arXiv subjects

Katherine E. Harborne

Publications and source records attributed to Katherine E. Harborne.

15 recordsLinked to original sources

arXiv2026

The MAGPI survey: Stellar population radial trends and mass assembly in star-forming galaxies at z~0.3

The evolution of galaxies from cosmic noon to the present day provides a key window to probe the balance between early, rapid bulge formation and prolonged disk growth. The epoch at $z \sim 0.3$ marks a crucial transitional phase between the peak of cosmic star formation and the predominantly quiescent local Universe. In this work, we examine the spatially resolved stellar populations of 34 galaxies at $z \sim 0.3$ to quantify radial gradients in age, stellar metallicity, and star formation activity, and disentangle the distinct evolutionary pathways of inner and outer galactic components. We utilise MUSE integral-field spectroscopy data cubes from the MAGPI survey at redshifts of $0.28 < z < 0.35$. Stellar population properties are derived using the spectral synthesis codes FADO and Starlight, and radial profiles are constructed by fitting isophotal annuli to the galaxy continuum emission. We further reconstruct star formation histories and cumulative mass assembly curves for inner and outer regions. We find pronounced negative radial gradients in age and negative to flat gradients in stellar metallicity. Inner regions are systematically older and more metal-rich than their surrounding outskirts, with age differences up to 3-4 Gyr in the most massive systems. H$α$ equivalent width profiles reveal centrally suppressed specific star formation in most galaxies. Star formation histories and mass assembly curves demonstrate that galaxy cores formed $80\%$ of their stellar mass rapidly, within the first 2-3 Gyr of cosmic time; while areas outside $\mathrm{1\,R_{eff}}$ assembled more gradually and sustained star formation to later epochs. Outskirts evolve primarily through extended, secular star formation, establishing the centrally concentrated quenching and inside-out growth that link high-redshift systems to the quiescent galaxies of the local Universe.

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arXiv2026

Consequences of radially correlated rotation curves for galaxy mass models

Consecutive points in rotation curve measurements are correlated with each other, but this is usually ignored when constructing galaxy mass models. We apply a recently proposed data-driven approach to include the characteristic amplitude and scale length of such correlations as `nuisance parameters'. We construct mass models for $134$ galaxies from the SPARC rotation curve compilation with Navarro-Frenk-White (NFW) and pseudo-isothermal sphere (pISO) models for the dark halo. Allowing for correlations in the rotation curves generally improves the goodness of fit for both halo models, often yielding a formally good fit ($χ^2_\mathrm{r}\approx 1$) and model uncertainties that seem more representative of the constraining power of the data. For both halo models the inference on the typical correlation amplitude and scale length are very similar and physically plausible, $\sim 20\,\mathrm{km}\,\mathrm{s}^{-1}$ and $\sim 5\,\mathrm{kpc}$, respectively. The parametric form that we use to describe the correlations is intentionally simple, and our fitting approach makes the parameters describing possible correlations prone to `absorbing' other systematic errors, so we regard these estimates as upper limits. Without allowing for correlations we find a statistical preference for the pISO over the NFW model for $88$/$134$ galaxies; this preference essentially disappears when correlations are allowed for. Accounting for correlations in rotation curves when constructing mass models fundamentally affects how they are interpreted, highlighting an important systematic uncertainty that affects evidence for cusps or cores in dark matter haloes.

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arXiv2026

A Census of Double-Peaked Lyman-alpha Emitters in MAGPI: Classification, Global Characteristics, and Spatially Resolved Properties

