Star Formation In Halos Research Articles

On the rise and fall of galactic ionizing output at the end of reionization

ABSTRACT Quasar absorption spectra measurements suggest that reionization proceeded rapidly, ended late at z ∼ 5.5, and was followed by a flat ionizing background evolution. Simulations that reproduce this behaviour often rely on a fine-tuned galaxy ionizing emissivity, which peaks at z ∼ 6–7 and drops a factor of 1.5–2.5 by z ∼ 5. This is puzzling since the abundance of galaxies is observed to grow monotonically during this period. Explanations for this include effects such as dust obscuration of ionizing photon escape and feedback from photoheating of the IGM. We explore the possibility that this drop in emissivity is instead an artefact of one or more modelling deficiencies in reionization simulations. These include possibly incorrect assumptions about the ionizing spectrum and/or inaccurate modelling of IGM clumping. Our results suggest that the need for a drop could be alleviated if simulations are underestimating the IGM opacity from massive, star-forming haloes. Other potential modelling issues either have a small effect or require a steeper drop when remedied. We construct an illustrative model in which the emissivity is nearly flat at reionization’s end, evolving only ∼0.05 dex at 5 < z < 7. More realistic scenarios, however, require a ∼0.1–0.3 dex drop. We also study the evolution of the Ly α effective optical depth distribution and compare to recent measurements. We find that models that feature a hard ionizing spectrum and/or are driven by faint, low-bias sources most easily reproduce the mean transmission and optical depth distribution of the forest simultaneously.

Heavy black hole seed formation in high-z atomic cooling halos

Context. Halos with masses in excess of the atomic limit are believed to be ideal environments in which to form heavy black hole seeds with masses above 103 M⊙. In cases where the H2 fraction is suppressed, this is expected to lead to reduced fragmentation of the gas and the generation of a top-heavy initial mass function. In extreme cases this can result in the formation of massive black hole seeds. Resolving the initial fragmentation scale and the resulting protostellar masses has, until now, not been robustly tested. Aims. We run zoom-in simulations of atomically cooled halos in which the formation of H2 is suppressed to assess whether they can truly resist fragmentation at high densities and tilt the initial mass function towards a more top-heavy form and the formation of massive black hole seeds. Methods. Cosmological simulations were performed with the moving mesh code AREPO, using a primordial chemistry network until z ∼ 11. Three haloes with masses in excess of the atomic cooling mass were then selected for detailed examination via zoom-ins. A series of zoom-in simulations, with varying levels of maximum spatial resolution, captured the resulting fragmentation and formation of metal-free stars using the sink particle technique. The highest resolution simulations resolved densities up to 10−6 g cm−3 (1018 cm−3) and captured a further 100 yr of fragmentation behaviour at the centre of the halo. Lower resolution simulations were then used to model the future accretion behaviour of the sinks over longer timescales. Results. Our simulations show intense fragmentation in the central region of the halos, leading to a large number of near-solar mass protostars. Even in the presence of a super-critical Lyman-Werner radiation field (JLW > 105J21), H2 continues to form within the inner ∼2000 au of the halo. Despite the increased fragmentation, the halos produce a protostellar mass spectrum that peaks at higher masses relative to standard Population III star-forming halos. The most massive protostars have accretion rates of 10−3–10−1 M⊙ yr−1 after the first 100 years of evolution, while the total mass of the central region grows at 1 M⊙ yr−1. Lower resolution zoom-ins show that the total mass of the system continues to accrete at ∼1 M⊙ yr−1 for at least 104 yr, although how this mass is distributed amongst the rapidly growing number of protostars is unclear. However, assuming that a fraction of stars can continue to accrete rapidly, the formation of a sub-population of stars with masses in excess of 103 M⊙ is likely in these halos. In the most optimistic case, we predict the formation of heavy black hole seeds with masses in excess of 104 M⊙, assuming an accretion behaviour in line with expectations from super-competitive accretion and/or frequent mergers with secondary protostars.

