Search

We measure escape fractions, $f_{\rm esc}$, of ionizing radiation from galaxies in the SPHINX suite of cosmological radiation-hydrodynamical simulations of reionization, resolving halos with $M_{\rm vir} \gtrapprox 7.5 \times 10^7 \ M_{\odot}$ with a minimum cell width of $\approx 10$ pc. Our new and largest $20$ co-moving Mpc wide volume contains tens of thousands of star-forming galaxies with halo masses up to a few times $10^{11} \ M_{\odot}$. The simulated galaxies agree well with observational constraints of the UV luminosity function in the Epoch of Reionization. The escape fraction fluctuates strongly in individual galaxies over timescales of a few Myrs, due to its regulation by supernova and radiation feedback, and at any given time a tiny fraction of star-forming galaxies emits a large fraction of the ionizing radiation escaping into the inter-galactic medium. Statistically, $f_{\rm esc}$ peaks in intermediate-mass, intermediate-brightness, and low-metallicity galaxies ($M_{*} \approx 10^7 \ M_{\odot}$, $M_{1500} \approx -17$, $Z\lesssim 5 \times 10^{-3} \ Z_{\odot}$), dropping strongly for lower and higher masses, brighter and dimmer galaxies, and more metal-rich galaxies. The escape fraction correlates positively with both the short-term and long-term specific star formation rate. According to SPHINX, galaxies too dim to be yet observed, with $M_{1500} \gtrapprox -17$, provide about $55$ percent of the photons contributing to reionization. The global averaged $f_{\rm esc}$ naturally decreases with decreasing redshift, as predicted by UV background models and low-redshift observations. This evolution is driven by decreasing specific star formation rates over cosmic time., Comment: 20 figures, 21 pages plus appendices. Accepted for publication in MNRAS

We present a new investigation of the intergalactic medium (IGM) near reionization using dark gaps in the Lyman-$\beta$ (Ly$\beta$) forest. With its lower optical depth, Ly$\beta$ offers a potentially more sensitive probe to any remaining neutral gas compared to commonly used Ly$\alpha$ line. We identify dark gaps in the Ly$\beta$ forest using spectra of 42 QSOs at $z_{\rm em}>5.5$, including new data from the XQR-30 VLT Large Programme. Approximately $40\%$ of these QSO spectra exhibit dark gaps longer than $10h^{-1}{\rm Mpc}$ at $z\simeq5.8$. By comparing the results to predictions from simulations, we find that the data are broadly consistent both with models where fluctuations in the Ly$\alpha$ forest are caused solely by ionizing ultraviolet background (UVB) fluctuations and with models that include large neutral hydrogen patches at $z, Comment: 17 pages, 13 figures, accepted for publication in ApJ. The Figure set and machine readable table are available at https://ydzhuastro.github.io/lyb.html

The presence of excess scatter in the Ly-$\alpha$ forest at $z\sim 5.5$, together with the existence of sporadic extended opaque Gunn-Peterson troughs, has started to provide robust evidence for a late end of hydrogen reionisation. However, low data quality and systematic uncertainties complicate the use of Ly-$\alpha$ transmission as a precision probe of reionisation's end stages. In this paper, we assemble a sample of 67 quasar sightlines at $z>5.5$ with high signal-to-noise ratios of $>10$ per $\leq 15$ km s$^{-1}$ spectral pixel, relying largely on the new XQR-30 quasar sample. XQR-30 is a large program on VLT/X-Shooter which obtained deep (SNR $>20$ per pixel) spectra of 30 quasars at $z>5.7$. We carefully account for systematics in continuum reconstruction, instrumentation, and contamination by damped Ly-$\alpha$ systems. We present improved measurements of the mean Ly-$\alpha$ transmission over $4.93.5 \sigma$). Our results indicate that reionisation-related fluctuations, whether in the UVB, residual neutral hydrogen fraction, and/or IGM temperature, persist in the intergalactic medium until at least $z=5.3$ ($t=1.1$ Gyr after the Big Bang). This is further evidence for a late end to reionisation., Comment: Accepted for publication in MNRAS. Full measurement datasets are available on the first author's website

