Recursos de colección

Caltech Authors (160.918 recursos)

Repository of works by Caltech published authors.

Group = Moore Center for Theoretical Cosmology and Physics

1. Modeling chemical abundance distributions for dwarf galaxies in the Local Group: the impact of turbulent metal diffusion

Escala, Ivanna; Wetzel, Andrew; Kirby, Evan N.; Hopkins, Philip F.; Ma, Xiangcheng; Wheeler, Coral; Kereš, Dušan; Faucher-Giguère, Claude-André; Quataert, Eliot
We investigate stellar metallicity distribution functions (MDFs), including Fe and ${\alpha}$-element abundances, in dwarf galaxies from the Feedback in Realistic Environments (FIRE) project. We examine both isolated dwarf galaxies and those that are satellites of a Milky Way-mass galaxy. In particular, we study the effects of including a sub-grid turbulent model for the diffusion of metals in gas. Simulations that include diffusion have narrower MDFs and abundance ratio distributions, because diffusion drives individual gas and star particles toward the average metallicity. This effect provides significantly better agreement with observed abundance distributions of dwarf galaxies in the Local Group, including the small intrinsic scatter in [${\alpha}$/Fe] vs. [Fe/H] (less than 0.1...

2. Fire in the field: simulating the threshold of galaxy formation

Fitts, Alex; Boylan-Kolchin, Michael; Elbert, Oliver D.; Bullock, James S.; Hopkins, Philip F.; Oñorbe, Jose; Wetzel, Andrew; Wheeler, Coral; Faucher-Giguère, Claude-André; Kereš, Dušan; Skillman, Evan D.; Weisz, Daniel R.
We present a suite of 15 cosmological zoom-in simulations of isolated dark matter haloes, all with masses of M_(halo) ≈ 10^(10) M_⊙ at z = 0, in order to understand the relationship among halo assembly, galaxy formation and feedback's effects on the central density structure in dwarf galaxies. These simulations are part of the Feedback in Realistic Environments (FIRE) project and are performed at extremely high resolution (m_(baryon) = 500 M_⊙, m_(dm) = 2500 M_⊙). The resultant galaxies have stellar masses that are consistent with rough abundance matching estimates, coinciding with the faintest galaxies that can be seen beyond the virial radius of...

3. Not so lumpy after all: modelling the depletion of dark matter subhaloes by Milky Way-like galaxies

Garrison-Kimmel, Shea; Wetzel, Andrew; Bullock, James S.; Hopkins, Philip F.; Boylan-Kolchin, Michael; Faucher-Giguère, Claude-André; Kereš, Dušan; Quataert, Eliot; Sanderson, Robyn E.; Graus, Andrew S.; Kelley, Tyler
Among the most important goals in cosmology is detecting and quantifying small (M_(halo)≃10^(6−9) M⊙) dark matter (DM) subhaloes. Current probes around the Milky Way (MW) are most sensitive to such substructure within ∼20 kpc of the halo centre, where the galaxy contributes significantly to the potential. We explore the effects of baryons on subhalo populations in ΛCDM using cosmological zoom-in baryonic simulations of MW-mass haloes from the Latte simulation suite, part of the Feedback In Realistic Environments (FIRE) project. Specifically, we compare simulations of the same two haloes run using (1) DM-only (DMO), (2) full baryonic physics and (3) DM...

4. Gaia Reveals a Metal-rich, in situ Component of the Local Stellar Halo

Bonaca, Ana; Conroy, Charlie; Wetzel, Andrew; Hopkins, Philip F.; Kereš, Dušan
We use the first Gaia data release, combined with the RAVE and APOGEE spectroscopic surveys, to investigate the origin of halo stars within ≾3 kpc from the Sun. We identify halo stars kinematically as moving at a relative speed of at least 220 km s^(−1) with respect to the local standard of rest. These stars are generally less metal-rich than the disk, but surprisingly, half of our halo sample is comprised of stars with [Fe/H] > -1. The orbital directions of these metal-rich halo stars are preferentially aligned with the disk rotation, in sharp contrast with the intrinsically isotropic orbital...

