Professor Andrew Bunker

Abstract:

We present gas-phase abundances of carbon (C), -elements (O, Ne, Si, and Ar), and iron (Fe) obtained from stacked spectra of high-z star-forming galaxies with the deep Near Infrared Spectrograph medium-resolution data from the James Webb Space Telescope Advanced Deep Extragalactic Survey. Our 564 sources at –7 have a median stellar mass of and a median star-formation rate of , placing them close to the star-formation main sequence. We find that the stacked spectrum of all our 564 sources has relatively low , moderate , and low values at a low gas-phase metallicity of (), suggesting dominant yields of core-collapse supernovae evolved from massive stars. The detection of a weak [Si iii] emission line in our stacked spectrum provides a silicon-to-oxygen abundance ratio of , which is lower than that of stars in the Milky Way disc and lower than expected by chemical evolution models, suggesting silicon depletion on to dust grains. Likewise, this Si/O value is lower than that we newly derive for two individual galaxies (GN-z11 and RXCJ2248) with negligible dust attenuation. By performing spectral stacking in bins of , star-formation rate (SFR), specific SFR (sSFR), and ultraviolet continuum slope , we identify [Fe iii] line detections in the high-sSFR bin and the blue- bin, both of which exhibit supersolar Fe/O ratios, while their C/O, Ar/O, and Si/O ratios are comparable to those of the all-sources stack. Our findings support a chemically young gas composition with rapid dust depletion in the general population of high-z star-forming galaxies, while raising the possibility of anomalous, selective Fe/O enhancement at the very early epoch of star formation.

Abstract:

James Webb Space Telescope (JWST)/NIRCam slitless spectroscopy enables dynamical mass measurements for typical star-forming galaxies only a billion years after the big bang. We model the H morpho-kinematics of 163 galaxies at redshift –6 from FRESCO and CONGRESS (with JADES imaging), using the geko code, and infer rotational velocities and dispersions within . Our sample spans –10 and –11. Gas masses are inferred from empirical scaling relations and combined with stellar masses to yield baryonic masses. The resulting median inferred gas-to-baryonic mass fraction is . Using these baryonic masses together with the dynamical masses, we derive dark-matter fractions within the H half-light radius, and find a high median value of , where is defined relative to the total (DM + baryonic) mass. About two-thirds of systems are DM-dominated within –1 kpc. We find that decreases with stellar mass, consistent with predictions from simulations. The stellar Tully–Fisher relation shows a tentative offset to higher at fixed and substantial intrinsic scatter, suggesting that the relation is only beginning to emerge at . We measure a negative correlation between and baryonic surface density , weaker but broadly consistent with trends at cosmic noon and at . Qualitatively comparing with modified NFW profiles coupled to an empirical stellar-to-halo mass relation suggests that the lowest () require cored inner DM profiles, while the highest fractions favour cuspier profiles, potentially reflecting adiabatic contraction. Overall, the elevated and at are compatible with progenitors of baryon-dominated systems at and naturally anticipate overmassive black holes at fixed .

Abstract:

The depth and coverage of the first years of James Webb Space Telescope observations have revealed low-luminosity active galactic nuclei (AGN) across a wide redshift range, shedding light on black hole (BH) assembly and feedback. We present our spectroscopic sample of 34 Type 1 AGN obtained from JADES survey data and spanning . Our sample of AGN probes a BH mass range of M at bolometric luminosities down to erg s. Most of these AGN are hosted in low-mass ( M) galaxies and are overmassive relative to the local relation, while remaining consistent with the local – relation. The wide redshift range provided by our sample allows us to trace the emergence of local – scaling relation across cosmic time. Additionally, we explore the capability of narrow-line diagnostics in identifying Type 2 AGN and find that a significant fraction of our AGN would be missed by them due to low metallicity or lack of high-energy ionizing photons. We explore the UV luminosity function of AGN and their hosts and find that it is subject to significant cosmic variance and is also dependent on the AGN bolometric luminosity. Finally, we show that the electron scattering scenario recently proposed to explain broad Balmer lines is untenable on multiple grounds showing that there is no evidence of significant BH mass overestimation.