Professor Andrew Bunker

Abstract:

Abstract We present JWST/NIRSpec IFU observations of the z = 7.152 galaxy system B14-65666, as part of the GA-NIFS survey. Line and continuum emission in this massive system (log10(M*/M⊙) = 9.8 ± 0.2) is resolved into two strong cores surrounded by diffuse emission, as seen in recent JWST/NIRCam imaging. Our dataset contains detections of [OII]λλ3726, 3729, [NeIII]λλ3869, 3968, Balmer lines, [OIII]λλ4959, 5007, HeIλ5875, and weak [OIII]λ4363. Each spectrum is fit with a model that consistently incorporates interstellar medium conditions (i.e., electron temperature, Te, electron density, ne, and colour excess, E(B − V)). The resulting line fluxes are used to constrain the gas-phase metallicity (Zg ~ 0.2 − 0.3 solar) and Hβ-based SFR 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 ionisation and higher metallicity compared to the predominantly lower-mass galaxies studied with the JWST/NIRSpec IFU so far at z > 5.5. Spaxel-by-spaxel fits reveal evidence for both narrow (FWHM <400 km s−1) and broad (FWHM >500 km s−1) line emission, the latter of which likely represents tidal interaction or outflows. Comparison to ALMA [C II]158μm and [O III]88μm 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 z > 4, but show contrasting properties (e.g., M*, Zg), suggesting distinct evolutionary pathways. Combining the NIRSpec IFU and ALMA datasets, our analysis opens new windows into the merging system B14-65666.

Abstract:

We present new MIRI F560W, F770W, and F1000W imaging of the galaxy GN-z11 at a redshift of 10.603. We report a significant detection (14 σ ) in the F560W and F770W images, and a marginal detection (3.2 σ ) in the F1000W filter. The new MIRI observations cover the optical-red spectral range and significantly extend previous NIRCam wavelength coverage from rest-frame 0.38 μm up to 0.86 μm. In this work, we analyse the spectral energy distribution (SED) combining this new MIRI imaging data with archival NIRSpec/Prism and MRS spectroscopy, and NIRCam imaging, i.e. covering the rest-frame 0.12–0.86 μm. New constraints such as the equivalent widths of the strong optical lines ([O  III ] λ 5008, H β and H α ) and the continuum emission at rest-frame 0.48 μm, 0.66 μm, and 0.86 μm, free of emission line contributions, are presented. The continuum emission shows a flat energy distribution, in f ν , up to 0.5 μm, compatible with the presence of a mixed stellar population of young (4 ± 1 Myr) and mature (63 ± 23 Myr) stars that also account for the [O  III ], H β , and H α emission lines. The continuum at rest-frame 0.66 μm shows a 36 ± 3% flux excess above the predicted flux for a mixed stellar population, pointing to the presence of an additional source contributing at these wavelengths. This excess increases to 91 ± 28% at rest-frame 0.86 μm, although with a large uncertainty due to the marginal detection in the F1000W filter. We consider that hot dust emission in the dusty torus around a type 2 active galactic nucleus (AGN) could be responsible for the observed excess. Alternatively, this excess could be due to hot dust emission or a photoluminiscence dust process (Extended Red Emission, ERE) under the extreme UV radiation field, as is observed in local metal-poor galaxies and in young compact starbursts. The presence of a type 1 AGN is not supported by the observed SED as the hot dust emission in luminous high- z quasi-stellar objects (QSOs) contributes at wavelengths above rest-frame 1 μm, and an additional ad hoc red source would be required to explain the observed flux excess at 0.66 and 0.86 μm. Additional deep MIRI imaging covering the rest-frame near-IR is needed to confirm the flux detection at 10 μm, and to discriminate between the different hot dust emission in the extreme starburst and AGN scenarios.

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.

Abstract:

Abstract Low surface brightness galaxies (LSBs) are an important class of galaxies that allow us to broaden our understanding of galaxy formation and test various cosmological models. We present a survey of low surface brightness galaxies at 0.4 < zphot < 0.8 in the GOODS-S field using JADES data. We model LSB surface brightness profiles, identifying those with $\bar{\mu }_{\rm eff} > 24$ mag arcsec−2 in the F200W JWST/NIRCam filter. We study the spatial distribution, number density, Sérsic profile parameters, and rest-frame colours of these LSBs. We compare the photometrically-derived star formation histories, mass-weighted ages, and dust attenuations of these galaxies with a high surface brightness (HSB) sample at similar redshift and a lower redshift (zphot < 0.4) LSB sample, all of which have stellar masses ≲ 108M⊙. We find that all samples have low star formation (SFR100 ≲ 0.01 M⊙ yr−1). The higher redshift LSBs and HSBs have similar star formation histories which show that the LSBs and HSBs possibly come from the same progenitors at z ≳ 2, though the histories are not well constrained for the LSB samples. The LSBs appear to have minimal dust, with most of our LSB samples showing AV < 1 mag. JWST has pushed our understanding of LSBs beyond the local Universe.