The birth of a galaxy – III. Propelling reionization with the faintest galaxies

By John H. Wise, V. Demchenko, M. Halicek, M. Norman, Matthew J. Turk, Tom Abel, Britton D. Smith. 2014

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MNRAS 442, 2560–2579 (2014) doi:10.1093/mnras/stu979 The birth of a galaxy – III. Propelling reionization with the faintest galaxies John H. Wise, 1‹ Vasiliy G. Demchenko, 1 Martin T. Halicek, 1 Michael L. Norman, 2 Matthew J. Turk, 3 Tom Abel 4 and Britton D. Smith 5 1 Center for Relativistic Astrophysics, Georgia Institute of Technology, 837 State Street, Atlanta, GA 30332, USA for Astrophysics and Space Sciences, University of California at San Diego, La Jolla, CA 92093, USA 3 Department of Astronomy, Columbia University, 538 West 120th Street, New York, NY 10027, USA 4 Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Menlo Park, CA 94025, USA 5 Institute of Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK 2 Center Accepted 2014 May 14. Received 2014 May 12; in original form 2014 March 24 Starlight from galaxies plays a pivotal role throughout the process of cosmic reionization. We present the statistics of dwarf galaxy properties at z > 7 in haloes with masses up to 10 9 M , using a cosmological radiation hydrodynamics simulation that follows their buildup starting with their Population III progenitors. We find that metal-enriched star formation is not restricted to atomic cooling (T vir ≥ 10 4 K) haloes, but can occur in haloes down to masses ∼10 6 M , especially in neutral regions. Even though these smallest galaxies only host up to 10 4 M of stars, they provide nearly 30 per cent of the ionizing photon budget. We find that the galaxy luminosity function flattens above M UV ∼ −12 with a number density that is unchanged at z 10. The fraction of ionizing radiation escaping into the intergalactic medium is inversely dependent on halo mass, decreasing from 50 to 5 per cent in the mass range log M/M = 7.0−8.5. Using our galaxy statistics in a semi-analytic reionization model, we find a Thomson scattering optical depth consistent with the latest Planck results, while still being consistent with the UV emissivity constraints provided by Lyα forest observations at z = 4–6. Key words: radiative transfer – methods: numerical – galaxies: dwarf – galaxies: formation – galaxies: high-redshift – dark ages, reionization, first stars. 1 I N T RO D U C T I O N Cosmic reionization is an extended process as individual H II regions grow around ionizing sources that gradually coalesce, culminating in a fully ionized Universe by z ∼ 6 (e.g. Gnedin & Ostriker 1997; Razoumov et al. 2002; Ciardi, Ferrara & White 2003; Sokasian et al. 2003; Furlanetto, Zaldarriaga & Hernquist 2004; Iliev et al. 2006; Robertson et al. 2010; Trac & Gnedin 2011; Zahn et al. 2011; So et al. 2014). However, there is still some tension between observational constraints on the timing and duration of reioniza- tion. First, the transmission fraction of z ∼ 6 quasar light blueward of Lyα through the intergalactic medium (IGM) indicates that the Universe was mostly ionized by this epoch (e.g. Gunn & Peterson 1965; Fan et al. 2002, 2006; Willott et al. 2007; Mortlock et al. 2011). Secondly, observations of the cosmic microwave background (CMB) from the Wilkinson Microwave Anisotropy Probe (WMAP) and Planck have measured the optical depth to Thomson scat- tering τ e = 0.089 +0.012 −0.014 , which corresponds to the Universe being E-mail: jwise@physics.gatech.edu ∼50 per cent ionized at z = 11.1 ± 1.1 (Planck Collaboration 2013). But the ionizing emissivity measured at z = 4–6 through Lyα forest observations cannot account for this measured τ e , indi- cating that the end of reionization must be photon starved (Bolton & Haehnelt 2007) and that the emissivity must have been higher during reionization. Third, the duration 1 of reionization has been constrained to occur within z < 7.9 by measuring the kinetic Sunyaev–Zel’dovich effect with the South Pole Telescope (Zahn et al. 2012). These observations suggest that reionization was an extended process, mainly occurring at 6 z 15. What population of ionizing sources drives this global and ex- tended transition? It is clear that quasars and the very brightest galaxies, both of which are too rare, do not significantly contribute to the overall ionizing photon budget of reionization (e.g. Shapiro 1986; Dijkstra et al. 2004; Willott et al. 2010; Grissom, Ballantyne & Wise 2014). Starlight from galaxies is thought to provide the vast majority of the ionizing photon budget from extrapolating the 1 Zahn et al. (2012) define z as the redshift elapsed between 20 and 99 per cent ionized. C 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society Downloaded from http://mnras.oxfordjournals.org/ by guest on September 12, 2016 ABSTRACT

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Feedback-regulated star formation and escape of LyC photons from mini-haloes during reionization (2016, methodology): “It can be seen that only massive Pop III stars with MPopIII >∼ 100 M are able to provide LyC photons to the IGM (Whalen et al. 2004), while almost all of the ionising radiation from MNRAS 000, 000–000 (0000) Pop III stars with MPopIII <∼ 70 M is absorbed inside the virial radius.”