Double-peaked Ly$α$ profiles provide critical insights into gas kinematics and the distribution of neutral hydrogen (HI) from the interstellar to the intergalactic medium (ISM to IGM), and serve as valuable diagnostics of ionising Lyman continuum (LyC) photon escape. We present a study of the global and spatially resolved properties of double-peaked Ly$α$ emitters (LAEs) based on VLT/MUSE data from the MAGPI survey. From a parent sample of 417 LAEs at z = 2.9 - 6.6 in the first 35 fields, we identify 108 double-peaked LAEs using an automated peak classification technique. We measure a double-peak fraction of $\sim37\%$ at $z < 4$, decreasing to $\sim14\%$ at $z > 4$, likely due to enhanced IGM attenuation. Approximately $17\%$ of the double-peaked LAEs are blue-dominated, possibly tracing gas inflows, though backscattering remains a viable alternative for sources without systemic redshift. The blue-to-total flux ratio exhibits a luminosity dependence: fainter lines generally show higher blue flux. We find a narrowing of the red peak at $z > 4$, despite the presence of the blue peak, indicating intrinsic galaxy evolution rather than IGM attenuation. Several LAEs exhibit residual flux in the absorption trough, with normalised trough flux anticorrelating with peak separation, reflecting variations in HI column density. We further investigate spatially resolved properties of ten red-dominated LAEs with extended Ly$α$ halos. Despite azimuthal variations, both the blue-to-total flux ratio and normalised trough flux density increase with radius, while peak separation decreases. The red peak asymmetry shows only minor radial changes. These trends are consistent with variations in shell outflow velocity and HI column density across the halos. Based on peak separation, red peak asymmetry, and residual trough flux, we identify five LAEs as strong LyC-leaker candidates.

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arXiv2026

Dynamical disequilibrium in dwarf galaxies: rethinking gas dynamics, rotation curves, and dark matter inference

We quantify departures from hydrodynamical and centrifugal equilibrium in the gas discs of low-mass ($10^{10.75}<M_\mathrm{200c}/\mathrm{M}_\odot<10^{11}$) galaxies from the COLIBRE cosmological hydrodynamical simulations. We evaluate the full Eulerian acceleration balance in the midplane and show that disequilibrium is widespread: equilibrium-based circular velocity estimates typically have errors of $\geq 10$ per cent ($\approx 75$ per cent of midplane gas by mass). Disequilibrium is strongest and the largest associated errors occur in the inner few kiloparsecs that are crucial for constraining the dark matter density profile. Correcting the circular velocity to account for pressure and convective terms does not reliably improve its recovery in strongly perturbed systems where time-dependent forces dominate the residual acceleration budget. Stellar feedback, self-gravitating gas clumps and AGN energy injection account for most strong local perturbations, and large-scale gravitational asymmetries act as a scaffold for disequilibrium. We classify gas discs into coherent, perturbed, and slow/erratic rotators and show that this classification correlates with galaxy properties like mass, morphology and tracers of recent feedback. A majority of galaxies in our sample would be unsuitable for standard rotation curve analysis. Much of the observed diversity in the shapes of dwarf galaxy rotation curves may stem from non-equilibrium gas motions rather than diversity in mass profiles - resolving the discrepancy is then first and foremost a problem in gas dynamics.

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arXiv2026

The MAGPI Survey: co-evolution of baryons and dark matter in star-forming disk-like galaxies at $0.1 \lesssim z \lesssim 0.85$

We present a comprehensive analysis of the dark matter (DM) content and its structural dependence in star-forming disk-like galaxies at intermediate redshifts ($0.1 \lesssim z \lesssim 0.85$), utilizing spatially resolved kinematic data from the MAGPI survey. We report the following: (1) Low stellar mass galaxies ($M_{\rm star} < 10^{9.5}\, M_\odot$) are strongly DM dominated across all radii, with average $\langle f_{_{\rm DM}} \rangle \sim 0.85$, while high-mass ($M_{\rm star} > 10^{10.5}\, M_\odot$) systems exhibit relatively low DM fractions in their inner regions ($\langle f_{_{\rm DM}} \rangle \sim 0.47$) which is equivalent to local massive disk galaxies (e.g., Milky Way and Andromeda). This suggests a mass-dependent structural dichotomy, most-likely governed by a combination of internal galactic processes and environmental influences. (2) A tight inverse correlation between $f_{_{\rm DM}}$ and baryon mass surface density ($Σ_{\rm bar}$), with intrinsic scatter of $\sim 0.11$ dex. This is consistent with an inside-out baryon assembly scenario and suggests that the fundamental structural correlations of galaxies were already established by $z\sim 0.85$. (3) No significant evolution in $f_{_{\rm DM}}$ with redshift across the MAGPI window, and when combined with higher-redshift ($0.6 \leq z \leq 1.5$) data from Sharma et al. 2025, we quantitatively show that the reported decline in $f_{_{\rm DM}}(z)$ is most-likely due to observational biases against low-mass systems at $z > 1$. These results offer empirical evidence for a scenario in which disk-like galaxies evolve through a co-regulated build-up of baryonic and DM components, preserving internal structural regularities (such as the total mass distribution and rotation-curve shape) throughout cosmic time.

