Highly r-process enhanced stars in ultra-faint dwarf galaxies

Abstract

Highly r-process enhanced metal-poor stars (MP r-II, $[Eu/Fe]>1$ and $[Fe/H]\lesssim -1.5$) have been observed in ultra-faint dwarf (UFD) galaxy, specifically in Reticulum~II (Ret~II). The fact that only a few UFDs contain such stars implies that the r-process site may reflect very rare, but individually prolific events, such as neutron star mergers (NSMs). Considering the relatively short star formation history (SFH) of UFDs, it is puzzling how they could experience such a rare phenomenon. In this work, we show the results of cosmological hydrodynamic zoom-in simulations of isolated UFDs ($M_{vir}\approx 10^7-10^8$ solar mass and $M_{\ast }\approx 10^3-10^4$ solar mass at $z=0$) to explain the formation of MP r-II stars in UFDs. We employ a simple toy model for NSM events, adopting parameters consistent with observations, such as the NSM rate (1 per $M_{\ast }\approx 10^5$ solar mass) and europium (Eu) mass ($M_{Eu}\approx 10^{-5}$ solar mass). We identify only one simulated galaxy ($M_{vir}\approx 4.6\times 10^7$, $M_{\ast }\approx 3.4\times 10^3$ solar mass at $z=0$) with abundances similar to Ret~II in a simulation volume that hosts $\sim 30$ UFD analogs, indicating that such abundances are possible but rare. By exploring a range of key parameters, we demonstrate that the most important factor in determining the formation of MP r-II stars in UFDs is how quickly subsequent stars can be formed out of r-process enriched gas. We find that it takes between 10 to 100~Myr to form the first and second burst of MP r-II stars. Over this period, Eu-polluted gas maintains the required high abundance ratios of $[Eu/Fe]>1$.

arXiv comment12 pages, 8 figures, Accepted for publication in MNRAS

References in corpus (114)

• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• Galactic Stellar and Substellar Initial Mass Function
• Gaia Data Release 2. Summary of the contents and survey properties
• The cosmological simulation code GADGET-2
• Populating a cluster of galaxies - I. Results at z=0
• The Average Star Formation Histories of Galaxies in Dark Matter Halos from z=0-8
• The observed properties of dwarf galaxies in and around the Local Group
• The Nucleosynthetic Signature of Population III
• An Ordinary Short Gamma-Ray Burst with Extraordinary Implications: Fermi-GBM Detection of GRB 170817A
• Small-Scale Challenges to the $\Lambda$CDM Paradigm
• Constraining the Evolution of the Ionizing Background and the Epoch of Reionization with z ~ 6 Quasars II: A Sample of 19 Quasars
• First results from the IllustrisTNG simulations: A tale of two elements -- chemical evolution of magnesium and europium
• Radiative transfer in a clumpy universe: IV. New synthesis models of the cosmic UV/X-ray background
• Star Formation Histories, Abundances and Kinematics of Dwarf Galaxies in the Local Group
• The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. II. UV, Optical, and Near-IR Light Curves and Comparison to Kilonova Models
• Spectroscopic identification of r-process nucleosynthesis in a double neutron star merger
• INTEGRAL Detection of the First Prompt Gamma-Ray Signal Coincident with the Gravitational Wave Event GW170817
• The physics driving the cosmic star formation history
• Multi-scale initial conditions for cosmological simulations
• The Universal Stellar Mass-Stellar Metallicity Relation for Dwarf Galaxies
• Double Compact Objects I: The Significance Of The Common Envelope On Merger Rates
• Nucleosynthesis and Evolution of Massive Metal-Free Stars
• Formation of Double Neutron Star Systems
• Production of all the r-process nuclides in the dynamical ejecta of neutron star mergers
• The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. IV. Detection of Near-infrared Signatures of r-process Nucleosynthesis with Gemini-South
• Eight New Milky Way Companions Discovered in First-Year Dark Energy Survey Data
• The Faintest Dwarf Galaxies
• Modelling Primordial Gas in Numerical Cosmology
• Near-Field Cosmology with Metal-Poor Stars
• Eight Ultra-faint Galaxy Candidates Discovered in Year Two of the Dark Energy Survey
• Model-independent evidence in favor of an end to reionization by z~6
• The First Galaxies
• The Birth of a Galaxy: Primordial Metal Enrichment and Stellar Populations
• Generic Spectrum and Ionization Efficiency of a Heavy Initial Mass Function for the First Stars
• Evidence of patchy hydrogen reionization from an extreme Ly$\alpha$ trough below redshift six
• Chemical yields from low- and intermediate-mass stars: model predictions and basic observational constraints
• The Tidal Evolution of Local Group Dwarf Spheroidals
• R-process enrichment from a single event in an ancient dwarf galaxy
• Forged in FIRE: cusps, cores, and baryons in low-mass dwarf galaxies
• Neutron star mergers versus core-collapse supernovae as dominant r-process sites in the early Galaxy
• Formation of the First Stars
• The r-process nucleosynthesis in the various jet-like explosions of magnetorotational core-collapse supernovae
• The Quenching of the Ultra-Faint Dwarf Galaxies in the Reionization Era
• Protostellar Collapse with Various Metallicities
• High-Resolution Spectroscopy of Extremely Metal-Poor Stars in the Least Evolved Galaxies: Ursa Major II and Coma Berenices
• The first chemical enrichment in the universe and the formation of hyper metal-poor stars
• Neutron Star Mergers Might not be the Only Source of r-Process Elements in the Milky Way
• Segue 1: An Unevolved Fossil Galaxy from the Early Universe
• The Origin of r-Process Elements in the Milky Way
• Be it therefore resolved: Cosmological Simulations of Dwarf Galaxies with Extreme Resolution
• Complete element abundances of nine stars in the r-process galaxy Reticulum II
• Reproducing the Stellar Mass/Halo Mass Relation in Simulated LCDM Galaxies: Theory vs Observational Estimates
• Production of the entire range of r-process nuclides by black hole accretion disc outflows from neutron star mergers
• The Star Formation Histories of Local Group Dwarf Galaxies II. Searching For Signatures of Reionization
• Consistent modelling of the meta-galactic UV background and the thermal/ionization history of the intergalactic medium
• The Orbital Histories of Magellanic Satellites Using Gaia DR2 Proper Motions
• Pre-galactic metal enrichment - The chemical signatures of the first stars
• Chemical Enrichment in the Faintest Galaxies: the Carbon and Iron Abundance Spreads in the Boötes I Dwarf Spheroidal Galaxy and the Segue 1 System
• Galactic r-process enrichment by neutron star mergers in cosmological simulations of a Milky Way-mass galaxy
• Neutrino-driven wind simulations and nucleosynthesis of heavy elements
• Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites
• EDGE: the mass-metallicity relation as a critical test of galaxy formation physics
• The History of R-Process Enrichment in the Milky Way
• Detailed Chemical Abundances in the r-Process-Rich Ultra-Faint Dwarf Galaxy Reticulum 2
• The Baryon Cycle of Dwarf Galaxies: Dark, Bursty, Gas-Rich Polluters
• The Missing Satellites of the Magellanic Clouds? Gaia Proper Motions of the Recently Discovered Ultra-Faint Galaxies
• Connecting the first galaxies with ultra faint dwarfs in the Local Group: chemical signatures of Population~III stars
• An R-process enhanced star in the dwarf galaxy Tucana III
• Organized Chaos: Scatter in the relation between stellar mass and halo mass in small galaxies
• Formation of Double Neutron Star systems as implied by observations
• High-Resolution Spectroscopy of Extremely Metal-Poor Stars in the Least Evolved Galaxies: Leo IV
• Quantifying the impact of the Large Magellanic Cloud on the structure of the Milky Way's dark matter halo using Basis Function Expansions
• Chemical Signatures of the First Galaxies: Criteria for One-Shot Enrichment
• Lyman-alpha emitters gone missing: evidence for late reionization?
• Radiative Stellar Feedback in Galaxy Formation: Methods and Physics
• Enrichment of r-process elements in dwarf spheroidal galaxies in chemo-dynamical evolution model
• The stellar-to-halo mass relation for Local Group galaxies
• The [Fe/H], [C/Fe], and [alpha/Fe] distributions of the Bootes I Dwarf Spheroidal Galaxy
• Identifying true satellites of the Magellanic Clouds
• Recovery from population III supernova explosions and the onset of second generation star formation
• The effect of feedback and reionization on star formation in low-mass dwarf galaxy haloes
• Neutron star mergers and rare core-collapse supernovae as sources of r-process enrichment in simulated galaxies
• Natal Kicks and Time Delays in Merging Neutron Star Binaries - Implications for r-process nucleosynthesis in Ultra Faint Dwarfs and in the Milky Way
• r-process Production Sites as inferred from Eu Abundances in Dwarf Galaxies
• Dark Matter in Dwarf Spheroidal Galaxies and Indirect Detection: A Review
• A Search for Point Sources of EeV Neutrons
• Enrichment history of r-process elements shaped by a merger of neutron star pairs
• A New Formation Channel for Double Neutron Stars Without Recycling: Implications for Gravitational Wave Detection
• The influence of binaries on galactic chemical evolution
• In Pursuit of the Least Luminous Galaxies
• The Old Host-Galaxy Environment of SSS17a, the First Electromagnetic Counterpart to a Gravitational Wave Source
• From actinides to zinc: Using the full abundance pattern of the brightest star in Reticulum II to distinguish between different r-process sites
• Chemical Abundances of new member stars in the Tucana II dwarf galaxy
• Chemical Diversity in the Ultra-faint Dwarf Galaxy Tucana II
• The observational signature of the first H II regions
• Chemical Abundance Analysis of Tucana III, the Second $r$-process Enhanced Ultra-Faint Dwarf Galaxy
• Simulating Neutron Star Mergers as r-process Sources in Ultra Faint Dwarf Galaxies
• Evidence for $\gtrsim 4$ Gyr timescales of neutron star mergers from Galactic archaeology
• Diffusion in supersonic, turbulent, compressible flows
• Detection of a population of carbon-enhanced metal-poor stars in the Sculptor dwarf spheroidal galaxy
• The role of faint population III supernovae in forming CEMP stars in ultra-faint dwarf galaxies
• The Origin of r-process Enhanced Metal-Poor Halo Stars In Now-Destroyed Ultra-Faint Dwarf Galaxies
• Retainment of r-process material in dwarf galaxies
• The delayed time distribution of massive double compact star mergers
• Origin of the CEMP-no Group Morphology in the Milky Way
• Chemical Feature of Eu abundance in the Draco dwarf spheroidal galaxy
• R-process enrichment in ultrafaint dwarf galaxies
• Turbulent mixing of r-process elements in the Milky Way
• On Neutron Star Mergers as the Source of r-process Enhanced Metal Poor Stars in the Milky Way
• Neutron Star Mergers as the Main Source of R-process: Natal Kicks And Inside-Out Evolution to The Rescue
• Evidence for r-process delay in very metal-poor stars
• The impact of turbulent mixing on the galactic r-process enrichment by binary neutron star mergers
• Probing the assembly of dwarf galaxies through cosmic time with damped Lyman-$\alpha$ absorption spectroscopy
• New Population Synthesis Models of the Cosmic UV Background

