We explored how to morphologically classify well-resolved jetted radio-loud active galactic nuclei (RLAGN) in the LOw Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS) using machine learning.We... Show moreWe explored how to morphologically classify well-resolved jetted radio-loud active galactic nuclei (RLAGN) in the LOw Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS) using machine learning.We investigated what morphology in total radio intensity maps can tell us about observed radio sources without complementary wavelength information and with limited visual inspection. We used a self-organising map (SOM) to model common radio morphologies and to reveal the rarest morphologies in LoTSS.Furthermore, we turned the radio source-component association problem into an object detection problem and trained an adapted Fast region convolutional neural network to mimic the grouping of source components into unique sources as performed by astronomers for LoTSS data.We also reduced the visual inspection required to find RLAGN remnant candidates based on their morphology, by using SOM-based features as input for a random forest classifier.Finally, we created a machine learning pipeline to identify giant radio galaxy (GRG) candidates and created a sample that contains more than ten thousand GRG. We then quantified the intrinsic GRG proper length distribution, the comoving GRG number density, and a current-day GRG lobe volume-filling fraction in clusters and filaments of the Cosmic Web. Show less
We explored the Universe using weak gravitational lensing, a phenomenon that occurs when light from distant galaxies is bent by the gravitational fields of closer cosmic objects, much like how a... Show moreWe explored the Universe using weak gravitational lensing, a phenomenon that occurs when light from distant galaxies is bent by the gravitational fields of closer cosmic objects, much like how a lens distorts light. Studying these distortions gives us insights into massive objects, such as galaxy clusters, and the large-scale structure of the Universe. However, analysing these weak lensing effects, though powerful, is challenging. Accurately detecting and interpreting these minute distortions require careful management of uncertainties, both from observational techniques and the models we employ. In our study, we rigorously controlled these uncertainties. By enhancing our analysis methods, we provided more accurate constraints on key cosmological parameters. Furthermore, we studied lensing effects around galaxy groups, shedding light on the relationship between the enigmatic dark matter – a difficult-to-detect but predominant component of the Universe – and the galaxies we observe. In conclusion, our research advanced the weak lensing analysis and broadened our understanding of the Universe. Show less
Migrant entrepreneurship is viewed as a pathway to substantive social integration, one that makes host countries more prosperous in the process. Accordingly, scholars have studied the social... Show moreMigrant entrepreneurship is viewed as a pathway to substantive social integration, one that makes host countries more prosperous in the process. Accordingly, scholars have studied the social context in which migrant entrepreneurs operate, and considered at length the range of policy options that governments can use to support their activities. Conversely, the issue of public attitudes to policies that support migrant entrepreneurship has been largely neglected. Leveraging the case of North Korean migrant entrepreneurs in South Korea, this article fills this gap in the literature by examining how the structure of government support within a broader “policy mix” for migrant entrepreneurship policies acts on public attitudes. Overall, it finds South Koreans are most supportive of migrant entrepreneurship policies endorsed and paid for by large companies through corporate taxation or loans to the individual, rather than the state, and which have a target goal of employment support for profitable migrant-run firms or joint ventures run by teams of natives and migrants. Notably, policies explicitly justified as tools to address discrimination actively discourage support. The specifics of the Korean case show that determinants of native hostility toward migrants apply to migrant entrepreneurship even when ethnic differences and many of the institutional barriers that apply in other cases do not exist, suggesting that ethnicity is not a major motivating factor; economic rationality and what is “good for South Korea” are. Show less
Gomez, S.; Villar, V.A.; Berger, E.; Gezari, S.; Velzen, S. van; Nicholl, M.; ... ; Alexander, K.D. 2023