Metal enrichment: the apex accretor perspective

The goal of this work is to devise a description of the enrichment process in large-scale structure that explains the available observations and makes predictions for future measurements. We took a spartan approach to this study, employing observational results and algebra to connect stellar assembly in star-forming halos with metal enrichment of the intra-cluster and group medium. On one hand, our construct is the first to provide an explanation for much of the phenomenology of metal enrichment in clusters and groups. It sheds light on the lack of redshift evolution in metal abundance, as well as the small scatter of metal abundance profiles, the entropy versus abundance anti-correlation found in cool core clusters, and the so-called Fe conundrum, along with several other aspects of cluster enrichment. On the other hand, it also allows us to infer the properties of other constituents of large-scale structure. We find that gas that is not bound to halos must have a metal abundance similar to that of the ICM and only about one-seventh to one-third of the Fe in the Universe is locked in stars. A comparable amount is found in gas in groups and clusters and, lastly and most importantly, about three-fifths of the total Fe is contained in a tenuous warm or hot gaseous medium in or between galaxies. We point out that several of our results follow from two critical but well motivated assumptions: 1) the stellar mass in massive halos is currently underestimated and 2) the adopted Fe yield is only marginally consistent with predictions from synthesis models and SN rates. One of the most appealing features of the work presented here is that it provides an observationally grounded construct where vital questions on chemical enrichment in the large-scale structure can be addressed. We hope that it may serve as a useful baseline for future works.

Validating Posteriors Obtained by an Emulator When Jointly Fitting Mock Data of the Global 21 cm Signal and High-z Galaxy UV Luminosity Function

Although neural-network-based emulators enable efficient parameter estimation in 21 cm cosmology, the accuracy of such constraints is poorly understood. We employ nested sampling to fit mock data of the global 21 cm signal and high-z galaxy ultraviolet luminosity function (UVLF) and compare for the first time the emulated posteriors obtained using the global signal emulator globalemu to the “true” posteriors obtained using the full model on which the emulator is trained using ARES. Of the eight model parameters we employ, four control the star formation efficiency (SFE) and thus can be constrained by UVLF data, while the remaining four control UV and X-ray photon production and the minimum virial temperature of star-forming halos () and thus are uniquely probed by reionization and 21 cm measurements. For noise levels of 50 and 250 mK in the 21 cm data being jointly fit, the emulated and “true” posteriors are consistent to within 1σ. However, at lower noise levels of 10 and 25 mK, globalemu overpredicts and underpredicts γ lo, an SFE parameter, by ≈3σ–4σ, while the “true” ARES posteriors capture their fiducial values within 1σ. We find that jointly fitting the mock UVLF and 21 cm data significantly improves constraints on the SFE parameters by breaking degeneracies in the ARES parameter space. Our results demonstrate the astrophysical constraints that can be expected for global 21 cm experiments for a range of noise levels from pessimistic to optimistic, as well as the potential for probing redshift evolution of SFE parameters by including UVLF data.

The Cosmic Ultraviolet Baryon Survey: Empirical Characterization of Turbulence in the Cool Circumgalactic Medium

This paper reports the first measurement of the relationship between turbulent velocity and cloud size in the diffuse circumgalactic medium (CGM) in typical galaxy halos at redshift z ≈ 0.4–1. Through spectrally resolved absorption profiles of a suite of ionic transitions paired with careful ionization analyses of individual components, cool clumps of size as small as l cl ∼ 1 pc and density lower than n H = 10−3 cm−3 are identified in galaxy halos. In addition, comparing the line widths between different elements for kinematically matched components provides robust empirical constraints on the thermal temperature T and the nonthermal motions b NT, independent of the ionization models. On average, b NT is found to increase with l cl following over three decades in spatial scale from l cl ≈ 1 pc to l cl ≈ 1 kpc. Attributing the observed b NT to turbulent motions internal to the clumps, the best-fit b NT–l cl relation shows that the turbulence is consistent with Kolmogorov at <1 kpc with a roughly constant energy transfer rate per unit mass of ϵ ≈ 0.003 cm2 s−3 and a dissipation timescale of ≲100 Myr. No significant difference is found between massive quiescent and star-forming halos in the sample on scales less than 1 kpc. While the inferred ϵ is comparable to what is found in C iv absorbers at high redshift, it is considerably smaller than observed in star-forming gas or in extended line-emitting nebulae around distant quasars. A brief discussion of possible sources to drive the observed turbulence in the cool CGM is presented.