5. The Importance of Preventive Feedback: Inference from Observations of the Stellar Masses and Metallicities of Milky Way Dwarf Galaxies

Lu, Yu; Benson, Andrew; Wetzel, Andrew; Mao, Yao-Yuan; Tonnesen, Stephanie; Peter, Annika H. G.; Boylan-Kolchin, Michael; Wechsler, Risa H.
Dwarf galaxies are known to have remarkably low star formation efficiency due to strong feedback. Adopting the dwarf galaxies of the Milky Way (MW) as a laboratory, we explore a flexible semi-analytic galaxy formation model to understand how the feedback processes shape the satellite galaxies of the MW. Using Markov Chain Monte Carlo, we exhaustively search a large parameter space of the model and rigorously show that the general wisdom of strong outflows as the primary feedback mechanism cannot simultaneously explain the stellar mass function and the mass–metallicity relation of the MW satellites. An extended model that assumes that a...

6. How decoherence affects the probability of slow-roll eternal inflation

Boddy, Kimberly K.; Carroll, Sean M.; Pollack, Jason
Slow-roll inflation can become eternal if the quantum variance of the inflaton field around its slowly rolling classical trajectory is converted into a distribution of classical spacetimes inflating at different rates, and if the variance is large enough compared to the rate of classical rolling that the probability of an increased rate of expansion is sufficiently high. Both of these criteria depend sensitively on whether and how perturbation modes of the inflaton interact and decohere. Decoherence is inevitable as a result of gravitationally sourced interactions whose strength are proportional to the slow-roll parameters. However, the weakness of these interactions means...

7. Radiation and the classical double copy for color charges

Goldberger , Walter D.; Ridgway, Alexander K.
We construct perturbative classical solutions of the Yang-Mills equations coupled to dynamical point particles carrying color charge. By applying a set of color to kinematics replacement rules first introduced by Bern, Carrasco and Johansson, these are shown to generate solutions of d-dimensional dilaton gravity, which we also explicitly construct. Agreement between the gravity result and the gauge theory double copy implies a correspondence between non-Abelian particles and gravitating sources with dilaton charge. When the color sources are highly relativistic, dilaton exchange decouples, and the solutions we obtain match those of pure gravity. We comment on possible implications of our findings...

8. When the Jeans do not Fit: How Stellar Feedback Drives Stellar Kinematics and Complicates Dynamical Modeling in Low-mass Galaxies

El-Badry, Kareem; Wetzel, Andrew R.; Geha, Marla; Quataert, Eliot; Hopkins, Philip F.; Kereš, Dušan; Chan, T. K.; Faucher-Giguère, Claude-André
In low-mass galaxies, stellar feedback can drive gas outflows that generate non-equilibrium fluctuations in the gravitational potential. Using cosmological zoom-in baryonic simulations from the Feedback in Realistic Environments project, we investigate how these fluctuations affect stellar kinematics and the reliability of Jeans dynamical modeling in low-mass galaxies. We find that stellar velocity dispersion and anisotropy profiles fluctuate significantly over the course of galaxies' starburst cycles. We therefore predict an observable correlation between star formation rate and stellar kinematics: dwarf galaxies with higher recent star formation rates should have systemically higher stellar velocity dispersions. This prediction provides an observational test of...

9. Star Formation Quenching Timescale of Central Galaxies in a Hierarchical Universe

Hahn, ChangHoon; Tinker, Jeremy L.; Wetzel, Andrew
Central galaxies make up the majority of the galaxy population, including the majority of the quiescent population at M_* > 10^(10)M_☉. Thus, the mechanism(s) responsible for quenching central galaxies play a crucial role in galaxy evolution as whole. We combine a high-resolution cosmological N-body simulation with observed evolutionary trends of the "star formation main sequence," quiescent fraction, and stellar mass function at z < 1 to construct a model that statistically tracks the star formation histories and quenching of central galaxies. Comparing this model to the distribution of central galaxy star formation rates in a group catalog of the SDSS...

10. Axion detection via Topological Casimir Effect

Cao, ChunJun; Zhitnitsky, Ariel
We propose a new table-top experimental configuration for the direct detection of dark matter QCD axions in the traditional open mass window 10^(-6)  eV ≲ m_a ≲ 10^(-2)  eV using nonperturbative effects in a system with nontrivial spatial topology. Different from most experimental setups found in literature on direct dark matter axion detection, which relies on ˙θ or ⃗∇θ, we found that our system is in principle sensitive to a static θ ≥ 10^(-14) and can also be used to set limit on the fundamental constant θ_(QED) which becomes the fundamental observable parameter of the Maxwell system if some conditions are met....