The difficulty of getting high escape fractions of ionizing photons from high-redshift galaxies: A view from the FIRE cosmological simulations (2015, methodology): “For example, Wise et al. (2014) performed radiative hydrodynamical simulations with state-of-art ISM physics and chemistry, star formation, and stellar feedback models and found fesc drops from 50% to 5% with increasing halo mass in 107– 108.5 M at z > 7.”
GALAXY PROPERTIES AND UV ESCAPE FRACTIONS DURING THE EPOCH OF REIONIZATION: RESULTS FROM THE RENAISSANCE SIMULATIONS (2016, methodology): “This finding validates the assumption of Wise et al. (2014) and Chen et al. (2014) that the galaxy population during this epoch is nearly invariant with redshift, which allowed them to increase their effective galaxy sample size by combining data sets at different redshifts into a single sample.”
A case study of hurdle and generalized additive models in astronomy: the escape of ionizing radiation (2018, background): “…simulations have found evidence for a strong dependence of fesc on galaxy mass and redshift (Ricotti & Shull 2000; Wood & Loeb 2000; Fujita et al. 2003; Yajima, Choi & Nagamine 2011; Paardekooper, Khochfar & Dalla Vecchia 2013; Wise et al. 2014; Paardekooper, Khochfar & Dalla Vecchia 2015).”
Conditions for Reionizing the Universe with a Low Galaxy Ionizing Photon Escape Fraction (2019, methodology): “…metals, gas can cool inefficiently via molecular hydrogen cooling, which is believed to be the dominant cooling mechanism for the first generation of Population III stars forming at z=15–30 (e.g., Yoshida et al. 2004; Maio et al. 2010; Johnson et al. 2013; Wise et al. 2014; Jaacks et al. 2018c).”
Cosmic Dawn (CoDa): the first radiation-hydrodynamics simulation of reionization and galaxy formation in the Local Universe (2015, background): “…with a fixed uniform UV background from Haardt & Madau (1996, 2012), and more recently with fully coupled RHD simulations (Pawlik et al. 2013; Wise et al. 2014; Jeon et al. 2014; Rosdahl et al. 2015; Aubert et al. 2015; Pawlik et al. 2015), as a reduction and possibly a suppression of star…”
Faint AGNs at z > 4 in the CANDELS GOODS-S field: looking for contributors to the reionization of the Universe (2015, background): “Faintest dwarf high redshift galaxies could behave in a different way showing larger escape fractions (see e.g. Fontanot et al. (2014)) and could be significant contributors to the cosmic reionization (Ferrara & Loeb (2013), Wise et al. (2014), Yue et al. (2014)).”
Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions (2019, background): “…fesc 4 Hubble Fellow. through simulations, since it depends sensitively on resolving the multi-phase ISM and the treatment of small-scale processes associated with galaxy formation, which, at present, are modeled in an approximate way (e.g., Wise et al. 2014; Ma et al. 2015; Trebitsch et al. 2017).”