Cited by in corpus (15)

• Signatures of R-process Enrichment in Supernovae from Collapsars
• Timing the r-Process Enrichment of the Ultra-Faint Dwarf Galaxy Reticulum II
• Origin of highly $r$-process-enhanced stars in a cosmological zoom-in simulation of a Milky Way-like galaxy
• A Statistical Detection of Wide Binary Systems in the Ultra-Faint Dwarf Galaxy Reticulum II
• Dwarf galaxy formation with and without dark matter-baryon streaming velocities
• Hydrodynamic mixing of accretion disk outflows in collapsars: implications for r-process signatures
• Discovery of an Extremely r-process-enhanced Thin-disk Star with [Eu/H] = +0.78
• The emergence of globular clusters and globular-cluster-like dwarfs
• Triggered Population III star formation: the effect of H${}_2$ self-shielding
• Exploring effects of IMF sampling and SN feedback injection on star formation and metallicity in ultra-faint dwarf galaxies
• Understanding Stellar Mass-Metallicity and Size Relations in Simulated Ultra-Faint Dwarf Galaxies
• The first r-process enhanced star confirmed to be a member of the Galactic bulge
• Segue 2 Recently Collided with the Cetus-Palca Stream: New Opportunities to Constrain Dark Matter in an Ultra-Faint Dwarf
• Structural parameters and possible association of the Ultra-Faint Dwarfs Pegasus III and Pisces II from deep Hubble Space Telescope photometry
• Forward-modelling the Luminosity, Distance, and Size distributions of the Milky Way Satellites