In the last decade there has been a sharp increase in the number of stellar surveys due to improvements in quality (spectral resolution) and quantity (multiplexing) of spectra. However, small high-fidelity stellar surveys like HARPS have not been fully realised as an experiment of element origins, despite its spectral resolution of 115,000 and wide sky coverage. The high-resolution HARPS spectra make it ideal for creating a data-driven nucleosynthesis model to investigate the correlations between elements and their underlying production channels. Here I present preliminary results of the high-precision abundances we have retrieved from HARPS spectra. The HARPS spectra were crossmatched with GAIA DR3 to create a high-fidelity catalogue of 6488 stars at SNR ~110, from which we are deriving 30+ abundances using the most recent spectral synthesis code Korg. These abundances will be used as inputs for our data-driven model, with the goal to quantify properties of the sources that underlie the data, and tap into the fractional contributions of the s-and r-process production channels of an ensemble of neutron capture elements.
Unveiling the cool CGM around quiescent galaxies with galaxy-galaxy lensing
The processes that cause some galaxies to stop forming stars and how such galaxies stay quiescent remain open questions. While quiescent galaxies have comparable amounts of cool gas in their outer circumgalactic medium (CGM) compared to their star-forming counterparts (e.g. Chen+ 2018), they have significantly less interstellar gas (Magdis +2021). Theories point to dynamical interactions with the hot corona as the primary process preventing cool gas from reaching the galaxy (Afruni+2019). However, there is a lack of understanding of the inner regions of the CGM of quiescent galaxies that is due to limitations in standard quasar-sightline methods, which lack spatial information in the needle-like beam. I will present work using galaxy-galaxy scale strong lenses which probe the inner 10--20 kpc of massive quiescent galaxies. We use Keck/KCWI IFU spectroscopy to spatially resolve MgII absorption around the quiescent galaxies tracing large amounts of cool (10^4K) atomic gas. Even at these close impact parameters, we find a comparable amount of cool gas compared to star-forming galaxies. Additionally, we show through detailed lens modelling of high resolution Hubble imaging that the lens model of one system reveals a diffuse component of significant mass consistent with the spatial extent of the MgII absorption. Our work shows the power of galaxy-scale gravitational lenses to not only probe the gas in the inner regions of the CGM, but to also independently probe the mass of the CGM due to its gravitational effect.
Observations and cosmological simulations tell us that disky, star-forming galaxies transform into elliptical, quenched galaxies. This transition can be driven, at least in part, by gas leaving the galaxy due to the energy injection from black holes in the galactic central region, known as active galactic nuclei, or AGN. Recently discovered FR0 sources, that host unresolved radio-loud sources and appear to be very common among a variety of galaxy types, could suggest that stalled jets play a crucial role in galaxy quenching.
Using the Arepo code we model the interstellar medium (ISM) in the central kiloparsec of a galaxy, with active turbulence driving and constant jet energy injection. With our simulations we find three main scenarios — jets passing almost unhindered through the ISM, jets being completely stalled near the injection scale, or the interesting intermediate stage when jets become highly disturbed and redirected by ISM structure. We show how the ISM's ram pressure and complex structure have a great impact on how the jet propagates.
This work sheds light on the open question of how energy from AGN couples to the gas in its host galaxy and in future our results can be utilised in building the next generation of cosmological simulations through making improvements on existing, often heuristic models of AGN.
Nebular emission in the early Universe
Nebular emission is one of the most powerful observational probes for studying galaxies across cosmic time. Emission line ratios provide constraints on ISM conditions, including temperature, density, and chemical compostion, and on the properties of ionising sources, giving insights into massive stars and/or accreting black holes. With JWST/NIRSpec, nebular emission lines have now been detected out to z~12, allowing us to make these measurements self-consistently across almost the entirety of cosmic history. However, the interpretation of observed emission lines is known to be very sensitive to assumptions of geometry, including the presence of temperature and density fluctuations. Despite this, it is common to model nebular regions with constant density models.
In this talk, I will discuss some of the most surprising nebular observations from the first two years of JWST observations, including peculiar chemical abundance ratios (e.g. N/O), strong nebular continuum emission, and high nebular temperatures. I will discuss the implications these have for galaxy formation and early stellar populations.
I will also introduce the MEGATRON simulation, the first cosmological simulation to include non-equilibrium photoionisation chemistry coupled to on-the-fly radiative transfer, thus allowing full forward-modelling of emission line observables. This provides a unique framework within which to use JWST/NIRSpec observations to test galaxy formation models.
