With a strategy of obtaining deep JWST imaging and following up interesting candidates with NIRSpec spectroscopy, the JADES survey has: broken the highest redshift spectroscopically confirmed record (twice); found possible evidence for the earliest black hole at z~10.6, though other explanations exist; found direct evidence for the stochasticity of star formation in early galaxies with the highest redshift ‘mini-quenched’ galaxy, and much more besides. I will summarise key results from JADES survey focusing on Chemical evolution and abundances of the earliest galaxies.
The astrophysical origins of the heaviest elements via rapid neutron capture remain unresolved, even with exciting recent progress in gravitational wave and astronomical observations. One key barrier to elucidating r-process origins using these new observables are the uncertainties that arise from the unknown properties of the thousands of nuclear species that participate in the r process. Here we consider the role played by nuclear physics uncertainties in our interpretations of r-process observables such as light curves, abundance patterns, and isotopic ratios. We will discuss the prospects for reducing these uncertainties via advances in nuclear theory and experiment and point out potential observables that may rise above current uncertainties.
The merging of two neutron stars can provide the conditions necessary for the production of the heaviest elements in the universe via the rapid neutron capture process (r-process). When this occurs, an abundance of material is produced lying far from nuclear stability, and the decays of these nuclei produce the electromagnetic signal: the kilonova. Modeling these kilonova signals, and indeed the entire merger system, remains subject to uncertainties stemming from both nuclear properties far from stability as well as from incomplete information regarding the evolution of the extreme astrophysical environment in which this occurs.
I will discuss current work aimed at approaching this problem from both an astrophysical perspective with magnetohydrodynamic simulations of the post-merger disk with neutrino transport, as well as from a nuclear perspective with detailed nucleosynthesis studies.
We measure stellar age for APOGEE giants using our Bayesian Machine Learning framework BINGO (Bayesian INference for Galactic archaeOlogy, Ciuca et al. 2024). After de-noising the data, we found a drop in metallicity with an increase in [Mg/Fe] at an early epoch, followed by a rapid chemical enrichment with increasing [Fe/H] and decreasing [Mg/Fe]. Comparing with the Milky Way-like zoom-in cosmological simulation Auriga, we discuss that this could be due to the early epoch of gas-rich merger. We further argue that this could be associated with the last massive merger of our Galaxy, the Gaia-Sausage-Enceladus merger, and discuss how it impacted the formation of the Galactic thick and thin disks and also the Galactic bar. We will also briefly introduce Japan Astrometry Satellite Mission for INfrared Exploration (JASMINE), which will reveal the Milky Way’s central core structure and its formation history with Gaia-level (~25 uas) astrometry in the NIR Hw-band, (1.0-1.6 um), Galactic centre archaeology survey.
The spectra currently emerging from ground- and space-based facilities are of exceptional resolution and cover a broad range of wavelengths. To meaningfully analyse these spectra, astronomers utilise complex modelling codes to simulate the astrophysical observations. The main inputs to these codes are radiative and collisional atomic data to include energy levels, transition probabilities, collision rates for electron-impact excitation/ionisation, photoionisation and recombination. While some of the data can be obtained experimentally, they are usually of insufficient accuracy or limited to a small number of transitions. The R-Matrix approach is credited as one of the most powerful and reliable tools in calculating these atomic data. Recent and ongoing developments of the relativistic parallel DARC codes have enabled an order of magnitude advance in the accuracy of the atomic structure and subsequent collision calculations that are now feasible for lowly ionised high Z ions.
In 2017 the first gravitational wave from a binary neutron star merger (NSM) was detected and the ejected matter created a bright glow called a Kilonova via r-process nucleosynthesis. Disentangling r-process abundances from the broad spectra of NSM is a challenging task that demands a high degree of rigour in calculations of the ejecta opacity and the atomic calculations that underpin them. Recent publications by the group at QUB report on extensive relativistic atomic structure and electron-impact excitation collision calculations for the species Au I-III, Pt I-III, Sr II, Y II and Te I-III, which were subsequently used in collisional-radiative models to investigate line ratio diagnostics in NSM environments.