Structure formation and the global 21-cm signal in the presence of Coulomb-like dark matter-baryon interactions

Many compelling dark matter (DM) scenarios feature Coulomb-like interactions between DM particles and baryons, in which the cross section for elastic scattering scales with relative particle velocity as ${v}^{\ensuremath{-}4}$. Previous studies have invoked such interactions to produce heat exchange between cold DM and baryons and alter the temperature evolution of hydrogen. Here, we present a comprehensive study of the effects of Coulomb-like scattering on structure formation, in addition to the known effects on the thermal history of hydrogen. We find that interactions which significantly alter the temperature of hydrogen at Cosmic Dawn also dramatically suppress the formation of galaxies that source the Lyman-$\ensuremath{\alpha}$ background, further affecting the global 21-cm signal. In particular, an interaction cross section at the current observational upper limit leads to a decrease in the abundance of star-forming halos by a factor of $\ensuremath{\sim}2$ at $z\ensuremath{\sim}20$, relative to cold, collisionless DM. We also find that DM that is 100% millicharged cannot reproduce the depth and the timing of the reported EDGES anomaly in any part of the parameter space. These results critically inform modeling of the global 21-cm signal and structure formation in cosmologies with DM--baryon scattering, with repercussions for future and upcoming cosmological data analysis.

Questioning Planck-selected star-forming high-redshift galaxy protoclusters and their fate

About 2100 star-forming galaxy protocluster candidates at z ∼ 1 − 4 were identified at sub-millimetre wavelengths in the Planck all-sky survey. Follow-up spectroscopic observations of a few candidates have confirmed the presence of actual galaxy overdensities with large star formation rates (SFRs). In this work, we use state-of-the-art hydrodynamical simulations to investigate whether the Planck high-z sub-millimetre sources (PHz) are progenitors of massive clusters at z = 0. To match the PHz sources with simulated halos, we select the most star-forming (SF) halos in 19 redshift bins from z = 3 to z = 1.3 in the TNG300 simulation of the IllustrisTNG project. At each redshift, the total SFR of the simulated protocluster candidates is computed from the SFR of all the galaxies within an aperture corresponding to the Planck beam size, including those along the line of sight (LOS). The simulations reproduce the Planck-derived SFRs as the sum of both the SFR of at least one of the most SF high-z halos and the average contribution from SF sources along the LOS. Focusing on the spectroscopically confirmed z ∼ 2 PHz protoclusters, we compare the observed properties of their galaxy members with those in the most SF simulated halos. We find a good agreement in the stellar mass and SFR distributions, and in the galaxy number counts, but the SFR-stellar mass relation of the simulated galaxies tends to be shifted to lower SFRs with respect to the observed galaxies. Based on the estimated final masses of the simulated halos, we infer that between 63% and 72% of the Planck-selected protoclusters will evolve into massive galaxy clusters by z = 0. Despite contamination from star-forming galaxies along the LOS, we thus confirm the efficiency of Planck in selecting star-forming protoclusters at cosmic noon with the simulations, and provide a new criterion for selecting the most massive cluster progenitors at high-z, using observables such as the number of galaxy members and their SFR distribution.

Astrophysical information from the Rayleigh-Jeans Tail of the CMB

One of the explanations for the recent EDGES-LOW band 21 cm measurements of a strong absorption signal around 80 MHz is the presence of an excess radio background to the Cosmic Microwave Background (CMB). Such excess can be produced by the decay of unstable particles into small mass dark photons which have a non-zero mixing angle with electromagnetism. We use the EDGES-LOW band measurements to derive joint constraints on the properties of the early galaxies and the parameters of such a particle physics model for the excess radio background. A Bayesian analysis shows that a high star formation efficiency and X-ray emission of 4–7 × 1048 erg per solar mass in stars are required along with a suppression of star formation in halos with virial temperatures ≲ 2 × 104 K. The same analysis also suggests a 68 percent credible intervals for the mass of the decaying dark matter particles, it's lifetime, dark photon mass and the mixing angle of the dark and ordinary photon oscillation of [10-3.5, 10-2.4] eV, [101.1, 102.7] × 13.8 Gyr, [10-12.2, 10-10] eV and [10-7, 10-5.6] respectively. This implies an excess radio background which is ≈ 5.7 times stronger than the CMB around 80 MHz. This value is a factor ∼ 3 higher than the previous predictions which used a simplified model for the 21 cm signal.