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arXiv2025

The MAGPI Survey: forward modelled gas-phase metallicity gradients in galaxies at $z\sim 0.3$

We measure the seeing-deconvolved gas-phase metallicity gradients of 70 star-forming galaxies at $z\sim 0.3$ from the MAGPI survey and investigate their relationship with galaxy properties to understand the mechanisms that influence the distribution of metals and shape the evolution of the galaxies. We use a Bayesian modelling technique, Blobby3D, which accounts for seeing effects (beam smearing) and can model the substructures of the flux distribution. The median metallicity gradient of our sample is $\nabla \mathrm{[O/H]}=-0.013^{+0.059}_{-0.033}$ dex/kpc. Among the galaxies in our sample, 32.9% have negative metallicity gradients (2$σ$ significance), 10.0% have positive gradients and 57.1% have flat gradients. The $\nabla \mathrm{[O/H]}$-$M_*$ relation of the MAGPI galaxies generally agrees with theoretical predictions, where a combination of stellar feedback, gas transport, and accretion shapes the metallicity profile, with the dominant processes varying with galaxy mass. We find a positive correlation between $\nabla \mathrm{[O/H]}$ and gas velocity dispersion ($r=0.36$), indicating that stronger gas turbulence is associated with flatter or inverted metallicity gradients, likely due to enhanced gas mixing. Additionally, smaller galaxies tend to have flatter or positive gradients, suggesting that metal dilution by gas accretion or removal via feedback-driven winds may outweigh metal enrichment in small galaxies.

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arXiv2025

The diverse star formation histories of early massive, quenched galaxies in modern galaxy formation simulations

We present a comprehensive study of the star formation histories of massive-quenched galaxies at $z=3$ in 3 semi-analytic models (SHARK, GAEA, GALFORM) and 3 cosmological hydrodynamical simulations (EAGLE, IllustrisTNG, Simba). We study the predicted number density and stellar mass function of massive-quenched galaxies, their formation and quenching timescales and star-formation properties of their progenitors. Predictions are disparate in all these diagnostics, for instance: (i) some simulations reproduce the observed number density of very massive-quenched galaxies ($>10^{11}\rm M_{\odot}$) but underpredict the high density of intermediate-mass ones, while others fit well the lower masses but underpredict the higher ones; (ii) In most simulations, except for GAEA and EAGLE, most massive-quenched galaxies had starburst periods, with the most intense ones happening at $4 300\rm M_{\odot}\,yr^{-1}$; (iii) quenching timescales are in the range $\approx 20-150$~Myr depending on the simulation; among other differences. These disparate predictions can be tied to the adopted Active Galactic Nuclei (AGN) feedback model. For instance, the explicit black-hole (BH) mass dependence to trigger the "radio mode" in IllustrisTNG and Simba makes it difficult to produce quenched galaxies with intermediate stellar masses, also leading to higher baryon collapse efficiencies ($\approx 15-30$%); while the strong bolometric luminosity dependence of the AGN outflow rate in GAEA leads to BHs of modest mass quenching galaxies. Current observations are unable to distinguish between these different predictions due to the small sample sizes. However, these predictions are testable with current facilities and upcoming observations, allowing a "true physics experiment" to be carried out.

