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Using the ASTRAEUS (semi-numerical rAdiative tranSfer coupling of galaxy formaTion and Reionization in N-body dark matter simUlationS) framework, we explore the impact of environmental density and radiative feedback on the assembly of galaxies and their host halos during the Epoch of Reionization. The ASTRAEUS framework allows us to study the evolution of galaxies with masses ($\rm 10^{8.2}M_\odot < M_{\rm h} < 10^{13}M_\odot$) in wide variety of environment ($-0.5 < {\rm log}(1+δ) < 1.3$ averaged over $(2~{\rm cMpc})^3$). We find that : (i) there exists a mass- and redshift- dependent "characteristic" environment (${\rm log} (1+δ_a(M_{\rm h}, z)) = 0.021\times (M_{\rm h}/M_\odot)^{0.16} + 0.07 z -1.12$, up to $z\sim 10$) at which galaxies are most efficient at accreting dark matter, e.g at a rate of $0.2\%$ of their mass every Myr at $z=5$; (ii) the number of minor and major mergers and their contributions to the dark matter assembly increases with halo mass at all redshifts and is mostly independent of the environment; (iii) at $z=5$ minor mergers contribute slightly more (by up to $\sim 10\%$) to the dark matter assembly while for the stellar assembly, major mergers dominate the contribution from minor mergers for $M_{\rm h}\lesssim 10^{11.5}M_\odot$ galaxies; (iv) radiative feedback quenches star formation more in low-mass galaxies ($M_{\rm h} \lesssim 10^{9.5}M_\odot$) in over-dense environments (${\rm log}(1+δ) > 0.5$); dominated by their major branch, this yields star formation histories biased towards older ages with a slower redshift evolution., 17 pages, 15 figures, submitted to MNRAS, comments welcome !

The locations of Ly-$\alpha$ emitting galaxies (LAEs) at the end of the Epoch of Reionisation (EoR) are expected to correlate with regions of ionised hydrogen, traced by the redshifted 21~cm hyperfine line. Mapping the neutral hydrogen around regions with detected and localised LAEs offers an avenue to constrain the brightness temperature of the Universe within the EoR by providing an expectation for the spatial distribution of the gas, thereby providing prior information unavailable to power spectrum measurements. We use a test set of 12 hours of observations from the Murchison Widefield Array (MWA) in extended array configuration, to constrain the neutral hydrogen signature of 58 LAEs, detected with the Subaru Hypersuprime Cam in the \textit{Silverrush} survey, centred on $z$=6.58. We assume that detectable emitters reside in the centre of ionised HII bubbles during the end of reionization, and predict the redshifted neutral hydrogen signal corresponding to the remaining neutral regions using a set of different ionised bubble radii. A prewhitening matched filter detector is introduced to assess detectability. We demonstrate the ability to detect, or place limits upon, the amplitude of brightness temperature fluctuations, and the characteristic HII bubble size. With our limited data, we constrain the brightness temperature of neutral hydrogen to $\Delta{\rm T}_B, Comment: 9 pages, 6 figures, accepted for publication in MNRAS

Next generation telescopes such as the James Webb Space Telescope (JWST) and the Nancy Grace Roman Space Telescope (NGRST) will enable us to study the first billion years of our Universe in unprecedented detail. In this work we use the ASTRAEUS (semi-numerical rAdiative tranSfer coupling of galaxy formaTion and Reionization in N-body dArk mattEr simUlationS) framework, that couples galaxy formation and reionization (for a wide range of reionization feedback models), to estimate the cosmic variance expected in the UV Luminosity Function (UV LF) and the Stellar Mass Function (SMF) in JWST surveys. We find that different reionization scenarios play a minor role in the cosmic variance. Most of the cosmic variance is completely driven by the underlying density field and increases above $100\%$ for ${\rm M}_{\rm UV} \sim -17.5 (-20)$ at $z =12 (6)$ for the JADES-deep survey (the deep JWST Advanced Extragalactic Survey with an area of 46 arcmin$^2$); the cosmic variance decreases with an increasing survey area roughly independently of redshift. We find that the faint-end (${\rm M}_{\rm UV} > -17$) slope of the Lyman Break Galaxies (LBGs) UV LF becomes increasingly shallower with increasing reionization feedback and show how JWST observations will be able to distinguish between different models of reionization feedback at $z>9$, even accounting for cosmic variance. We also show the environments (in terms of density and ionization fields)of Lyman Break Galaxies during the EoR, finding that the underlying over-density and ionization fraction scale positively with the UV luminosity. Finally, we also provide a public software tool to allow interested readers to compute cosmic variance for different redshifts and survey areas., 16 pages, 13 figures. Accepted for publication in MNRAS