11. The AGORA High-resolution Galaxy Simulations Comparison Project. II. Isolated Disk Test

Kim, Ji-hoon; Hopkins, Philip F.; Hummels, Cameron B.
Using an isolated Milky Way-mass galaxy simulation, we compare results from nine state-of-the-art gravito-hydrodynamics codes widely used in the numerical community. We utilize the infrastructure we have built for the AGORA High-resolution Galaxy Simulations Comparison Project. This includes the common disk initial conditions, common physics models (e.g., radiative cooling and UV background by the standardized package Grackle) and common analysis toolkit yt, all of which are publicly available. Subgrid physics models such as Jeans pressure floor, star formation, supernova feedback energy, and metal production are carefully constrained across code platforms. With numerical accuracy that resolves the disk scale height, we...

12. The Structure and Dynamical Evolution of the Stellar Disk of a Simulated Milky Way-Mass Galaxy

Ma, Xiangcheng; Hopkins, Philip F.; Wetzel, Andrew R.; Kirby, Evan N.; Anglés-Alcázar, Daniel; Faucher-Giguère, Claude-André; Kereš, Dušan; Quataert, Eliot
We study the structure, age and metallicity gradients, and dynamical evolution using a cosmological zoom-in simulation of a Milky Way-mass galaxy from the Feedback in Realistic Environments project. In the simulation, stars older than 6 Gyr were formed in a chaotic, bursty mode and have the largest vertical scaleheights (1.5–2.5 kpc) by z = 0, while stars younger than 6 Gyr were formed in a relatively calm, stable disc. The vertical scaleheight increases with stellar age at all radii, because (1) stars that formed earlier were thicker ‘at birth’, and (2) stars were kinematically heated to an even thicker distribution...

13. The connection between the host halo and the satellite galaxies of the Milky Way

Lu, Yu; Benson, Andrew; Mao, Yao-Yuan; Tonnesen, Stephanie; Peter, Annika H. G.; Wetzel, Andrew R.; Boylan-Kolchin, Michael; Wechsler, Risa H.
Many properties of the Milky Way's (MW) dark matter halo, including its mass-assembly history, concentration, and subhalo population, remain poorly constrained. We explore the connection between these properties of the MW and its satellite galaxy population, especially the implication of the presence of the Magellanic Clouds for the properties of the MW halo. Using a suite of high-resolution N-body simulations of MW-mass halos with a fixed final M_(vir) ~ 10^(12.1),M_⊙, we find that the presence of Magellanic Cloud-like satellites strongly correlates with the assembly history, concentration, and subhalo population of the host halo, such that MW-mass systems with Magellanic Clouds...

14. The connection between the host halo and the satellite galaxies of the Milky Way

Lu, Yu; Benson, Andrew; Mao, Yao-Yuan; Tonnesen, Stephanie; Peter, Annika H. G.; Wetzel, Andrew R.; Boylan-Kolchin, Michael; Wechsler, Risa H.
Many properties of the Milky Way's (MW) dark matter halo, including its mass-assembly history, concentration, and subhalo population, remain poorly constrained. We explore the connection between these properties of the MW and its satellite galaxy population, especially the implication of the presence of the Magellanic Clouds for the properties of the MW halo. Using a suite of high-resolution N-body simulations of MW-mass halos with a fixed final M_(vir) ~ 10^(12.1),M_⊙, we find that the presence of Magellanic Cloud-like satellites strongly correlates with the assembly history, concentration, and subhalo population of the host halo, such that MW-mass systems with Magellanic Clouds...

15. The connection between the host halo and the satellite galaxies of the Milky Way

Lu, Yu; Benson, Andrew; Mao, Yao-Yuan; Tonnesen, Stephanie; Peter, Annika H. G.; Wetzel, Andrew R.; Boylan-Kolchin, Michael; Wechsler, Risa H.
Many properties of the Milky Way's (MW) dark matter halo, including its mass-assembly history, concentration, and subhalo population, remain poorly constrained. We explore the connection between these properties of the MW and its satellite galaxy population, especially the implication of the presence of the Magellanic Clouds for the properties of the MW halo. Using a suite of high-resolution N-body simulations of MW-mass halos with a fixed final M_(vir) ~ 10^(12.1),M_⊙, we find that the presence of Magellanic Cloud-like satellites strongly correlates with the assembly history, concentration, and subhalo population of the host halo, such that MW-mass systems with Magellanic Clouds...

