Publications by authors named "Irene Shivaei"

Article Synopsis
  • Recent observations from the James Webb Space Telescope (JWST) have found many massive-galaxy candidates in the early Universe, stretching further back in time and at lower brightness levels than previously seen.
  • These findings initially posed challenges to the Λ cold dark-matter model, but the new study's results show no significant conflicts when accounting for spectroscopic redshifts.
  • The research highlights three ultra-massive galaxies that convert a notably high percentage of baryons into stars, suggesting they play a significant role in cosmic star-formation rates at redshifts 5 to 6.
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Local and low-redshift (z < 3) galaxies are known to broadly follow a bimodal distribution: actively star-forming galaxies with relatively stable star-formation rates and passive systems. These two populations are connected by galaxies in relatively slow transition. By contrast, theory predicts that star formation was stochastic at early cosmic times and in low-mass systems.

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Several theories have been proposed to describe the formation of black hole seeds in the early Universe and to explain the emergence of very massive black holes observed in the first thousand million years after the Big Bang. Models consider different seeding and accretion scenarios, which require the detection and characterization of black holes in the first few hundred million years after the Big Bang to be validated. Here we present an extensive analysis of the JWST-NIRSpec spectrum of GN-z11, an exceptionally luminous galaxy at z = 10.

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Large dust reservoirs (up to approximately 10M) have been detected in galaxies out to redshift z ≃ 8, when the age of the Universe was only about 600 Myr. Generating substantial amounts of dust within such a short timescale has proven challenging for theories of dust formation and has prompted the revision of the modelling of potential sites of dust production, such as the atmospheres of asymptotic giant branch stars in low-metallicity environments, supernova ejecta and the accelerated growth of grains in the interstellar medium. However, degeneracies between different evolutionary pathways remain when the total dust mass of galaxies is the only available observable.

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