In this work, we use the {\sc astraeus} (seminumerical rAdiative tranSfer coupling of galaxy formaTion and Reionization in N-body dArk mattEr simUlationS) framework which couples galaxy formation and reionization in the first billion years. Exploring a number of models for reionization feedback and the escape fraction of ionizing radiation from the galactic environment ($f_\mathrm{esc}$), we quantify how the contribution of star-forming galaxies {(with halo masses $M_h>10^{8.2}$M$_\odot$)} to reionization depends on the radiative feedback model, $f_\mathrm{esc}$, and the environmental over-density. Our key findings are: (i) for constant $f_\mathrm{esc}$ models, intermediate-mass galaxies (with halo masses of $M_h\simeq10^{9-11}$M$_\odot$ and absolute UV magnitudes of $M_{UV} \sim -15$ to $-20$) in intermediate-density regions drive reionization; (ii) scenarios where $f_\mathrm{esc}$ increases with decreasing halo mass shift the galaxy population driving reionization to lower-mass galaxies ($M_h\lesssim10^{9.5}$M$_\odot$) with lower luminosities ($M_{UV} \gtrsim-16$) and over-densities; (iii) reionization imprints its topology on the ionizing emissivity of low-mass galaxies ($M_h\lesssim10^{9}$M$_\odot$) through radiative feedback. Low-mass galaxies experience a stronger suppression of star formation by radiative feedback and show lower ionizing emissivities in over-dense regions; (iv) a change in $f_\mathrm{esc}$ with galaxy properties has the largest impact on the sources of reionization and their detectability, with the radiative feedback strength and environmental over-density playing a sub-dominant role; (v) JWST-surveys (with a limiting magnitude of $M_{UV} = -16$) will be able to detect the galaxies providing $\sim 60-70\%$ ($\sim 10\%$) of reionization photons at $z=7$ for constant $f_\mathrm{esc}$ models (scenarios where $f_\mathrm{esc}$ increases with decreasing halo mass)., 14 pages, 13 figures, accepted for publication in MNRAS

Recent work has shown that UV-luminous reionization-era galaxies often exhibit strong Lyman-alpha emission despite being situated at redshifts where the IGM is thought to be substantially neutral. It has been argued that this enhanced Ly α transmission reflects the presence of massive galaxies in overdense regions which power large ionized bubbles. An alternative explanation is that massive galaxies shift more of their Ly α profile to large velocities (relative to the systemic redshift) where the IGM damping wing absorption is reduced. Such a mass-dependent trend is seen at lower redshifts, but whether one exists at z ∼ 7 remains unclear owing to the small number of existing systemic redshift measurements in the reionization era. This is now changing with the emergence of [C ii]-based redshifts from ALMA. Here, we report MMT/Binospec Ly α spectroscopy of eight UV-bright (MUV ∼ −22) galaxies at z ≃ 7 selected from the ALMA REBELS survey. We detect Ly α in four of eight galaxies and use the [C ii] systemic redshifts to investigate the Ly α velocity profiles. The Ly α lines are significantly redshifted from systemic (average velocity offset = 223 km s–1) and broad (FWHM ≈ 300–650 km s−1), with two sources showing emission extending to ≈750 km s−1. We find that the broadest Ly α profiles are associated with the largest [C ii] line widths, suggesting a potential link between the Ly α FWHM and the dynamical mass. Since Ly α photons at high velocities transmit efficiently through the z = 7 IGM, our data suggest that velocity profiles play a significant role in boosting the Ly α visibility of the most UV-luminous reionization-era galaxies.