16. Reconciling Dwarf Galaxies with ΛCDM Cosmology: Simulating A Realistic Population of Satellites Around a Milky Way-Mass Galaxy

Wetzel, Andrew R.; Hopkins, Philip F.; Kim, Ji-Hoon; Faucher-Giguère, Claude-André; Kereš, Dušan; Quataert, Eliot
Low-mass "dwarf" galaxies represent the most significant challenges to the cold dark matter (CDM) model of cosmological structure formation. Because these faint galaxies are (best) observed within the Local Group (LG) of the Milky Way (MW) and Andromeda (M31), understanding their formation in such an environment is critical. We present first results from the Latte Project: the Milky Way on Feedback in Realistic Environments (FIRE). This simulation models the formation of an MW-mass galaxy to z = 0 within ΛCDM cosmology, including dark matter, gas, and stars at unprecedented resolution: baryon particle mass of 7070 M_⊙ with gas kernel/softening that...

17. Strong CMB Constraint On P-Wave Annihilating Dark Matter

An, Haipeng; Wise, Mark B.; Zhang, Yue
We consider a dark sector consisting of dark matter that is a Dirac fermion and a scalar mediator. This model has been extensively studied in the past. If the scalar couples to the dark matter in a parity conserving manner then dark matter annihilation to two mediators is dominated by the P-wave channel and hence is suppressed at very low momentum. The indirect detection constraint from the anisotropy of the Cosmic Microwave Background is usually thought to be absent in the model because of this suppression. In this letter we show that dark matter annihilation via bound state formation occurs...

18. De Sitter Space Without Dynamical Quantum Fluctuations

Boddy, Kimberly K.; Carroll, Sean M.; Pollack, Jason
We argue that, under certain plausible assumptions, de Sitter space settles into a quiescent vacuum in which there are no dynamical quantum fluctuations. Such fluctuations require either an evolving microstate, or time-dependent histories of out-of-equilibrium recording devices, which we argue are absent in stationary states. For a massive scalar field in a fixed de Sitter background, the cosmic no-hair theorem implies that the state of the patch approaches the vacuum, where there are no fluctuations. We argue that an analogous conclusion holds whenever a patch of de Sitter is embedded in a larger theory with an infinite-dimensional Hilbert space, including...

19. Breathing FIRE: How Stellar Feedback Drives Radial Migration, Rapid Size Fluctuations, and Population Gradients in Low-Mass Galaxies

El-Badry, Kareem; Wetzel, Andrew; Geha, Marla; Hopkins, Philip F.; Kereš, Dušan; Chan, T. K.; Faucher-Giguère, Claude-André
We examine the effects of stellar feedback and bursty star formation on low-mass galaxies (M_(star) = 2 × 10^6 − 5 × 10^(10) M_⊙) using the Feedback in Realistic Environments (FIRE) simulations. While previous studies emphasized the impact of feedback on dark matter profiles, we investigate the impact on the stellar component: kinematics, radial migration, size evolution, and population gradients. Feedback-driven outflows/inflows drive significant radial stellar migration over both short and long timescales via two processes: (1) outflowing/infalling gas can remain star-forming, producing young stars that migrate ~1 kpc within their first 100 Myr, and (2) gas outflows/inflows drive strong...

20. Anisotropic Diffusion in Mesh-Free Numerical Magnetohydrodynamics

Hopkins, Philip F.
We extend recently developed mesh-free Lagrangian methods for numerical magnetohydrodynamics (MHD) to arbitrary anisotropic diffusion equations, including: passive scalar diffusion, Spitzer–Braginskii conduction and viscosity, cosmic ray diffusion/streaming, anisotropic radiation transport, non-ideal MHD (Ohmic resistivity, ambipolar diffusion, the Hall effect) and turbulent ‘eddy diffusion’. We study these as implemented in the code gizmo for both new meshless finite-volume Godunov schemes (MFM/MFV). We show that the MFM/MFV methods are accurate and stable even with noisy fields and irregular particle arrangements, and recover the correct behaviour even in arbitrarily anisotropic cases. They are competitive with state-of-the-art AMR/moving-mesh methods, and can correctly treat anisotropic...

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