Rapid star formation in the bulges of spiral and starburst galaxies leads to regions of the interstellar medium that are higher in metals than typically found in the disk of spiral galaxies, such as our Milky Way. Stars that form out of such gas span a range in metallicities, with many of them super solar. We have calculated new stellar evolutionary and nucleosynthesis models for close to the entire low to massive stellar range (1-8Msun and 11-30Msun). These models cover a range of metallicities from sub-solar to approximately six times solar metallicity.
The convective mixing episode known as the ‘third dredge up,’ occurs in the last active phase of evolution for low and intermediate mass stars--the thermally pulsing asymptotic giant branch. Our results from this mass range show that the efficiency of these mixing episodes declines drastically with increasing metallicity. Consequently, the yields of our most metal-rich low mass models are dominated by H-burning products and are relatively free of primary C and s-process products.
In the massive stellar models, we find stripped supernovae are produced at much lower initial masses in comparison to their lower metallicity counterparts. Black hole formation requires higher initial masses with increasing metallicity. For the models that do undergo a typical core collapse supernovae, we find that C, Si and S yields decrease with increasing metallicity. The O, Ne and Mg yields experience an increase, and Eu is destroyed in all models, however the degree of destruction lessens with increasing Z.
State-of-the-art numerical simulation suites are powerful theoretical tools with which to address systematics in methods that are used for analysis in cosmological surveys.
Future optical and near-infrared surveys will provide us with detailed 3D maps of galaxy positions, weak lensing and cluster abundances - all of which will be used to quantify the large-scale structure. It is therefore crucial that the methods we use to measure the clustering of galaxies and matter be robust to systematics in order to accurately extract cosmological information. In this body of work, we use cosmological-hydrodynamical simulations to better understand complex physical processes that inhibit our ability to interpret clustering statistics. We first investigate how feedback can impact the total matter distribution in and around halos and use the Cosmology and Astrophysics for MachinE Learning Simulations (CAMELS) to train a machine learning algorithm on baryon content and halo abundance to predict the suppression of total matter clustering. We further address galaxy assembly bias as a systematic in the use of galaxy clustering as a cosmological probe. Utilizing the IllustrisTNG simulation suite in conjunction with machine learning tools, we provide alternative models of the galaxy-halo connection which incorporate global halo properties. Lastly, we address the intrinsic alignment of galaxies as a systematic in weak lensing signals. We measure the projected correlations of galaxy shapes with respect to different tracers of large-scale structure in the MillenniumTNG simulation and report strong alignment signals with dependence on redshift and morphology.
Understanding the relationship between stellar feedback and a galaxy's metal content is essential for unraveling the baryon cycle. The fundamental metallicity relation (FMR), a three-parameter correlation between stellar mass, gas-phase metallicity, and star formation rate, serves as a valuable tool for tracing the evolution of galactic gas dynamics across cosmic epochs. Surprisingly, previous studies indicate no redshift-dependence in the FMR up to z ~ 2.5. However, recent observations from JWST challenge this view, suggesting evolution of the FMR in the early universe. We propose a framework to reconcile these discrepancies and shed light on the evolving nature of the FMR. We corroborate the JWST findings, identifying evidence of FMR evolution in the cosmological simulations Illustris, IllustrisTNG, and EAGLE. Additionally, we find the FMR is sensitive to variations in stellar feedback implementation between the different simulation models. We further predict that simulations incorporating burstier stellar feedback should have a much weaker FMR. These findings underscore the significance of the high-redshift FMR as a sensitive probe for delineating the underlying physics governing galaxy formation in the early universe and emphasize the need of high-redshift JWST observations.
Bridging the universe with young star clusters
Massive stars within young star clusters underpin galaxy evolution physics. Massive stars shape their environments through mechanical feedback, ionisation, and heavy element enrichment of the interstellar medium (ISM). Yet, our understanding of these stars' chemical composition, especially at low metallicity, remains uncertain. This limits our ability to quantify how they interact with the ISM and the resulting emission line observables. By quantifying chemical abundance ratios over cosmic time and integrating them into stellar and photoionisation models self-consistently, we are starting to accurately predict galaxy properties across epochs. In this presentation, we will merge stellar models with observations of star forming regions, linking the formation of stars to the global galactic environment. We will explore significant knowledge gaps, paving the way to quantify energy, metal, and matter flows on 10 parsec scales. Additionally, we highlight how JWST observations are addressing the disparity between local and high-redshift realms. We’ll end by demonstrating how this work establishes a foundational framework for future investigations with MAVIS, which will enable detailed characterisations of resolved stellar populations beyond our cosmic neighbourhood.