The physical and chemical properties of the circumgalactic medium (CGM) at $z\gtrsim6$ have been studied successfully through the absorption in the spectra of background Quasi-Stellar Objects (QSOs). One of the most crucial questions is to investigate the nature and location of the source galaxies that give rise to these early metal absorbers. Theoretical models suggest that momentum-driven outflows from typical star-forming galaxies can eject metals into the CGM and the intergalactic medium (IGM) at z=5-6. Deep, dedicated surveys have searched for Ly$\alpha$ emission associated with strong CIV absorbers at $z\approx 6$, but only a few Ly$\alpha$ emitter candidates have been detected. Interpreting these detections is moreover ambiguous because Ly$\alpha$ is a resonant line, raising the need for complementary techniques for detecting absorbers' host galaxies. Here, using Atacama Large Millimeter Array (ALMA), we report a [C II] 158$\mu$m emitter associated with a strong low-ionization absorber, OI, at $z=5.978$. The projected impact parameter between OI and [C II] emitter is 20.0 kpc. The measured [C II] luminosity is $7.0\times 10^7$ solar luminosities. Further analysis indicates that strong OI absorbers may reside in the circumgalactic medium of massive halos one to two orders of magnitude more massive than expected values., Comment: Published in Nature Astronomy on Sep 27, 2021; 45 pages; authors' version. Link to the paper: https://www.nature.com/articles/s41550-021-01471-4

Our understanding of the intergalactic medium at redshifts $z=5$-$6$ has improved considerably in the last few years due to the discovery of quasars with $z>6$ that enable Lyman-$\alpha$ forest studies at these redshifts. A realisation from this has been that hydrogen reionization could end much later than previously thought, so that large "islands" of cold, neutral hydrogen could exist in the IGM at redshifts $z=5$-$6$. By using radiative transfer simulations of the IGM, we consider the implications of the presence of these neutral hydrogen islands for the 21-cm power spectrum signal and its potential detection by experiments such as HERA, SKA, LOFAR, and MWA. In contrast with previous models of the 21-cm signal, we find that thanks to the late end of reionization the 21-cm power in our simulation continues to be as high as $\Delta^2_{21}=10~\mathrm{mK}^2$ at $k\sim 0.1~h/$cMpc at $z=5$-$6$. This value of the power spectrum is several orders of magnitude higher than that in the conventional models considered in the literature for these redshifts. Such high values of the 21-cm power spectrum should be detectable by HERA and SKA1-LOW in $\sim 1000$ hours, assuming optimistic foreground subtraction. This redshift range is also attractive due to relatively low sky temperature and potentially greater abundance of multiwavelength data., Comment: 14 pages, 6 figures, 2 tables. Accepted for publication in MNRAS

A late end to reionisation at redshift $z\simeq 5.3$ is consistent with observed spatial variations in the Ly$\alpha$ forest transmission and the deficit of Ly$\alpha$ emitting galaxies around extended Ly$\alpha$ absorption troughs at $z=5.5$. In this model, large islands of neutral hydrogen should persist in the diffuse intergalactic medium (IGM) until $z\simeq 6$. We use a novel, hybrid approach that combines high resolution cosmological hydrodynamical simulations with radiative transfer to predict the incidence of strong 21 cm forest absorbers with optical depths $\tau_{21}>10^{-2}$ from the diffuse IGM in these late reionisation models. We include the effect of redshift space distortions on the simulated 21 cm forest spectra, and treat the highly uncertain heating of the pre-reionisation IGM by soft X-rays as a free parameter. For a model with only modest IGM pre-heating, such that average gas kinetic temperatures in the diffuse IGM remain below $T_{\rm K}\simeq 10^{2} \rm\, K$, we find that strong 21 cm forest absorption lines should persist until $z=6$. For a sample of $\sim 10$ sufficiently radio loud background sources, a null-detection of 21 cm forest absorbers at $z\simeq 6$ with SKA1-low or possibly LOFAR should provide an informative lower limit on the still largely unconstrained soft X-ray background at high redshift and the temperature of the pre-reionisation IGM., Comment: 18 pages, 11 figures, 4 tables. Accepted for publication in MNRAS

The physical and chemical properties of the circumgalactic medium (CGM) at z ≳ 6 have been studied successfully through the absorption in the spectra of background Quasi-Stellar Objects (QSOs) 1–3. One of the most crucial questions is to investigate the nature and location of the source galaxies that give rise to these early metal absorbers4–6. Theoretical models suggest that momentum-driven outflows from typical star-forming galaxies can eject metals into the CGM and the intergalactic medium (IGM), with the projected separation between absorbers and galaxies expected to range from 5 to 50 proper kpc at z=5–6 7–10. Deep, dedicated surveys have searched for Lyα emission associated with strong CIV absorbers at z ≈ 6, but only a few Lyα emitter candidates have been detected. Interpreting these detections is moreover ambiguous because Lyα is a resonant line11–13, raising the need for complementary techniques for detecting absorbers’ host galaxies. Here, using Atacama Large Millimeter Array (ALMA), we report, for the first time, the [C II] 158µm emission and the far-infrared dust continuum associated with a strong low-ionization absorber, O I, at z = 5.978. The [C II] luminosity is 73 million solar luminosities, corresponding to a dark matter halo mass of 100 billion solar masses. This is one to two orders of magnitude more massive than typical values predicted from cosmological simulations9, 16.

