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In a novel approach employing implicit likelihood inference (ILI), also known as likelihood-free inference, we calibrate the parameters of cosmological hydrodynamic simulations against observations, which has previously been unfeasible due to the high computational cost of these simulations. For computational efficiency, we train neural networks as emulators on ∼1000 cosmological simulations from the CAMELS project to estimate simulated observables, taking as input the cosmological and astrophysical parameters, and use these emulators as surrogates for the cosmological simulations. Using the cosmic star formation rate density (SFRD) and, separately, the stellar mass functions (SMFs) at different redshifts, we perform ILI on selected cosmological and astrophysical parameters (Ω_m,σ₈, stellar wind feedback, and kinetic black hole feedback) and obtain full six-dimensional posterior distributions. In the performance test, the ILI from the emulated SFRD (SMFs) can recover the target observables with a relative error of 0.17% (0.4%). We find that degeneracies exist between the parameters inferred from the emulated SFRD, confirmed with new full cosmological simulations. We also find that the SMFs can break the degeneracy in the SFRD, which indicates that the SMFs provide complementary constraints for the parameters. Further, we find that a parameter combination inferred from an observationally inferred SFRD reproducesmore »the target observed SFRD very well, whereas, in the case of the SMFs, the inferred and observed SMFs show significant discrepancies that indicate potential limitations of the current galaxy formation modeling and calibration framework, and/or systematic differences and inconsistencies between observations of the SMFs.

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We present the results of high-resolution adaptive optics imaging observations of four kinematically identified recoiling supermassive black hole (rSMBH) candidates. Ellipse fitting was carried out to measure the spatial offset between the active galactic nucleus (AGN) and the centre of the host galaxy. Two rSMBH candidates (J1713 + 3523 and J2054 + 0049) are found to be offset AGN. However, the Very Long Baseline Array 1.5 GHz continuum imaging observation and spectral decomposition of the [O iii]5007 line suggest that J1713 + 3523 is a dual AGN and its spatial offset is not due to a recoil event. The spatial offset between the AGN and the centre of the host galaxy in J2054 + 0049 is 0.06 ± 0.01 arcsec (201 ± 22 pc). Spectral decomposition of J2054 + 0049 also suggests that it could be a dual AGN system and the measured spatial offset may not be due to a recoil event.

We present the statistical redshift distribution of a large sample of low-surface-brightness (LSB) galaxies identified in the first 200 deg²of the Hyper Suprime-Cam Strategic Survey Program. Through cross-correlation with the NASA–SDSS Atlas, we find that the majority of objects lie withinz< 0.15 or ∼500 Mpc, yielding a mass range ofM_*≈ 10⁷−10⁹M_⊙and a size range ofr_eff,g≈ 1−8 kpc. We find a peak in the distance distribution within 100 Mpc, corresponding mostly to ∼10⁷M_⊙galaxies that fall on the known mass–size relation. There is also a tail in the redshift distribution out toz≈ 0.15, comprising more massive (M_*= 10⁸− 10⁹M_⊙) galaxies at the larger end of our size range. We see tentative evidence that at the higher-mass end (M_*> 10⁸M_⊙), the LSB galaxies do not form a smooth extension of the mass–size relation of higher-surface-brightness galaxies, perhaps suggesting that the LSB galaxy population is distinct in its formation path.

ABSTRACT We report the formation of bound star clusters in a sample of high-resolution cosmological zoom-in simulations of z ≥ 5 galaxies from the Feedback In Realistic Environments project. We find that bound clusters preferentially form in high-pressure clouds with gas surface densities over $10^4\, \mathrm{ M}_{\odot }\, {\rm pc}^{-2}$, where the cloud-scale star formation efficiency is near unity and young stars born in these regions are gravitationally bound at birth. These high-pressure clouds are compressed by feedback-driven winds and/or collisions of smaller clouds/gas streams in highly gas-rich, turbulent environments. The newly formed clusters follow a power-law mass function of dN/dM ∼ M−2. The cluster formation efficiency is similar across galaxies with stellar masses of ∼107–$10^{10}\, \mathrm{ M}_{\odot }$ at z ≥ 5. The age spread of cluster stars is typically a few Myr and increases with cluster mass. The metallicity dispersion of cluster members is ∼0.08 dex in $\rm [Z/H]$ and does not depend on cluster mass significantly. Our findings support the scenario that present-day old globular clusters (GCs) were formed during relatively normal star formation in high-redshift galaxies. Simulations with a stricter/looser star formation model form a factor of a few more/fewer bound clusters per stellar mass formed, whilemore »the shape of the mass function is unchanged. Simulations with a lower local star formation efficiency form more stars in bound clusters. The simulated clusters are larger than observed GCs due to finite resolution. Our simulations are among the first cosmological simulations that form bound clusters self-consistently in a wide range of high-redshift galaxies.« less