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arXiv2024

The MAGPI Survey: radial trends in star formation across different cosmological simulations in comparison with observations at $z \sim$ 0.3

We investigate the internal and external mechanisms that regulate and quench star formation (SF) in galaxies at $z \sim 0.3$ using MAGPI observations and the EAGLE, Magneticum, and IllustrisTNG cosmological simulations. Using SimSpin to generate mock observations of simulated galaxies, we match detection/resolution limits in star formation rates and stellar mass, along with MAGPI observational details including the average point spread function and pixel scale. While we find a good agreement in the slope of the global star-forming main sequence (SFMS) between MAGPI observations and all three simulations, the slope of the resolved SFMS does not agree within 1 $-$ 2$σ$. Furthermore, in radial SF trends, good agreement between observations and simulations exists only for galaxies far below the SFMS, where we capture evidence for inside-out quenching. The simulations overall agree with each other between $\sim1.5-4 \ R_{\rm e}$ but show varying central suppression within $R \sim 1.5 \ R_{\rm e}$ for galaxies on and below the SFMS, attributable to different AGN feedback prescriptions. All three simulations show similar dependencies of SF radial trends with environment. Central galaxies are subject to both internal and external mechanisms, showing increased SF suppression in the centre with increasing halo mass, indicating AGN feedback. Satellite galaxies display increasing suppression in the outskirts as halo mass increases, indicative of environmental processes. These results demonstrate the power of spatially resolved studies of galaxies; while global properties align, radial profiles reveal discrepancies between observations and simulations and their underlying physics.

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arXiv2024

The MAGPI Survey: Orbital distributions, intrinsic shapes, and mass profiles for MAGPI-like Eagle galaxies using Schwarzschild dynamical models

Schwarzschild dynamical models are now regularly employed in large surveys of galaxies in the local and distant Universe to derive information on galaxies' intrinsic properties such as their orbital structure and their (dark matter and stellar) mass distribution. Comparing the internal orbital structures and mass distributions of galaxies in the distant Universe with simulations is key to understanding what physical processes are responsible for shaping galaxy properties. However it is first crucial to understand whether observationally derived properties are directly comparable with intrinsic ones in simulations. To assess this, we build Schwarzschild dynamical models for MUSE-like IFS cubes (constructed to be like those obtained by the MAGPI survey) of 75 galaxies at z ~ 0.3 from the Eagle simulations. We compare the true particle-derived properties with the galaxies' model-derived properties. In general, we find that the models can recover the true galaxy properties qualitatively well, with the exception of the enclosed dark matter, where we find a median offset of 48%, which is due to the assumed NFW profile not being able to reproduce the dark matter distribution in the inner region of the galaxies. We then compare our model-derived properties with Schwarzschild models-derived properties of observed MAGPI galaxies and find good agreement between MAGPI and Eagle: the majority of our galaxies (57%) have non-oblate shapes within 1 effective radius. More triaxial galaxies show higher fractions of hot orbits in their inner regions and tend to be more radially anisotropic.

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arXiv2024

The MAGPI Survey: the evolution and drivers of gas turbulence in intermediate-redshift galaxies

We measure the ionised gas velocity dispersions of star-forming galaxies in the MAGPI survey ($z\sim0.3$) and compare them with galaxies in the SAMI ($z\sim0.05$) and KROSS ($z\sim1$) surveys to investigate how the ionised gas velocity dispersion evolves. For the first time, we use a consistent method that forward models galaxy kinematics from $z=0$ to $z=1$. This method accounts for spatial substructure in emission line flux and beam smearing. We investigate the correlation between gas velocity dispersion and galaxy properties to understand the mechanisms that drive gas turbulence. We find that in both MAGPI and SAMI galaxies, the gas velocity dispersion more strongly correlates with the star-formation rate surface density ($Σ_{\rm SFR}$) than with a variety of other physical properties, and the average gas velocity dispersion is similar, at the same $Σ_{\rm SFR}$, for SAMI, MAGPI and KROSS galaxies. The results indicate that mechanisms related to $Σ_{\rm SFR}$ could be the dominant driver of gas turbulence from $z\sim1$ to $z\sim0$, for example, stellar feedback and/or gravitational instability. The gas velocity dispersion of MAGPI galaxies is also correlated with the non-rotational motion of the gas, illustrating that in addition to star-formation feedback, gas transportation and accretion may also contribute to the gas velocity dispersion for galaxies at $z\sim 0.3$. KROSS galaxies only have a moderate correlation between gas velocity dispersion and $Σ_{\rm SFR}$ and a higher scatter of gas velocity dispersion with respect to $Σ_{\rm SFR}$, in agreement with the suggestion that other mechanisms, such as gas transportation and accretion, are relatively more important at higher redshift galaxies.

