| 1. |
- Agertz, Oscar, et al.
(författare)
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EDGE : The mass-metallicity relation as a critical test of galaxy formation physics
- 2020
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 491:2, s. 1656-1672
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Tidskriftsartikel (refereegranskat)abstract
- We introduce the 'Engineering Dwarfs at Galaxy Formation's Edge' (EDGE) project to study the cosmological formation and evolution of the smallest galaxies in the Universe. In this first paper, we explore the effects of resolution and sub-grid physics on a single low-mass halo (Mhalo = 109M⊙), simulated to redshift z = 0 at amass and spatial resolution of ∼ 20 M⊙ and ∼3 pc. We consider different star formation prescriptions, supernova feedback strengths, and on-the-fly radiative transfer (RT). We show that RT changes the mode of galactic self-regulation at this halo mass, suppressing star formation by causing the interstellar and circumgalactic gas to remain predominantly warm (∼104K) even before cosmic reionization. By contrast, without RT, star formation regulation occurs only through starbursts and their associated vigorous galactic outflows. In spite of this difference, the entire simulation suite (with the exception of models without any feedback) matches observed dwarf galaxy sizes, velocity dispersions, V-band magnitudes, and dynamical mass-to-light-ratios. This is because such structural scaling relations are predominantly set by the host dark matter halo, with the remaining model-to-model variation being smaller than the observational scatter. We find that only the stellar mass-metallicity relation differentiates the galaxy formation models. Explosive feedback ejects more metals from the dwarf, leading to a lower metallicity at a fixed stellar mass. We conclude that the stellar mass-metallicity relation of the very smallest galaxies provides a unique constraint on galaxy formation physics.
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| 2. |
- Agertz, Oscar, et al.
(författare)
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Vintergatan - i. The origins of chemically, kinematically, and structurally distinct discs in a simulated milky way-mass galaxy
- 2021
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 503:4, s. 5826-5845
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Tidskriftsartikel (refereegranskat)abstract
- Spectroscopic surveys of the Milky Way's stars have revealed spatial, chemical, and kinematical structures that encode its history. In this work, we study their origins using a cosmological zoom simulation, VINTERGATAN, of a MilkyWay-mass disc galaxy. We find that in connection to the last major merger at z ∼ 1.5, cosmological accretion leads to the rapid formation of an outer, metal-poor, low-[α/Fe] gas disc around the inner, metal-rich galaxy containing the old high-[α/Fe] stars. This event leads to a bimodality in [α/Fe] over a range of [Fe/H]. A detailed analysis of how the galaxy evolves since z ∼ 1 is presented. We demonstrate the way in which inside-out growth shapes the radial surface density and metallicity profile and how radial migration preferentially relocates stars from the inner disc to the outer disc. Secular disc heating is found to give rise to increasing velocity dispersions and scale heights with stellar age, which together with disc flaring explains several trends observed in the MilkyWay, including shallower radial [Fe/H] profiles above the mid-plane.We show how the galaxy formation scenario imprints non-trivial mappings between structural associations (i.e. thick and thin discs), velocity dispersions, α-enhancements, and ages of stars; e.g. the most metal-poor stars in the low-[α/Fe] sequence are found to have a scale height comparable to old high-[α/Fe] stars. Finally, we illustrate how at low spatial resolution, comparable to the thickness of the galaxy, the proposed pathway to distinct sequences in [α/Fe]-[Fe/H] cannot be captured.
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| 3. |
- Bruce, Louise C, et al.
(författare)
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A multi-lake comparative analysis of the General Lake Model (GLM) : Stress-testing across a global observatory network
- 2018
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Ingår i: Environmental Modelling & Software. - : Elsevier BV. - 1364-8152 .- 1873-6726. ; 102, s. 274-291
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Tidskriftsartikel (refereegranskat)abstract
- The modelling community has identified challenges for the integration and assessment of lake models due to the diversity of modelling approaches and lakes. In this study, we develop and assess a one-dimensional lake model and apply it to 32 lakes from a global observatory network. The data set included lakes over broad ranges in latitude, climatic zones, size, residence time, mixing regime and trophic level. Model performance was evaluated using several error assessment metrics, and a sensitivity analysis was conducted for nine parameters that governed the surface heat exchange and mixing efficiency. There was low correlation between input data uncertainty and model performance and predictions of temperature were less sensitive to model parameters than prediction of thermocline depth and Schmidt stability. The study provides guidance to where the general model approach and associated assumptions work, and cases where adjustments to model parameterisations and/or structure are required.
