Professor Andrew Bunker

Abstract:

We present the search and characterisation of ionised outflows in a sample of 15 star-forming systems at z $ and outflow velocities V_ with no evidence of active galactic nuclei (AGNs) observed with the JWST/NIRSpec instrument in Integral Field Spectroscopic mode (IFS) as part of the `Galaxy Assembly with NIRSpec IFS' (GA-NIFS) program. Some of the target systems are comprised of various individual galaxies, adding up to a total of 40 individual objects. Our sample encompasses the high mass end of the galaxy populations, with most of the sample having stellar masses within log_10 (M_⋆/M_⊙) = 9.5-11, while previous studies on high-z star formation driven outflows generally contain galaxies of log_10 (M_⋆/M_⊙)$<9.5$. Leveraging the spatially resolved information and rest-frame optical coverage provided by NIRSpec IFS data, we analysed the and ̋a emission lines to search for broad kinematic components associated with galactic outflows. Crucially, the IFS observations allowed us to directly isolate the regions hosting the outflows, rather than relying on integrated spectra. We identified signatures of ionised outflows in 16 individual galaxies/regions (in 13 out of 15 systems), although we consider two of them only as `candidates', as they could be related to mergers or tidal interactions. After constraining their spatial location and extent, we characterised the integrated properties of the outflowing gas and evaluated the impact on the host galaxies. We find that the outflowing gas is more dust attenuated (by A_ ̊m V mag on average) and metal enriched (sim0.13 dex) than the interstellar medium of the host galaxies, suggesting that outflows contribute to distributing dust and metals around them. The outflows identified in this study present velocity dispersions within σ_ ̊m out km s -1 ̊m out km s^-1. Considering also less luminous and less massive star-forming galaxies from previous works, there is a statistically significant correlation between outflow velocity (v_̊m out) and star formation rate (SFR). The generally low mass-loading factors (η= _ ̊m M ̊m out /SFR $<1, in nine out of 14 outflows) obtained for the ionised outflows suggest that they do not suppress star formation in the host galaxies. Moreover, their velocities are not high enough to escape their hosts and reach the circumgalactic medium. Our results indicate that ejective feedback through ionised outflows is inefficient in high-mass and luminous star-forming galaxies within the first 2 Gyr of cosmic time.

Abstract:

Massive quenched galaxies at z>3 challenge models of early galaxy evolution, as their rapid formation and abrupt quenching require efficient feedback, which is often linked to active galactic nuclei (AGNs). The quiescent galaxy at z=3.064 is a key example of this population. Previous JWST/NIRSpec integral field unit (IFU) observations revealed an AGN-driven outflow and uncovered a compact pair of AGNs separated by sim5 kpc. In addition, VLT/MUSE spectroscopy identified a third AGN candidate at a projected distance of sim30 kpc, associated with a luminous łya emitter (LAE2) characterised by high-ionisation UV lines, although rest-frame optical diagnostics were not previously available. We aim to confirm the nature of LAE2 using rest-frame optical diagnostics enabled by new JWST observations, and to characterise the physical and ionisation properties of both LAE2 and a distinct nearby łya emitter (LAE1) that lacks any detectable continuum counterpart. Through this analysis, we investigated the interplay among low-mass satellites, black-hole growth, and the ionised environment of a quenched massive galaxy at high redshift. We analysed new JWST/NIRSpec IFU observations targeting the optical nebular lines of LAE1 and LAE2, including and ∋i, complemented with VLT/MUSE IFU spectroscopy, as part of the GA-NIFS project. We extracted integrated and spatially resolved spectra, constructed emission-line maps, and used standard diagnostic diagrams to determine ionisation sources and kinematics. LAE2 exhibits rest-frame UV–optical-line ratios fully consistent with an embedded AGN. Its and emission displays a clumpy morphology and irregular, non-rotating kinematics on sub-kiloparsec scales. Except for łya, LAE1 remains undetected in all nebular lines and in JWST imaging; its łya emission is broad (σ ∼ 200 ̨ms) and asymmetric. The similarity of the LAE1 and LAE2 łya profiles in both velocity and flux suggests that LAE1 traces resonantly scattered emission powered by LAE2 rather than in situ star formation (although the latter cannot be completely ruled out). Our analysis reveals that the environment of contains both multi-black-hole activity and gas structures on tens-of-kiloparsec scales, offering new insights into how feedback, accretion, and satellite interactions influence the late evolutionary stages of quenched massive galaxies.