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arXiv2024

The MAGPI Survey: Massive slow rotator population in place by $z \sim 0.3$

We use the `Middle Ages Galaxy Properties with Integral field spectroscopy' (MAGPI) survey to investigate whether galaxies have evolved in the distribution of their stellar angular momentum in the past 3-4 Gyr, as probed by the observational proxy for spin, $λ_{R}$. We use 2D stellar kinematics to measure $λ_{R}$ along with detailed photometric models to estimate galaxy ellipticity. The combination of these measurements quantifies the kinematic classes of `fast rotators' and the rarer `slow rotators', which show no regular rotation in their line-of-sight velocity fields. We compare 51 MAGPI galaxies with $\log_{10} (M_{\star}/\mathrm{M}_\odot) > 10$ to carefully drawn samples of MaNGA galaxies in the local Universe, selected to represent possible descendants of the MAGPI progenitors. The EAGLE simulations are used to identify possible evolutionary pathways between the two samples, explicitly accounting for progenitor bias in our results and the varied evolutionary pathways a galaxy might take between the two epochs. We find that the occurrence of slow rotating galaxies is unchanged between the MAGPI ($z \sim 0.3$) and MaNGA ($z \sim 0$) samples, suggesting the massive slow rotator population was already in place $\sim 4$ Gyr ago and has not accumulated since. There is a hint of the MAGPI sample having an excess of high $λ_{R}$ galaxies compared to the MaNGA sample, corresponding to more ordered rotation, but statistically the samples are not significantly different. The large-scale stellar kinematics, as quantified through the $λ_{R}$ parameter, of galaxies at $z \sim 0.3$ have already evolved into the diversity of structures seen today in the local Universe.

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arXiv2024

The MAGPI Survey: Evolution of radial trends in star formation activity across cosmic time

Using adaptive optics with the Multi-Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT), the Middle Ages Galaxy Properties with Integral Field Spectroscopy (MAGPI) survey allows us to study the spatially resolved Universe at a crucial time of ~4 Gyr ago ($z$ ~ 0.3) when simulations predict the greatest diversity in evolutionary pathways for galaxies. We investigate the radial trends in the star formation (SF) activity and luminosity-weighted stellar ages as a function of offset from the star-forming main sequence (SFMS) for a total of 294 galaxies. Using both H$α$ emission and the 4000 Angstrom break (i.e., D4000) as star formation rate (SFR) tracers, we find overall flat radial profiles for galaxies lying on and above the SFMS, suggestive of physical processes that enhance/regulate SF throughout the entire galaxy disc. However, for galaxies lying below the SFMS, we find positive gradients in SF suggestive of inside-out quenching. Placing our results in context with results from other redshift regimes suggests an evolution in radial trends at $z$ ~ 0.3 for SF galaxies above the SFMS, from uniformly enhanced SF at $z$ ~ 1 and $z$ ~ 0.3 to centrally enhanced SF at $z$ ~ 0 (when averaged over a wide range of mass). We also capture higher local SFRs for galaxies below the SFMS compared to that of $z$ ~ 0, which can be explained by a larger population of quenched satellites in the local Universe and/or different treatments of limitations set by the D4000-sSFR relation.

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arXiv2023

The distribution of stellar orbits in Eagle galaxies -- the effect of mergers, gas accretion, and secular evolution

The merger history of a galaxy is thought to be one of the major factors determining its internal dynamics, with galaxies having undergone different types or mergers (e.g. dry, minor or major mergers) predicted to show different dynamical properties. We study the instantaneous orbital distribution of galaxies in the Eagle simulation, colouring the orbits of the stellar particles by their stellar age, in order to understand whether stars form in particular orbits (e.g. in a thin or thick disc). We first show that Eagle reproduces well the observed stellar mass fractions in different stellar orbital families as a function of stellar mass and spin parameter at z = 0. We find that the youngest stars reside in a thin disc component that can extend to the very inner regions of galaxies, and that older stars have warmer orbits, with the oldest ones showing orbits consistent with both hot and counter-rotating classifications, which is consistent with the trend found in the Milky-Way and other disc galaxies. We also show that counter-rotating orbits trace galaxy mergers - in particular dry mergers, and that in the absence of mergers, counter-rotating orbits can also be born from highly misaligned gas accretion that leads to star formation.

