arXiv subjects

Andreea S. Font

Publications and source records attributed to Andreea S. Font.

At least 19 recordsLinked to original sources

arXiv2026

Co-evolution of Supermassive Black Holes and their Host L* galaxies: implications for Milky Way and M31

We investigate the origin of the scatter in supermassive black hole (BH) masses among L* galaxies, using the ARTEMIS and EAGLE simulations. We classify galaxies by their central BH-to-stellar mass ratios and track systems with the lowest and highest ratios (LBH and HBH, respectively). Although these populations have similar properties at z~ 2, they diverge significantly towards lower redshifts. LBH galaxies maintain higher gas fractions and sustain star formation, while HBHs form stars earlier, experience faster BH growth, more efficient feedback, and subsequent quenching. The simulations broadly match the observed scatter in the BH masses and galaxy morphologies in the L* regime, linking it to differences in merger histories. Galaxies with more active merger histories host more massive BHs at present and are predominantly elliptical, whereas those with quieter histories host lower-mass BHs and tend to be disc-like. Mergers induce BH growth through enhanced gas accretion and direct BH-BH coalescences. However, these channels operate differently: in HBH galaxies, BHs grow primarily (~90%) through gas accretion, whereas in LBHs they grow through both gas accretion and BH--BH mergers, in comparable fractions. These results suggest that the contrasting BH masses in the Milky Way and M31 may arise from differences in their merger histories. We also investigate the role of feedback from supernovae (SN) versus active galactic nuclei (AGN) on these scales. AGN feedback appears to be the primary mechanism responsible for quenching MW-mass systems, although SN feedback remains the dominant regulator of their overall evolution.

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arXiv2026

Implications of a contracted dark matter halo for the Milky Way's inferred virial mass

We investigate how reliably the global properties of Milky Way-mass dark matter haloes can be recovered from dynamical data over a limited radial range, particularly $\lesssim 30~\mathrm{kpc}$ where observations are most sensitive but baryonic processes modify the halo structure. Using the ARTEMIS simulations, which produce varying degrees of baryon-induced contraction, we fit dark matter profiles over restricted radial ranges using commonly adopted parametric models. Assuming negligible observational uncertainties allows the systematic errors from these choices to be isolated. When fits are confined to inner radii, an NFW profile underestimates the virial mass by a factor of $\approx 2$ on average ($\approx 4$ for some systems), and the concentration by a factor of $\approx 2$. Einasto and generalised-NFW models provide excellent local fits but retain similar global biases. In contrast, the contracted halo prescription from Cautun et al. (2020) yields stable extrapolations and recovers unbiased halo mass estimates over all radii. The inferred mass improves systematically with increasing radial coverage, and tracers beyond $\gtrsim 50~\mathrm{kpc}$ largely eliminate the mean bias for all models. The local dark matter density at the Solar radius is recovered to within $\lesssim 5\%$ for all profiles other than NFW. These biases are sufficient to reconcile recent low Milky Way mass estimates derived from inner rotation-curve analyses with the canonical $\approx 10^{12}~\mathrm{M}_\odot$. We additionally find a halo-to-halo scatter of $\gtrsim 0.1$ dex ($\approx 25\%$) persists even under idealised conditions, setting a likely lower limit for the precision of halo mass estimates.

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arXiv2026

A simulation-based inference of the Milky Way merger history

Accreted stars in the Milky Way (MW) preserve information about the progenitor galaxies where they formed in their chemical and kinematic properties. In this study, we use the chemo-dynamical signatures in the merger debris to approximate the posterior distribution of disrupted satellite properties at the time of infall. Adopting a simulation-based inference framework, we train an ensemble of normalizing flows using samples of merger debris from the Auriga suite of simulations of MW-like galaxies. Applying this methodology to a local sample of accreted stars in the MW, we infer the lookback times, stellar and halo masses, and halo mass merger ratios of several known accretion events in the Galaxy: Gaia Enceladus-Sausage (GES), Helmi streams, Heracles, I'itoi, LMS-1/Wukong, Sagittarius (Sgr), Sequoia and Thamnos. Our predictions align with the accretion time and mass estimates from the literature, and the expected relation between the progenitor stellar masses and debris metallicities across redshifts. The total stellar mass accreted from these events is predicted to be $2.2^{+1.1}_{-0.6}\times10^{9}~\rm{M_{\odot}}$, with GES and Sgr being the largest contributors. The predicted stellar mass accreted from fully disrupted progenitors in the stellar halo is $1.3^{+1.0}_{-0.5}\times10^{9}~\rm{M_{\odot}}$, which is consistent with previous mass measurements of this component. We provide a prediction for the evolution of the MW halo mass until the accretion of Sgr ($z\approx1$): specifically, we find that the mass growth of the Galaxy from the time of its first merger ($z\approx5$) to $z\approx2$ exceeds the total mass of the known progenitors accreted during that interval, suggesting the presence of unidentified substructures. Our estimate of the Galaxy halo mass after the Sgr merger, but prior to the accretion of the Magellanic Clouds, is $5.9^{+1.4}_{-1.1}\times10^{11}~\rm{M_{\odot}}$.