In this work, we have implemented a detailed physical model of galaxy chemical enrichment into the ${\it Astraeus}$ (semi-numerical rAdiative tranSfer coupling of galaxy formaTion and Reionization in N-body dark matter simUlationS) framework which couples galaxy formation and reionization in the first billion years. Simulating galaxies spanning over 2.5 orders of magnitude in halo mass with $M_h \sim 10^{8.9-11.5} M_\odot$ ($M_h \sim 10^{8.9-12.8} M_\odot$) at $z \sim 10 ~ (5)$, we find: (i) smooth-accretion of metal-poor gas from the intergalactic medium (IGM) plays a key role in diluting the interstellar medium (ISM) metallicity which is effectively restored due to self-enrichment from star formation; (ii) a redshift averaged gas-mass loading factor that depends on the stellar mass as $\eta_g \approx 1.38 ({M_*}/{10^{10} M_\odot})^{-0.43}$; (iii) the mass-metallicity relation is already in place at $z \sim 10$ and shows effectively no redshift evolution down to $z \sim 5$; (iv) for a given stellar mass, the metallicity decreases with an increase in the star formation rate (SFR); (v) the key properties of the gas-phase metallicity (in units of 12+log(O/H), stellar mass, SFR and redshift are linked through a high-redshift fundamental plane of metallicity (HFPZ) for which we provide a functional form; (vi) the mass-metallicity-SFR relations are effectively independent of the reionization radiative feedback model for $M_* \geq 10^{6.5} M_\odot$ galaxies; (vii) while low-mass galaxies ($M_h \leq 10^9 M_\odot$) are the key contributors to the metal budget of the IGM at early times, higher mass halos provide about 50% of the metal budget at lower-redshifts., Comment: Accepted to MNRAS

We compute the bispectra of the 21cm signal during the Epoch of Reionization for three different reionization scenarios that are based on a dark matter N-body simulation combined with a self-consistent, semi-numerical model of galaxy evolution and reionization. Our reionization scenarios differ in their trends of ionizing escape fractions ($f_\mathrm{esc}$) with the underlying galaxy properties and cover the physically plausible range, i.e. $f_\mathrm{esc}$ effectively decreasing, being constant, or increasing with halo mass. We find the 21cm bispectrum to be sensitive to the resulting ionization topologies that significantly differ in their size distribution of ionized and neutral regions throughout reionization. From squeezed to stretched triangles, the 21cm bispectra features a change of sign from negative to positive values, with ionized and neutral regions representing below-average and above-average concentrations contributing negatively and positively, respectively. The position of the change of sign provides a tracer of the size distribution of the ionized and neutral regions, and allows us to identify three major regimes that the 21cm bispectrum undergoes during reionization. In particular the regime during the early stages of reionization, where the 21cm bispectrum tracks the peak of the size distribution of the ionized regions, provides exciting prospects for pinning down reionization with the forthcoming Square Kilometre Array., Comment: 16 pages, 7 figures. Accepted for publication in MNRAS

Weakly interacting cold dark matter (CDM) particles, which are otherwise extremely successful in explaining various cosmological observations, exhibit a number of problems on small scales. One possible way of solving these problems is to invoke (so-called) warm dark matter (WDM) particles with masses $m_x \sim$ keV. Since the formation of structure is delayed in such WDM models, it is natural to expect that they can be constrained using observations related to the first stars, e.g., the 21 cm signal from cosmic dawn. In this work, we use a detailed galaxy formation model, Delphi, to calculate the 21 cm signal at high-redshifts and compare this to the recent EDGES observations. We find that while CDM and 5 keV WDM models can obtain a 21 cm signal within the observed redshift range, reproducing the amplitude of the observations requires the introduction of an excess radio background. On the other hand, WDM models with $m_x \leq 3$ keV can be ruled out since they are unable to match either the redshift range or the amplitude of the EDGES signal, irrespective of the parameters used. Comparable to values obtained from the low-redshift Lyman Alpha forest, our results extend constraints on the WDM particle to an era inaccessible by any other means; additional forthcoming 21 cm data from the era of cosmic dawn will be crucial in refining such constraints., Comment: Accepted to MNRAS