We compare a sample of five high-resolution, high S/N Ly$\alpha$ forest spectra of bright $65$ with those obtained from mock absorption spectra from the Sherwood and Sherwood-Relics suites of hydrodynamical simulations of the intergalactic medium (IGM). We use a profile fitting procedure for the inverted transmitted flux, $1-F$, similar to the widely used Voigt profile fitting of the transmitted flux $F$ at lower redshifts, to characterise the transmission spikes that probe predominately underdense regions of the IGM. We are able to reproduce the width and height distributions of the transmission spikes, both with optically thin simulations of the post-reionization Universe using a homogeneous UV background and full radiative transfer simulations of a late reionization model. We find that the width of the fitted components of the simulated transmission spikes is very sensitive to the instantaneous temperature of the reionized IGM. The internal structures of the spikes are more prominant in low temeperature models of the IGM. The width distribution of the observed transmission spikes, which require high spectral resolution ($\leq $ 8 km/s) to be resolved, is reproduced for optically thin simulations with a temperature at mean density of $T_0= (11000 \pm 1600,10500\pm 2100,12000 \pm 2200)$ K at $z= (5.4,5.6,5.8)$. This is weakly dependent on the slope of the temperature-density relation, which is favoured to be moderately steeper than isothermal. In the inhomogeneous, late reionization, full radiative transfer simulations where islands of neutral hydrogen persist to $z\sim5.3$, the width distribution of the observed transmission spikes is consistent with the range of $T_0$ caused by spatial fluctuations in the temperature-density relation., Comment: 20 pages (+10 pages appendices), 12 figures (+14 figures appendices); Accepted in MNRAS; Main results are summarized in Fig. 10, Fig. 12 and Table 3

We present an analysis of the evolution of the Lyman-series forest into the epoch of reionization using cosmological radiative transfer simulations in a scenario where reionization ends late. We explore models with different midpoints of reionization and gas temperatures. We find that once the simulations have been calibrated to match the mean flux of the observed Lyman-$\alpha$ forest at $4 < z < 6$, they also naturally reproduce the distribution of effective optical depths of the Lyman-$\beta$ forest in this redshift range. We note that the tail of the largest optical depths that is most challenging to match corresponds to the long absorption trough of ULAS J0148+0600, which we have previously shown to be rare in our simulations. We consider the evolution of the Lyman-series forest out to higher redshifts, and show that future observations of the Lyman-$\beta$ forest at $z>6$ will discriminate between different reionization histories. The evolution of the Lyman-$\alpha$ and Lyman-$\gamma$ forests are less promising as a tool for pushing studies of reionization to higher redshifts due to the stronger saturation and foreground contamination, respectively., Comment: 10 pages, 9 figures, 1 table. Accepted to MNRAS

The thermal state of the post-reionization IGM is sensitive to the timing of reionization and the nature of the ionizing sources. We have modelled here the thermal state of the IGM in cosmological radiative transfer simulations of a realistic, extended, spatially inhomogeneous hydrogen reionization process, carefully calibrated with Ly-alpha forest data. We compare these with cosmological simulations run using a spatially homogeneous ionizing background. The simulations with a realistic growth of ionized regions and a realistic spread in reionization redshifts show, as expected, significant spatial fluctuations in the temperature-density relation (TDR) of the post-reionization IGM. The most recently ionized regions are hottest and exhibit a flatter TDR. In simulations consistent with the average TDR inferred from Ly-alpha forest data, these spatial fluctuations have a moderate but noticeable effect on the statistical properties of the Ly-alpha opacity of the IGM at z ~ 4-6. This should be taken into account in accurate measurements of the thermal properties of the IGM and the free-streaming of dark matter from Ly-alpha forest data in this redshift range. The spatial variations of the TDR predicted by our simulations are, however, smaller by about a factor two than would be necessary to explain the observed large spatial opacity fluctuations on large (> 50 comoving Mpc/h) scales at z > 5.5., 17 pages, 11 figures. Accepted to MNRAS