Abstract:

The ultraviolet (UV) continuum slope of galaxies, , is a powerful diagnostic of the metallicity and ages of stars, nebular gas properties, dust content, and the escape of Lyman continuum (LyC) photons. In this study, we present measurements for 395 spectroscopically confirmed galaxies at selected primarily from JADES, using high-quality JWST (James Webb Space Telescope) NIRSpec/PRISM spectra. We find a median , finding a mild increase in blueness of with increasing redshift and fainter UV magnitudes. Interestingly, we find evidence for reddening of the average at , deviating from the trend observed at . Using stacked spectra in bins of redshift and , we derive trends between and dust attenuation, metallicity, ionization parameter, and stellar age indicators, finding a lack of dust attenuation to be the dominant driver of bluer -values. We further report five galaxies with , which show a range of spectroscopic properties and signs of significant LyC photon leakage. Finally, we show that the redder -values at may require rapid build-up of dust reservoirs in the very early Universe or a significant contribution from the nebular continuum emission to the observed UV spectra, with the nebular continuum fraction depending on the gas temperatures and densities. We show that in the absence of dust, nebular emission at cm can reproduce the range of red that we see in our sample. Higher gas densities can also redden the nebular continuum emission, potentially explaining the observed -values.

Abstract:

We present James Web Space Telescope/NIRSpec dense-shutter spectroscopy (DSS). This novel observing strategy with the NIRSpec/multi-shutter assembly (MSA) deliberately permits a high number of controlled spectral overlaps to reach extreme multiplex while retaining the low background of slit spectroscopy. In a single configuration over the JADES Origins Field, we opened shutters on all faint ( mag) candidates, prioritizing emission-line science and rejecting only bright continuum sources. Using 33.6 and 35.8 ks on-source in G235M and G395M, we observed a single mask with 850 sources, obtaining spectroscopic redshifts for 540 galaxies over . The per-configuration target density in DSS mode is 4–5 higher than standard no- and low-overlap MSA strategies (<200 sources), with no loss in redshift precision or accuracy. Line-flux sensitivities are 30 per cent lower at fixed exposure time, matching the expected increase in background noise, but the gain in survey speed is 5 in our setup, more than justifying the penalty. The measured line sensitivity exceeds NIRCam slitless spectroscopy by at least ( in exposure time) at , demonstrating that DSS is a compelling method to gain deep, wide-band spectra for large samples. Crucially, NIRSpec/MSA could deliver even higher target allocation densities than those used here. We derive H α-based star-formation rates, gas-phase metallicities (including a large sample suitable for strong-line calibrations), and identify rare mini-quenched galaxies and broad-line AGN. DSS is immediately applicable wherever deep imaging enables robust pre-selection and astrometry, providing an efficient method to obtain large samples of faint emission-line galaxies, a compelling middle ground between the completeness of slitless surveys and the sensitivity and bandwidth of NIRSpec/MSA.

Abstract:

Transient astronomy of the early, high-redshift (z > 3) Universe is an unexplored regime that offers the possibility of probing the first stars and the epoch of reionization. During Cycles 1 and 2 of the James Webb Space Telescope (JWST), the JWST Advanced Deep Extragalactic Survey program enabled one of the first searches for transients in deep images (∼30 AB mag) over a relatively wide area (25 arcmin2). One transient, AT 2023adsv, was discovered with an F200W magnitude of 28.04 AB mag, and subsequent JWST observations revealed that the transient is a likely supernova (SN) in a host with zspec = 3.613 ± 0.001 and an inferred metallicity at the position of the SN of Z* = 0.3 ± 0.1 Z⊙. At this redshift, the first detections in F115W and F150W show that AT 2023adsv had bright rest-frame UV flux at the time of discovery. The multiband light curve of AT 2023adsv is best matched by a template of a Type IIP SN (SN IIP) with a peak absolute magnitude of MB ≈ −18.3 AB mag. We find a good match to a 20 M⊙ red supergiant progenitor star with an explosion energy of 2 × 1051 erg, likely higher than normally observed in the local Universe, but consistent with SNe IIP drawn from local, lower-metallicity environments. AT 2023adsv is the most distant photometrically classified SN IIP yet discovered with a spectroscopic redshift measurement, and may represent a global shift in SN IIP properties as a function of redshift.