Fluctuating feedback-regulated escape fraction of ionizing radiation in low-mass, high-redshift galaxies (2017, methodology): “More recently, several simulations have been undertaken, either in an idealized galaxy setup or in a full cosmological context (e.g. Wise & Cen 2009; Wise et al. 2014; Razoumov & Sommer-Larsen 2010; Kim et al. 2013; Paardekooper et al. 2013; Kimm & Cen 2014; Yajima et al. 2014; Ma et al. 2015; Kimm…”
Great Optically Luminous Dropout Research Using Subaru HSC (GOLDRUSH). I. UV Luminosity Functions at $z \sim 4-7$ Derived with the Half-Million Dropouts on the 100 deg$^2$ Sky (2017, background): “They have ∗ Based on data collected at the Subaru Telescope and retrieved from the HSC data archive system, which is operated by the Subaru Telescope and Astronomy Data Center at National Astronomical Observatory of Japan. investigated the shape of the UV LF down to ∼ −14 mag, at around which many c”
Low-redshift Lyman continuum leaking galaxies with high [O iii]/[O ii] ratios (2018, background): “It has also been suggested that fesc(LyC) tends to be higher in low-mass galaxies (Wise et al. 2014; Trebitsch et al. 2017).”
The First Billion Years project: the escape fraction of ionizing photons in the epoch of reionization (2015, background): “…simulations find ranges between fesc < 10% (Razoumov & Sommer-Larsen 2006, 2007; Gnedin et al. 2008; Paardekooper et al. 2011; Kim et al. 2013) and fesc > 80% (Wise & Cen 2009; Razoumov & Sommer-Larsen 2010), with likely a strong mass and redshift dependence (Yajima et al. 2010; Wise et al. 2014).”
GRACKLE: a chemistry and cooling library for astrophysics (2016, background): “…calculations (e.g. Iliev et al. 2014; Mesinger et al. 2016), or coupled with the hydrodynamics, which is becoming more commonplace in galaxy and star formation simulations (e.g. Wise et al. 2014; Rosdahl et al. 2015; Ocvirk et al. 2015; Baczynski et al. 2015; Pawlik et al. 2016; Rosen et al. 2016).”
Charting the parameter space of the global 21-cm signal (2016, background): “However, the possibility of star formation via metal cooling in the early universe and its contribution to the total star formation is highly uncertain (e.g., Jeon et al. 2014; Wise et al. 2014; O’Shea et al. 2015; Cohen et al. 2016).”
ARE ULTRA-FAINT GALAXIES AT z = 6–8 RESPONSIBLE FOR COSMIC REIONIZATION? COMBINED CONSTRAINTS FROM THE HUBBLE FRONTIER FIELDS CLUSTERS AND PARALLELS (2015, background): “While cosmological simulations point to a halo mass limit of 106M⊙ for early galaxy formation (Jaacks et al. 2012; Kimm & Cen 2014; Wise et al. 2014), the depth of current observations however limits the exploration of the LF to galaxies brighter than ∼0.1L⋆.”
CONTRASTING GALAXY FORMATION FROM QUANTUM WAVE DARK MATTER, ψDM, WITH ΛCDM, USING PLANCK AND HUBBLE DATA (2015, background): “…when incorporating all relevant processes which may affect ultraviolet (UV) ionization (e.g., Springel & Hernquist 2003; Bromm & Yoshida 2011; Wise et al. 2014), including early galactic outflows (e.g., Frye et al. 2002) and their feedback effects (e.g., Scannapieco & Broadhurst 2001; Pieri…”
The SPHINX Cosmological Simulations of the First Billion Years: the Impact of Binary Stars on Reionization★ (2018, background): “The possible contribution from metal-free (PopIII) stars has been considered in recent state-of-the-art models (Wise et al. 2014; Kimm et al. 2017) and the general conclusion is that they have relatively little direct impact on reionization at z < 10.”
The z ∼ 6 Luminosity Function Fainter than −15 mag from the Hubble Frontier Fields: The Impact of Magnification Uncertainties (2016, background): “…to less efficient atomic and molecular hydrogen cooling, respectively (Muñoz & Loeb 2011; Krumholz & Dekel 2012; Kuhlen et al. 2013; Jaacks et al. 2013; Wise et al. 2014; Liu et al. 2016; Gnedin 2016; Finlator et al. 2016), while 7 For example, the HFF program does not feature deep observations…”
Detection of high Lyman continuum leakage from four low-redshift compact star-forming galaxies (2016, background): “…of cosmic reionization predict that the least massive galaxies have the highest fesc(LyC) (e.g Razoumov & Sommer-Larsen 2010; Yajima et al. 2011; Wise et al. 2014), while other studies find relatively low escape fractions, fesc(LyC) ≈ 5 %, with no strong dependence on galaxy mass and cosmic…”