A long (110 cMpc/$h$) and deep absorption trough in the Ly$\alpha$ forest has been observed extending down to redshift 5.5 in the spectrum of ULAS J0148+0600. Although no Ly$\alpha$ transmission is detected, Ly$\beta$ spikes are present which has led to claims that the gas along this trough must be ionized. Using high resolution cosmological radiative transfer simulations in large volumes, we show that in a scenario where reionization ends late ($z \sim 5.2$), our simulations can reproduce troughs as long as observed. In this model, we find that the troughs are caused by islands of neutral hydrogen. Small ionized holes within the neutral islands allow for the transmission of Ly$\beta$. We have also modelled the Ly$\alpha$ emitter population around the simulated troughs, and show that there is a deficit of Ly$\alpha$ emitters close to the trough as is observed., Comment: 11 pages, 8 figures. Accepted for publication in MNRAS

High-redshift QSO spectra show large spatial fluctuations in the Ly-alpha opacity of the intergalactic medium on surprisingly large scales at z>~5.5. We present a radiative transfer simulation of cosmic reionization driven by galaxies that reproduces this large scatter and the rapid evolution of the Ly-alpha opacity distribution at 5~6. Reionization is complete at z=5.3 in our model, and 50% of the volume of the Universe is ionized at z=7. Agreement with the Ly-alpha forest data in such a late reionization model requires a rapid evolution of the ionizing emissivity of galaxies that peaks at z~6.8. The late end of reionization results in a large scatter in the photoionisation rate and the neutral hydrogen fraction at redshifts as low as z, Comment: 5 pages, 3 figures; accepted for publication in MNRAS

We present the detailed science case, and brief descriptions of the telescope design, site, and first light instrument plans for a new ultra-wide field submillimeter observatory, CCAT-prime, that we are constructing at a 5600 m elevation site on Cerro Chajnantor in northern Chile. Our science goals are to study star and galaxy formation from the epoch of reionization to the present, investigate the growth of structure in the Universe, improve the precision of B-mode CMB measurements, and investigate the interstellar medium and star formation in the Galaxy and nearby galaxies through spectroscopic, polarimetric, and broadband surveys at wavelengths from 200 m to 2 mm. These goals are realized with our two first light instruments, a large field-of-view (FoV) bolometer-based imager called Prime-Cam (that has both camera and an imaging spectrometer modules), and a multi-beam submillimeter heterodyne spectrometer, CHAI. CCAT-prime will have very high surface accuracy and very low system emissivity, so that combined with its wide FoV at the unsurpassed CCAT site our telescope/instrumentation combination is ideally suited to pursue this science. The CCAT-prime telescope is being designed and built by Vertex Antennentechnik GmbH. We expect to achieve first light in the spring of 2021., Ground-based and Airborne Telescopes VII, June 10-15, 2018, Austin, USA, Series: Proceedings of SPIE; no. 10700

We present the Technicolor Dawn simulations, a suite of cosmological radiation-hydrodynamic simulations of the first 1.2 billion years. By modeling a spatially-inhomogeneous UVB on-the-fly with 24 frequencies and resolving dark matter halos down to $10^8 M_\odot$ within 12 $h^{-1}$ Mpc volumes, our simulations unify observations of the intergalactic and circumgalactic media, galaxies, and reionization into a common framework. The only empirically-tuned parameter, the fraction $f_{\mathrm{esc,gal}}(z)$ of ionizing photons that escape the interstellar medium, is adjusted to match observations of the Lyman-$\alpha$ forest and the cosmic microwave background. With this single calibration, our simulations reproduce the history of reionization; the stellar mass-star formation rate relation of galaxies; the number density and metallicity of damped Lyman-$\alpha$ absorbers (DLAs) at $z\sim5$; the abundance of weak metal absorbers; the ultraviolet background (UVB) amplitude; and the Lyman-$\alpha$ flux power spectrum at $z=5.4$. The galaxy stellar mass and UV luminosity functions are underproduced by $\leq2\times$, suggesting an overly vigorous feedback model. The mean transmission in the Lyman-$\alpha$ forest is underproduced at $z4$ Ryd UVB. Solving this problem by increasing metal yields would overproduce both weak absorbers and DLA metallicities. Instead, the observed strength of high-ionization emission from high-redshift galaxies and absorption from their environments suggest that the ionizing flux from conventional stellar population models is too soft., Comment: 24 pages, 17 figures, accepted to MNRAS