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| 4. |
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| 5. |
- Goater, Alex, et al.
(författare)
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EDGE : The direct link between mass growth history and the extended stellar haloes of the faintest dwarf galaxies
- 2024
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711. ; 527:2, s. 2403-2412
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Tidskriftsartikel (refereegranskat)abstract
- Ultra-f aint dw arf galaxies (UFDs) are commonly found in close proximity to the Milky Way and other massive spiral galaxies. As such, their projected stellar ellipticity and extended light distributions are often thought to owe to tidal forces. In this paper, we study the projected stellar ellipticities and faint stellar outskirts of tidally isolated ultra-faints drawn from the 'Engineering Dwarfs at Galaxy Formation's Edge' (EDGE) cosmological simulation suite. Despite their tidal isolation, our simulated dwarfs exhibit a wide range of projected ellipticities (0.03 < ϵ < 0.85), with many possessing anisotropic extended stellar haloes that mimic tidal tails, but owe instead to late-time accretion of lower mass companions. Furthermore, we find a strong causal relationship between ellipticity and formation time of a UFD, which is robust to a wide variation in the feedback model. We show that the distribution of projected ellipticities in our suite of simulated EDGE dwarfs matches well with a sample of 19 Local Group dwarf galaxies and a sample of 11 isolated dwarf galaxies. Given ellipticity in EDGE arises from an ex-situ accretion origin, the agreement in shape indicates the ellipticities of some observed dwarfs may also originate from a non-tidal scenario. The orbital parameters of these observed dwarfs further support that they are not currently tidally disrupting. If the baryonic content in these galaxies is still tidally intact, then the same may be true for their dark matter content, making these galaxies in our Local Group pristine laboratories for testing dark matter and galaxy formation models.
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| 6. |
- Grisdale, Kearn, et al.
(författare)
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The impact of stellar feedback on the density and velocity structure of the interstellar medium
- 2017
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 466:1, s. 1093-1110
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Tidskriftsartikel (refereegranskat)abstract
- We study the impact of stellar feedback in shaping the density and velocity structure of neutral hydrogen (H I) in disc galaxies. For our analysis, we carry out ~4.6 pc resolution N-body+adaptive mesh refinement hydrodynamic simulations of isolated galaxies, set up to mimic a Milky Way and a Large and Small Magellanic Cloud. We quantify the density and velocity structure of the interstellar medium using power spectra and compare the simulated galaxies to observedHI in local spiral galaxies from THINGS (TheHI Nearby Galaxy Survey). Our models with stellar feedback give an excellent match to the observed THINGS HI density power spectra. We find that kinetic energy power spectra in feedback-regulated galaxies, regardless of galaxy mass and size, show scalings in excellent agreement with supersonic turbulence (E(k) ∝ k-2) on scales below the thickness of the HI layer. We show that feedback influences the gas density field, and drives gas turbulence, up to large (kpc) scales. This is in stark contrast to density fields generated by large-scale gravity-only driven turbulence. We conclude that the neutral gas content of galaxies carries signatures of stellar feedback on all scales.
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| 7. |
- Muni, Claudia, et al.
(författare)
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From particles to orbits : precise dark matter density profiles using dynamical information
- 2024
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711. ; 527:3, s. 9250-9262
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Tidskriftsartikel (refereegranskat)abstract
- We introduce a new method to calculate dark matter halo density profiles from simulations. Each particle is ‘smeared’ over its orbit to obtain a dynamical profile that is averaged over a dynamical time, in contrast to the traditional approach of binning particles based on their instantaneous positions. The dynamical and binned profiles are in good agreement, with the dynamical approach showing a significant reduction in Poisson noise in the innermost regions. We find that the inner cusps of the new dynamical profiles continue inward all the way to the softening radius, reproducing the central density profile of higher resolution simulations within the 95 per cent confidence intervals, for haloes in virial equilibrium. Folding in dynamical information thus provides a new approach to improve the precision of dark matter density profiles at small radii, for minimal computational cost. Our technique makes two key assumptions that the halo is in equilibrium (phase mixed) and the potential is spherically symmetric. We discuss why the method is successful despite strong violations of spherical symmetry in the centres of haloes, and explore how substructures disturb equilibrium at large radii.
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| 8. |
- Orkney, Matthew D.A., et al.