Currently, the explanation behind the explosion mechanism of core collapse supernovae is yet to be fully understood. New insight to this phenomena may come through observations of 44Ti cosmic gamma rays; this technique compares the observed flux of cosmic 44Ti gamma rays to that predicted by state-of-the-art models of supernova explosions. In doing so, the mass cut point of the star can be found. However, a road block in this procedure comes from a lack of precision in the nuclear reactions that destroy 44Ti in supernovae, most notably the reactions 44T(alpha,p)47V and 45V(p,gamma)46Cr. Therefore, this study aims to better understand the 45V(p,gamma)46Cr reaction by performing gamma-ray spectroscopy of 46Cr with the aim of identifying proton-unbound resonant states.
The experiment was conducted at the ATLAS facility at Argonne National Laboratory, using the GRETINA+FMA setup, where 46Cr was produced via the fusion-evaporation reaction 12C(36Ar,2n). The cross section for producing 46Cr, in this reaction, is estimated to be in the mu b range. Nevertheless, with the power of the GRETINA+FMA setup, we show that it is possible to cleanly identify gamma rays in 46Cr. These include decays from previously unidentified states above the proton-emission threshold, corresponding to resonances in the 45V + p system.
Type-I X-ray bursts are interpreted as thermonuclear explosions in the atmospheres of accreting neutron stars in close binary systems. During these bursts, sufficiently high temperatures are achieved such that “breakout” from the hot CNO cycle occurs. This results in a whole new set of thermonuclear reactions known as the rp process. This process involves a series of rapid proton captures resulting in the synthesis of very proton-rich nuclei up to the Sn – Te (A ∼ 100) mass region. Various sensitivity studies have highlighted the 59Cu(p,γ)60Zn reaction as significant in its impact on energy generation along the rp -process path within X-ray bursts, and hence, the resultant light curve and final isotopic burnt ashes composition. In particular, competition between the 59Cu(p,α)56Ni and 59Cu(p,γ)60Zn reactions within the NiCu cycle directly determines whether the pathway of nucleosynthesis flows towards higher mass regions. At present, stellar reaction rates for both of these astrophysical processes are based entirely on statistical-model calculations. Recently, however, an indirect study of the nucleus 60Zn has surprisingly shown a plateau in the level-density of states in the region of interest, contrary to the usual expectation of exponential growth with increasing excitation energy. As a result, a statistical-model approach of the 59Cu(p,γ) reaction rate may be insufficient, and it is therefore now essential to explore the properties of excited states in 60Zn that influence the astrophysical 59Cu(p,γ)60Zn reaction. Specifically, the 59Cu(p,γ) reaction is expected to be dominated by resonant capture to excited states above the proton-emission threshold in 60Zn, Sp = 5105.0(4) keV, that lie within the Gamow energy window, Ecm ∼ 0.7 – 1.5 MeV. In this work, we aim to utilise the 59Cu(d,n) reaction in inverse kinematics at the Facility for Rare Isotope Beams (FRIB) to obtain the first measurement of single-particle properties of resonances in the 59Cu(p,γ) reaction. Specifically, 60Zn ions separated within the S800 spectrometer and identified prompt with respect to γ-rays detected by the GRETINA array will be used to determine the energy and angle-integrated cross sections of key resonance states, while neutrons detected by the LENDA array will be used to constrain the distribution of spin-parity assignments across the relevant excitation energy region of Type-I X-ray burst nucleosynthesis.