We present two bright galaxy candidates at z~12-13 identified in our H-dropout Lyman break selection with 2.3 deg2 near-infrared deep imaging data. These galaxy candidates, selected after careful screening of foreground interlopers, have spectral energy distributions showing a sharp discontinuity around 1.7 um, a flat continuum at 2-5 um, and non-detections at 12 galaxy. An ALMA program targeting one of the candidates shows a tentative 4sigma [OIII]88um line at z=13.27, in agreement with its photometric redshift estimate. The number density of the z~12-13 candidates is comparable to that of bright z~10 galaxies, and is consistent with a recently proposed double power-law luminosity function rather than the Schechter function, indicating little evolution in the abundance of bright galaxies from z~4 to 13. Comparisons with theoretical models show that the models cannot reproduce the bright end of rest-frame ultraviolet luminosity functions at z~10-13. Combined with recent studies reporting similarly bright galaxies at z~9-11 and mature stellar populations at z~6-9, our results indicate the existence of a number of star-forming galaxies at z>10, which will be detected with upcoming space missions such as James Webb Space Telescope, Nancy Grace Roman Space Telescope, and GREX-PLUS., 20 pages, 13 figures, accepted for publication in ApJ

We use the \textsc{astraeus} framework, that couples an N-body simulation with a semi-analytic model for galaxy formation and a semi-numerical model for reionization, to quantify the star formation histories (SFHs) of galaxies in the first billion years. Exploring four models of radiative feedback, we fit the SFH of each galaxy at $z>5$ as $\mathrm{log}(\mathrm{SFR}(z))=-\alpha(1 + z)+\beta$; star formation is deemed stochastic if it deviates from this fit by more than $\Delta_\mathrm{SFR}=0.6\,$dex. Our key findings are: (i) The fraction of stellar mass formed and time spent in the stochastic phase decrease with increasing stellar mass and redshift $z$. While galaxies with stellar masses of $M_\star\sim10^7M_\odot$ at $z\sim5~(10)$ form $\sim70\%~(20\%)$ of their stellar mass in the stochastic phase, this reduces to $ 10^{10}M_\odot$; (ii) the fractional mass assembled and lifetime spent in the stochastic phase do not significantly change with the radiative feedback model used; (iii) at all redshifts, $\alpha$ increases (decreases for the strongest radiative feedback model) with stellar mass for galaxies with $M_\star\lesssim 10^{8.5}M_\odot$ and converges to $\sim0.18$ for more massive galaxies; $\beta$ always increases with stellar mass. Our proposed fits can reliably recover the stellar masses and mass-to-light ratios for galaxies with $M_\star\sim10^{8-10.5}M_\odot$ and $M_{UV}\sim-17~{\rm to}~-23$ at $z\sim 5-9$. This physical model can therefore be used to derive the SFHs for galaxies observed by a number of forthcoming instruments., Comment: 19 pages, 14 figures, accepted for publication in MNRAS

Over the past decades, rest-frame ultraviolet (UV) observations have provided large samples of UV luminous galaxies at redshift (z) greater than 6, during the so-called epoch of reionization. While a few of these UV identified galaxies revealed significant dust reservoirs, very heavily dust-obscured sources at these early times have remained elusive. They are limited to a rare population of extreme starburst galaxies, and companions of rare quasars. These studies conclude that the contribution of dust-obscured galaxies to the cosmic star formation rate density at $z>6$ is sub-dominant. Recent ALMA and Spitzer observations have identified a more abundant, less extreme population of obscured galaxies at $z=3-6$. However, this population has not been confirmed in the reionization epoch so far. Here, we report the discovery of two dust-obscured star forming galaxies at $z=6.6813\pm0.0005$ and $z=7.3521\pm0.0005$. These objects are not detected in existing rest-frame UV data, and were only discovered through their far-infrared [CII] lines and dust continuum emission as companions to typical UV-luminous galaxies at the same redshift. The two galaxies exhibit lower infrared luminosities and star-formation rates than extreme starbursts, in line with typical star-forming galaxies at $z\sim7$. This population of heavily dust-obscured galaxies appears to contribute 10-25 per cent to the $z>6$ cosmic star formation rate density., 16 pages, 7 figures, 4 tables, published in Nature