(författare)
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EDGE : the puzzling ellipticity of Eridanus II's star cluster and its implications for dark matter at the heart of an ultra-faint dwarf
- 2022
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 515:1, s. 185-200
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Tidskriftsartikel (refereegranskat)abstract
- The Eridanus II (EriII) 'ultra-faint' dwarf has a large (15 pc) and low-mass (4.3 × 103 M·) star cluster (SC) offset from its centre by 23 ± 3 pc in projection. Its size and offset are naturally explained if EriII has a central dark matter core, but such a core may be challenging to explain in a ΛCDM cosmology. In this paper, we revisit the survival and evolution of EriII's SC, focusing for the first time on its puzzlingly large ellipticity (0.31+0.05-0.06). We perform a suite of 960 direct N-body simulations of SCs, orbiting within a range of spherical background potentials fit to ultra-faint dwarf (UFD) galaxy simulations. We find only two scenarios that come close to explaining EriII's SC. In the first scenario, EriII has a low-density dark matter core (of size ∼70 pc and density ≲ 2× 108, M⊙ , kpc-3). In this model, the high ellipticity of EriII's SC is set at birth, with the lack of tidal forces in the core allowing its ellipticity to remain frozen for long times. In the second scenario, EriII's SC orbits in a partial core, with its high ellipticity owing to its imminent tidal destruction. However, this latter model struggles to reproduce the large size of EriII's SC, and it predicts substantial tidal tails around EriII's SC that should have already been seen in the data. This leads us to favour the cored model. We discuss potential caveats to these findings, and the implications of the cored model for galaxy formation and the nature of dark matter.
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| 9. |
- Orkney, Matthew D.A., et al.
(författare)
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EDGE : the shape of dark matter haloes in the faintest galaxies
- 2023
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711. ; 525:3, s. 3516-3532
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Tidskriftsartikel (refereegranskat)abstract
- Collisionless dark matter only (DMO) structure formation simulations predict that dark matter (DM) haloes are prolate in their centres and triaxial towards their outskirts. The addition of gas condensation transforms the central DM shape to be rounder and more oblate. It is not clear, however, whether such shape transformations occur in 'ultra-faint' dwarfs, which have extremely low baryon fractions. We present the first study of the shape and velocity anisotropy of ultra-faint dwarf galaxies that have gas mass fractions of fgas(r < Rhalf) < 0.06. These dwarfs are drawn from the Engineering Dwarfs at Galaxy formation's Edge (EDGE) project, using high-resolution simulations that allow us to resolve DM halo shapes within the half-light radius (∼100 pc). We show that gas-poor ultra-faints (M200c ≤ 1.5 × 109 M⊙; fgas < 10-5) retain their pristine prolate DM halo shape even when gas, star formation, and feedback are included. This could provide a new and robust test of DM models. By contrast, gas-rich ultra-faints (M200c > 3 × 109 M⊙; fgas > 10-4) become rounder and more oblate within ∼10 half-light radii. Finally, we find that most of our simulated dwarfs have significant radial velocity anisotropy that rises to at R 3Rhalf. The one exception is a dwarf that forms a rotating gas/stellar disc because of a planar, major merger. Such strong anisotropy should be taken into account when building mass models of gas-poor ultra-faints.
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| 10. |
- Orkney, Matthew D.A., et al.
(författare)
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EDGE : Two routes to dark matter core formation in ultra-faint dwarfs
- 2021
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 504:3, s. 3509-3522
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Tidskriftsartikel (refereegranskat)abstract
- In the standard Lambda cold dark matter paradigm, pure dark matter simulations predict dwarf galaxies should inhabit dark matter haloes with a centrally diverging density 'cusp'. This is in conflict with observations that typically favour a constant density 'core'. We investigate this 'cusp-core problem' in 'ultra-faint' dwarf galaxies simulated as part of the 'Engineering Dwarfs at Galaxy formation's Edge' project. We find, similarly to previous work, that gravitational potential fluctuations within the central region of the simulated dwarfs kinematically heat the dark matter particles, lowering the dwarfs' central dark matter density. However, these fluctuations are not exclusively caused by gas inflow/outflow, but also by impulsive heating from minor mergers. We use the genetic modification approach on one of our dwarf's initial conditions to show how a delayed assembly history leads to more late minor mergers and, correspondingly, more dark matter heating. This provides a mechanism by which even ultra-faint dwarfs ($M_∗ \lt 10^5\, \text{M}_{\odot }$), in which star formation was fully quenched at high redshift, can have their central dark matter density lowered over time. In contrast, we find that late major mergers can regenerate a central dark matter cusp, if the merging galaxy had sufficiently little star formation. The combination of these effects leads us to predict significant stochasticity in the central dark matter density slopes of the smallest dwarfs, driven by their unique star formation and mass assembly histories.
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