Professor Andrew Bunker

Abstract:

We explore the kinematic gas properties of six 5.5 < z < 7.4 galaxies in the JWST Advanced Deep Extragalactic Survey (JADES), using high-resolution JWST/NIRSpec multi-object spectroscopy of the rest-frame optical emission lines [O III ] and H α . The objects are small and of low stellar mass (∼1 kpc; M * ∼ 10 7 − 9 M ⊙ ), less massive than any galaxy studied kinematically at z > 1 thus far. The cold gas masses implied by the observed star formation rates are about ten times higher than the stellar masses. We find that their ionised gas is spatially resolved by JWST, with evidence for broadened lines and spatial velocity gradients. Using a simple thin-disc model, we fit these data with a novel forward-modelling software that accounts for the complex geometry, point spread function, and pixellation of the NIRSpec instrument. We find the sample to include both rotation- and dispersion-dominated structures, as we detect velocity gradients of v ( r e )∼100 − 150 km s −1 , and we find velocity dispersions of σ 0 ∼ 30 − 70 km s −1 that are comparable to those at cosmic noon. The dynamical masses implied by these models ( M dyn ∼ 10 9 − 10 M ⊙ ) are higher than the stellar masses by up to a factor 40, and they are higher than the total baryonic mass (gas + stars) by a factor of ∼3. Qualitatively, this result is robust even if the observed velocity gradients reflect ongoing mergers rather than rotating discs. Unless the observed emission line kinematics is dominated by outflows, this implies that the centres of these galaxies are dominated by dark matter or that star formation is three times less efficient, leading to higher inferred gas masses.

Abstract:

We present the properties of 17 faint Lyman-α emitting galaxies (LAEs) at z > 5.8 from the JWST Advanced Deep Extragalactic Survey (JADES) spectroscopic data in the Hubble Ultra Deep Field/GOODS-S. These LAEs span a redshift range z ≈ 5.8 − 8.0 and a UV magnitude range MUV ≈ −17 to −20.6, with the Lyα equivalent width (EW) in the range ≈25 − 350 Å. The detection of other rest-optical emission lines in the spectra of these LAEs enables the determination of accurate systemic redshifts and Lyα velocity offsets, as well as the physical and chemical composition of their stars and interstellar media. These faint LAEs are consistent with metal-poor systems with high ionization parameters, similar to the general galaxy population at z > 6. We measured an average ionizing photon production efficiency, log(ξion/erg−1 Hz) ≈ 25.57 across our LAEs, which does not evolve strongly with redshift. We report an anti-correlation between the Lyα escape fraction and the velocity offset from systemic redshift, consistent with model expectations. We further find that the strength and velocity offset of Lyα are neither correlated with galaxy spectroscopic properties nor with ξion. We find a decrease in Lyα escape fractions with redshift, indicative of decreasing sizes of ionized bubbles around LAEs at high redshifts. We used a range of galaxy properties to predict Lyman continuum escape fractions for our LAEs, finding that the ionizing photon output into the intergalactic medium from our LAEs remains roughly constant across the observed Lyα EW, showing a mild increase at fainter UV magnitudes and at higher redshifts. We derived correlations between the ionizing photon output from LAEs and their UV magnitudes, Lyα strengths and redshifts, which can be used to constrain the ionizing photon contribution of LAEs at z > 6 towards cosmic reionization

Abstract:

Dust-obscured galaxies are thought to represent an early evolutionary phase of massive galaxies in which the active galactic nucleus (AGN) is still deeply buried in significant amounts of dusty material and its emission is strongly suppressed. The unprecedented sensitivity of the James Webb Space Telescope (JWST) enabled us for the first time to detect the rest-frame optical emission of heavily obscured AGNs and unveil the properties of the hidden accreting super-massive black holes (BHs). In this work, we present the JWST/NIRSpec integral field spectroscopy (IFS) data of ALESS073.1, a massive (log( M ⋆ / M ⊙ ) = 10.98) dusty, star-forming galaxy at z = 4.755 hosting an AGN at its center. The detection of a very broad (> 9000 km s −1 ) H α emission associated with the broad line region (BLR) confirms the presence of a BH (log( M BH / M ⊙ ) > 8.7) accreting at less than 18% of its Eddington limit. The identification of the BLR classifies the target as a type 1 AGN despite the observed high column density of N H ∼ 10 24 cm −2 . The rest-frame optical emission lines also reveal a fast (∼1700 km s −1 ) ionized gas outflow marginally resolved in the galaxy center. The high sensitivity of NIRSpec allowed us to perform the kinematic analysis of the narrow H α component, which indicates that the warm ionized gas velocity field is consistent with disk rotation. Interestingly, we find that in the innermost nuclear regions (< 1.5 kpc), the intrinsic velocity dispersion of the disk reaches ∼150 km s −1 , which is ∼2 − 3 times higher than the velocity dispersion inferred from the [C  II ] 158 μm line tracing mostly cold gas. Since at large radii the velocity dispersion of the warm and cold gas are comparable, we conclude that the outflows are injecting turbulence in the warm ionized gas in the central region, but they are not sufficiently powerful to disrupt the dense gas and quench star formation. These findings support the scenario that dust-obscured galaxies represent the evolutionary stage preceding the unobscured quasar when all gas and dust are removed from the host

Abstract:

We use SEDz*—a code designed to chart the star formation histories (SFHs) of 6 < z < 12 galaxies—to analyze the spectral energy distributions (SEDs) of 894 galaxies with deep JWST/NIRCam imaging by JADES in the GOODS-S field. We show how SEDz* matches observed SEDs using stellar-population templates, graphing the contribution of each epoch by epoch to confirm the robustness of the technique. Very good SED fits for most SFHs demonstrate the compatibility of the templates with stars in the first galaxies—as expected, because their light is primarily from main-sequence A stars, free of post-main-sequence complexity, and insensitive to heavy-element compositions. We confirm earlier results from Dressler et al. (1) There are four types of SFHs: SFH1, burst; SFH2, stochastic; SFH3, “contiguous” (three epochs), and SFH4, “continuous” (four to six epochs). (2) Starbursts—both single and multiple—are predominant (∼70%) in this critical period of cosmic history, although longer SFHs (0.5-1.0 Gyr) contribute one-third of the accumulated stellar mass. These 894 SFHs contribute 1011.14, 1011.09, 1011.00, and 1010.60 M ⊙ for SFH1-4, respectively, adding up to ∼4 × 1011 M ⊙ by z = 6 for this field. We suggest that the absence of rising SFHs could be explained as an intense dust-enshrouded phase of star formation lasting tens of Myr that preceded each of the SFHs we measure. We find no strong dependencies of SFH type with the large-scale environment; however, the discovery of a compact group of 30 galaxies, 11 of which had first star formation at z = 11-12, suggests that long SFHs could dominate in rare, dense environments