We introduce a new self-consistent model of galaxy evolution and reionization, ASTRAEUS (semi-numerical rAdiative tranSfer coupling of galaxy formaTion and Reionization in N-body dArk mattEr simUlationS), which couples a state-of-the-art N-body simulation with the semi-analytical galaxy evolution DELPHI and the semi-numerical reionization scheme CIFOG. ASTRAEUS includes all the key processes of galaxy formation and evolution (including accretion, mergers, supernova and radiative feedback) and follows the time and spatial evolution of the ionized regions in the intergalactic medium (IGM). Importantly, it explores different radiative feedback models that cover the physically plausible parameter space, ranging from a weak and delayed to a strong and immediate reduction of gas mass available for star formation. From our simulation suite that covers the different radiative feedback prescriptions and ionization topologies, we find that radiative feedback continuously reduces star formation in galaxies with $M_h, 26 pages, 16 figures, accepted for publication in MNRAS

Detections of the cross correlation signal between the 21cm signal during reionization and high-redshift Lyman Alpha emitters (LAEs) are subject to observational uncertainties which mainly include systematics associated with radio interferometers and LAE selection. These uncertainties can be reduced by increasing the survey volume and/or the survey luminosity limit, i.e. the faintest detectable Lyman Alpha (Ly$\alpha$) luminosity. We use our model of high-redshift LAEs and the underlying reionization state to compute the uncertainties of the 21cm-LAE cross correlation function at $z\simeq6.6$ for observations with SKA1-Low and LAE surveys with $\Delta z=0.1$ for three different values of the average IGM ionization state ($\langle\chi_\mathrm{HI}\rangle$=0.1, 0.25, 0.5). At $z\simeq6.6$, we find SILVERRUSH type surveys, with a field of view of 21 deg$^2$ and survey luminosity limits of $L_\alpha\geq7.9\times10^{42}$erg~s$^{-1}$, to be optimal to distinguish between an inter-galactic medium (IGM) that is 50%, 25% and 10% neutral, while surveys with smaller fields of view and lower survey luminosity limits, such as the 5 and 10 deg$^2$ surveys with WFIRST, can only discriminate between a 50% and 10% neutral IGM., Comment: 5 pages, 3 figures, accepted for publication in MNRAS

The exact role of quasars during the Epoch of Reionization remains uncertain. With consensus leaning towards quasars producing a negligible amount of ionizing photons, we pose an alternate question: Can quasars indirectly contribute to reionization by allowing ionizing photons from stars to escape more easily? Using the Semi-Analytic Galaxy Evolution model to evolve a galaxy population through cosmic time, we construct an idealized scenario in which the escape fraction of stellar ionizing photons ($f_\mathrm{esc}$) is boosted following quasar wind events, potentially for several dynamical times. We find that under this scenario, the mean value of $f_\mathrm{esc}$ as a function of galaxy stellar mass peaks for intermediate mass galaxies. This mass dependence will have consequences for the 21cm power spectrum, enhancing power at small scales and suppressing it at large scales. This hints that whilst quasars may not directly contribute to the ionizing photon budget, they could influence reionization indirectly by altering the topology of ionized regions., Comment: 5 pages, 3 figures

Reionization represents an important epoch in the history in the Universe, when the first stars and galaxies gradually ionize the neutral hydrogen in the intergalactic medium (IGM). Understanding the nature of the ionizing sources, the associated ionization of the IGM, and its impact on subsequent structure formation and galaxy evolution by means of radiative feedback effects, represent key outstanding questions in current astrophysics. High-redshift galaxy observations and simulations have significantly extended our knowledge on the nature of high-redshift galaxies. However, essential properties such as the escape fraction of ionizing photons from galaxies into the IGM and their dependency on galactic properties remain essentially unknown, but determine significantly the distribution and time evolution of the ionized regions during reionization. Analyzing this ionization topology by means of the neutral hydrogen sensitive 21cm signal with radio interferometers such as SKA offers a complementary and unique opportunity to determine the nature of these first galaxies. I will show results from a self-consistent semi-numerical model of galaxy evolution and reionization, and discuss the potential of inferring galactic properties with the 21cm signal as well as the impact of reionization on the high-redshift galaxy population and its evolution.