Accurate predictions of the physics of interstellar medium are vital for understanding galaxy formation and evolution. Modeling photoionized regions with complex geometry produces realistic ionization structures within the nebulae, providing the necessary physical predictions to interpret data. 3D photoionization codes built with Monte Carlo techniques provide powerful tools to produce the ionizing radiation field with fractal geometry, which includes the regions ionized by both stellar and diffuse photons. In this talk, we will present a new self-consistent three-dimensional photoionization code -- Messenger Monte-Carlo MAPPINGS V (M^3), which is designed for modeling nebulae in arbitrary three-dimensional geometries. We will present nebula models with complex geometries created by M^3, and will further show how nebular geometry influences the ionizing radiation field and emission-line behaviour. Our research has important implications for studies of emission-line behaviors in the era of LVM and JWST.
The chemical evolution of the Universe is governed by the nucleosynthesis contribution from stars. Massive stars are responsible for producing most of the elements between C and Fe, with longer lived sources such as Type Ia supernovae producing much of the iron peak, while low-mass red giant stars contribute significant quantities of C, N and F. Elements heavier than Fe are made by neutron captures, where two main processes have been identified to operate in nature: the slow and rapid neutron capture processes (or s- and r-processes). The stellar site of the s-process has been identified to primarily be low-mass red giant stars, while the r-process occurs in merging neutron stars and rare energetic supernovae that result from the deaths of massive stars. In this talk I will review our current understanding of the origin of elements, their astrophysical sites, and discuss outstanding problems.
The Structural Evolution of Galaxies Across Cosmic Time
One of the stunning surprises from JWST's first year of observations of the extragalactic sky is that not only are we detecting large numbers of galaxies in the early universe but that many of these galaxies are resolved and show great structural detail. For the first time, we can quantify the morphological structure of galaxies well into the epoch of reionzation and constrain how these galaxies grew over cosmic time. I will present an analysis of the morphological and size evolution of galaxies in the early universe, from z=2-12+, using deep multi-band NIRCam imaging from several public survey fields including CEERS, NGDEEP, PRIMER, and COSMOS-Web. Our morphological measurements include quantitative measures, such as surface brightness profile fitting and non-parametric fits, visual morphologies, and machine learning approaches.
Exploring ISM and HII Regions in Extreme Starbursts with BlueMUSE
Local extreme starburst galaxies, many located in dwarf low-metallicity galaxies, provide perfect laboratories to characterise the physical processes that drive galaxy assembly and evolution, as star-formation is driven under conditions similar to those of the primitive galaxies, many of them now under study thanks to the JWST. However, the physical processes ruling star-formation, gas cycle, chemical enrichment, and the properties of both the stars and the ISM occur on different scales, and hence detailed maps of both local (sub-kpc level) and global properties of galaxies are needed. At the same time, spectroscopic observations need to be deep enough for detecting not only the bright emission lines including the critical [O II] 3727, but key, faint emission lines such as [O III] 4363 or He II 4686. "ISM and HII regions in extreme starbursts" has been identified as the Key Science Case for BlueMUSE Working Group 2: Nearby Galaxies. In this talk, I will provide an overview of the topic and how BlueMUSE can indeed dramatically advance our knowledge and understanding of starbursts, ISM, IGM, and HII regions in nearby galaxies. For this, I will also present some preliminary results of the "HI KOALA IFS Dwarf galaxy Survey" (Hi-KIDS), that uses KOALA+AAOmega at the Anglo-Australian Telescope (AAT) to get good-quality IFS data of a sample of ~100 nearby dwarf and irregular galaxies for which we already have 21cm HI interferometric data.
The properties and impact of the first generation of stars (Population III) remain largely unknown and unconstrained due to the lack of direct observations of Population III stars and early galaxies. Bridging the knowledge gap in this domain requires joint insights from galactic archaeology and simulations of the early Universe. My work uses a combination of simulations and observations to examine the first steps of chemical enrichment and the processes that give rise to the scatter in elemental abundances in co-natal groups of stars. Using the Aeos star-by-star cosmological hydrodynamic simulations, I will illustrate the non-monotonic enrichment of early halos from Population III supernovae. Furthermore, I will show that halos lose the majority of the chemical yield produced by Population III supernovae to the surrounding circumgalactic or intergalactic medium until they attain a critical mass, after which they retain re-accreted and injected material. As halos lose their metals to the surrounding medium, these metals mix with yields from stars in neighboring halos before being re-accreted to the galaxy. Metal mixing, in addition to stochastic star formation and varying ratios of nucleosynthetic sources play a role in producing the abundance scatter observed in co-natal groups of stars. To constrain the relative influence of these processes, measurements of the intrinsic abundance scatter for populations of dwarf galaxies and star clusters are key. I will review the work that I have undertaken to make these measurements with the APOGEE survey data, and discuss the constraints that these provide for future work with simulations.
