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We report 18 dust continuum detections (≥3.3σ) at ∼88 and 158 |$\mu{\rm m}$| out of 49 ultraviolet (UV)-bright galaxies (M_UV < −21.3 mag) at |$z$| > 6.5, observed by the Cycle-7 Atacama Large Millimeter/submillimeter Array (ALMA) Large Program, Reionization-Era Bright Emission Line Survey (REBELS) and its pilot programs. This has more than tripled the number of dust continuum detections known at |$z$| > 6.5. Out of these 18 detections, 12 are reported for the first time as part of REBELS. In addition, 15 of the dust continuum detected galaxies also show a [C ii]|$_{\rm 158\,{\rm \mu m}}$| emission line, providing us with accurate redshifts. We anticipate more line emission detections from six targets (including three continuum detected targets) where observations are still ongoing. We estimate that all of the sources have an infrared (IR) luminosity (L_IR) in a range of |$3\!-\!8 \times 10^{11}\, {\rm L_\odot }$|⁠, except for one with |$L_{\rm IR} = 1.5^{+0.8}_{-0.5} \times 10^{12}\, \, {\rm L_{\odot }}$|⁠. Their fraction of obscured star formation is significant at |${\gtrsim} 50{{\ \rm per\ cent}}$|⁠, despite being UV-selected galaxies. Some of the dust continuum detected galaxies show spatial offsets (∼0.5–1.5 arcsec) between the rest-UV and far-IR emission peaks. These separations could imply spatially decoupled phases of obscured and unobscured star formation, but a higher spatial resolution observation is required to confirm this. REBELS offers the best available statistical constraints on obscured star formation in UV-luminous galaxies at |$z$| > 6.5.

Theoretical models predict that core-collapse supernovae (CCSNe) can be efficient dust producers (0.1–1.0 M_⊙), potentially accounting for most of the dust production in the early Universe. Observational evidence for this dust production efficiency is however currently limited to only a few CCSN remnants (e.g. SN 1987A, Crab nebula). In this paper, we revisit the dust mass produced in Cassiopeia A (Cas A), a ∼330-yr old O-rich Galactic supernova remnant (SNR) embedded in a dense interstellar foreground and background. We present the first spatially resolved analysis of Cas A based on Spitzer and Herschel infrared and submillimetre data at a common resolution of ∼0.6 arcmin for this 5 arcmin diameter remnant following a careful removal of contaminating line emission and synchrotron radiation. We fit the dust continuum from 17 to 500 μm with a four-component interstellar medium and supernova (SN) dust model. We find a concentration of cold dust in the unshocked ejecta of Cas A and derive a mass of 0.3–0.5 M_⊙ of silicate grains freshly produced in the SNR, with a lower limit of ≥0.1–0.2 M_⊙. For a mixture of 50 per cent of silicate-type grains and 50 per cent of carbonaceous grains, we derive a total SN dust mass between 0.4 and 0.6 M_⊙. These dust mass estimates are higher than from most previous studies of Cas A and support the scenario of SN-dominated dust production at high redshifts. We furthermore derive an interstellar extinction map for the field around Cas A which towards Cas A gives average values of A_V = 6–8 mag, up to a maximum of A_V = 15 mag.

We analyse FIR dust continuum measurements for 14 galaxies (redshift z ≈ 7) in the ALMA Reionization Era Bright Emission Line Survey (REBELS) Large Program to derive their physical properties. Our model uses three input data, i.e. (a) the UV spectral slope, β, (b) the observed UV continuum flux at 1500 Å, F₁₅₀₀, (c) the observed continuum flux at |$\approx 158\, \mu$|m, F₁₅₈, and considers Milky Way (MW) and SMC extinction curves, along with different dust geometries. We find that REBELS galaxies have 28−90.5 per cent of their star formation obscured; the total (UV+IR) star formation rates are in the range |$31.5 \lt {\rm SFR}/({\rm M}_\odot \, {\rm yr}^{-1}) \lt 129.5$|⁠. The sample-averaged dust mass and temperature are |$(1.3\pm 1.1)\times 10^7 \, \mathrm{M}_\odot$| and 52 ± 11 K, respectively. However, in some galaxies dust is particularly abundant (REBELS-14, |$M^{\prime }_{\rm d} \approx 3.4 \times 10^7 \, \mathrm{M}_\odot$|⁠), or hot (REBELS-18, |$T^{\prime }_{\rm d} \approx 67$| K). The dust distribution is compact (<0.3 kpc for 70 per cent of the galaxies). The inferred dust yield per supernova is |$0.1 \le y_{\rm d}/\, \mathrm{M}_\odot \le 3.3$|⁠, with 70 per cent of the galaxies requiring |$y_{\rm d} \lt 0.25 \, \mathrm{M}_\odot$|⁠. Three galaxies (REBELS-12, 14, 39) require |$y_{\rm d} \gt 1 \, \mathrm{M}_\odot$|⁠, which is likely inconsistent with pure SN production, and might require dust growth via accretion of heavy elements from the interstellar medium. With the SFR predicted by the model and a MW extinction curve, REBELS galaxies detected in [C ii] nicely follow the local L_CII−SFR relation, and are approximately located on the Kennicutt–Schmidt relation. The sample-averaged gas depletion time is |$0.11\, y_{\rm P}^{-2}$| Gyr, where y_P is the ratio of the gas-to-stellar distribution radius. For some systems, a solution simultaneously matching the observed (β, F₁₅₀₀, F₁₅₈) values cannot be found. This occurs when the index I_m = (F₁₅₈/F₁₅₀₀)/(β − β_int), where β_int is the intrinsic UV slope, exceeds |$I_m^{*}\approx 1120$| for an MW curve. For these objects, we argue that the FIR and UV emitting regions are not co-spatial, questioning the use of the IRX–β relation.

