Professor Andrew Bunker

Abstract:

James Webb Space Telescope (JWST) has revealed a population of ‘Little Red Dots’ (LRDs): compact, red objects at redshifts with ‘v’-shaped spectral energy distributions, broad permitted lines, and, often, hydrogen Balmer absorption. We use NIRSpec/IFS data from the BlackTHUNDER survey to study the H α line in the LRD Abell2744-QSO1 at , which is a confirmed active galactic nucleus (AGN) due to time-variable equivalent width (EW) in its broad emission lines. The H α spectral profile is non-Gaussian, requiring at least two Gaussian components. We also detect a narrow-line Gaussian component, and strong H α absorption (EW relative to the continuum ), confirming a connection between the strong Balmer break and line absorption. The absorber is at rest with respect to broad H α , suggesting that the gas cannot be interpreted as an inflow or outflow, forming instead a long-lived structure. Its velocity dispersion is , consistent with the value inferred from the analysis of the Balmer break. Based on H α , we infer a black hole mass of , smaller but close to the previous estimates based on H β . The Eddington ratio is 0.09. Combining the high signal-to-noise ratio of the narrow H α line with the spectral resolution of the G395H grating, we infer a narrow-line intrinsic dispersion , which places a stringent constraint on the black hole-to-dynamical mass ratio of this system to be , confirming the overmassive nature of the black hole and potentially leaving little room for a host galaxy.

Abstract:

We present JWST/NIRSpec IFU observations of the galaxy system B14-65666, as part of the GA-NIFS survey. Line and continuum emission in this massive system () is resolved into two strong cores surrounded by diffuse emission, as seen in recent JWST/NIRCam imaging. Our data set contains detections of [O ii], [Ne iii], Balmer lines, [O iii], He i, and weak [O iii]. Each spectrum is fit with a model that consistently incorporates interstellar medium conditions (i.e. electron temperature, , electron density, , and colour excess, ). The resulting line fluxes are used to constrain the gas-phase metallicity ( solar) and H-based star formation rate for each region. Common line ratio diagrams (O32–R23, R3–R2, Ne3O2–R23) reveal that each line-emitting region lies at the intersection of low- and high-redshift galaxies, suggesting low ionization and higher metallicity compared to the predominantly lower-mass galaxies studied with the JWST/NIRSpec IFU so far at . Spaxel-by-spaxel fits reveal evidence for both narrow (FWHM km s) and broad (FWHM km s) line emission, the latter of which likely represents tidal interaction or outflows. Comparison to ALMA [C ii]158m and [O iii]88 m data shows a similar velocity structure, and we explore optical-far infrared diagnostics. The two core galaxies both lie on the mass-metallicity relation at , but show contrasting properties (e.g. , ), suggesting distinct evolutionary pathways. Combining the NIRSpec IFU and ALMA data sets, our analysis opens new windows into the merging system B14-65666.

Abstract:

Abstract JWST uncovered a large number of massive quiescent galaxies (MQGs) at z > 3, which theoretical models struggle to reproduce. Explaining the number density of such objects requires extremely high conversion efficiency of baryons into stars in early dark matter halos. Using stellar kinematics, we can investigate the processes shaping the mass assembly histories of MQGs. We present high-resolution JWST/NIRSpec integral field spectroscopy of GS-9209, a massive, compact quiescent galaxy at z = 4.66 (log (M*/M⊙) = 10.52 ± 0.06, Reff = 220 ± 20 pc). Full spectral fitting of the spatially resolved stellar continuum reveals a clear rotational pattern, yielding a spin parameter of $\lambda _{2R_{\rm eff}} = 0.85 \pm 0.10$. This study suggests that at least a fraction of the earliest quiescent galaxies were fast rotators and that quenching was a dynamically gentle process, preserving the stellar disc even in highly compact objects. Using Jeans anisotropic modelling and assuming a NFW profile, we measure a dark matter fraction of $f_{\rm DM} \left(<2 R_{\rm eff} \right) = 14.5^{+6.0}_{-4.2} \%$. Our findings use stellar kinematics to confirm the massive nature of early quiescent galaxies, previously inferred from stellar population modelling. We suggest that GS-9209 has a similar structure to low-redshift ‘relic’ galaxies. However, unlike relic galaxies which have bottom-heavy initial mass functions (IMF), the dynamically inferred stellar mass-to-light ratio of GS-9209 is consistent with a Milky-Way like IMF. The kinematical properties of GS-9209 are different from those of z < 1 early-type galaxies and more similar to those of recently quenched post-starburst galaxies at z > 2.