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arXiv2026

Optimized HDBSCAN clustering for reconstructing the merger history of the Milky Way: applications and limitations

Clustering algorithms can help reconstruct the assembly history of the Milky Way by identifying groups of stars sharing similar properties in a kinematical or chemical abundance space. Despite being promising tools, their efficiency has not yet been fully tested in a realistic cosmological framework. We investigate the effectiveness of the HDBSCAN clustering algorithm in the recovery of the progenitors of Milky Way-type galaxies, using several systems from the Auriga suite of simulations. We develop a methodology aimed at improving the efficiency of the algorithm and avoiding fragmentation: First, we use a 12-dimensional feature space including a range of chemodynamical properties and stellar ages; furthermore, we optimise the algorithm using information from the internal structure of the clusters of accreted stars. We show that our approach yields good results in terms of both purity and completeness of clusters for galaxies with different types of accretion histories. We also evaluate the decrease in efficiency due to contamination by in situ stars. While for accreted-only haloes the algorithm matches well the recovered clusters with the individual progenitors and is able to recover accretion events up to a redshift of accretion $z_{\rm acc}\sim3$, for accreted + in situ haloes it can only identify the more recent accretion events ($z_{\rm acc} < 1$). However, the purity of the identified clusters remains remarkably high even in this case. Our results suggest that HDBSCAN can efficiently identify accreted debris in Milky Way-type galaxies in realistic conditions, however, it requires careful optimization to provide valid results.

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arXiv2025

Measuring and modelling the Splash with APOGEE/Gaia and ARTEMIS

Using combined data from SDSS-IV/APOGEE and Gaia, we study the chemo-dynamical properties of the Splash population in comparison with those of the high-alpha disc. We investigate a wide range of abundance ratios, finding that the Splash differs from the high-alpha disc overall. However, these differences result from a smooth variation of chemical compositions as a function of orbital properties. The Splash occupies the high-alpha, high-[Al,K/Fe], and low-[Mn/Fe] end of the high-alpha disk population. In agreement with previous studies, we find that Splash stars are distributed over large heights from the Galactic mid-plane. To further elucidate the relation between the Splash and the high-alpha disk, we turn to simulations. Using a sample of Milky Way-like galaxies with and without major accretion events from the ARTEMIS simulations, we find that Splash-like populations are ubiquitous, though not always resulting from major mergers. Lower mass progenitors can also generate Splash-like features, as long as they are on retrograde orbits. Moreover, we find a strong correlation between the mass fraction of Splash stars and the fraction of retrograde accreted stars in the disk. Some galaxies with minor (retrograde) mergers contain more pronounced Splash populations than others with major, but prograde, mergers. For stars in the high-alpha disks, we also find a decrease in the [alpha/Fe] with increasing orbital angular momentum. This trend is found in hosts with both major or minor mergers. Our results suggest that a number of relatively low-mass mergers on retrograde orbits could result in populations that are qualitatively similar to the Splash.

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arXiv2025

GalactiKit: reconstructing mergers from $z=0$ debris using simulation-based inference in Auriga

We present GalactiKit, a data-driven methodology for estimating the lookback infall time, stellar mass, halo mass and mass ratio of the disrupted progenitors of Milky Way-like galaxies at the time of infall. GalactiKit uses simulation-based inference to extract the information on galaxy formation processes encoded in the Auriga cosmological MHD simulations of Milky Way-mass halos to create a model that relates the properties of mergers to those of the corresponding merger debris at $z=0$. We investigate how well GalactiKit can reconstruct the merger properties given the dynamical, chemical, and the combined chemo-dynamical information of debris. For this purpose, three models were implemented considering the following properties of merger debris: (a) total energy and angular momentum, (b) iron-to-hydrogen and alpha-to-iron abundance ratios, and (c) a combination of all of these. We find that the kinematics of the debris can be used to trace the lookback time at which the progenitor was first accreted into the main halo. However, chemical information is necessary for inferring the stellar and halo masses of the progenitors. In both models (b) and (c), the stellar masses are predicted more accurately than the halo masses, which could be related to the scatter in the stellar mass-halo mass relation. Model (c) provides the most accurate predictions for the merger parameters, which suggests that combining chemical and dynamical data of debris can significantly improve the reconstruction of the Milky Way's assembly history.