Galaxies do not have the same metallicity everywhere. This simple fact has substantial consequences in many areas of astronomy — for example, transients such as pair-instability supernovae (PISNe) and gamma-ray bursts (GRBs) are expected to originate from low-metallicity stars. If galaxies are assumed to have the same metallicity throughout, then this limits the formation sites of GRB to low-metallicity galaxies, and PISNe to the lowest metallicity galaxies in the earliest, most distant regions of the Universe. However, cosmological simulations such as IllustrisTNG suggest that the internal metallicity profiles of galaxies vary substantially, especially at higher redshifts. When we account for the three-dimensional chemical inhomogeneities present within these galaxy, we find that the masses, metallicities, and star formation rates of the population of GRB host galaxies that we observe is consistent with the predictions from IllustrisTNG under the collapsar model of GRB formation. Extending this model to PISNe, we predict the number of PISNe that will be visible to the Euclid-DEEP survey to be 13 per year, or 77 over its lifetime. This number is an order of magnitude larger than the values that would be expected if chemical inhomogeneities within galaxies is ignored (~1.2 per year, or 7 over the lifetime of the mission).
JWST has been transformative in probing the early Universe. While we have been rapidly building up the number of z>6 galaxies, we have also been able to probe the properties of stars, gas, and dust in these early galaxies in great detail. In addition to these expected advancements in the high-z frontier, there has been discoveries of the unexpected. Some of these also challenge our current understanding of galaxy formation. I will summarise some of the these key results that have come from JWST observations over the last two years and discuss how the first light instruments in E-ELT can further advance our understanding of the early cosmos by bridging the gaps between current ground and space based observatories.
Digging for the first stars
The oldest stars in our Galaxy are a fossil record of the very first generation of stars. Their chemical makeup carries clues to the properties of these first stars, in particular their masses and properties of their supernovae. The field has made great progress in the small-sample stage, where the oldest (most iron-poor) stars known can be directly mapped to individual supernovae in the early Universe. The interpretation requires accurately estimated chemical abundances, through advanced spectroscopic modelling. Beyond this, the mapping of chemical abundances to supernova properties is not as obvious as it might seem. I will present resent progress and setbacks in the field.
The highly neutral intergalactic medium during the Epoch of Reionization (EoR) is expected to dampen Lyman-alpha emission, providing a unique window into the morphology of reionization and the underlying sources shaping the EoR. In this workshop, I will present our latest findings on reionization constraints, employing two distinct observables – the Lyman-alpha forests and the presence of Lyman-alpha emitters (LAEs).
Utilizing measurements from ground-based, wide-field, integral-field spectrographs such as those on the VLT, we apply a Bayesian framework in conjunction with contemporary galaxy and CMB observations. Our analysis indicates that reionization persists until as late as z~5.4, with low-mass galaxies emerging as the primary contributors to the UV ionizing budget.
Subsequently, I will delve into a semi-analytical model assessing the detectability of LAEs during the EoR. Notably, our findings reveal that brighter galaxies are less affected by Lyman-alpha damping-wing absorption. This luminosity-dependent attenuation explains why Lyman-alpha emission has predominantly been observed in the brightest galaxies at z>~8.
Observations of the total (baryonic and dark matter) mass distribution evolution with redshift are crucial to testing galaxy evolution theories and simulations. To measure the total mass distribution, galaxy-scale strong gravitational lenses complement the resolved dynamical observations currently limited to z < 0.5. We use Gravitational Lens Efficient Explorer (GLEE) software to model a sample of seven galaxy-scale lenses from the ASTRO 3D Galaxy Evolution with Lenses (AGEL) survey. The AGEL lenses, modeled using HST/WFC3 F140W images, have deflector redshifts between 0.3< z< 0.9. Assuming a power-law density profile with slope gamma, we measure the total mass density profile for the deflector galaxies via lens modeling. We also measure the stellar velocity dispersions for four lenses and obtain the velocity dispersions from SDSS for the remaining lenses to test our lens models by comparing the observed and model-predicted velocity dispersions. We measure an average density profile slope of -1.95+/-0.09 for the seven AGEL lenses and a gamma--z relation that does not evolve with redshift at z<1. Although our result is consistent with some observational studies and simulations, it conflicts with other studies at z<1 that suggest the gamma--z relation evolves with redshift. The apparent conflicts among observations and simulations may be due to a combination of 1) systematics in the lensing and dynamical modeling, 2) challenges in comparing observables to predictions from simulations, and 3) assuming a simple power-law for the mass distribution. By providing more deflectors at z>0.5, the AGEL survey will provide more substantial constraints on whether the mass profiles evolve with redshift as predicted by current theoretical models.
