Emma Curtis-Lake

The active galactic nuclei (AGN) uncovered by JWST in the early Universe are highly abundant and seemingly overmassive with respect to local scaling relations, challenging standard models of black hole formation and growth. Yet it remains unclear whether they trace an efficient early growth channel, represent the observable tail of a broader population, or reflect systematic uncertainties in mass estimates. We introduce the aesopica project, a suite of twelve mid-volume (L = 60 cMpc) cosmological simulations based on the fable galaxy formation model, varying the black hole seed mass across the theoretical formation channels (Mseed = 102–105 M⊙), the accretion efficiency, including super-Eddington bursts, and the supernova feedback strength. We forward-model observational selection with balmersopica, a mock JWST broad-line survey pipeline that assesses the detectability of each simulated AGN for a given grating and exposure time. We find that the bulk of the JWST AGN population can be assembled from any seed mass provided the accretion efficiency is high, although light seeds require the most favourable accretion conditions explored. Applying broad-line selection naturally recovers the apparently overmassive population, with the detected AGN lying furthest above the intrinsic MBH–Mstellar relation for inefficient accretion models. The selected AGN lie on the local, weakly evolving MBH–σstellar relation, supporting a scenario where black holes assemble before the stellar component is fully established. Since efficient accretion rapidly erases the imprint of the initial seed mass, the low-mass end of the black hole mass function and host gas-phase metallicities offer the most promising discriminants between seeding channels.

We present the star formation and dust content properties for a sample of 646 galaxies at redshifts 3 < z < 7 as part of the JADES survey. Our analysis is based on measurements of the H α /H β Balmer decrement using medium resolution ( R ∼ 1000) spectroscopic observations with the JWST/NIRSpec microshutter assembly. Stellar masses and star formation rates (SFRs) are inferred with Prospector using deep multiband imaging. We utilize the Balmer decrement to measure dust-corrected H α -based SFRs, taking into account the subsolar metallicities observed in galaxies at high redshift. We confirm, with our large sample size, that the correlation between the Balmer decrement and stellar mass is already established out to z ∼ 7. We find that the relation between the Balmer decrement and stellar mass does not significantly evolve from the local Universe to z ∼ 7. We investigate the UV slope as a function of the Balmer optical depth and find that the best-fit correlation for our high redshift sample is specific SFR (sSFR) dependent and significantly different at high redshift when compared to galaxies at z ≈ 0 and z ≈ 2. For the highest sSFR galaxies in our sample, there is no significant correlation between the UV slope and Balmer optical depth. This is evidence that the UV slope should be used with great caution to correct for dust in high redshift galaxies.

GHZ2 is among the highest-redshift galaxies discovered to date, exhibiting a spectrum rich with prominent emission lines in the rest-frame ultraviolet (UV) and optical. These features raise critical questions about the mechanism powering this nebular emission, in particular the extremely strong C iv λ 1548+1551 emission (rest-frame equivalent width of 45 Å). Here we aim to quantify the active galactic nucleus (AGN) contribution within this system using the BEAGLE -AGN tool to simultaneously fit the spectrum and photometry of GHZ2. We consider a range of models with and without AGN components, allowing us to disentangle the stellar and AGN contribution of GHZ2 for the first time simultaneously using all observed emission lines. We conclude that a partial contribution by an AGN is significantly favored based on χ ² comparisons between models with and without an AGN component, measuring an AGN contribution of 97 − 2 + 1 %, and 64 − 12 + 23 % for the C IV λ 1548+1551 and C III ] λ 1908 emission lines, respectively. We estimate the black hole mass using the accretion luminosity ( L _acc ) from the best-fit BEAGLE -AGN model, inferring a value of log ₁₀ ( M _BH / M _⊙ ) = 7.19 − 0.03 + 0.03 , assuming an Eddington ratio of η = 0.5 (with a much larger systematic uncertainty of ∼1 dex). The inferred black hole mass to stellar mass ratio is 0.06 − 0.02 + 0.02 (statistically), consistent with other high-redshift AGN systems. If the black hole interpretation is confirmed, GHZ2 would represent the most distant black hole identified to date, making it an ideal laboratory to study AGN growth and their role in shaping high-redshift galactic evolution.

Post-starburst (PSB) galaxies, having recently experienced a starburst followed by rapid quenching, are excellent laboratories to probe physical mechanisms that drive starbursts and shutting down of star formation. Integral-field spectroscopy reveals the galaxies’ spatially resolved properties, where observed directional patterns can be linked to the galaxies’ past evolution. We measure the resolved star formation histories, stellar metallicity evolution, and dust properties of three local PSBs from the MaNGA survey, down to 0.5 arcsec resolution ($\sim 0.3\,$kpc) using a hierarchical Bayesian model. Local parameters were constrained simultaneously with parameters describing spatial trends. We found that all three galaxies first experienced an outer, weaker, and slower quenching starburst, followed by a central, stronger and faster quenching starburst that peaked $\sim 1\,$Gyr after the first. The central starbursts induced a significantly stronger rise in stellar metallicity compared to the outer starbursts. These results are consistent with the effects of a recent gas-rich (wet) merger, where the first pericentre passage triggered starbursts in the outer regions, while the later coalescence triggers a stronger centralized starburst. We find non-axisymmetric features in the maps of burst mass fraction and dust attenuation in all galaxies, which could be caused by tidal effects during the recent merger. Comparisons with literature binary merger simulations suggest that the galaxies’ rapid quenching was driven by gas consumption and the stabilization against gas gravitational collapse by a growing spheroid, while AGN feedback was not necessarily a primary cause.

Our understanding of the physical properties of star-forming galaxies during the Epoch of Reionization (EoR; at z > 6) suffers from degeneracies among the apparent properties of the stars, nebular gas, and dust. These degeneracies are most prominent with photometry, which has insufficient (1) spectral resolution and (2) rest-frame spectral coverage. We explore ways to break these degeneracies with a sample of N = 22 high-redshift star-forming galaxies at 7 < z _phot ≤ 9, using some of the deepest existing imaging from JWST/NIRCam and JWST/MIRI with JADES. Key to this study is the imaging from JWST/MIRI at 7.7 μ m, which provides coverage of the rest-frame I band at the observed redshifts. We infer stellar population properties and rest-frame colors using a variety of filter sets and star formation history (SFH) assumptions to explore the impact of these choices. Evaluating these quantities both with and without the 7.7 μ m data point shows that dense spectral coverage with JWST/NIRCam (eight or more filters, including at least one medium-band at λ _obs ≈ 4–5 μ m) can compensate for lacking the rest-frame I -band coverage for the vast majority (≈80%) of our sample. Furthermore, these galaxy properties are most consistently determined by assuming the delayed-tau SFH, which provides the smallest offsets and scatters around these offsets when including JWST/MIRI. Within extragalactic surveys like JADES and CEERS, our findings suggest that robust characterization of the stellar population properties and rest-frame colors for typical high-redshift star-forming galaxies (i.e., galaxies with M _UV ≈ −20 and β _UV ≈ −2) is possible with JWST/NIRCam alone at z ≈ 8.