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arXiv2024

ARTEMIS emulator: exploring the effect of cosmology and galaxy formation physics on Milky Way-mass haloes and their satellites

We present the new ARTEMIS Emulator suite of high resolution (baryon mass of $2.23 \times 10^{4}$ $h^{-1}$M$_{\odot}$) zoom-in simulations of Milky Way mass systems. Here, three haloes from the original ARTEMIS sample have been rerun multiple times, systematically varying parameters for the stellar feedback model, the density threshold for star formation, the reionisation redshift and the assumed warm dark matter (WDM) particle mass (assuming a thermal relic). From these simulations emulators are trained for a wide range of statistics that allow for fast predictions at combinations of parameters not originally sampled, running in $\sim 1$ms (a factor of $\sim 10^{11}$ faster than the simulations). In this paper we explore the dependence of the central haloes' stellar mass on the varied parameters, finding the stellar feedback parameters to be the most important. When constraining the parameters to match the present-day stellar mass halo mass relation inferred from abundance matching we find that there is a strong degeneracy in the stellar feedback parameters, corresponding to a freedom in formation time of the stellar component for a fixed halo assembly history. We additionally explore the dependence of the satellite stellar mass function, where it is found that variations in stellar feedback, the reionisation redshift and the WDM mass all have a significant effect. The presented emulators are a powerful tool which allows for fundamentally new ways of analysing and interpreting cosmological hydrodynamic simulations. Crucially, allowing their free (subgrid) parameters to be varied and marginalised, leading to more robust constraints and predictions.

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arXiv2024

Applying machine learning to Galactic Archaeology: how well can we recover the origin of stars in Milky Way-like galaxies?

We present several machine learning (ML) models developed to efficiently separate stars formed in-situ in Milky Way-type galaxies from those that were formed externally and later accreted. These models, which include examples from artificial neural networks, decision trees and dimensionality reduction techniques, are trained on a sample of disc-like, Milky Way-mass galaxies drawn from the ARTEMIS cosmological hydrodynamical zoom-in simulations. We find that the input parameters which provide an optimal performance for these models consist of a combination of stellar positions, kinematics, chemical abundances ([Fe/H] and [$α$/Fe]) and photometric properties. Models from all categories perform similarly well, with area under the precision-recall curve (PR-AUC) scores of $\simeq 0.6$. Beyond a galactocentric radius of $5$~kpc, models retrieve $>90\%$ of accreted stars, with a sample purity close to $60\%$, however the purity can be increased by adjusting the classification threshold. For one model, we also include host galaxy-specific properties in the training, to account for the variability of accretion histories of the hosts, however this does not lead to an improvement in performance. The ML models can identify accreted stars even in regions heavily dominated by the in-situ component (e.g., in the disc), and perform well on an unseen suite of simulations (the Auriga simulations). The general applicability bodes well for application of such methods on observational data to identify accreted substructures in the Milky Way without the need to resort to selection cuts for minimising the contamination from in-situ stars.

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arXiv2024

Differences in the properties of disrupted and surviving satellites of Milky-Way-mass galaxies in relation to their host accretion histories

