Steep faint-end slopes of galaxy mass and luminosity functions at z≥ 6 and the implications for reionization

Jaacks, Jason; Choi, June-Seek; Nagamine, Kentaro; Thompson, Robert M.; Varghese, Saju

doi:10.1111/j.1365-2966.2011.20150.x

Cited by 87 publications

(163 citation statements)

References 64 publications

(170 reference statements)

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“…The steep rise of the SFR function in the presence of radiative heating and SNe at low SFRs down to the SFRs that our simulations do not accurately resolve is consistent with that seen in previous works (e.g., Finlator, Davé,Özel 2011;Jaacks et al 2012;Cai et al 2014), and with extrapolations of the observed SFR function (e.g., Smit et al 2012;Bouwens et al 2014a;Finkelstein et al 2014;Duncan et al 2014). Because the mass scale below which photoheating affects the SFRs of galaxies is close to the mass scale below which efficient gas cooling requires the presence of molecular hydrogen or metals, quantifying the precise impact of reionization on the UV luminosity function will require more detailed, higher-resolution simulations of galaxy formation that include the relevant gas physics.…”

Section: The Uv Luminosity Function As a Probe Of Reionizationsupporting

confidence: 91%

Spatially adaptive radiation-hydrodynamical simulations of galaxy formation during cosmological reionization

Pawlik

Schaye

Vecchia

2015

Monthly Notices of the Royal Astronomical Society

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We present a suite of cosmological radiation-hydrodynamical simulations of the assembly of galaxies driving the reionization of the intergalactic medium (IGM) at z 6. The simulations account for the hydrodynamical feedback from photoionization heating and the explosion of massive stars as supernovae (SNe). Our reference simulation, which was carried out in a box of size 25 h −1 comoving Mpc using 2 × 512 3 particles, produces a reasonable reionization history and matches the observed UV luminosity function of galaxies. Simulations with different box sizes and resolutions are used to investigate numerical convergence, and simulations in which either SNe or photoionization heating or both are turned off, are used to investigate the role of feedback from star formation. Ionizing radiation is treated using accurate radiative transfer at the high spatially adaptive resolution at which the hydrodynamics is carried out. SN feedback strongly reduces the star formation rates (SFRs) over nearly the full mass range of simulated galaxies and is required to yield SFRs in agreement with observations. Photoheating helps to suppress star formation in low-mass galaxies, but its impact on the cosmic SFR is small. Because the effect of photoheating is masked by the strong SN feedback, it does not imprint a signature on the UV galaxy luminosity function, although we note that our resolution is insufficient to model star-forming minihaloes cooling through molecular hydrogen transitions. Photoheating does provide a strong positive feedback on reionization because it smooths density fluctuations in the IGM, which lowers the IGM recombination rate substantially. Our simulations demonstrate a tight non-linear coupling of galaxy formation and reionization, motivating the need for the accurate and simultaneous inclusion of photoheating and SN feedback in models of the early Universe.

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Section: The Uv Luminosity Function As a Probe Of Reionizationsupporting

confidence: 91%

Spatially adaptive radiation-hydrodynamical simulations of galaxy formation during cosmological reionization

Pawlik

Schaye

Vecchia

2015

Monthly Notices of the Royal Astronomical Society

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“…For instance, our LF results at z ∼ 7 are in good agreement with the hydrodynamical simulations of Jaacks et al (2012) with M å = −20.82 and log(f å ) = −3.74, although they predict a steeper faint-end slope of α = −2.30 down to a similar lower magnitude limit of M UV = −15. Theoretical models by Mason et al (2015) find a closer slope of α = −1.95 ± 0.17 down to a magnitude limit of M UV = −12, corresponding to a halo mass of 10 9 M e .…”

Section: The Uv Lf At Z = 6-7supporting

confidence: 85%

“…For comparison, the faint-end slope at z < 0.5 is very shallow (α ∼ −1.3), which indicates a decreasing contribution of faint star-forming galaxies to the total star formation density toward lower redshift Schiminovich et al 2005). The predicted evolution of the dark matter halo mass function based on cosmological simulations predicts an even steeper slope of α ∼ 2.3 of the UV LF at high redshift (Jaacks et al 2012). The deepest HST observations of blank fields, such as the XDF, put constraints on the faint-end slope down to an absolute magnitude of M 17.5 AB UV~-.…”

Section: Introductionmentioning

confidence: 96%

“…However, the ability of galaxies to reionize the universe relies on the extent of the steep faintend slope down to lower luminosities, typically around 0.001 L å at z ∼ 7. 11 While cosmological simulations point to a halo mass limit of 10 6 M e 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 ∼0.1 L å . One particularly efficient way Note.…”

Section: Introductionmentioning

confidence: 99%

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ARE ULTRA-FAINT GALAXIES ATz= 6–8 RESPONSIBLE FOR COSMIC REIONIZATION? COMBINED CONSTRAINTS FROM THE HUBBLE FRONTIER FIELDS CLUSTERS AND PARALLELS