We present deep spectroscopic follow-up observations of the Bremer Deep Field (BDF) where the two $z\sim$7 bright Ly$\alpha$ emitters (LAE) BDF521 and BDF3299 were previously discovered by Vanzella et al. (2011) and where a factor of $\sim$3-4 overdensity of faint LBGs has been found by Castellano et al. (2016). We confirm a new bright Ly$\alpha$ emitter, BDF2195, at the same redshift of BDF521, $z=7.008$, and at only $\sim$90 kpc physical distance from it, confirming that the BDF area is likely an overdense, reionized region. A quantitative assessment of the Ly$\alpha$ fraction shows that the number of detected bright emitters is much higher than the average found at z$\sim$7, suggesting a high Ly$\alpha$ transmission through the inter-galactic medium (IGM). However, the line visibility from fainter galaxies is at odds with this finding, since no Ly$\alpha$ emission is found in any of the observed candidates with $M_{UV}>$-20.25. This discrepancy can be understood either if some mechanism prevents Ly$\alpha$ emission from fainter galaxies within the ionized bubbles from reaching the observer, or if faint galaxies are located outside the reionized area and bright LAEs are solely responsible for the creation of their own HII regions. A thorough assessment of the nature of the BDF region and of its sources of re-ionizing radiation will be made possible by JWST spectroscopic capabilities., ERC STFC

We calculate Lyman Alpha Emitter (LAE) angular correlation functions (ACFs) at $z \simeq 6.6$ and the fraction of lifetime (for the 100 Myrs preceding $z\simeq6.6$) galaxies spend as Lyman Break Galaxies (LBGs) or as LBGs with Lyman Alpha (Ly$\alpha$) emission using a model that combines SPH cosmological simulations (GADGET-2), dust attenuation and a radiative transfer code (pCRASH). The ACFs are a powerful tool that significantly narrows the 3D parameter space allowed by LAE Ly$\alpha$ and UV luminosity functions (LFs) alone. With this work, we simultaneously constrain the escape fraction of ionizing photons $f_{esc}=0.05-0.5$, the mean fraction of neutral hydrogen in the intergalactic medium (IGM) $\langle \chi_{HI} \rangle \leq 0.01$ and the dust-dependent ratio of the escape fractions of Ly$\alpha$ and UV continuum photons $f_{\alpha}/f_c=0.6-1.2$. Our results show that reionization has the largest impact on the amplitude of the ACFs, and its imprints are clearly distinguishable from those of $f_{esc}$ and $f_\alpha/f_c$. We also show that galaxies with a critical stellar mass of $M_* = 10^{8.5} (10^{9.5})M_{\odot}$ produce enough luminosity to stay visible as LBGs (LAEs). Finally, the fraction of time during the past 100 Myrs prior to z=6.6 a galaxy spends as a LBG or as a LBG with Ly$\alpha$ emission increases with the UV magnitude (and the stellar mass $M_*$): considering observed (dust and IGM attenuated) luminosities, the fraction of time a galaxy spends as a LBG (LAE) increases from 65% to 100% (0-100%) as $M_{UV}$ decreases from $M_{UV} = -18.0$ to $-23.5$ ($M_*$ increases from $10^8-10^{10.5} M_{\odot}$). Thus in our model the brightest (most massive) LBGs most often show Ly$\alpha$ emission., Comment: 11 pages, 7 figures, accepted for publication in MNRAS, comments welcome

We have developed a modular semi-numerical code that computes the time and spatially dependent ionization of neutral hydrogen (HI), neutral (HeI) and singly ionized helium (HeII) in the intergalactic medium (IGM). The model accounts for recombinations and provides different descriptions for the photoionization rate that are used to calculate the residual HI fraction in ionized regions. We compare different semi-numerical reionization schemes to a radiative transfer (RT) simulation. We use the RT simulation as a benchmark, and find that the semi-numerical approaches produce similar HII and HeII morphologies and power spectra of the HI 21cm signal throughout reionization. As we do not track partial ionization of HeII, the extent of the double ionized helium (HeIII) regions is consistently smaller. In contrast to previous comparison projects, the ionizing emissivity in our semi-numerical scheme is not adjusted to reproduce the redshift evolution of the RT simulation, but directly derived from the RT simulation spectra. Among schemes that identify the ionized regions by the ratio of the number of ionization and absorption events on different spatial smoothing scales, we find those that mark the entire sphere as ionized when the ionization criterion is fulfilled to result in significantly accelerated reionization compared to the RT simulation. Conversely, those that flag only the central cell as ionized yield very similar but slightly delayed redshift evolution of reionization, with up to 20% ionizing photons lost. Despite the overall agreement with the RT simulation, our results suggests that constraining ionizing emissivity sensitive parameters from semi-numerical galaxy formation-reionization models are subject to photon nonconservation., Comment: 21 pages, 11 Figures, accepted for publication in MNRAS

