sampled cadence and sensitivity, in line with previous work. We provide the full catalogue of these sources, the largest of candidate radio variables to date. Transient sources found with archival counterparts include a pulsar (B1845-01) and an OH maser star (OH 30.1–0.7), in addition to the recovery of known stellar flares and X-ray binary jets in our observations. Data from the MeerLICHT optical telescope, along with estimates of long time-scale variability induced by scintillation, imply that the majority of the new variables are active galactic nuclei. This tells us that citizen scientists can discover phenomena varying on time-scales from weeks to several years. The success both in terms of volunteer engagement and scientific merit warrants the continued development of the project, while we use the classifications from volunteers to develop machine learning techniques for finding transients.

Abstract:

We present the first measurement of the H I mass function (HIMF) using data from MeerKAT, based on 276 direct detections from the MeerKAT International GigaHertz Tiered Extragalactic Exploration (MIGHTEE) Survey Early Science data covering a period of approximately a billion years (0 ≤ z ≤ 0.084). This is the first HIMF measured using interferometric data over non-group or cluster field, i.e. a deep blank field. We constrain the parameters of the Schechter function that describes the HIMF with two different methods: 1/Vmax and modified maximum likelihood (MML). We find a low-mass slope α=−1.29+0.37−0.26 , ‘knee’ mass log10(M∗/M⊙)=10.07+0.24−0.24 and normalization log10(ϕ∗/Mpc−3)=−2.34+0.32−0.36 (H0 = 67.4 km s−1 Mpc−1) for 1/Vmax , and α=−1.44+0.13−0.10 , ‘knee’ mass log10(M∗/M⊙)=10.22+0.10−0.13 and normalization log10(ϕ∗/Mpc−3)=−2.52+0.19−0.14 for MML. When using 1/Vmax we find both the low-mass slope and ‘knee’ mass to be consistent within 1σ with previous studies based on single-dish surveys. The cosmological mass density of H I is found to be slightly larger than previously reported: ΩHI=5.46+0.94−0.99×10−4h−167.4 from 1/Vmax and ΩHI=6.31+0.31−0.31×10−4h−167.4 from MML but consistent within the uncertainties. We find no evidence for evolution of the HIMF over the last billion years.

Abstract:

The transformation and evolution of a galaxy is strongly influenced by interactions with its environment. Neutral hydrogen (H i) is an excellent way to trace these interactions. Here, we present H i observations of the spiral galaxy NGC 895, which was previously thought to be isolated. High-sensitivity H i observations from the MeerKAT large survey project MIGHTEE reveal possible interaction features, such as extended spiral arms and the two newly discovered H i companions, that drive us to change the narrative that it is an isolated galaxy. We combine these observations with deep optical images from the Hyper Suprime Camera to show an absence of tidal debris between NGC 895 and its companions. We do find an excess of light in the outer parts of the companion galaxy MGTH_J022138.1-052631, which could be an indication of external perturbation and thus possible sign of interactions. Our analysis shows that NGC 895 is an actively star-forming galaxy with a SFR of 1.75 ± 0.09[M⊙/yr], a value typical for high-stellar mass galaxies on the star-forming main sequence. It is reasonable to state that different mechanisms may have contributed to the observed features in NGC 895, and this emphasizes the need to revisit the target with more detailed observations. Our work shows the high potential and synergy of using state-of-the-art data in both H i and optical to reveal a more complete picture of galaxy environments.