Description
Organisers: Conor Byrne, Stephanie Monty, Ankur Upadhyaya, Louise Welsh; co organisers: Nathan Adams, Karla Arellano-Cordova, Andreea Font, Robert Izzard, Chiaki Kobayashi, Christopher Lovell, Katherine Ormerod, Vadim Rusakov, Aayush Saxena, Ragandeep Singh Sidhu, Charlotte Simmonds, Elizabeth Stanway
The origin and build-up of chemical elements in stars, dust and gas throughout the Universe is a fundamental question in modern astrophysics. Addressing this requires understanding stellar nucleosynthesis, stellar evolution and galaxy evolution across all epochs and length scales. Progress hinges on combining constraints from cutting-edge observational facilities with state-of-the-art theoretical models of stars, the Milky Way, galaxies, and the interstellar and intergalactic medium.
The advent of JWST has revolutionized studies of chemical and galactic evolution at the earliest epochs. Interpreting these observations requires advanced stellar, galactic and chemical evolution models encompassing many physical processes, including: nuclear and atomic physics, chemistry and dust formation. Combining and discussing the results from these different areas is necessary to forge a unified model of the early Universe.
One area in which models need refinement is accurately representing the conditions in the distant Universe. Observations of extreme stellar populations such as young, massive stars at low metallicity and future studies with ELT are valuable tools to bridge the gap between high- and low-redshift stellar populations. A close relationship between observations and models is essential; high-quality observations constrain models, while improved models provide better insight into early chemical and galactic evolution.
This session targets these open questions from observational and theoretical perspectives, involving stellar and galactic astronomers. Through short talks and focused discussion, we will bring together the considerable leadership and expertise of UK-based researchers in these fields, gain insight into uncertainties and limitations of data interpretation, and outline a roadmap to addressing these challenges.
Galactic chemical enrichment mechanisms have primarily been constrained by alpha-enrichment ([ฮฑ/Fe]) and metallicity ([Fe/H]) measurements from deep absorption-line spectra of individual stars in the Milky Way (MW) and some local group dwarf galaxies. At larger distances out to high-redshifts (z>2), such measurements are only possible from integrated light from galaxies, almost exclusively...
A slew of results from JWST spectroscopy have allowed us to start constraining the chemistry of galaxies over the vast majority of cosmic time. Rest-frame optical NIRSpec spectroscopy has provided the community with a large sample of galaxies with strong emission lines. Simultaneously, a number of programmes has provided deep spectroscopy resulting in a few dozen galaxies with detections of...
Elemental abundance ratios provide a unique constraint on the rate of enrichment via different physical processes (e.g. CCSNe vs Type-Ia SNe), yielding insights into galaxy evolution, star-formation timescales and chemical enrichment. At $z>2$, most observations are sensitive to the oxygen abundance, though recent developments in methodology and the advent of JWST spectroscopy have enabled the...
Detailed modelling of the formation and evolution of dust is important to explain the high dust content in z~7 galaxies observed with ALMA, as well as the carbonaceous dust in z~8 galaxies observed with JWST. The latter is particularly difficult to explain with our current theories of dust formation, which depend on Asymptotic Giant Branch (AGB) stars to be the main factories of carbonaceous...
Recent JWST observations have revolutionised our understanding of chemical evolution and physical conditions in galaxies during the epoch of reionisation, revealing surprisingly compact morphologies, bursty star-formation histories, and intriguing chemical signatures. Accurate interpretation of these observations demands sophisticated theoretical frameworks that self-consistently integrate...
Thanks to the exquisite capabilities of ALMA observatory, we were able to study dusty galaxies at EoR through their dust continuum and FIR emission lines. With these observations, a rapid buildup of dust in the early Universe. Until the launch of JWST, studying the rest-frame of optical emission of these sources was out of reach for astronomers.
In this talk, I will present one of the...
Several studies reported unexpected abundances of C, N, O elements in metal-poor nebulae in the first billion years of the universe. As these elements are produced via different pathways and on different timescales, such features present a unique opportunity to learn about the early metal enrichment and beginnings of galaxy evolution. This study focuses on the galaxies exhibiting enhanced N/O...
The oldest, most metal-poor stars in and around the Milky Way were born in pristine environments in the early Universe. Observations of local very metal-poor stars ([Fe/H] < -2.0) show that many of these stars have exceptionally high carbon abundances. These carbon-enhanced metal-poor (CEMP) stars consist of two main classes: the CEMP-no stars are thought to have been born carbon-rich,...
Observations with JWST have opened a new window into the physical conditions, properties, and chemical abundance patterns of galaxies at high redshift. We present the chemical abundances of C, N, and O of two star-forming galaxies (SFGs) at z~5 from the Early eXtragalactic Continuum and Emission Line Science (EXCELS) survey. We compare the C and N in concert with O for these, finding elevated...
