After two ALMA observing cycles, only a handful of [C II] 158 µm emission line searches in z > 6 galaxies have reported a positive detection, questioning the applicability of the local [C II]-SFR relation to high-z systems. To investigate this issue we use the Vallini et al. (2013, V13) model, based on high-resolution, radiative transfer cosmological simulations to predict the [C II] emission from the interstellar medium of a z ≈ 7 (halo mass M h = 1.17 × 10 11 M ) galaxy. We improve the V13 model by including (a) a physically-motivated metallicity (Z) distribution of the gas, (b) the contribution of Photo-Dissociation Regions (PDRs), (c) the effects of Cosmic Microwave Background on the [C II] line luminosity. We study the relative contribution of diffuse neutral gas to the total [C II] emission (F diff /F tot ) for different SFR and Z values. We find that the [C II] emission arises predominantly from PDRs: regardless of the galaxy properties, F diff /F tot ≤ 10% since, at these early epochs, the CMB temperature approaches the spin temperature of the [C II] transition in the cold neutral medium (T CMB ∼ T CNM s ∼ 20 K). Our model predicts a high-z [C II]-SFR relation consistent with observations of local dwarf galaxies (0.02 < Z/Z < 0.5). The [C II] deficit suggested by actual data (L CII < 2.0 × 10 7 L in BDF3299 at z ≈ 7.1) if confirmed by deeper ALMA observations, can be ascribed to negative stellar feedback disrupting molecular clouds around star formation sites. The deviation from the local [C II]-SFR would then imply a modified Kennicutt-Schmidt relation in z > 6 galaxies. Alternatively/in addition, the deficit might be explained by low gas metallicities (Z < 0.1 Z ).

We present our new Atacama Large Millimeter/Submillimeter Array (ALMA) observations targeting [O iii]88 μm, [C ii]158 μm, [N ii]122 μm, and dust-continuum emission for three Lyman break galaxies at z = 6.0293–6.2037, identified in the Subaru/Hyper Suprime-Cam survey. We clearly detect [O iii] and [C ii] lines from all of the galaxies at 4.3–11.8σ levels, and identify multi-band dust-continuum emission in two of the three galaxies, allowing us to estimate infrared luminosities and dust temperatures simultaneously. In conjunction with previous ALMA observations for six galaxies at z > 6, we confirm that all the nine z = 6–9 galaxies have high [O iii]/[C ii] ratios of , ∼10 times higher than z ∼ 0 galaxies. We also find a positive correlation between the [O iii]/[C ii] ratio and the Lyα equivalent width (EW) at the ∼90% significance level. We carefully investigate physical origins of the high [O iii]/[C ii] ratios at z = 6–9 using Cloudy, and find that high density of the interstellar medium, low C/O abundance ratio, and the cosmic microwave background attenuation are responsible to only a part of the z = 6–9 galaxies. Instead, the observed high [O iii]/[C ii] ratios are explained by 10–100 times higher ionization parameters or low photodissociation region (PDR) covering fractions of 0%–10%, both of which are consistent with our [N ii] observations. The latter scenario can be reproduced with a density-bounded nebula with PDR deficit, which would enhance the Lyα, Lyman continuum, and ionizing photons escape from galaxies, consistent with the [O iii]/[C ii]-Lyα EW correlation we find.

We investigate the morphology of the [Cii] emission in a sample of "normal" star-forming galaxies at 5 < z < 7.2 in relation to their UV (rest-frame) counterpart. We use new ALMA observations of galaxies at z ∼ 6−7, as well as a careful re-analysis of archival ALMA data. In total 29 galaxies were analysed, 21 of which are detected in [Cii]. For several of the latter the [Cii] emission breaks into multiple components. Only a fraction of these [Cii] components, if any, is associated with the primary UV systems, while the bulk of the [Cii] emission is associated either with fainter UV components, or not associated with any UV counterpart at the current limits. By taking into account the presence of all these components, we find that the L [CII] -SFR relation at early epochs is fully consistent with the local relation, but it has a dispersion of 0.48±0.07 dex, which is about two times larger than observed locally. We also find that the deviation from the local L [CII] -SFR relation has a weak anti-correlation with the EW(Lyα). The morphological analysis also reveals that [Cii] emission is generally much more extended than the UV emission. As a consequence, these primordial galaxies are characterised by a [Cii] surface brightness generally much lower than expected from the local Σ [CII] − Σ SFR relation. These properties are likely a consequence of a combination of different effects, namely: gas metallicity, [Cii] emission from obscured star-forming regions, strong variations of the ionisation parameter, and circumgalactic gas in accretion or ejected by these primeval galaxies.

We present new ALMA observations of the [Oiii]88µm line and high angular resolution observations of the [Cii]158µm line in a normal star forming galaxy at z=7.1. Previous [Cii] observations of this galaxy had detected [Cii] emission consistent with the Lyα redshift but spatially slightly offset relative to the optical (UV-rest frame) emission. The new [Cii] observations reveal that the [Cii] emission is partly clumpy and partly diffuse on scales larger than about 1kpc.[Oiii] emission is also detected at high significance, offset relative to the optical counterpart in the same direction as the [Cii] clumps, but mostly not overlapping with the bulk of the [Cii] emission. The offset between different emission components (optical/UV and different far-IR tracers) is similar to that which is observed in much more powerful starbursts at high redshift. We show that the [Oiii] emitting clump cannot be explained in terms of diffuse gas excited by the UV radiation emitted by the optical galaxy, but it requires excitation by in-situ (slightly dust obscured) star formation, at a rate of about 7 M yr −1 . Within 20 kpc from the optical galaxy the ALMA data reveal two additional [Oiii] emitting systems, which must be star forming companions. We discuss that the complex properties revealed by ALMA in the z∼7.1 galaxy are consistent with expectations by recent models and cosmological simulations, in which differential dust extinction, differential excitation and different metal enrichment levels, associated with different subsystems assembling a galaxy, are responsible for the various appearance of the system when observed with distinct tracers.