Atek

Richard

Jauzac

et al. 2015

ApJ

211

229

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We use deep Hubble Space Telescope imaging of the Frontier Fields to accurately measure the galaxy rest-frame ultraviolet luminosity function (UV LF) in the redshift range z ∼ 6-8. We combine observations in three lensing clusters, A2744, MACS 0416, and MACS 0717, and their associated parallelfields to select high-redshift dropout candidates. We use the latest lensing models to estimate the flux magnification and the effective survey volume in combination with completeness simulations performed in the source plane. We report the detection of 227 galaxy candidates at z = 6-7 and 25 candidates at z ∼ 8. While the total survey area is about 4 arcmin 2 in each parallel field, it drops to about 0.6-1 arcmin 2 in the cluster core fields because of the strong lensing. We compute the UV LF at z ∼ 7 using the combined galaxy sample and perform Monte Carlo simulations to determine the best-fit Schechter parameters. We are able to reliably constrain the LF down to an absolute magnitude of M UV = −15.25, which corresponds to 0.005 L å . More importantly, we find that the faint-end slope remains steep down to this magnitude limit with 2.04 . Our results confirm the most recent results in deep blank fields but extend the LF measurements more than two magnitudes deeper. The UV LF at z ∼ 8 is not very well constrained below M UV = −18 owing to the small number statistics and incompleteness uncertainties. To assess the contribution of galaxies to cosmic reionization, we derive the UV luminosity density at z ∼ 7 by integrating the UV LF down to an observational limit of M UV = −15. We show that our determination of log(ρ UV ) = 26.2 ± 0.13 (erg s −1 Hz −1 Mpc −3 ) can be sufficient to maintain reionization with an escape fraction of ionizing radiation of f esc = 10%-15%. Future Hubble Frontier Fields observations will certainly improve the constraints on the UV LF at the epoch of reionization, paving the way to more ambitious programs using cosmic telescopes with the next generation of large aperture telescopes such as the James Webb Space Telescope and the European Extremely Large Telescope.

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“…The latter prediction is supported by observations that the two strongest C IV absorbers at z ∼ 6 are physically associated with Lyman-α emitters (Díaz et al 2014), whose stellar mass is characteristically 10 8 -10 10 M⊙ (Lidman et al 2012). The tendency for low-ionization metal absorbers to trace predominantly lower-mass galaxies (Becker et al 2011;Finlator et al 2013;Kulkarni et al 2013) immediately promotes them to a critical constraint on the origin of the UVB and of cosmological reionization because current models for reionization tend to rely heavily on low-mass galaxies to provide the required flux of ionizing photons (Finlator et al 2011;Alvarez et al 2012;Kuhlen & Faucher-Giguère 2012;Jaacks et al 2012;Robertson et al 2013;Duffy et al 2014;Wise et al 2014). Such systems are generally too faint to be observed in emission, hence low-ionization absorbers will remain the only way to constrain their abundance for the foreseeable future.…”

Section: Introductionmentioning

confidence: 99%

The reionization of carbon

Finlator

Thompson

Huang

et al. 2015

Monthly Notices of the Royal Astronomical Society

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109

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Observations suggest that C II was more abundant than C IV in the intergalactic medium towards the end of the hydrogen reionization epoch (z ∼ 6). This transition provides a unique opportunity to study the enrichment history of intergalactic gas and the growth of the ionizing background (UVB) at early times. We study how carbon absorption evolves from z = 10-5 using a cosmological hydrodynamic simulation that includes a self-consistent multifrequency UVB as well as a well-constrained model for galactic outflows to disperse metals. Our predicted UVB is within ∼ 2-4× of that from Haardt & Madau (2012), which is fair agreement given the uncertainties. Nonetheless, we use a calibration in post-processing to account for Lyman-α forest measurements while preserving the predicted spectral slope and inhomogeneity. The UVB fluctuates spatially in such a way that it always exceeds the volume average in regions where metals are found. This implies both that a spatially-uniform UVB is a poor approximation and that metal absorption is not sensitive to the epoch when HII regions overlap globally even at column densites of 10 12 cm −2 . We find, consistent with observations, that the C II mass fraction drops to low redshift while C IV rises owing the combined effects of a growing UVB and continued addition of carbon in low-density regions. This is mimicked in absorption statistics, which broadly agree with observations at z = 6-3 while predicting that the absorber column density distributions rise steeply to the lowest observable columns. Our model reproduces the large observed scatter in the number of low-ionization absorbers per sightline, implying that the scatter does not indicate a partially-neutral Universe at z ∼ 6.

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Steep faint-end slopes of galaxy mass and luminosity functions at z≥ 6 and the implications for reionization

Cited by 87 publications

References 64 publications

Spatially adaptive radiation-hydrodynamical simulations of galaxy formation during cosmological reionization

Spatially adaptive radiation-hydrodynamical simulations of galaxy formation during cosmological reionization

ARE ULTRA-FAINT GALAXIES ATz= 6–8 RESPONSIBLE FOR COSMIC REIONIZATION? COMBINED CONSTRAINTS FROM THE HUBBLE FRONTIER FIELDS CLUSTERS AND PARALLELS

The reionization of carbon

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