From the chemo-dynamical properties of tidal debris in the Milky Way, it has been inferred that the dwarf satellites that have been disrupted had different chemical abundances from their present-day counterparts of similar mass that survive today, specifically, they had lower [Fe/H] and higher [Mg/Fe]. Here we use the ARTEMIS simulations to study the relation between the chemical abundances of disrupted progenitors of MW-mass galaxies and their stellar mass, and the evolution of the stellar mass - metallicity relations (MZR) of this population with redshift. We find that these relations have significant scatter, which correlates with the accretion redshifts ($z_{\rm acc}$) of satellites, and with their cold gas fractions. We investigate the MZRs of dwarf populations accreted at different redshifts and find that they have similar slopes, and also similar with the slope of the MZR of the surviving population ($\approx 0.32$). However, the entire population of disrupted dwarfs displays a steeper MZR, with a slope of $\approx 0.48$, which can be explained by the changes in the mass spectrum of accreted dwarf galaxies with redshift. We find strong relations between the (mass-weighted) $\langle z_{\rm acc} \rangle$ of the disrupted populations and their global chemical abundances ($\langle$[Fe/H]$\rangle$ and $\langle$[Mg/Fe]$\rangle$), which suggests that chemical diagnostics of disrupted dwarfs can be used to infer the types of merger histories of their hosts. For the case of the MW, our simulations predict that the bulk of the disrupted population was accreted at $\langle z_{\rm acc} \rangle \approx 2$, in agreement with other findings. We also find that disrupted satellites form and evolve in denser environments, closer to their hosts, than their present-day counterparts.

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arXiv2023

Taking the Milky Way for a spin: disc formation in the ARTEMIS simulations

We investigate the formation (spin-up) of galactic discs in the ARTEMIS simulations of Milky Way-mass galaxies. In almost all galaxies discs spin up at higher [Fe/H] than the Milky Way (MW). Those that contain an analogue of the Gaia Sausage-Enceladus (GSE) spin up at a lower average metallicity than those without. We identify six galaxies with spin-up metallicity similar to that of the MW, which form their discs $\sim 8-11$ Gyr ago. Five of these experience a merger similar to the GSE. The spin-up times correlate with the halo masses at early times: galaxies with early spin-up have larger virial masses at a lookback time $t_L=12$ Gyr. The fraction of stars accreted from outside the host galaxy is smaller in galaxies with earlier spin-ups. Accreted fractions small enough to be comparable to the MW are only found in galaxies with the earliest disc formation and large initial virial masses ($M_\mathrm{200c} \approx2\times10^{11}M_\odot$ at $t_L=12$ Gyr). We find that discs form when the halo's virial mass reaches a threshold of $M_\mathrm{200c}\approx(6\pm3)\times10^{11}M_\odot$, independent of the spin-up time. However, the failure to form a disc in other galaxies appears to be instead related to mergers at early times. We also find that discs form when the central potential is not particularly steep. Our results indicate that the MW assembled its mass and formed its disc earlier than the average galaxy of a similar mass.

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arXiv2023

The FLAMINGO project: revisiting the $S_8$ tension and the role of baryonic physics

A number of recent studies have found evidence for a tension between observations of large-scale structure (LSS) and the predictions of the standard model of cosmology with the cosmological parameters fit to the cosmic microwave background (CMB). The origin of this '$S_8$ tension' remains unclear, but possibilities include new physics beyond the standard model, unaccounted for systematic errors in the observational measurements and/or uncertainties in the role that baryons play. Here we carefully examine the latter possibility using the new FLAMINGO suite of large-volume cosmological hydrodynamical simulations. We project the simulations onto observable harmonic space and compare with observational measurements of the power and cross-power spectra of cosmic shear, CMB lensing, and the thermal Sunyaev-Zel'dovich (tSZ) effect. We explore the dependence of the predictions on box size and resolution, cosmological parameters including the neutrino mass, and the efficiency and nature of baryonic 'feedback'. Despite the wide range of astrophysical behaviours simulated, we find that baryonic effects are not sufficiently large to remove the $S_8$ tension. Consistent with recent studies, we find the CMB lensing power spectrum is in excellent agreement with the standard model, whilst the cosmic shear power spectrum, tSZ effect power spectrum, and the cross-spectra between shear, CMB lensing, and the tSZ effect are all in varying degrees of tension with the CMB-specified standard model. These results suggest that some mechanism is required to slow the growth of fluctuations at late times and/or on non-linear scales, but that it is unlikely that baryon physics is driving this modification.

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arXiv2023

SP(k) -- A hydrodynamical simulation-based model for the impact of baryon physics on the non-linear matter power spectrum

