Near-Field Limits on the Role of Faint Galaxies in Cosmic Reionization

Abstract

Reionizing the Universe with galaxies appears to require significant star formation in low-mass halos at early times, while local dwarf galaxy counts tell us that star formation has been minimal in small halos around us today. Using simple models and the ELVIS simulation suite, we show that reionization scenarios requiring appreciable star formation in halos with $M_{\mathrm{vir}}\approx 10^8{M}_{\odot }$ at $z=8$ are in serious tension with galaxy counts in the Local Group. This tension originates from the seemingly inescapable conclusion that 30 - 60 halos with $M_{\mathrm{vir}}>10^8{M}_{\odot }$ at $z=8$ will survive to be distinct bound satellites of the Milky Way at $z=0$. Reionization models requiring star formation in such halos will produce dozens of bound galaxies in the Milky Way's virial volume today (and 100 - 200 throughout the Local Group), each with $\gtrsim 10^5{M}_{\odot }$ of old stars ($\gtrsim 13$ Gyr). This exceeds the stellar mass function of classical Milky Way satellites today, even without allowing for the (significant) post-reionization star formation observed in these galaxies. One possible implication of these findings is that star formation became sharply inefficient in halos smaller than $\sim 10^9{M}_{\odot }$ at early times, implying that the high-$z$ luminosity function must break at magnitudes brighter than is often assumed (at ${\mathrm{M}}_{\mathrm{UV}}\approx -14$). Our results suggest that JWST (and possibly even HST with the Frontier Fields) may realistically detect the faintest galaxies that drive reionization. It remains to be seen how these results can be reconciled with the most sophisticated simulations of early galaxy formation at present, which predict substantial star formation in $M_{\mathrm{vir}}\sim 10^8{M}_{\odot }$ halos during the epoch of reionization.

arXiv comment6 pages, 4 figures; minor updates. Published in MNRAS Letters

References in corpus (32)

• Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• Large scale bias and the peak background split
• 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
• Properties of galaxies reproduced by a hydrodynamic simulation
• Constraints on the relationship between stellar mass and halo mass at low and high redshift
• Modeling Luminosity-Dependent Galaxy Clustering Through Cosmic Time
• The Milky Way's bright satellites as an apparent failure of LCDM
• Radiative Transfer in a Clumpy Universe: III. The Nature of Cosmological Ionizing Sources
• How do galaxies populate Dark Matter halos?
• New Constraints on Cosmic Reionization from the 2012 Hubble Ultra Deep Field Campaign
• The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations
• The Birth of a Galaxy - III. Propelling reionisation with the faintest galaxies
• ELVIS: Exploring the Local Volume in Simulations
• Concordance models of reionization: implications for faint galaxies and escape fraction evolution
• The UV Luminosity Function of star-forming galaxies via dropout selection at redshifts z ~ 7 and 8 from the 2012 Ultra Deep Field campaign
• The Birth of a Galaxy. II. The Role of Radiation Pressure
• The Galaxy Luminosity Function during the Reionization Epoch
• Frontier Fields: High-Redshift Predictions and Early Results
• The Luminosity Function at z~8 from 97 Y-band dropouts: Inferences About Reionization
• Where are the Fossils of the First Galaxies? II. True Fossils, Ghost Halos, and the Missing Bright Satellites
• The High-$z$ Universe Confronts Warm Dark Matter: Galaxy Counts, Reionization and the Nature of Dark Matter
• The effect of feedback and reionization on star formation in low-mass dwarf galaxy haloes
• Galactic Outflows and Photoionization Heating in the Reionization Epoch
• Fossil remnants of reionization in the halo of the Milky Way
• Constraining the Minimum Mass of High-Redshift Galaxies and Their Contribution to the Ionization State of the IGM
• Resolving Globular Cluster Formation within a Cosmological Context
• A suppressed contribution of low mass galaxies to reionization due to supernova feedback
• The earliest stars and their relics in the Milky Way
• Metals and ionizing photons from dwarf galaxies
• Effects of stellar rotation on star formation rates and comparison to core-collapse supernova rates
• A Predicted New Population of UV-faint Galaxies at z>4