We present models of low- and high-ionization metal-line absorbers (O I, C II, C IV and Mg II) during the end of the reionization epoch, at z ~ 6. Using four cosmological hydrodynamical simulations with different feedback schemes (including the Illustris and Sherwood simulations) and two different choices of hydro-solver, we investigate how the overall incidence rate and equivalent width distribution of metal-line absorbers varies with the galactic wind prescription. We find that the O I and C II absorbers are reasonably insensitive to the feedback scheme. All models, however, struggle to reproduce the observations of C IV and Mg II, which are probing down to lower overdensities than O I and C II at z ~ 6, suggesting that the metals in the simulations are not being transported out into the IGM efficiently enough. The situation is improved but not resolved if we choose a harder (but still reasonable) and/or (locally) increased UV background at z ~ 6., LCK acknowledges the support of an Isaac Newton Studentship, the Cambridge Trust and STFC. Support by the FP7 ERC Advanced Grant Emergence-320596 is gratefully acknowledged. EP acknowledges support from the Kavli Foundation. SB was supported by the National Aeronautics and Space Administration through Einstein Postdoctoral Fellowship Award Number PF5-160133 issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060. JSB acknowledges the support of a Royal Society University Research Fellowship. This work used the DIRAC Shared Memory Processing system at the University of Cambridge, operated by the COSMOS Project at the Department of Applied Mathematics and Theoretical Physics on behalf of the STFC DiRAC HPC Facility (www.dirac.ac.uk). This equipment was funded by BIS National E-infrastructure capital grant ST/J005673/1, STFC capital grant ST/H008586/1 and STFC DiRAC Operations grant ST/K00333X/1. This work also used the DiRAC Data Analytic system at the University of Cambridge, operated by the University of Cambridge High Performance Computing Service on behalf of the STFC DiRAC HPC Facility (www.dirac.ac.uk). This equipment was funded by BIS National E-infrastructure capital grant (ST/K001590/1), STFC capital grants ST/H008861/1 and ST/H00887X/1, and STFC DiRAC Operations grant ST/K00333X/1. DiRAC is part of the National E-Infrastructure. We acknowledge PRACE for awarding us access to the Curie supercomputer, based in France at the Tres Grand Centre de Calcul (TGCC), through the 8th regular call., This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/ 10.1093/mnras/stw1306

QSO near-zones are an important probe of the the ionization state of the IGM at z ~ 6-7, at the end of reionization. We present here high-resolution cosmological 3D radiative transfer simulations of QSO environments for a wide range of host halo masses, 10$^{10-12.5}$ M_sun. Our simulated near-zones reproduce both the overall decrease of observed near-zone sizes at 6 < z < 7 and their scatter. The observable near-zone properties in our simulations depend only very weakly on the mass of the host halo. The size of the H II region expanding into the IGM is generally limited by (super-)Lyman Limit systems loosely associated with (low-mass) dark matter haloes. This leads to a strong dependence of near-zone size on direction and drives the large observed scatter. In the simulation centred on our most massive host halo, many sightlines show strong red damping wings even for initial volume averaged neutral hydrogen fractions as low as ~ 10$^{-3}$. For QSO lifetimes long enough to allow growth of the central supermassive black hole while optically bright, we can reproduce the observed near-zone of ULAS J1120+0641 only with an IGM that is initially neutral. Our results suggest that larger samples of z > 7 QSOs will provide important constraints on the evolution of the neutral hydrogen fraction and thus on how late reionization ends., Comment: This is a pre-copyedited, author-produced PDF of an article accepted for publication in MNRAS following peer review. 19 pages, 17 figures and 3 tables

Low ionization metal absorption due to OI has been identified as an important probe of the physical state of the inter-/circumgalactic medium at the tail-end of reionization. We use here high-resolution hydrodynamic simulations to interpret the incidence rate of OI absorbers at z~6 as observed by Becker et al. (2011). We infer weak OI absorbers (EW > 0.1 A) to have typical HI column densities in the range of sub-DLAs, densities of 80 times the mean baryonic density and metallicities of about 1/500 th solar. This is similar to the metallicity inferred at similar overdensities at z~3, suggesting that the metal enrichment of the circumgalactic medium around low-mass galaxies has already progressed considerably by z~6. The apparently rapid evolution of the incidence rates for OI absorption over the redshift range 55. We predict the incidence rate of OI absorbers to continue to rise rapidly with increasing redshift as the IGM becomes more neutral. If the distribution of metals extends to lower density regions, OI absorbers will allow the metal enrichment of the increasingly neutral filamentary structures of the cosmic web to be probed., Comment: 13 pages, 10 figures, 1 table, accepted to MNRAS