EDGE: The Origin of Scatter in Ultra-faint Dwarf Stellar Masses and Surface Brightnesses

Rey, Martin P.; Pontzen, Andrew; Agertz, Oscar; Orkney, Matthew D. A.; Read, Justin I.; Saintonge, A.; Pedersen, C.

doi:10.3847/2041-8213/ab53dd

Cited by 76 publications

(96 citation statements)

References 46 publications

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“…The stellar masses of the ultrafaint satellites are so small that they are beyond the reach of the current generation of cosmological hydrodynamical simulations, such as A (Sawala et al 2016;Fattahi et al 2016), A (Grand et al 2017) or F (Hopkins et al 2014(Hopkins et al , 2018, which, at best, have a stellar mass resolution of ★ ∼ 10 3 −10 4 M , although higher resolution may be achieved in simulations of isolated dwarf galaxies (e.g. Read et al 2016;Jeon et al 2017;Corlies et al 2018;Wheeler et al 2018;Munshi et al 2019;Rey et al 2019;Agertz et al 2020). Instead, we use the technique of semi-analytic galaxy modelling in which mass resolution is not an issue.…”

Section: Introductionmentioning

confidence: 99%

The little things matter: relating the abundance of ultrafaint satellites to the hosts’ assembly history

Bose

Deason

Belokurov

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Ultrafaint dwarf galaxies ($M_\star \le 10^{5}\, {\rm M}_\odot$) are relics of an early phase of galaxy formation. They contain some of the oldest and most metal-poor stars in the Universe which likely formed before the epoch of hydrogen reionization. These galaxies are so faint that they can only be detected as satellites of the Milky Way. They are so small that they are not resolved in current cosmological hydrodynamic simulations. Here, we combine very high-resolution cosmological N-body simulations with a semi-analytic model of galaxy formation to study the demographics and spatial distribution of ultrafaint satellites in Milky Way-mass haloes. We show that the abundance of these galaxies is correlated with the assembly history of the host halo: at fixed mass, haloes assembled earlier contain, on average, more ultrafaint satellites today than haloes assembled later. We identify simulated galactic haloes that experience an ancient Gaia-Enceladus-Sausage-like and a recent LMC-like accretion event and find that the former occurs in 33 per cent of the sample and the latter in 9 per cent. Only 3 per cent experience both events and these are especially rich in ultrafaint satellites, most acquired during the ancient accretion event. Our models predict that the radial distribution of satellites is more centrally concentrated in early-forming haloes. Accounting for the depletion of satellites by tidal interactions with the central disc, we find a very good match to the observed radial distribution of satellites in the Milky Way over the entire radial range. This agreement is mainly due to the ability of our model to track ‘orphan’ galaxies after their subhaloes fall below the resolution limit of the simulation.

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Section: Introductionmentioning

confidence: 99%

The little things matter: relating the abundance of ultrafaint satellites to the hosts’ assembly history

Bose

Deason

Belokurov

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…Using the genetic modification approach (Roth et al 2016;Rey & Pontzen 2018;Stopyra et al 2020), we can create alternative mass accretion histories for a galaxy. Rey et al (2019) modified one of the fiducial resolution EDGE dwarfs, Halo1459, such that it assembled later. They found that this leads to a larger, lower surface brightness, and lower metallicity dwarf -more similar to Eridanus II.…”

Section: Core Formation From Minor Mergersmentioning

confidence: 99%

“…They found that this leads to a larger, lower surface brightness, and lower metallicity dwarf -more similar to Eridanus II. As such, in this section, we resimulate the genetically modified later forming dwarfs from Rey et al (2019) at higher resolution to study how late formation impacts the central dark matter density.…”

Section: Core Formation From Minor Mergersmentioning

confidence: 99%

“…In this paper, we use a suite of high resolution cosmological zoom simulations from the Engineering Dwarfs at Galaxy formation's Edge (EDGE) project (Rey et al 2019;Agertz et al 2020;Rey et al 2020;Pontzen et al 2020) to explore whether dark matter core formation can proceed even in the very smallest dwarf galaxies. Our simulations model galaxies over the mass range 200c ∼ 1 − 4 × 10 9 M , consistent with ultra-faint dwarfs, and reach a spatial resolution of ∼ 3 pc, sufficient to resolve even very small dark matter cores.…”

Section: Introductionmentioning

confidence: 99%

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EDGE: two routes to dark matter core formation in ultra-faint dwarfs

Orkney

Read

Rey

et al. 2021

Monthly Notices of the Royal Astronomical Society

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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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“…One possible way to generate a zoom simulation is to calculate the entire cosmological volume at high resolution, then degrade the sampling outside the target region. This is inefficient, however, and entirely infeasible for some applications; for example, in the EDGE suite (Rey et al 2019a;Agertz et al 2020), the initial conditions resolution corresponds to an effective grid of 32768 3 . Storing a single such grid at double precision requires 32 terabytes; manipulating it is entirely out of reach.…”

Section: Zoom Initial Conditionsmentioning

confidence: 99%

GenetIC—A New Initial Conditions Generator to Support Genetically Modified Zoom Simulations

Stopyra

Pontzen

Peiris

et al. 2021

ApJS

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We present genetIC, a new code for generating initial conditions for cosmological N-body simulations. The code allows precise, user-specified alterations to be made to arbitrary regions of the simulation (while maintaining consistency with the statistical ensemble). These "genetic modifications" allow, for example, the history, mass, or environment of a target halo to be altered in order to study the effect on their evolution. The code natively supports initial conditions with nested zoom regions at progressively increasing resolution. Modifications in the highresolution region must propagate self-consistently onto the lower-resolution grids; to enable this while maintaining a small memory footprint, we introduce a Fourier-space filtering approach to generating fields at variable resolution. Due to a close correspondence with modifications, constrained initial conditions can also be produced by genetIC (for example, with the aim of matching structures in the local universe). We test the accuracy of modifications performed within zoom initial conditions. The code achieves subpercent precision, which is easily sufficient for current applications in galaxy formation.

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EDGE: The Origin of Scatter in Ultra-faint Dwarf Stellar Masses and Surface Brightnesses

Cited by 76 publications

References 46 publications

The little things matter: relating the abundance of ultrafaint satellites to the hosts’ assembly history

The little things matter: relating the abundance of ultrafaint satellites to the hosts’ assembly history

EDGE: two routes to dark matter core formation in ultra-faint dwarfs

GenetIC—A New Initial Conditions Generator to Support Genetically Modified Zoom Simulations

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