A Self-Calibrating Halo-Based Group Finder: Application to SDSS

Abstract We apply a new galaxy group-finder to the Main Galaxy Sample of the SDSS. This algorithm introduces new freedom to assign halos to galaxies that is self-calibrated by comparing the catalog to complementary data. These include galaxy clustering data and measurements of the total satellite luminosity from deep-imaging data. We present constraints on the galaxy-halo connection for star-forming and quiescent populations. The results of the self-calibrated group catalog differ in several key ways from previous group catalogs and halo-occupation analyses. The transition halo mass scale, where half of the halos contain quiescent central galaxies, is at M h ∼ 1012.4 h −1 M ⊙, significantly higher than other constraints. Additionally, the width of the transition from predominantly star-forming halos to quiescent halos occurs over a narrower range in halo mass. Quiescent central galaxies in low-mass halos are significantly more massive than star-forming centrals at the same halo mass, but this difference reverses above the transition halo mass. We find that the scatter in log M * at fixed M h is ∼0.2 dex for massive halos, in agreement with previous estimates, but rises sharply at lower halo masses. The halo masses assigned by the group catalog are in good agreement with weak-lensing estimates for star-forming and quiescent central galaxies. We discuss possible improvements to the algorithm made clear by this first application to data. The group catalog is made publicly available.

Predicting Localized Primordial Star Formation with Deep Convolutional Neural Networks

Abstract We investigate applying 3D deep convolutional neural networks as fast surrogate models of the formation and feedback effects of primordial stars in hydrodynamic cosmological simulations of the first galaxies. Here, we present the surrogate model to predict localized primordial star formation; the feedback model will be presented in a subsequent paper. The star formation prediction model consists of two submodels: the first is a 3D volume classifier that predicts which (10 comoving kpc)3 volumes will host star formation, followed by a 3D Inception-based U-net voxel segmentation model that predicts which voxels will form primordial stars. We find that the combined model predicts primordial star-forming volumes with high skill, with F 1 &gt; 0.995 and true skill score (TSS) &gt;0.994. The star formation is localized within the volume to ≲53 voxels (∼1.6 comoving kpc3) with F 1 &gt; 0.399 and TSS &gt;0.857. Applied to simulations with low spatial resolution, the model predicts star-forming regions in the same locations and at similar redshifts as sites in resolved full-physics simulations that explicitly model primordial star formation and feedback. When applied to simulations with lower mass resolution, we find that the model predicts star-forming regions at later redshift due to delayed structure formation resulting from lower mass resolution. Our model predicts primordial star formation without halo finding, so it will be useful in spatially under-resolved simulations that cannot resolve primordial star-forming halos. To our knowledge, this is the first model that can predict primordial star-forming regions that match highly resolved cosmological simulations.

Cosmic Dawn II (CoDa II): a new radiation-hydrodynamics simulation of the self-consistent coupling of galaxy formation and reionization

ABSTRACT Cosmic Dawn II (CoDa II) is a new, fully coupled radiation-hydrodynamics simulation of cosmic reionization and galaxy formation and their mutual impact, to redshift z &amp;lt; 6. With 40963 particles and cells in a 94 Mpc box, it is large enough to model global reionization and its feedback on galaxy formation while resolving all haloes above 108 M⊙. Using the same hybrid CPU–GPU code RAMSES–CUDATON as CoDa I in Ocvirk et al. (2016), CoDa II modified and re-calibrated the subgrid star formation algorithm, making reionization end earlier, at z ≳ 6, thereby better matching the observations of intergalactic Lyman α opacity from quasar spectra and electron-scattering optical depth from cosmic microwave background fluctuations. CoDa II predicts a UV continuum luminosity function in good agreement with observations of high-z galaxies, especially at z = 6. As in CoDa I, reionization feedback suppresses star formation in haloes below ∼2 × 109 M⊙, though suppression here is less severe, a possible consequence of modifying the star formation algorithm. Suppression is environment dependent, occurring earlier (later) in overdense (underdense) regions, in response to their local reionization times. Using a constrained realization of lambda cold dark matter constructed from galaxy survey data to reproduce the large-scale structure and major objects of the present-day Local Universe, CoDa II serves to model both global and local reionization. In CoDa II, the Milky Way and M31 appear as individual islands of reionization, i.e. they were not reionized by the progenitor of the Virgo cluster, or by nearby groups, or by each other.