Until now, galaxy properties and chemical evolution in the lower metallicity regime have remained relatively uncharted, with considerable scatter. For example, chemical abundances like N/O ratios exhibit a scatter of 0.1โ0.3 dex at an oxygen abundance of 12+log(O/H) < 7.69 (~0.1 $Z_{\odot}$), likely driven by stochastic chemical enrichment. Additionally, recent JWST observations have revealed...
Globular clusters serve as important tracers of their host galaxies' chemical evolution and star formation history. In this study, we present a comprehensive chemical abundance analysis of Sextans A GC-1, a globular cluster located in a low-surface-brightness dwarf irregular galaxy on the outskirts of the Local Group. Using integrated-light spectroscopy, we determine the clusterโs detailed...
The fundamental metallicity relation (FMR) โ the three-way trend between galaxy stellar masses, star-formation rates (SFRs) and gaseous metallicities โ remains amongst the most studied extragalactic relations. Furthermore, more compact galaxies possess higher average metallicities at a given stellar mass, such that metallicity correlates particularly tightly with gravitational potential....
Understanding chemical evolution in galaxies requires tracing how gas-phase metallicity evolves across cosmic time. Metallicity reflects a complex interplay between star formation, feedback, and gas flows. A key question is which galaxy properties most strongly influence metallicity. While stellar mass has long been considered the primary driver, recent studies suggest gravitational potential...
The Milky Wayโs formation history is encoded in its chemical diversity, shaped by both in-situ star formation and accretion. Using GALAH DR3, we construct a high-dimensional chemical space from 17 element abundances for 9,923 metal-poor stars. This space is then transformed into a lower-dimensional latent representation using Principal Component Analysis, capturing dominant patterns in...
Thorne-ลปytkow Objects (TลปOs) are a class of hybrid stars, originally proposed by Thorne & ลปytkow (1977), consisting of a neutron star core, surrounded by a diffuse, convective, giant envelope. Recent work by Farmer et al. (2023) to produce models of TลปOs in MESA has reignited interest in structures of these objects.
All plausible formation mechanisms for TลปOs involve a binary interaction,...
The Pair Instability (PI) boundary was previously thought to be robustly determined by theory as starting at $~50 M_\odot$. Recent Gravitational Wave observations such as GW190521 suggested otherwise, igniting a flurry of theories and predictions, which has had significant follow-on implications for stellar populations in Population II and III environments. Stars above the PI boundary are...
Understanding how environments impact galaxy evolution is pivotal in unraveling the interplay between internal processes and external environmental effects. Using cosmological hydrodynamical simulations (EAGLE, IllustrisTNG), we explore the environmental dependence of the gas-phase mass-metallicity relation (MZR) from zโผ2.3 to z=0. We found that, at fixed stellar mass, central galaxies in...
In this talk, I will present a new view on the chemical elements in stars, dust, and gas at high redshift from the cosmological-scale galaxy evolution simulation, L-Galaxies.
L-Galaxies is currently the only cosmological simulation to simultaneously include models for detailed chemical enrichment, binary stellar evolution, and dust formation. This allows L-Galaxies to track the precise...
Various solutions have been proposed to solve the high-redshift `bright galaxy problem', such as more efficient star formation, bursty star formation, and variable initial mass functions. While equally interesting, each scenario must also differ in how these stellar populations couple to the interstellar medium (ISM) through stellar feedback. In this talk, I will present first results from the...
The advent of JWST has allowed us to peer further into the Universe than we've ever been able to before. With over 20 galaxies observed beyond redshift 10, we are now able to observe the formation of galaxies at a time where we still expect the formation of population III (Pop. III) stars. In this talk I will introduce the MEGATRON simulation of a Milky Way-mass galaxy at redshift 0, and its...
Molecular clouds are the cradle of stars: comprehending their composition and evolution is key to understanding the processes and materials that go on to form stars and planets. Ices make up 90% of the condensible molecular reservoir in such clouds and can only be observed as absorption features against a background stellar continuum. With thanks to its spectral resolution and sensitivity,...
The statistical properties of a population of binary stars are determined in large part by the joint distribution of the masses of their components at their time of formation. These masses determine the binary stars' subsequent evolution. However, this joint distribution is known neither from first principles, since theory is insufficiently developed, nor from observation, since observational...
Dust attenuation in galaxies exhibit variability due to factors such as metallicity, redshift, and whether it is a quenched or star-forming galaxy. Using observations with both NIRSpec and NIRCam aboard JWST from the Blue Jay survey, a mass-selected sample of 145 galaxies in the COSMOS field at cosmic noon (1.7 < z < 1.3) was compiled to connect the enigmatic nature of the dust attenuation law...