Our paradigm of galaxy formation is being transformed by JWST, ALMA, and local Galactic archaeology surveys (Gaia, H3, APOGEE), which suggest that disk galaxies, including our Milky Way (MW), form surprisingly early, z>4, and prevail throughout the cosmic history. I will present insights into disk formation from new high-resolution cosmological zoom-in simulations focusing on the early evolution of an MW-like galaxy progenitor. This galaxy was drawn from the TNG50 cosmological simulation as one of the closest MW analogs in terms of mass assembly history, early disk formation, and chemo-kinematic structure of the stellar disk at z=0. Resimulating this galaxy with detailed modeling of multiphase ISM, turbulence-regulated star formation, and on-the-fly radiative transfer enables us to investigate the disk formation during the first few Gyr of the universe's evolution and to highlight both the differences and similarities between such early disk galaxies and nearby star-forming galaxies.
The formation of massive black hole binaries (MBHBs) is a direct consequence of galaxy mergers. Their evolution within the final parsec is most likely dominated by interactions with circumbinary disks (CBDs), and remains unresolved by current telescopes.
In the coming years, multimessenger observations will yield new insights about the populations of MBHBs in their final stages of coalescence. These observations will include:
- an imminent detection of the gravitational wave background (GWB) emitted by MBHBs and detected by pulsar timing arrays (PTAs);
- detection of a large sample of MBHB sub-parsec candidates with the Vera Rubin observatory, thus yielding insight into the population statistics of coalescing MBHBs;
- mergers of MBHBs with LISA.
In this talk I will present the to-date largest suite of hydrodynamic simulations of eccentric, unequal mass binaries interacting with CBDs, yielding CBD-driven evolution rates for sub-parsec MBHBs. I will discuss how interactions with CBDs shape the orbital dynamics of MBHBs. Based on a sample of MBHBs motivated by cosmological simulations, I will show that CBD dynamics plays a key role in MBHB evolution, and leaves an unmistakeable signature in the population statistics of binaries as they evolve towards merger.
Modern galaxy formation models are now able to reproduce an incredible array of observed galaxy properties. And yet, some of these successful cutting edge models treat critical processes (e.g., supernova feedback, AGN feedback, etc.) in qualitatively distinct ways. This creates a real challenge: how can we meaningfully constrain galaxy formation models in a landscape where highly varied models arrive at seemingly similar agreement with observations? In this talk, I will overview the state of modern galaxy formation models, with an emphasis on star formation, stellar feedback, and AGN. I will discuss the qualitative agreements between these models, but also highlight areas of tension. I will then discuss key areas in which models are still likely inadequately treating the underlying physical processes, and suggest some areas where new observational constraints would be most impactful.
The achievement of gender parity in a large astrophysics research centre
Separating Star Formation, Active Galactic Nuclei, and Shocks in Galaxies
The cosmic evolution of galaxies and supermassive black holes (SMBHs) is believed to be correlated through interlinked physical processes. However, two aspects of the galaxy-BH correlation remain unclear: the fueling of actively accreting black holes (called Active Galactic Nuclei or AGNs) and the physical process of AGN feedback. Previous attempts to answer these questions using single-aperture spectra of galaxies have fallen short, as they only consider the dominant excitation source in the spectrum and cannot rule out the involvement of other excitation sources such as supermassive black holes, star formation, and shock excitations. Here, we present a solution for the mixing mechanisms in galaxy spectra analysis by building a new theoretical three-dimensional (3D) diagram to simultaneously separate star formation, AGN, and shocks in galaxies with integral field spectroscopy (IFU) data. This new 3D diagram incorporates the most up-to-date and self-consistent theoretical models for HII regions, AGN narrow-line regions, and the time-dependent shocks and precursor models. The inclusion of theoretical models in the new 3D diagram independently constrains the parameter space for each mechanism and provides information on the gas metallicity, ionization states, and shock velocity along with the separation. By applying this new 3D diagram, researchers can obtain detailed maps of the mechanism distribution, gas metallicity, and ionization states for individual galaxies. This will enable more comprehensive studies on AGN feedback and star formation across cosmic time.