Constraining structure formation using EDGES

The experiment to detect the global epoch of reionization signature (EDGES) collaboration reported the detection of a line at 78 MHz in the sky-averaged spectrum due to neutral hydrogen (\\ion{H}{i}) 21-cm hyperfine absorption of cosmic microwave background (\\cmb) photons at redshift z∼ 17. This requires that the spin temperature of \\ion{H}{i} be coupled to the kinetic temperature of the gas at this redshift through the scattering of \\lya photons emitted by massive stars. To explain the experimental result, star formation needs to be sufficiently efficient at z∼ 17 and this can be used to constrain models in which small-scale structure formation is suppressed (\\dmf models), either due to dark matter free-streaming or non-standard inflationary dynamics. We combine simulations of structure formation with a simple recipe for star formation to investigate whether these models emit enough Lyman-α photons to reproduce the experimental signal for reasonable values of the star formation efficiency, f⋆. We find that a thermal warm dark matter (\\wdm) model with mass mWDM∼ 4.3 keV is consistent with the timing of the signal for f⋆ ≲ 2%. The exponential growth of structure around z∼ 17 in such a model naturally generates a sharp onset of the absorption. A warmer model with mWDM∼3 keV requires a higher star formation efficiency, f⋆∼ 6%, which is a factor of few above predictions of current star formation models and observations of satellites in the Milky Way. However, uncertainties in the process of star formation at these redshifts do not allow to derive strong constrains on such models using 21-cm absorption line. The onset of the 21-cm absorption is generally slower in \\dmf than observed in cold dark matter (\\cdm) models, unless some process significantly suppresses star formation in halos with masses below ~108h-1M⊙.

Extreme Primordial Star Formation Enabled by High-redshift Quasars

Abstract High-redshift quasars emit copious X-ray photons that heat the intergalactic medium to temperatures up to ∼106 K. At such high temperatures the primordial gas will not form stars until it is assembled into dark matter halos with masses of up to ∼1011 M ⊙, at which point the hot gas collapses and cools under the influence of gravity. Once this occurs, there is a massive reservoir of primordial gas from which stars can form, potentially setting the stage for the brightest Population (Pop) III starbursts in the early universe. Supporting this scenario, recent observations of quasars at z ∼ 6 have revealed a lack of accompanying Lyα emitting galaxies, consistent with suppression of primordial star formation in halos with masses below ∼1010 M ⊙. Here we model the chemical and thermal evolution of the primordial gas as it collapses into such a massive halo irradiated by a nearby quasar in the run-up to a massive Pop III starburst. We find that, within ∼100 kpc of the highest-redshift quasars discovered to date, the Lyman–Werner flux produced in the quasar host galaxy may be high enough to stimulate the formation of a direct collapse black hole (DCBH). A survey with single pointings of the NIRCam instrument at individually known high-z quasars may be a promising strategy for finding Pop III stars and DCBHs with the James Webb Space Telescope.

Results from EDGES High-Band. III. New Constraints on Parameters of the Early Universe

Abstract We present new constraints on parameters of cosmic dawn and the epoch of reionization derived from the EDGES High-Band spectrum (90–190 MHz). The parameters are probed by evaluating global 21 cm signals generated with the recently developed Global21cm tool. This tool uses neural networks trained and tested on ∼30,000 spectra produced with semi-numerical simulations that assume the standard thermal evolution of the cosmic microwave background and the intergalactic medium. From our analysis, we constrain at 68% (1) the minimum virial circular velocity of star-forming halos to V c &lt; 19.3 km s−1, (2) the X-ray heating efficiency of early sources to f X &gt; 0.0042, and (3) the low-energy cutoff of the X-ray spectral energy distribution to ν min &lt; 2.3 keV. We also constrain the star formation efficiency (f *), the electron scattering optical depth (τ e), and the mean-free path of ionizing photons (R mfp). We recompute the constraints after incorporating into the analysis four estimates for the neutral hydrogen fraction from high-z quasars and galaxies, and a prior on τ e from Planck 2018. The largest impact of the external observations is on the parameters that most directly characterize reionization. Specifically, we derive the combined 68% constraints τ e &lt; 0.063 and R mfp &gt; 27.5 Mpc. The external observations also have a significant effect on V c due to its degeneracy with τ e, while the constraints on f *, f X, and ν min, remain primarily determined by EDGES.