We study the formation and evolution of a sample of Lyman Break Galaxies in the Epoch of Reionisation by using high-resolution (∼ 10 pc), cosmological zoom-in simulations part of the serra suite. In serra, we follow the interstellar medium (ISM) thermo-chemical non-equilibrium evolution, and perform on-the-fly radiative transfer of the interstellar radiation field (ISRF). The simulation outputs are post-processed to compute the emission of far infrared lines ([C II], [N II], and [O III]). At z = 8, the most massive galaxy, "Freesia", has an age t 409 Myr, stellar mass M 4.2 × 10 9 M , and a star formation rate SFR 11.5 M yr −1 , due to a recent burst. Freesia has two stellar components (A and B) separated by 2.5 kpc; other 11 galaxies are found within 56.9 ± 21.6 kpc. The mean ISRF in the Habing band is G = 7.9 G 0 and is spatially uniform; in contrast, the ionisation parameter is U = 2 +20 −2 × 10 −3 , and has a patchy distribution peaked at the location of star-forming sites. The resulting ionising escape fraction from Freesia is f esc 2%. While [C II] emission is extended (radius 1.54 kpc), [O III] is concentrated in Freesia-A (0.85 kpc), where the ratio Σ [OIII] /Σ [CII] 10. As many high-z galaxies, Freesia lies below the local [C II]-SFR relation. We show that this is the general consequence of a starburst phase (pushing the galaxy above the Kennicutt-Schmidt relation) which disrupts/photodissociates the emitting molecular clouds around star-forming sites. Metallicity has a sub-dominant impact on the amplitude of [C II]-SFR deviations.

The recent discovery of dusty galaxies well into the Epoch of Reionization (redshift z > 6) poses challenging questions about the properties of the interstellar medium in these pristine systems. By combining state-of-the-art hydrodynamic and dust radiative transfer simulations, we address these questions focusing on the recently discovered dusty galaxy A2744 YD4 (z = 8.38, Laporte et al. 2017). We show that we can reproduce the observed spectral energy distribution (SED) only using different physical values with respect to the inferred ones by Laporte et al. (2017), i.e. a star formation rate of SFR = 78 M yr −1 , a factor ≈ 4 higher than deduced from simple Spectral Energy Distribution fitting. In this case we find: (a) dust attenuation (corresponding to τ V = 1.4) is consistent with a Milky Way extinction curve; (b) the dust-to-metal ratio is low, f d ∼ 0.08, implying that early dust formation is rather inefficient; (c) the luminosity-weighted dust temperature is high, T d = 91 ± 23 K, as a result of the intense (≈ 100× MW) interstellar radiation field; (d) due to the high T d , the ALMA Band 7 detection can be explained by a limited dust mass, M d = 1.6 × 10 6 M . Finally, the high dust temperatures might solve the puzzling low infrared excess recently deduced for high-z galaxies from the IRX-β relation.

ALMA observations have revealed that [C$\scriptstyle \rm II$]158μm line emission in high-z galaxies is ≈2 − 3 × more extended than the UV continuum emission. Here we explore whether surface brightness dimming (SBD) of the [C$\scriptstyle \rm II$] line is responsible for the reported [C$\scriptstyle \rm II$] deficit, and the large L[OIII]/L[CII] luminosity ratio measured in early galaxies. We first analyse archival ALMA images of nine z &gt; 6 galaxies observed in both [C$\scriptstyle \rm II$] and [O$\scriptstyle \rm III$]. After performing several uv-tapering experiments to optimize the identification of extended line emission, we detect [C$\scriptstyle \rm II$] emission in the whole sample, with an extent systematically larger than the [O$\scriptstyle \rm III$] emission. Next, we use interferometric simulations to study the effect of SBD on the line luminosity estimate. About 40% of the extended [C$\scriptstyle \rm II$] component might be missed at an angular resolution of 0.8″, implying that L[CII] is underestimated by a factor ≈2 in data at low (&lt;7) signal-to-noise ratio. By combining these results, we conclude that L[CII] of z &gt; 6 galaxies lies, on average, slightly below the local L[CII] − SFR relation (Δz = 6 − 9 = −0.07 ± 0.3), but within the intrinsic dispersion of the relation. SBD correction also yields L[OIII]/L[CII] &lt; 10, i.e. more in line with current hydrodynamical simulations.

We report the discovery of 10-kpc [Cii] 158µm halos surrounding star-forming galaxies in the early Universe. We choose deep ALMA data of 18 galaxies each with a star-formation rate of ≃ 10 − 70 M ⊙ with no signature of AGN whose [Cii] lines are individually detected at z = 5.153−7.142, and conduct stacking of the [Cii] lines and dust-continuum in the uv-visibility plane. The radial profiles of the surface brightnesses show a 10-kpc scale [Cii] halo at the 9.2σ level, significantly more extended than the HST stellar continuum data by a factor of ∼ 5 on the exponential-profile basis, as well as the dust continuum. We compare the radial profiles of [Cii] and Lyα halos universally found in star-forming galaxies at this epoch, and find that the scale lengths agree within 1σ level. While two independent hydrodynamical zoom-in simulations match the dust and stellar continuum properties, the simulations cannot reproduce the extended [C ii] line emission. The existence of the extended [Cii] halo is the evidence of outflow remnants in the early galaxies and suggest that the outflows may be dominated by cold-mode outflows expelling the neutral gas.