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1. What causes the formation of discs and end of bursty star formation?

   https://doi.org/10.1093/mnras/stad1902  

   Hopkins, Philip_F; Gurvich, Alexander_B; Shen, Xuejian; Hafen, Zachary; Grudić, Michael_Y; Kurinchi-Vendhan, Shalini; Hayward, Christopher_C; Jiang, Fangzhou; Orr, Matthew_E; Wetzel, Andrew; et al (June 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT As they grow, galaxies can transition from irregular/spheroidal with ‘bursty’ star formation histories (SFHs), to discy with smooth SFHs. But even in simulations, the direct physical cause of such transitions remains unclear. We therefore explore this in a large suite of numerical experiments re-running portions of cosmological simulations with widely varied physics, further validated with existing FIRE simulations. We show that gas supply, cooling/thermodynamics, star formation model, Toomre scale, galaxy dynamical times, and feedback properties do not have a direct causal effect on these transitions. Rather, both the formation of discs and cessation of bursty star formation are driven by the gravitational potential, but in different ways. Disc formation is promoted when the mass profile becomes sufficiently centrally concentrated in shape (relative to circularization radii): we show that this provides a well-defined dynamical centre, ceases to support the global ‘breathing modes’ that can persist indefinitely in less-concentrated profiles and efficiently destroy discs, promotes orbit mixing to form a coherent angular momentum, and stabilizes the disc. Smooth SF is promoted by the potential or escape velocity Vesc (not circular velocity Vc) becoming sufficiently large at the radii of star formation that cool, mass-loaded (momentum-conserving) outflows are trapped/confined near the galaxy, as opposed to escaping after bursts. We discuss the detailed physics, how these conditions arise in cosmological contexts, their relation to other correlated phenomena (e.g. inner halo virialization, vertical disc ‘settling’), and observations. 

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2. Biological formation of ethylene

   https://doi.org/10.1039/D3CB00066D  

   Hausinger, Robert P.; Rifayee, Simahudeen Bathir; Thomas, Midhun G.; Chatterjee, Shramana; Hu, Jian; Christov, Christo Z. (August 2023, RSC Chemical Biology)

   Ethylene formation by the ethylene-forming enzyme (EFE) and 1-aminocyclopropane-1-carboxylate oxidase (ACCO). 

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3. Stacked Star Formation Rate Profiles of Bursty Galaxies Exhibit “Coherent” Star Formation

   https://doi.org/10.3847/2041-8213/aa8f93  

   Orr, Matthew E.; Hayward, Christopher C.; Nelson, Erica J.; Hopkins, Philip F.; Faucher-Giguère, Claude-André; Kereš, Dušan; Chan, T. K.; Schmitz, Denise M.; Miller, Tim B. (November 2017, The Astrophysical Journal)
4. Star formation beyond galaxies: widespread in-situ formation of intra-cluster stars

   https://doi.org/10.33232/001c.127132  

   Ahvazi, Niusha; Sales, Laura V; Navarro, Julio F; Benson, Andrew; Boselli, Alessandro; D'Souza, Richard (January 2024, The Open Journal of Astrophysics)

   We study the fraction of the intra-cluster light (ICL) formed in-situ in the three most massive clusters of the TNG50 simulation, with virial masses $\sim {10}^{14}$. We find that a significant fraction of ICL stars ( $8\%$- $28\%$) are born in-situ. This amounts to a total stellar mass comparable to the central galaxy itself. Contrary to simple expectations, only a sub-dominant fraction of these in-situ ICL stars are born in the central regions and later re-distributed to more energetic orbits during mergers. Instead, many in-situ ICL stars form directly hundreds of kiloparsecs away from the central galaxy, in clouds condensing out of the circum-cluster medium. The simulations predict a present-date diffuse star formation rate of $$1 ${\mathrm{M}}_{\odot }$/yr, with higher rates at higher redshifts. The diffuse star forming component of the ICL is filamentary in nature, extends for hundreds of kiloparsecs and traces the distribution of neutral gas in the cluster host halo. We discuss briefly how numerical details of the baryonic treatment in the simulation, in particular the density threshold for star formation and the equation of state, may play a role in this result. We conclude that a sensitivity of $1.6\times {10}^{-19}-2.6\times {10}^{-18}$erg s ${}^{-1}$cm ${}^{-2}$arcsec ${}^{-2}$in H ${}_{\alpha }$flux (beyond current observational capabilities) would be necessary to detect this diffuse star-forming component in galaxy clusters. 

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5. Cosmological simulations of galaxy formation

   https://doi.org/10.1038/s42254-019-0127-2  

   Vogelsberger, Mark; Marinacci, Federico; Torrey, Paul; Puchwein, Ewald (January 2020, Nature Reviews Physics)