Signature of excess radio background in the 21-cm global signal and power spectrum

The recent tentative detection by the EDGES Low-Band antenna of the hydrogen 21-cm line from cosmic dawn, if confirmed, is the first ever signature observed from the epoch of primordial star formation. However, the magnitude and the shape of this signal are incompatible with standard astrophysical predictions, requiring either colder than expected gas, or an excess radio background above the Cosmic Microwave Background (CMB) radiation. In this paper we explore the latter option, investigating possible 21-cm signals in models with a phenomenological excess radio background together with the standard astrophysical modeling. Assuming uniform radiation with a synchrotron-like spectrum existing throughout cosmic history, we show that such a radio background, in addition to explaining the EDGES Low-Band signal, enhances the power spectrum. The signal during cosmic dawn and reionization strongly depends on both the intensity of the radio background and the astrophysical parameters. We verify the broad agreement of our models with the detected feature, including additional constraints from the EDGES High-Band data, high-redshift quasars, and observational limits on the extragalactic radio background. The data imply a lower limit on the star formation efficiency of 2.8\%, an upper limit on the minimum mass of star-forming halos of M$_{\rm h}\sim 10^9$ M$_\odot$ at $z = 17$, and a lower limit on the excess radio background of 1.9 times the CMB at the 78 MHz cosmic dawn frequency (corresponding to 0.1\% of the CMB at 1.42 GHz). The properties of X-ray sources remain unconstrained. We also show that during the dark ages, such a radio background saturates the 21-cm signal, imprinting a unique signature in both the global signal and the power spectrum.

On the Faint End of the Galaxy Luminosity Function in the Epoch of Reionization: Updated Constraints from the HST Frontier Fields

Abstract Ultra-faint galaxies are hosted by small dark matter halos with shallow gravitational potential wells, hence their star formation activity is more sensitive to feedback effects. The shape of the faint end of the high-z galaxy luminosity function (LF) contains important information on star formation and its interaction with the reionization process during the Epoch of Reionization. High-z galaxies with have only recently become accessible thanks to the Frontier Fields (FFs) survey combining deep HST imaging and the gravitational lensing effect. In this paper we investigate the faint end of the LF at redshift &gt;5 using the data of FFs clusters Abell 2744 (A2744), MACSJ0416.1-2403 (M0416), MACSJ0717.5+3745 (M0717), and MACSJ1149.5+2223 (M1149). We analyze both an empirical and a physically motivated LF model to obtain constraints on a possible turnover of LF at faint magnitudes. In the empirical model the LF drops fast when the absolute UV magnitude is much larger than a turnover absolute UV magnitude . We obtain (15.2) at the 1 (2)σ confidence level (C.L.) for z ∼ 6. In the physically motivated analytical model, star formation in halos with circular velocity below is fully quenched if these halos are located in ionized regions. Using updated lensing models and new additional FFs data, we re-analyze previous constraints on and f esc presented by Castellano et al. using a smaller data set. We obtain new constraints on km s−1 and f esc ≲ 56% (both at 2σ C.L.) and conclude that there is no turnover detected so far from the analyzed FFs data. Forthcoming JWST observations will be key to tightening these constraints further.

Characterizing circumgalactic gas around massive ellipticals at z ∼ 0.4 – I. Initial results★

