We quantify the distribution of [OIII]+Hβ line strengths at z≃7 using a sample of 20 bright ($\mathrm{M}_{\mathrm{UV}}^{ }$ ≲ -21) galaxies. We select these systems over wide-area fields (2.3 deg2 total) using a new colour-selection which precisely selects galaxies at z≃6.63–6.83, a redshift range where blue Spitzer/IRAC [3.6]−[4.5] colours unambiguously indicate strong [OIII]+Hβ emission. These 20 galaxies suggest a log-normal [OIII]+Hβ EW distribution with median EW = 759$^{{+112}{4.5pt}}_{{-113}{4.5pt}}$ Å and standard deviation = 0.26$^{{+0.06}{4.5pt}}_{{-0.05}{4.5pt}}$ dex. We find no evidence for strong variation in this EW distribution with UV luminosity. The typical [OIII]+Hβ EW at z≃7 implied by our sample is considerably larger than that in massive star forming galaxies at z≃2, consistent with a shift toward larger average sSFR (4.4 Gyr−1) and lower metallicities (0.16 Z⊙). We also find evidence for the emergence of a population with yet more extreme nebular emission ([OIII]+Hβ EW>1200 Å) that is rarely seen at lower redshifts. These objects have extremely large sSFR (>30 Gyr−1), as would be expected for systems undergoing a burst or upturn in star formation. While this may be a short-lived phase, our results suggest that 20% of the z≃7 population has such extreme nebular emission, implying that galaxies likely undergo intense star formation episodes regularly at z>6. We argue that this population may be among the most effective ionizing agents in the reionization era, both in terms of photon production efficiency and escape fraction. We furthermore suggest that galaxies passing through this large sSFR phase are likely to be very efficient in forming bound star clusters.

We present an original phenomenological model to describe the evolution of galaxy number counts, morphologies, and spectral energy distributions across a wide range of redshifts (0.2 < z < 15) and stellar masses [log(M/M ) ≥ 6]. Our model follows observed mass and luminosity functions of both star-forming and quiescent galaxies, and reproduces the redshift evolution of colors, sizes, star-formation and chemical properties of the observed galaxy population. Unlike other existing approaches, our model includes a self-consistent treatment of stellar and photoionized gas emission and dust attenuation based on the BEAGLE tool. The mock galaxy catalogs generated with our new model can be used to simulate and optimize extragalactic surveys with future facilities such as the James Webb Space Telescope (JWST), and to enable critical assessments of analysis procedures, interpretation tools, and measurement systematics for both photometric and spectroscopic data. As a first application of this work, we make predictions for the upcoming JWST Advanced Deep Extragalactic Survey (JADES), a joint program of the JWST/NIRCam and NIRSpec Guaranteed Time Observations teams. We show that JADES will detect, with NIRCam imaging, thousands of galaxies at z 6, and tens at z 10 at m AB 30 (5σ) within the 236 arcmin 2 of the survey. The JADES data will enable accurate constraints on the evolution of the UV luminosity function at z > 8, and resolve the current debate about the rate of evolution of galaxies at z 8. Ready to use mock catalogs and software to generate new realizations are publicly available as the JAdes extraGalactic Ultradeep Artificial Realizations (JAGUAR) package.

Reionization-era galaxies tend to exhibit weak Lyα emission, likely reflecting attenuation from an increasingly neutral IGM. Recent observations have begun to reveal exceptions to this picture, with strong Lyα emission now known in four of the most massive z=7–9 galaxies in the CANDELS fields, all of which also exhibit intense [OIII]+Hβ emission (EW&gt;800 Å). To better understand why Lyα is anomalously strong in a subset of massive z ≃ 7 − 9 galaxies, we have initiated an MMT/Binospec survey targeting a larger sample (N=22) of similarly luminous (≃1–6 L$^{\ast }_{\mathrm{UV}}$) z≃7 galaxies selected over very wide-area fields (∼3 deg2). We confidently (&gt;7σ) detect Lyα in 78 per cent (7/9) of galaxies with strong [OIII]+Hβ emission (EW&gt;800 Å) as opposed to only 8 per cent (1/12) of galaxies with more moderate (EW=200-800 Å) [OIII]+Hβ. We argue that the higher Lyα EWs of the strong [OIII]+Hβ population likely reflect enhanced ionizing photon production efficiency owing to their large sSFRs (≳30 Gyr−1). We also find evidence that Lyα transmission from massive galaxies declines less rapidly over 6 &lt; z &lt; 7 than in low-mass lensed systems. In particular, our data suggest no strong evolution in Lyα transmission, consistent with a picture wherein massive z≃7 galaxies often reside in large ionized regions. We detect three closely-separated (R = 1.7 physical Mpc) z≃7 Lyα emitters in our sample, conceivably tracing a large ionized structure that is consistent with this picture. We detect tentative evidence for an overdensity in this region, implying a large ionizing photon budget in the surrounding volume.

