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Star-forming clumps have been found to significantly influence the star formation of gas-rich |$z\gt 1$| galaxies. Using public data from JWST /NIRCam (Cosmic Evolution Survey; COSMOS-Web) and Atacama Large (sub-)Millimeter Array (ALMA; Fiber-Multi Object Spectrograph or FMOS-COSMOS survey), we study a sample of 32 massive (⁠|$\gt 10^{10.5}\, \rm {\rm M}_{\odot }$|⁠) main-sequence galaxies at |$z_{\rm spec}\sim 1.5$| with |$\sim 0.3\, \rm kpc$| resolution. We create composite morphological models consisting of bulge, disc, and clumps to fully 'deconstruct' the galaxy images. With the resulting measurements of the flux and size of these components, we find the following: (i) the combined contribution of clumps is 1–30 per cent towards the net star formation of the host while contributing 1–20 per cent to its stellar mass. The clumps show a correlation between their stellar mass and star formation rate (SFR), but have an increased specific SFR relative to the star formation main-sequence, with offsets ranging from |$0 \lesssim \Delta \log \rm sSFR \lesssim 0.4$|⁠. They feature star formation surface densities of |$10^{-2}-10^{2}\, \rm {\rm M}_{\odot }\, yr^{ -1}\, kpc^{-2}$|⁠ , consistent with values observed in both local star-forming and starburst galaxies. (ii) The detected clumps span a large range of characteristic sizes (⁠|$r_{e} \sim 0.1 - 1\, \rm kpc$|⁠) and stellar masses (⁠|$\sim 10^{8.0-9.5}\, \rm {\rm M}_{\odot }$|⁠). We estimate a mass–size relation (⁠|$r_{e} \propto \rm M_{\star }^{\, 0.52 \pm 0.07}$|⁠) along with a stellar mass function (slope, |$\alpha = - 1.85 \pm 0.19$|⁠), both suggesting a hierarchical nature similar to that expected in star-forming regions in local galaxies. (iii) Our measurements agree with the properties of stellar clumps in |$z\gtrsim 1$| lensed systems, bridging the gap between lensed and unlensed studies by detecting structures at sub-kpc scales. (iv) Clumps are found to be preferentially located along spiral features visible primarily in the residual rest frame near-IR images. In conclusion, we present an observation-based, coherent picture of star-forming clumps in galaxies at |$z \gt 1$|⁠. [ABSTRACT FROM AUTHOR]

The current paradigm for the co-evolution of galaxies and their supermassive black holes postulates that dust-obscured active galactic nuclei (AGNs) represent a transitional phase towards a more luminous and unobscured state. However, our understanding of dusty AGNs and their host galaxies at early cosmic times is inadequate due to observational limitations. Here, we present JWST observations of CID-931, an X-ray-detected AGN at a spectroscopic redshift of |$z_{\rm spec}=4.91$|⁠. Multiband NIRCam imaging from the COSMOS-Web program reveals an unresolved red core, similar to JWST-discovered dusty AGNs. Strikingly, the red core is surrounded by at least eight massive star-forming clumps spread over |${1{^{\prime \prime}_{.}}6} \approx 10\,\,{\rm kpc}$|⁠ , each of which has a stellar mass of |$10^9$| – |$10^{10}\, M_{\odot }$| and a radius of |$\sim$| 0.1–1 kpc. The whole system amounts to |$10^{11}\, M_{\odot }$| in stellar mass, higher than typical star-forming galaxies at the same epoch. In this system, gas inflows and/or complex merger events may trigger clump formation and AGN activity, thus leading to the rapid formation of a massive galaxy hosting a supermassive black hole. Future follow-up observations will provide new insights into the evolution of the galaxy–black hole relationship during such transitional phases in the early universe. [ABSTRACT FROM AUTHOR]

At fixed galaxy stellar mass, there is a clear observational connection between structural asymmetry and offset from the star-forming main sequence, ΔSFMS. Herein, we use the TNG50 simulation to investigate the relative roles of major mergers (stellar mass ratios μ ≥ 0.25), minor (0.1 ≤ μ < 0.25), and mini mergers (0.01 ≤ μ < 0.1) in driving this connection amongst star-forming galaxies (SFGs). We use dust radiative transfer post-processing with SKIRT to make a large, public collection of synthetic Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) images of simulated IllustrisTNG (TNG) galaxies over 0.1 ≤ z ≤ 0.7 with log (M ⋆/M⊙) ≥ 9 (∼750 k images). Using their instantaneous star formation rates (SFRs), known merger histories/forecasts, and HSC-SSP asymmetries, we show (1) that TNG50 SFGs qualitatively reproduce the observed trend between ΔSFMS and asymmetry and (2) a strikingly similar trend emerges between ΔSFMS and the time-to-coalescence for mini mergers. Controlling for redshift, stellar mass, environment, and gas fraction, we show that individual mini merger events yield small enhancements in SFRs and asymmetries that are sustained on long time-scales (at least ∼3 Gyr after coalescence, on average) – in contrast to major/minor merger remnants which peak at much greater amplitudes but are consistent with controls only ∼1 Gyr after coalescence. Integrating the boosts in SFRs and asymmetries driven by μ ≥ 0.01 mergers since z  = 0.7 in TNG50 SFGs, we show that mini mergers are responsible for (i) 55 per cent of all merger-driven star formation and (ii) 70 per cent of merger-driven asymmetric structure. Due to their relative frequency and prolonged boost time-scales, mini mergers dominate over their minor and major counterparts in driving star formation and asymmetry in SFGs. [ABSTRACT FROM AUTHOR]