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arXiv2021

The diverse nature and formation paths of slow rotator galaxies in the EAGLE simulations

We use a sample of $z=0$ galaxies visually classified as slow rotators (SRs) in the EAGLE hydrodynamical simulations to explore the effect of galaxy mergers on their formation, characterise their intrinsic galaxy properties, and study the connection between quenching and kinematic transformation. SRs that have had major or minor mergers (mass ratios $\ge 0.3$ and $0.1-0.3$, respectively) tend to have a higher triaxiality parameter and ex-situ stellar fractions than those that had exclusively very minor mergers or formed in the absence of mergers ("no-merger" SRs). No-merger SRs are more compact, have lower black hole-to-stellar mass ratios and quenched later than other SRs, leaving imprints on their $z=0$ chemical composition. For the vast majority of SRs we find that quenching, driven by active galactic nuclei feedback, precedes kinematic transformation, except for satellite SRs, in which these processes happen in tandem. However, in $\approx 50$\% of these satellites, satellite-satellite mergers are responsible for their SR fate, while environment (i.e. tidal field and interactions with the central) can account for the transformation in the rest. By splitting SRs into kinematic sub-classes, we find that flat SRs prefer major mergers; round SRs prefer minor or very minor mergers; prolate SRs prefer gas-poor mergers. Flat and prolate SRs are more common among satellites hosted by massive halos ($>10^{13.6}\,\rm M_{\odot}$) and centrals of high masses ($M_{\star} > 10^{10.5}\, \rm M_{\odot}$). Although EAGLE galaxies display kinematic properties that broadly agree with observations, there are areas of disagreement, such as inverted stellar age and velocity dispersion profiles. We discuss these and how upcoming simulations can solve them.

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arXiv2021

The SAMI Galaxy Survey: a statistical approach to an optimal classification of stellar kinematics in galaxy surveys

Large galaxy samples from multi-object IFS surveys now allow for a statistical analysis of the z~0 galaxy population using resolved kinematics. However, the improvement in number statistics comes at a cost, with multi-object IFS survey more severely impacted by the effect of seeing and lower S/N. We present an analysis of ~1800 galaxies from the SAMI Galaxy Survey and investigate the spread and overlap in the kinematic distributions of the spin parameter proxy $λ_{Re}$ as a function of stellar mass and ellipticity. For SAMI data, the distributions of galaxies identified as regular and non-regular rotators with \textsc{kinemetry} show considerable overlap in the $λ_{Re}$-$\varepsilon_e$ diagram. In contrast, visually classified galaxies (obvious and non-obvious rotators) are better separated in $λ_{Re}$ space, with less overlap of both distributions. Then, we use a Bayesian mixture model to analyse the observed $λ_{Re}$-$\log(M_*/M_{\odot})$ distribution. Below $\log(M_{\star}/M_{\odot})\sim10.5$, a single beta distribution is sufficient to fit the complete $λ_{Re}$ distribution, whereas a second beta distribution is required above $\log(M_{\star}/M_{\odot})\sim10.5$ to account for a population of low-$λ_{Re}$ galaxies. While the Bayesian mixture model presents the cleanest separation of the two kinematic populations, we find the unique information provided by visual classification of kinematic maps should not be disregarded in future studies. Applied to mock-observations from different cosmological simulations, the mixture model also predicts bimodal $λ_{Re}$ distributions, albeit with different positions of the $λ_{Re}$ peaks. Our analysis validates the conclusions from previous smaller IFS surveys, but also demonstrates the importance of using kinematic selection criteria that are dictated by the quality of the observed or simulated data.

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