The James Webb Space Telescope (JWST) is expected to observe galaxies at z &gt; 10 that are presently inaccessible. Here, we use a self-consistent empirical model, the UniverseMachine, to generate mock galaxy catalogues and lightcones over the redshift range z = 0 − 15. These data include realistic galaxy properties (stellar masses, star formation rates, and UV luminosities), galaxy–halo relationships, and galaxy–galaxy clustering. Mock observables are also provided for different model parameters spanning observational uncertainties at z &lt; 10. We predict that Cycle 1 JWST surveys will very likely detect galaxies with M* &gt; 107 M⊙ and/or M1500 &lt; −17 out to at least z ∼ 13.5. Number density uncertainties at z &gt; 12 expand dramatically, so efforts to detect z &gt; 12 galaxies will provide the most valuable constraints on galaxy formation models. The faint-end slopes of the stellar mass/luminosity functions at a given mass/luminosity threshold steepen as redshift increases. This is because observable galaxies are hosted by haloes in the exponentially falling regime of the halo mass function at high redshifts. Hence, these faint-end slopes are robustly predicted to become shallower below current observable limits (M* &lt; 107 M⊙ or M1500 &gt; −17). For reionization models, extrapolating luminosity functions with a constant faint-end slope from M1500 = −17 down to M1500 = −12 gives the most reasonable upper limit for the total UV luminosity and cosmic star formation rate up to z ∼ 12. We compare to three other empirical models and one semi-analytic model, showing that the range of predicted observables from our approach encompasses predictions from other techniques. Public catalogues and lightcones for common fields are available online.

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We include a fully coupled treatment of metal and dust enrichment into the Delphi semi-analytic model of galaxy formation to explain the dust content of 13 Lyman Break Galaxies (LBGs) detected by the Atacama Large millimetre Array (ALMA) REBELS Large Program at z ≃ 7. We find that the galaxy dust mass, Md, is regulated by the combination of SNII dust production, astration, shock destruction, and ejection in outflows; grain growth (with a standard timescale τ0 = 30 Myr) plays a negligible role. The model predicts a dust-to-stellar mass ratio of $\sim 0.07-0.1{{\ \rm per\ cent}}$ and a UV-to-total star formation rate relation such that log(ψUV) = −0.05 [log(ψ)]2 + 0.86 log(ψ) − 0.05 (implying that 55-80 per cent of the star formation is obscured) for REBELS galaxies with stellar mass $M_* = 10^{9-10} \rm M_\odot$. This relation reconciles the intrinsic UV luminosity of LBGs with their observed luminosity function at z = 7. However, 2 out of the 13 systems show dust-to-stellar mass ratios ($\sim 0.94-1.1{{\ \rm per\ cent}}$) that are up to 18 × larger than expected from the fiducial relation. Due to the physical coupling between dust and metal enrichment, even decreasing τ0 to very low values (0.3 Myr) only increases the dust-to-stellar mass ratio by a factor ∼2. Given that grain growth is not a viable explanation for such high observed ratios of the dust-to-stellar mass, we propose alternative solutions.

ALMA observations have revealed the presence of dust in the first generations of galaxies in the Universe. However, the dust temperature Td remains mostly unconstrained due to the few available FIR continuum data at redshift z &gt; 5. This introduces large uncertainties in several properties of high-z galaxies, namely their dust masses, infrared luminosities, and obscured fraction of star formation. Using a new method based on simultaneous [C $\scriptstyle \rm II$] 158μm line and underlying dust continuum measurements, we derive Td in the continuum and [C $\scriptstyle \rm II$] detected z ≈ 7 galaxies in the ALMA Large Project REBELS sample. We find 39 K &lt; Td &lt; 58 K, and dust masses in the narrow range Md = (0.9 − 3.6) × 107M⊙. These results allow us to extend for the first time the reported Td(z) relation into the Epoch of Reionization. We produce a new physical model that explains the increasing Td(z) trend with the decrease of gas depletion time, tdep = Mg/SFR, induced by the higher cosmological accretion rate at early times; this hypothesis yields Td∝(1 + z)0.4. The model also explains the observed Td scatter at a fixed redshift. We find that dust is warmer in obscured sources, as a larger obscuration results in more efficient dust heating. For UV-transparent (obscured) galaxies, Td only depends on the gas column density (metallicity), $T_{\rm d} \propto N_{\rm H}^{1/6}$ (Td∝Z−1/6). REBELS galaxies are on average relatively transparent, with effective gas column densities around NH ≃ (0.03 − 1) × 1021cm−2. We predict that other high-z galaxies (e.g. MACS0416-Y1, A2744-YD4), with estimated Td ≫ 60 K, are significantly obscured, low-metallicity systems. In fact Td is higher in metal-poor systems due to their smaller dust content, which for fixed LIR results in warmer temperatures.

We present the results of a new sensitive survey of neutral hydrogen above and below the Galactic Center with the Green Bank Telescope. The observations extend up to Galactic latitude with an effective angular resolution of 9.′5 and an average rms brightness temperature noise of 40 mK in a 1 channel. The survey reveals the existence of a population of anomalous high-velocity clouds extending up to heights of about 1.5 kpc from the Galactic plane and showing no signature of Galactic rotation. These clouds have local standard of rest velocities , and assuming a Galactic Center origin, they have sizes of a few tens of parsec and neutral hydrogen masses spanning . Accounting for selection effects, the cloud population is symmetric in longitude, latitude, and V LSR. We model the cloud kinematics in terms of an outflow expanding from the Galactic Center and find the population consistent with being material moving with radial velocity distributed throughout a bicone with opening angle . This simple model implies an outflow luminosity erg s−1 over the past 10 Myr, consistent with star formation feedback in the inner region of the Milky Way, with a cold gas mass-loss rate . These clouds may represent the cold gas component accelerated in the nuclear wind driven by our Galaxy, although some of the derived properties challenge current theoretical models of the entrainment process.