Professor Andrew Bunker

Abstract:

Abstract JWST has revealed a large population of massive black holes (BHs) in the early Universe with unusual properties which mark them as distinct from low-redshift active galactic nuclei. Such findings have prompted the development of new models of BH formation and growth, and of their co-evolution with host galaxies. Linking the gas-phase metallicity of BH environments to seed masses is key to understanding which evolutionary pathways could explain the population of JWST-discovered BHs. We present new high-resolution JWST NIRSpec/IFU observations covering the rest-frame optical emission lines of a Little Red Dot (LRD) at z = 3.55, known as The Cliff, from the ‘Red Unknowns: Bright Infrared Extragalactic Survey’ (RUBIES). We find evidence for low metallicity (Z = 0.016 ± 0.003 Z⊙) based on the low narrow-line [O iii]λ5007/Hβ ratio, supported by the non-detection of low-ionisation emission lines such as [O ii]λλ3727,3729 and [N ii]λλ6548,6583. We find that the observed properties of The Cliff, including its overmassive BH, can be reproduced by some simulations of black hole growth and evolution down to z ∼ 3.5. However, such outcomes require high seed masses (104 − 105 M⊙) and appear rarely within a simulation volume comparable to the 3 < z < 4 RUBIES volume, highlighting the unusual nature of The Cliff. Future simulations and numerical models will help to uncover how such a metal-poor system managed to develop a massive black hole and persist to such low redshift.

Abstract:

Abstract We present the first spatially resolved kinematic evidence for dust in the outflows of Active Galactic Nuclei (AGN). We utilise observations from JWST with NIRSpec IFU and MIRI MRS data of 10 local Seyferts and use Principal Component Analysis (PCA) tomography to extract the kinematics of Polycyclic Aromatic Hydrocarbon (PAH) features. PAHs comprise the smallest carbonaceous dust molecules in the Interstellar Medium (ISM), and produce emission features in the infrared providing the potential to measure kinematics. This is however challenging due to their broad shapes and variations in their intrinsic profile, prompting the need for techniques such as PCA tomography. We find that the velocity of the PAHs is similar to the molecular gas as traced by the rotational transitions of H2, where for NGC 5728 and NGC 7582, both disk and outflow are present. We detect the outflow in the kinematics of large and neutral PAHs, namely the 11.3 μm and 17 μm PAH features, where after subtracting the disk, the velocity field matches that of high-ionisation potential lines such as [NeVI] (7.65 μm, IP = 158 eV). Finally, we fail to detect kinematics of the 6.2 μm PAH due to an altered intrinsic profile while the the 3.3 μm PAH kinematics purely trace the circumnuclear disk. This suggests the PAHs in the outflow are more neutral and larger than in star-forming regions, consistent with PAH band ratios in previous studies of AGN.

Abstract:

Ultracool T (Teff ≈ 500–1200 K) and Y dwarfs (Teff ⪅ 500 K) have historically been found only a few hundred parsecs from the Sun. The sensitivity and wavelength coverage of the NIRCam instrument on board the James Webb Space Telescope offer a unique method for finding low-temperature brown dwarfs in deep extragalactic datasets out to multiple kiloparsecs. Here we report on the selection of a sample of 41 brown dwarfs and brown dwarf candidates across the JWST Advanced Deep Extragalactic Survey in the GOODS-S and GOODS-N regions. We introduce a new open-source Bayesian tool, Near-Infrared Fitting for T and Y dwarfs (NIFTY), to derive effective temperatures, metallicities, and distances from JWST photometry. We find that 31 candidates have fits consistent with T dwarf temperatures out to 5–6 kpc, and 10 candidates have fits consistent with Y dwarf temperatures out to 1–2 kpc. The majority of the sources are best fit with subsolar metallicity models. We report proper motions for 10 brown dwarf candidates (three are newly presented), and calculate the number density of T and Y dwarfs as a function of temperature and distance above the Milky Way midplane. We further discuss how Y dwarfs can serve as contaminants in the search for ultra-high-redshift galaxies. Together, these results demonstrate the power of deep JWST extragalactic imaging to probe the coldest substellar populations far beyond the solar neighborhood, providing new constraints on the Milky Way’s structure and brown dwarf demographics.

Abstract:

JWST has discovered an early period of galaxy formation that was more vigorous than expected, which has challenged our understanding of the early Universe. In this work, we present the longest spectroscopic integration ever acquired by JWST/MIRI (tobs ≈ 51 hr). This spectrum covers the brightest rest-frame optical nebular emission lines for the luminous galaxy JADES-GS-z14-0 at z = 14.18. Most notably, we detect [O III]λλ4959, 5007 at ≈14σ and Hα at ≈4σ with these ultradeep observations. These lines reveal that JADES-GS-z14-0 has low dust attenuation with a recent star formation rate of SFR ≈ 8 ± 2M⊙ yr−1, star formation rate surface density of ΣSFR ≈ 20 ± 5M⊙ yr−1 kpc−2, and ionizing photon production efficiency of ξion ≈ 1025.3±0.1 Hz erg−1. Using standard strong-line diagnostics, we infer a gas-phase oxygen abundance of log10(O/H)+12≈7.5±0.2 (≈6%Z⊙), carbon-to-oxygen ratio of [C/O] ≈ −0.4 ± 0.2, ionization parameter of log10(U)≳−2.4 , and density of nH ≈ 690 ± 200 cm−3. Using detailed photoionization modeling, we instead derive log10(O/H)+12≈8.5−0.4+0.4 (≈60%Z⊙), log10(U)≈−1.4−0.4+0.3 , and nH≈540−320+520cm−3 . The inferred properties of JADES-GS-z14-0 are similar to those measured for similarly luminous galaxies at z > 10 with previous MIRI/Spectroscopy, such as GHZ2/GLASSz12, GN-z11, and MACS0647-JD1. These results suggest extreme ionization conditions and rapid metal enrichment less than 300 Myr after the Big Bang. Existing simulations are unable to reproduce the empirical and inferred properties of JADES-GS-z14-0. This work demonstrates an important step toward understanding the formation of the first stars and heavy elements in the Universe. Future work will focus on the detection of the rest-frame optical continuum and its interpretation for the stellar population properties of JADES-GS-z14-0.