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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:

The interplay between atomic gas and the star formation history (SFH) of a galaxy are intrinsically linked, and we need to decouple these dependencies to understand their role in galaxy formation and evolution. In this paper, we analyse the SFH of 203 galaxies from the MIGHTEE-H i Survey Early Science Release data, cross-matched to with multiwavelength photometry across the COSMOS and XMM-LSS fields. We focus on the relationships between H i properties and star formation, with a sample which primarily traces gas-rich, star-forming systems at low redshift, extending to low stellar masses and probing regimes that are difficult to access with optically selected samples. A strong correlation emerges between a galaxy’s H i-to-stellar mass ratio and the time of formation, alongside an inverse correlation between stellar mass and time of formation, regardless of the inferred SFH. Additionally, galaxies with lower stellar masses and higher H i-to-stellar mass ratios exhibit longer gas depletion times compared to more massive galaxies, which appear to have depleted their gas and formed stars more efficiently. This suggests that smaller, gas-rich galaxies have higher depletion times due to shallower potential wells and less efficient star formation. Within this H i-selected sample, the efficiency of star formation is regulated primarily by stellar mass and gas fraction, with low-mass galaxies retaining extended atomic reservoirs due to inefficient conversion of H i into stars.

Abstract:

Abstract Disc winds from active galactic nuclei (AGN) can be launched by radiation pressure acting on spectral lines. However, launching a line-driven wind in the X-ray rich environment of AGN is challenging, as the wind easily gets over-ionized. Previous simulations suggested that X-ray self-shielding could enable line driving, though it remained unclear whether this relied on simplified treatments of radiation and ionization. Here, we revisit the X-ray shielding scenario using the first multi-frequency, multi-directional Monte-Carlo radiative photo-ionization hydrodynamical simulations of AGN line-driven winds. We find that sustaining a steady wind with mass-loss rates of ≈20% of the accretion rate requires an unrealistically weak X-ray flux (αOX < −3). For stronger X-ray emission (−3 < αOX < −1), self-shielding is only transient, leading to episodic ejections with mass-loss rates approaching the accretion rate. Our steady winds naturally produce FeLoBAL, HiBAL, and broad emission line signatures, depending on the disc spectral energy distribution and the observer’s inclination. At moderate X-ray luminosities (αOX ∼ −3), transient winds can generate short-lived BAL and ultra-fast outflow (UFO) features. At the highest X-ray luminosities (αOX ∼ −1), the winds are too ionized to form BALs, but still produce UFOs. These results imply that additional physics is required to explain BAL outflows at realistic X-ray levels and to drive winds strong enough for AGN feedback. Nonetheless, our simulations provide a new framework for interpreting the observed diversity of AGN outflow signatures with fully coupled radiation and dynamics.

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.