Upcoming large-scale structure surveys will measure the matter power spectrum to approximately percent level accuracy with the aim of searching for evidence for new physics beyond the standard model of cosmology. In order to avoid biasing our conclusions, the theoretical predictions need to be at least as accurate as the measurements for a given choice of cosmological parameters. However, recent theoretical work has shown that complex physical processes associated with galaxy formation (particularly energetic feedback processes associated with stars and especially supermassive black holes) can alter the predictions by many times larger than the required accuracy. Here we present $\texttt{SP(k)}$, a model for the effects of baryon physics on the non-linear matter power spectrum based on a new large suite of hydrodynamical simulations. Specifically, the ANTILLES suite consists of 400 simulations spanning a very wide range of the "feedback landscape" and show that the effects of baryons on the matter power spectrum can be understood at approaching the percent level in terms of the mean baryon fraction of haloes, at scales of up to $k \lesssim 10 \, h \, $Mpc$^{-1}$ and redshifts up to $z=3$. For the range of scales and redshifts that will be probed by forthcoming cosmic shear measurements, most of the effects are driven by galaxy group-mass haloes ($M \sim 10^{13-14}$ M$_\odot$). We present a simple Python implementation of our model, available at $\href{https://github.com/jemme07/pyspk}{\mathrm{https{:}//github.com/jemme07/pyspk}}$, which can be used to incorporate baryon effects in standard gravity-only predictions, allowing for marginalisation over baryon physics within cosmological pipelines.

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arXiv2022

A correlation between accreted stellar kinematics and dark matter halo spin in the ARTEMIS simulations

We report a correlation between the presence of a Gaia-Sausage-Enceladus (GSE) analogue and dark matter halo spin in the ARTEMIS simulations of Milky Way-like galaxies. The haloes which contain a large population of accreted stars on highly radial orbits (like the GSE) have lower spin on average than their counterparts with more isotropic stellar velocity distributions. The median modified spin parameters $λ^\prime$ differ by a factor of $\sim1.7$ at the present-day, with a similar value when the haloes far from virial equilibrium are removed. We also show that accreted stars make up a smaller proportion of the stellar populations in haloes containing a GSE analogue, and are stripped from satellites with stellar masses typically $\sim4$ times smaller. Our findings suggest that the higher spin of DM haloes without a GSE-like feature is due to mergers with large satellites of stellar mass $\sim10^{10}M_\odot$, which do not result in prominent radially anisotropic features like the GSE.

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arXiv2022

GOGREEN: a critical assessment of environmental trends in cosmological hydrodynamical simulations at z ~ 1

Recent observations have shown that the environmental quenching of galaxies at z ~ 1 is qualitatively different to that in the local Universe. However, the physical origin of these differences has not yet been elucidated. In addition, while low-redshift comparisons between observed environmental trends and the predictions of cosmological hydrodynamical simulations are now routine, there have been relatively few comparisons at higher redshifts to date. Here we confront three state-of-the-art suites of simulations (BAHAMAS+MACSIS, EAGLE+Hydrangea, IllustrisTNG) with state-of-the-art observations of the field and cluster environments from the COSMOS/UltraVISTA and GOGREEN surveys, respectively, at z ~ 1 to assess the realism of the simulations and gain insight into the evolution of environmental quenching. We show that while the simulations generally reproduce the stellar content and the stellar mass functions of quiescent and star-forming galaxies in the field, all the simulations struggle to capture the observed quenching of satellites in the cluster environment, in that they are overly efficient at quenching low-mass satellites. Furthermore, two of the suites do not sufficiently quench the highest-mass galaxies in clusters, perhaps a result of insufficient feedback from AGN. The origin of the discrepancy at low stellar masses (Mstar <~ 1E10 Msun), which is present in all the simulations in spite of large differences in resolution, feedback implementations, and hydrodynamical solvers, is unclear. The next generation of simulations, which will push to significantly higher resolution and also include explicit modelling of the cold interstellar medium, may help to shed light on the low-mass tension.

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arXiv2022

Merger-induced galaxy transformations in the ARTEMIS simulations

Using the ARTEMIS set of 45 high-resolution cosmological simulations, we investigate a range of merger-induced dynamical transformations of Milky Way-like galaxies. We first identify populations of accreted stars on highly radial orbits, similar to the 'Gaia Sausage' in the Milky Way. We show that $\approx1/3$ of the ARTEMIS galaxies contain a similar feature, and confirm that they usually comprise stellar debris from the most massive accreted satellite. Selecting 15 galaxies with discs at the present-day, we study their changes around the times of the GS-like mergers. Dark matter haloes of many of these exhibit global changes in shape and orientation, with almost half becoming significantly more spherical when the mergers occur. Focusing on the galaxies themselves, we find that 4/15 have stellar discs which experience large changes in the orientation of their angular momentum (AM) axes, at rates of up to $\sim60$ degrees Gyr$^{-1}$. By calculating the orbital angular momentum axes of the satellites before they are accreted, we show that there is a tendency for the disc's AM to become more aligned with this axis after the merger. We also investigate the origin of in situ retrograde stars, analogous to the 'Splash' in the Milky Way. Tracing them back to earlier snapshots, we demonstrate that they were often disrupted onto their extreme orbits by multiple early mergers. We also find that the total mass of these stars outside the central regions positively correlates with the total accreted stellar mass.

