Professor Andrew Bunker

Abstract:

Over the past few years JWST has been a major workhorse in detecting and constraining the metal enrichment of the first galaxies in the early Universe and finding the source of the ionisation of their interstellar medium. In this work, we present new deep JWST/NIRSpec spectroscopy of GS-z11-1, a galaxy at z = 11.28, in which we report the detection of multiple rest-frame UV and optical emission lines: CIII]λλ1907,09, CIV]λλ1548,51, [OII]λλ3726,29, [NeIII]λ3869, Hγ and tentative evidence for HeIIλ1640. The ionisation properties of GS-z11-1 are consistent with star formation, with potential contribution from an active galactic nucleus (AGN). We estimate a galaxy stellar mass of log(M⋆/M⊙) = 7.8±0.2 and log(SFR/(M⊙ yr−1))= 0.32±0.11 for the fiducial SF-only models. We measured C/O from the SED modelling of C/O = 1.20±0.15 × solar. This is one of the highest C/O abundances at z>10, and it is consistent with either PopII and PopIII enrichment paths. Despite this source being extremely compact, with a half-light radius of 73±10 pc, we see no increased equivalent width of NIV] and NIII] emission lines as seen in some other compact sources at similar redshifts, a potential signature of second-generation stars in GCs. Overall, this galaxy exhibits low metallicity and high ionisation parameter consistent with intense star-formation or AGN activity in the early Universe, possibly observed before the enrichment by the second generation of stars in proto-globular clusters in the core of the galaxy.

Abstract:

Active galactic nuclei (AGNs), star formation (SF), and galaxy interactions can drive turbulence in the gas of the interstellar medium (ISM), which, in turn, plays a role in SF taking place within galaxies. The impact on molecular gas is of particular importance, as it serves as the primary fuel for SF. Our goal is to investigate the origin of turbulence and the emission of molecular gas, as well as low-and-intermediate-ionisation gas, in the inner few kpc of both AGN hosts and star-forming galaxies (SFGs). We used archival JWST MIRI/MRS observations of a sample consisting of 54 galaxies at z<0.1. We present flux measurements for the H_2 S(5)łambda6.9091μm ii łambda6.9853μm ii łambda5.3403μm, and iii łambda8.9914μm emission lines along with velocity dispersion estimated by the W_̊m 80 parameter. For galaxies with coronal line emission, we included measurements of the v łambda5.6098μm line. We compared the line ratios to photoionisation and shock models to explore the origin of the gas emission. AGNs exhibit broader emission lines than SFGs, with the largest velocity dispersions observed in radio-strong (RS) AGNs. The H_2 gas is less turbulent compared to ionised gas, while coronal gas presents higher velocity dispersions. The W_ 80 values for the ionised gas show a decrease when going from the nucleus out to radii of approximately 0.5--1 kpc, followed by an outward increase up to 2--3 kpc. In contrast, the H_2 line widths generally display increasing profiles with distance from the center. Correlations between the W_̊m 80 parameter and line ratios such as H_2:S(5)/ ii and ii ii indicate that the most turbulent gas is associated with shocks, enhancing H_2 and ii emissions. Based on the observed line ratios and velocity dispersions, the ii emission is consistent with predictions of fast shock models, while the H_2 emission is likely associated with molecules formed in the post-shock region. We speculate that these shocked gas regions are produced by AGN outflows and jet-cloud interactions in AGN-dominated sources; whereas in SFGs, they might be created through stellar winds and mergers. This shock-induced gas heating may be an important mechanism of AGN (or stellar) feedback, preventing the gas from cooling and forming new stars.