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• The Frontier Fields: Survey Design
• Directly Observing the Galaxies Likely Responsible for Reionization
• Not so lumpy after all: modeling the depletion of dark matter subhalos by Milky Way-like galaxies
• The Evolution of the Intergalactic Medium
• The z~6 Luminosity Function Fainter than -15 mag from the Hubble Frontier Fields: The Impact of Magnification Uncertainties
• The Extreme Faint End of the UV Luminosity Function at $z\sim 6$ Through Gravitational Telescopes: a comprehensive assessment of strong lensing uncertainties
• Galaxy Properties and UV Escape Fractions During Epoch of Reionization: Results from the Renaissance Simulations
• Simulating galaxies in the reionization era with FIRE-2: galaxy scaling relations, stellar mass functions, and luminosity functions
• Hubble Frontier Fields First Complete Cluster Data: Faint Galaxies at $z\sim 5-10$ for UV Luminosity Functions and Cosmic Reionization
• Galaxy UV-luminosity function and reionization constraints on axion dark matter
• Gravitational probes of dark matter physics
• Binary Stars Can Provide the "Missing Photons" Needed for Reionization
• Self-Consistent Modeling of Reionization in Cosmological Hydrodynamical Simulations
• Legacy of star formation in the pre-reionization universe
• Semi-analytic forecasts for JWST -- IV. Implications for cosmic reionization and LyC escape fraction
• The Formation Times and Building Blocks of Milky Way-mass Galaxies in the FIRE Simulations
• The Local Group as a time machine: studying the high-redshift Universe with nearby galaxies
• The Globular Cluster - Dark Matter Halo Connection
• Spatially adaptive radiation-hydrodynamical simulations of galaxy formation during cosmological reionization
• The Very Faint End of the UV Luminosity Function over Cosmic Time: Constraints from the Local Group Fossil Record
• Local Group Ultra-Faint Dwarf Galaxies in the Reionization Era
• Sizes of Lensed Lower-luminosity z=4-8 Galaxies from the Hubble Frontier Field Program
• On the faint-end of the high-$z$ galaxy luminosity function
• A Predicted Correlation Between Age Gradient and Star Formation History in FIRE Dwarf Galaxies
• Cold or Warm? Constraining Dark Matter with Primeval Galaxies and Cosmic Reionization after Planck
• Connecting Faint End Slopes of the Lyman-$\alpha$ emitter and Lyman-break Galaxy Luminosity Functions
• Elevated UV luminosity density at Cosmic Dawn explained by non-evolving, weakly mass-dependent star formation efficiency
• Mapping the Escape Fraction of Ionizing Photons Using Resolved Stars: A Much Higher Escape Fraction for NGC 4214
• Where are All the Gas-Bearing Local Dwarf Galaxies? Quantifying Possible Impacts of Reionization
• The Minimum Halo Mass for Star Formation at z = 6 - 8
• The Local Group: The Ultimate Deep Field
• Globular Cluster Formation from Colliding Substructure
• Stellar Mass Function of Active and Quiescent Galaxies via the Continuity Equation
• Globular Clusters in High-Redshift Dwarf Galaxies: A Case Study from the Local Group
• Evolution of a dwarf satellite galaxy embedded in a scalar field dark matter halo
• Galaxy Evolution at High Redshift: Obscured Star Formation, GRB Rates, Cosmic Reionization, and Missing Satellites
• Push it to the limit: Local Group constraints on high-redshift stellar mass functions for Mstar > 10^5 Msun
• The potential role of NGC 205 in generating Andromeda's vast thin co-rotating plane of satellite galaxies
• Constraining SN feedback: a tug of war between reionization and the Milky Way satellites
• Building Blocks of the Milky Way's Accreted Spheroid
• Imaging reionization's last phases with I-front Lyman-$\alpha$ emissions