We present a new Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) absorption-line survey to study halo gas around 16 luminous red galaxies (LRGs) at z=0.21-0.55. The LRGs are selected uniformly with stellar mass Mstar>1e11 Msun and no prior knowledge of the presence/absence of any absorption features. Based on observations of the full Lyman series, we obtain accurate measurements of neutral hydrogen column density N(HI) and find that high-N(HI) gas is common in these massive quiescent halos with a median of <log N(HI)> = 16.6 at projected distances d<~160 kpc. We measure a mean covering fraction of optically-thick gas with log N(HI)>~17.2 of <kappa>LLS=0.44^{+0.12}_{-0.11} at d<~160 kpc and <kappa>LLS=0.71^{+0.11}_{-0.20} at d<~100 kpc. The line-of-sight velocity separations between the HI absorbing gas and LRGs are characterized by a mean and dispersion of <v_{gas-gal}>=29 km/s and \sigma_v_{gas-gal}=171 km/s. Combining COS FUV and ground-based echelle spectra provides an expanded spectral coverage for multiple ionic transitions, from low-ionization MgII and SiII, to intermediate ionization SiIII and CIII, and to high-ionization OVI absorption lines. We find that intermediate ions probed by CIII and SiIII are the most prominent UV metal lines in LRG halos with a mean covering fraction of <kappa(CIII)>_{0.1}=0.75^{+0.08}_{-0.13} for W(977)>=0.1 Ang at d<160 kpc, comparable to what is seen for CIII in L* and sub-L* star-forming and red galaxies but exceeding MgII or OVI in quiescent halos. The COS-LRG survey shows that massive quiescent halos contain widespread chemically-enriched cool gas and that little distinction between LRG and star-forming halos is found in their HI and CIII content.

Sprai: coupling of radiative feedback and primordial chemistry in moving mesh hydrodynamics

In this paper we introduce a new radiative transfer code SPRAI (Simplex Photon Radiation in the Arepo Implementation) based on the SimpleX radiation transfer method. This method, originally used only for post-processing, is now directly integrated into the Arepo code and takes advantage of its adaptive unstructured mesh. Radiated photons are transferred from the sources through the series of Voronoi gas cells within a specific solid angle. From the photon attenuation we derive corresponding photon fluxes and ionization rates and feed them to a primordial chemistry module. This gives us a self-consistent method for studying dynamical and chemical processes caused by ionizing sources in primordial gas. Since the computational cost of the SimpleX method does not scale directly with the number of sources, it is convenient for studying systems such as primordial star-forming halos that may form multiple ionizing sources.

No Ly α emitters detected around a QSO at z = 6.4: Suppressed by the QSO?

Abstract Understanding how quasars’ (QSOs’) ultraviolet (UV) radiation affects galaxy formation is vital to our understanding of the reionization era. Using a custom-made narrow-band filter, NB906, on Subaru/Suprime-Cam, we investigated the number density of Ly α emitters (LAEs) around a QSO at z = 6.4. To date, this is the highest redshift narrow-band observation, where LAEs around a luminous QSO are investigated. Due to the large field of view of Suprime-Cam, our survey area is ∼5400 cMpc2, much larger than previous studies at z = 5.7 (∼200 cMpc2). In this field, we previously found a factor of 7 overdensity of Lyman break galaxies. Based on this, we expected to detect ∼100 LAEs down to NB906 = 25 ABmag. However, our 6.4 h exposure found none. The obtained upper limit on the number density of LAEs is more than an order lower than the blank fields. Furthermore, this lower density of LAEs spans a large scale of 10 pMpc across. A simple argument suggests that a strong UV radiation from the QSO can suppress star formation in haloes with Mvir &amp;lt; 1010 M⊙ within a pMpc from the QSO, but the deficit at the edge of the field (5 pMpc) remains to be explained.

Small-scale Intensity Mapping: Extended Lyα, Hα, and Continuum Emission as a Probe of Halo Star Formation in High-redshift Galaxies

Abstract Lyα halos are observed ubiquitously around star-forming galaxies at high redshift, but their origin is still a matter of debate. We demonstrate that the emission from faint unresolved satellite sources, , clustered around the central galaxies may play a major role in generating spatially extended Lyα, continuum (UV + VIS), and Hα halos. We apply the analytic formalism developed in Mas-Ribas &amp; Dijkstra to model the halos around Lyman Alpha Emitters (LAEs) at z = 3.1, for several different satellite clustering prescriptions. In general, our UV and Lyα surface brightness profiles match the observations well at physical kpc from the centers of LAEs. We discuss how our profiles depend on various model assumptions and how these can be tested and constrained with future Hα observations by the James Webb Space Telescope (JWST). Our analysis shows how spatially extended halos constrain (i) the presence of otherwise undetectable satellite sources, (ii) the integrated, volumetric production rates of Lyα and LyC photons, and (iii) their population-averaged escape fractions. These quantities are all directly relevant for understanding galaxy formation and evolution and, for high enough redshifts, cosmic reionization.