We couple state of the art cosmological simulations (GADGET-2) with a dust model and a radiative transfer code (pCRASH) to build a complete model for high-redshift Lyman Alpha emitters (LAEs). Identifying simulated galaxies with dust-attenuated UV magnitudes of MUV 6 −17 as Lyman Break Galaxies (LBGs), we successfully validate our simulations by comparing against observed LBG ultraviolet luminosity functions (UV LFs), stellar mass functions, stellar mass densities (SMD) and specific star formation rates (sSFR) at z ≃ 6 − 8. Due to the poor constraints available on the escape fraction of H I ionizing photons (fesc) from galaxies, we use five different values fesc = 0.05,0.25,0.5,0.75,0.95 to post-process the cosmological simulation with pCRASH. Starting from a completely neutral Universe, we run pCRASH until reionization is complete, i.e. the average neutral hydrogen (H I ) fraction drops to hχHIi ≃10 4 . For a given fesc and hχHIicombination, the only free-parameter left to match model results to observations is the relative escape of Lyman Alpha (Lyα ) and continuum photons from the galactic environment (f�/fc). Starting from a scenario wherein dust is homogeneously distributed (f�/fc ≃ 0.68), we find that the observed LAE UV and Lyα luminosity functions (LFs) jointly constrain fesc ≃ 0.05 and hχHIi 6 0.1. In the scenario that dust is clumped, we find a three-dimensional degeneracy between fesc, hχHIi and f�/fc such that a decrease in the intrinsic Lyα luminosity can be compensated by an increase in the Lyα transmission through the intergalactic medium and/or an increasing Lyα escape out of the galactic environment. In the latter scenario, the theoretical model can be reconciled with observations for a much larger parameter space: hχHIi ≃0.5−10 4 , fesc ≃ 0.05−0.50 and f�/fc = 0.6−1.8. In other words, if dust is indeed clumped in the interstellar medium of high-redshift galaxies, we can not differentiate between a Universe which is either completely ionized or half neutral, or has an fesc ranging between 5-50%.

We study the signatures of reionization and ionizing properties of the early galaxies in the cross-correlations between the 21cm emission from the spin-flip transition of neutral hydrogen (H I ) and the underlying galaxy population, in particular a sub-population of galaxies visible as Lyman Alpha Emitters (LAEs). With both observables simultaneously derived from a z ' 6.6 hydrodynamical simulation (GADGET-2) snapshot post-processed with a radiative transfer code (pCRASH) and a dust model, we perform a parameter study and aim to constrain both the average intergalactic medium (IGM) ionization state (1 − hχHI i) and the reionization topology (outside-in versus inside-out). We find that in our model LAEs occupy the densest and most-ionized regions resulting in a very strong anti-correlation between the LAEs and the 21cm emission. A 1000 h SKA-LOW1 - Subaru Hyper Suprime Cam experiment can provide constraints on hχHI i, allowing us to distinguish between IGM ionization levels of 50%, 25%, 10% and fully ionized at scales r ∼ 0.1. Further, 1000 h SKA-LOW1 observations should be able to confirm the inside-out scenario by detecting a lower 21cm brightness temperature (by about 2-10 mK) in the densest regions ( >∼ 2 arcminute scales) hosting LAEs compared to lower-density regions devoid of them.