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arXiv2022

High-resolution synthetic UV-submm images for Milky Way-mass simulated galaxies from the ARTEMIS project

We present redshift-zero synthetic dust-aware observations for the 45 Milky Way-mass simulated galaxies of the ARTEMIS project, calculated with the SKIRT radiative transfer code. The post-processing procedure includes components for star-forming regions, stellar sources, and diffuse dust. We produce and publicly release realistic high-resolution images for 50 commonly-used broadband filters from ultraviolet to sub-millimetre wavelengths and for 18 different viewing angles. We compare the simulated ARTEMIS galaxies to observed galaxies in the DustPedia database with similar stellar mass and star formation rate, and to synthetic observations of the simulated galaxies of the Auriga project produced in previous work using a similar post-processing technique. In all cases, global galaxy properties are derived using SED fitting. We find that, similar to Auriga, the post-processed ARTEMIS galaxies generally reproduce the observed scaling relations for global fluxes and physical properties, although dust extinction at FUV/UV wavelengths is underestimated and representative dust temperatures are lower than observed. At a resolved scale, we compare multi-wavelength non-parametric morphological properties of selected disc galaxies across the data sets. We find that the ARTEMIS galaxies largely reproduce the observed morphological trends as a function of wavelength, although they appear to be more clumpy and less symmetrical than observed. We note that the ARTEMIS and Auriga galaxies occupy adjacent regions in the specific star formation versus stellar mass plane, so that the synthetic observation data sets supplement each other.

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arXiv2022

Quenching of satellite galaxies of Milky Way analogues: reconciling theory and observations

The vast majority of low-mass satellite galaxies around the Milky Way and M31 appear virtually devoid of cool gas and show no signs of recent or ongoing star formation. Cosmological simulations demonstrate that such quenching is expected and is due to the harsh environmental conditions that satellites face when joining the Local Group (LG). However, recent observations of Milky Way analogues in the SAGA survey present a very different picture, showing the majority of observed satellites to be actively forming stars, calling into question the realism of current simulations and the typicality of the LG. Here we use the ARTEMIS suite of high-resolution cosmological hydrodynamical simulations to carry out a careful comparison with observations of dwarf satellites in the LG, SAGA, and the Local Volume (LV) survey. We show that differences between SAGA and the LG and LV surveys, as well as between SAGA and the ARTEMIS simulations, can be strongly reduced by considering differences in the host mass distributions and (more importantly) observational selection effects, specifically that low-mass satellites which have only recently been accreted are more likely to be star-forming, have a higher optical surface brightness, and are therefore more likely to be included in the SAGA survey. This picture is confirmed using data from the deeper LV survey, which shows pronounced quenching at low masses, in accordance with the predictions of LCDM-based simulations.

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arXiv2021

Towards a universal model for the density profiles of dark matter haloes

It is well established from cosmological simulations that dark matter haloes are not precisely self-similar and an additional parameter, beyond their concentration, is required to accurately describe their spherically-averaged mass density profiles. We present, for the first time, a model to consistently predict both halo concentration, $c$, and this additional `shape' parameter, $α$, for a halo of given mass and redshift for a specified cosmology. Following recent studies, we recast the dependency on mass, redshift, and cosmology to a dependence on `peak height'. We show that, when adopting the standard definition of peak height, which employs the so-called spherical top hat (STH) window function, the concentration--peak height relation has a strong residual dependence on cosmology (i.e., it is not uniquely determined by peak height), whereas the $α$--peak height relation is approximately universal when employing the STH window function. Given the freedom in the choice of window function, we explore a simple modification of the STH function, constraining its form so that it produces universal relations for concentration and $α$ as a function of peak height using a large suite of cosmological simulations. It is found that universal relations for the two density profile parameters can indeed be derived and that these parameters are set by the linear power spectrum, $P(k)$, filtered on different scales. We show that the results of this work generalise to any (reasonable) combination of $P(k)$ and background expansion history, $H(z)$, resulting in accurate predictions of the density profiles of dark matter haloes for a wide range of cosmologies.

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