Galaxy's stellar haloes, including their globular cluster populations, are known to build up through the accretion of smaller systems. With Gaia DR3 kinematic data, we uncovered several new small substructures in the local stellar halo, namely the ED-2, 3, 4, 5 and 6; the ED streams. I will present the chemical follow-up of these streams, using targeted high-resolution UVES spectroscopy to...
Simba-C is a new galaxy formation simulation that updates the successful Simba model to include the state-of-the-art chem5 chemical evolution model from C. Kobayashi. Simba-C opens up a range of new testable predictions for cosmic chemical evolution in galaxies. I will present results from Simba-C on abundances and abundance ratios in galactic stellar populations as well as intra-cluster gas...
Recent JWST observations have revealed extreme emission-line strengths, unexpected chemical enrichment patterns, and unusual spectral features in high-redshift galaxies, challenging our understanding of early stellar populations. Using the Maraston stellar population model with the latest Geneva tracks, we incorporate nebular emission via Cloudy and compare our results to other models, finding...
I present the most comprehensive study of major galaxy mergers (stellar mass ratio 1:4) to date, focusing on the underexplored redshift range of zโผ3โ9. Using NIRCam imaging and NIRSpec spectroscopic data from the JADES GTO program, I examine galaxy close pair fractions, major merger rates, and mass accretion rates to assess the role of mergers in galaxy growth. Close pair fractions are...
We have not yet observed the epoch at which disc galaxies emerge in the Universe. While high-$z$ measurements of large-scale features such as bars and spiral arms trace the evolution of disc galaxies, such methods cannot directly quantify featureless discs in the early Universe. Here we identify a substantial population of apparently featureless disc galaxies in the Cosmic Evolution Early...
Constraining metal enrichment across cosmic time is an essential ingredient in understanding galaxy evolution. Acquiring high-quality data is crucial for this, and JWST has generated significant progress in this field. Concurrently, a growing population of high-redshift Active Galactic Nuclei (AGN) has emerged, many of which exhibit interesting patterns of elemental metallicity. Works...
The origin of chemical abundances has been studied in great detail for decades from observation surveys (such as APOGEE and LAMOST) to nucleosynthetic models of stellar structure and cosmic events. However, it can be difficult to differentiate the relationship between elements from chemical abundance patterns due to stellar migration and star misclassifications in surveys. In our present work,...
Lyman Continuum (LyC) escape is a fundamental parameter for understanding the evolution of galaxies and the intergalactic medium (IGM). To shed light on the connection between LyC escape, stellar population properties, and morphology, we investigate the escape fraction (๐esc) of LyC photons. Direct observation of LyC at the Epoch of Reionisation (zโณ6) is impeded by absorption, necessitating...
Studies of gas kinematics at z<4 have built a picture where star-forming galaxies evolve from thick gas rich disks at cosmic noon to dynamically cold disks in the local Universe. Pushing these analyses to higher redshifts is crucial for both understanding the origin of the dynamical populations we see in the local universe and tracing their evolution in cosmic time to uncover the conditions...
The Sagittarius (Sgr) dwarf galaxy experienced its first in-fall into the Milky Way (MW) about 5 Gyr ago. As it is being tidally stripped by the MW, its core and two stellar streams are now visible in the Sky. Given its proximity, it is an ideal test-bed for galactic chemo-dynamical models. So far, studies have typically focussed on metal-rich and relatively young stars, given that they are...
Fresh observations are rapidly advancing our understanding of galaxy formation and evolution. The ability to accurately interpret a galaxyโs emission spectrum hinges on the application of spectral energy distribution (SED) modelling, which critically depends on the choice of model templates and underlying assumptions. Numerous models and frameworks exist, the choice from which introduces...
The chemical and galactic evolution of the Universe is a fundamental question in modern astrophysics, recently advanced by observations from the JWST. These high-quality observations not only enhance our knowledge of the gas properties, also provide an opportunity to study stellar populations and their key characteristics, an area that has received less attention in much of the current...
One of the most remarkable outputs from the James Webb Space Telescope (JWST) has been the incredible spectral data covering various UV-optical emission lines in the high-redshift Universe (z>5). Multiple emission lines originating from the nebular regions of these galaxies have been observed, and using calibrations based on line ratios, the community have been able to infer quantities such as...
Historic merger events are expected to leave imprints of their collisions in the stellar haloโs phase space and chemodynamics. However, interpreting such imprints is complicated by the complex hierarchical history expected in LCDM (Rey M. P.et al. , 2023, MNRAS, 521, 995 10.1093/mnras/stad513). Here, we explore the impact of merging within the PARADIGM simulations (Joshi G. D. et al ,...