We present the analysis of deep HST multi-band imaging of the BDF field specifically designed to identify faint companions around two of the few Ly-alpha emitting galaxies spectroscopically confirmed at z~7 (Vanzella et al. 2011). Although separated by only 4.4 proper Mpc these galaxies cannot generate HII regions large enough to explain visibility of their Ly-alpha line, thus requiring a population of fainter ionizing sources in their vicinity. We use deep HST and VLT-Hawk-I data to select z~7 Lyman break galaxies around the emitters. We select 6 new robust z~7 LBGs at Y~26.5-27.5 whose average spectral energy distribution is consistent with the objects being at the redshift of the close-by Ly-alpha emitters. The resulting number density of z~7 LBGs in the BDF field is a factor ~3-4 higher than expected in random pointings of the same size. We compare these findings with cosmological hydrodynamic plus radiative transfer simulations of a universe with a half neutral IGM: we find that indeed Ly-alpha emitter pairs are only found in completely ionized regions characterized by significant LBG overdensities. Our findings match the theoretical prediction that the first ionization fronts are generated within significant galaxy overdensities and support a scenario where faint, "normal" star-forming galaxies are responsible for reionization., Comment: Accepted for publication in The Astrophysical Journal Letters. 6 pages, 5 figures

We consider a relativistically moving blob consisting of an isotropic electron distribution that Compton-scatters photons from an external isotropic radiation field. We compute the resulting beaming pattern, i.e. the distribution of the scattered photons, in the blob frame as well as in the observer's frame by using the full Klein-Nishina cross section and the exact incident photon distribution. In the Thomson regime the comparison of our approach with Dermer 1995 results in concurrent characteristics but different absolute number of the scattered photons by a factor of f_corr = 3.09. Additionally, our calculation yields a slightly lower boost factor which varies the more from the corresponding value in Dermer 1995 the higher the spectral index p of the electron distribution gets., Comment: 11 pages, 5 figures, accepted for publication in Advances in Space Research

Previous research has established the importance of the nouns and noun modification in academic writing because of their commonness and complexity. However, little is known about how noun modification varies across the rhetorical sections of research articles. Such a perspective is important because it reflects the interplay between communicative function and linguistic form. This study used a corpus of empirical research articles from the fields of applied linguistics and language teaching to explore the connection between article sections (Introduction, Methods, Results, Discussion; IMRD) and six types of noun modification: relative clauses, ing-clause postmodifiers, ed-clause postmodifiers, prepositional postmodifiers, premodifying nouns, and attributive adjectives. First, the frequency of these six types of noun modification was compared across IMRD sections. Second, the study also used a hand coded analysis of the structure and structural patterns of a sample of noun phrases through IMRD sections. The results of the analyses showed that noun modification is not uniform across IMRD sections. Significant differences were found in the rates of use for attributive adjectives, premodifying nouns, and prepositional phrase postmodifiers. There were no significant differences between sections for relative clauses, ing-clause postmodifiers, or edclause postmodifiers. The differences between sections for attributive adjectives, premodifying nouns, and prepositional phrases illustrate the way the functions of these structures intersects with the functions of IMRD sections. For example, Methods sections describe research methods, which often have premodifying nouns (corpus analysis, conversation

One of the most important parameters in characterizing the Epoch of Reionization, the escape fraction of ionizing photons, $f_\mathrm{esc}$, remains unconstrained both observationally and theoretically. With recent work highlighting the impact of galaxy-scale feedback on the instantaneous value of $f_\mathrm{esc}$, it is important to develop a model in which reionization is self-consistently coupled to galaxy evolution. In this work, we present such a model and explore how physically motivated functional forms of $f_\mathrm{esc}$ affect the evolution of ionized hydrogen within the intergalactic medium. Using the $21$cm power spectrum evolution, we investigate the likelihood of observationally distinguishing between a constant $f_\mathrm{esc}$ and other models that depend upon different forms of galaxy feedback. We find that changing the underlying connection between $f_\mathrm{esc}$ and galaxy feedback drastically alters the large-scale $21$cm power. The upcoming Square Kilometre Array Low Frequency instrument possesses the sensitivity to differentiate between our models at a fixed optical depth, requiring only $200$ hours of integration time focused on redshifts $z = 7.5-8.5$. Generalizing these results to account for a varying optical depth will require multiple $800$ hour observations spanning redshifts $z = 7-10$. This presents an exciting opportunity to observationally constrain one of the most elusive parameters during the Epoch of Reionization., 14 pages, 8 figures, 2 tables