The AT2017gfo has added to the growing interest in r-process elements, which are expected to be particularly abundant in the nucleosynthesis trajectories of neutron star mergers. With the choice of elements guided by nuclear physics at particular values of Y_e, our group calculates atomic data catered for modelling of the astrophysical objects without the use of local-thermodynamic-equilbirum using collisional radiative modelling. By enforcing observed luminosities, we are then able to make mass estimates of the candidate ions. This serves particularly as a test of the calculated atomic data and, based on the feasibility of the mass estimate, also the underlying nucleosynthesis theory. This event, as well as the GRB230307A last year sport features consistent with the fine structure lines of Te and W, which are particularly interesting to atomic and nuclear physicists likes – as these species lie at the second and third peaks respectively of the r-process abundance. These features also occur at the late stage collisionally dominated regime of the events, making an optically thin model suitable for their analysis. Collisional radiative modelling, and particularly mass estimation of these species in and out of LTE will be discussed.
Carbon burning is a key step in the evolution of massive stars, Type 1a supernovae and superbursts in x-ray binary systems. Nevertheless, our understanding of this critical fusion reaction is not as complete as might be desirable to fully constrain astrophysical models. This limitation centres of the difficulty in determining the $^{12}$C+$^{12}$C fusion cross section at energies corresponding to the Gamow window for these different scenarios as it relies on extrapolation of direct measurements made at higher energies. Such direct fusion measurements are complicated by the presence of resonances at and below the Coulomb barrier. These resonances have traditionally been associated with the formation of short-lived molecular states based on $^{12}$C+$^{12}$C or similar alpha-conjugate systems. Despite study of these resonances over many years, a comprehensive theoretical model accounting for their existence and structure is presently lacking.
Given the difficulties associated with direct fusion studies of the $^{12}$C+$^{12}$C reaction, indirect studies which can identify potential resonances within the respective Gamow windows are of high value. In this respect, a study of the $^{24}$Mg($alpha$,$alpha$’)$^{24}$Mg reaction has identified several 0$^{+}$ states in $^{24}$Mg, close to the $^{12}$C+$^{12}$C threshold, which predominantly decay to $^{20}$Ne(ground state) + $alpha$ [1]. Not only were these states newly identified but surprisingly they were not observed in previously well-studied $^{20}$Ne($alpha$,$alpha_0$)$^{20}$Ne resonance scattering, potentially suggesting that they have a dominant $^{12}$C+$^{12}$C cluster structure. Given the very low angular momentum associated with sub-barrier fusion, these states, which sit in the Gamow window for massive stars, may play a decisive role in $^{12}$C+$^{12}$C fusion. We present estimates of updated $^{12}$C+$^{12}$C fusion reaction rates based on likely parameters for such resonances [1].
A fascinating aspect of the identification of these potential 0$^+$ cluster states in $^{24}$Mg close to the break-up threshold for $^{12}$C+$^{12}$C and similar channels such as $^{16}$O+$^8$Be is the circumstantial similarity to the situation in $^{12}$C with the Hoyle state at the break-up threshold and the critical role that it plays in in helium burning.
Nucleosynthesis yields from sub-Chandrasekhar (sub M-ch) and Chandrasekhar (M-ch) SN Ia progenitors have been discussed and debated for decades on their contributions to iron peak elements in the cosmos. Investigating SNe Ia in ultra-faint dwarf galaxies (UFDs) and dwarf spheroidal galaxies (dSphs) with different star formation and chemical enrichment histories may shed light on the progenitors in different environments. To this end, we incorporate metallicity dependent SN Ia yields from different progenitors within our novel inhomogeneous chemical evolution model, i-GEtool, and compare the predicted chemical abundances to observations in different UFD and dSph galaxies. While the observed [Mn/Mg] ratios increase towards higher metallicities both within single galaxies and when considering galaxies with different metallicity distributions, the observed [Ni/Mg] ratios show a weaker correlation. In my talk, I will show that our models for UFD and dSph can reproduce the observed trends along with their scatter without invoking any contribution from sub M-ch SN Ia progenitors, at variance with previous studies in the literature. I will discuss the implications of our findings for the observed iron peak elemental abundances in the Milky Way halo and disks, outlining our future plan.