We present specific star formation rates (sSFRs) for 40 ultraviolet (UV)-bright galaxies at z ∼ 7–8 observed as part of the Reionization Era Bright Emission Line Survey (REBELS) Atacama Large Millimeter/submillimeter Array (ALMA) large programme. The sSFRs are derived using improved star formation rate (SFR) calibrations and spectral energy distribution (SED)-based stellar masses, made possible by measurements of far-infrared (FIR) continuum emission and [C ii]-based spectroscopic redshifts. The median sSFR of the sample is |$18_{-5}^{+7}$| Gyr⁻¹, significantly larger than literature measurements lacking constraints in the FIR, reflecting the larger obscured SFRs derived from the dust continuum relative to that implied by the UV+optical SED. We suggest that such differences may reflect spatial variations in dust across these luminous galaxies, with the component dominating the FIR distinct from that dominating the UV. We demonstrate that the inferred stellar masses (and hence sSFRs) are strongly dependent on the assumed star formation history in reionization-era galaxies. When large sSFR galaxies (a population that is common at z > 6) are modelled with non-parametric star formation histories, the derived stellar masses can increase by an order of magnitude relative to constant star formation models, owing to the presence of a significant old stellar population that is outshined by the recent burst. The [C ii] line widths in the largest sSFR systems are often very broad, suggesting dynamical masses capable of accommodating an old stellar population suggested by non-parametric models. Regardless of these systematic uncertainties among derived parameters, we find that sSFRs increase rapidly toward higher redshifts for massive galaxies (9.6 < log (M_*/M_⊙) < 9.8), evolving as (1 + z)^1.7 ± 0.3, broadly consistent with expectations from the evolving baryon accretion rates.

Interstellar dust and starlight are modeled for the galaxies of the project “Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel.” The galaxies were observed by the Infrared Array Camera and the Multiband Imaging Photometer for Spitzer on Spitzer Space Telescope, and the Photodetector Array Camera and Spectrometer and the Spectral and Photometric Imaging Receiver on Herschel Space Observatory. With data from 3.6 to 500 μm, dust models are strongly constrained. Using a physical dust model, for each pixel in each galaxy we estimate (1) dust surface density, (2) dust mass fraction in polycyclic aromatic hydrocarbons (PAHs), (3) distribution of starlight intensities heating the dust, (4) total infrared (IR) luminosity emitted by the dust, and (5) IR luminosity originating in subregions with high starlight intensity. The dust models successfully reproduce the observed global and resolved spectral energy distributions. With the angular resolution of Herschel, we obtain well-resolved maps (available online) for the dust properties. As in previous studies, we find the PAH fraction to be an increasing function of metallicity, with a threshold oxygen abundance Z/Z _⊙ ≈ 0.1, but we find the data to be fitted best with increasing linearly with above a threshold value of 0.15(O/H)_⊙. We obtain total dust masses for each galaxy by summing the dust mass over the individual map pixels; these “resolved” dust masses are consistent with the masses inferred from a model fit to the global photometry. The global dust-to-gas ratios obtained from this study are found to correlate with galaxy metallicities. Systems with Z/Z _⊙ ≳ 0.5 have most of their refractory elements locked up in dust, whereas in systems with Z/Z _⊙ ≲ 0.3 most of these elements tend to remain in the gas phase. Within galaxies, we find that is suppressed in regions with unusually warm dust with . With knowledge of one long-wavelength flux density ratio (e.g., f ₁₆₀/f ₅₀₀), the minimum starlight intensity heating the dust ( ) can be estimated to within ∼50%, despite a variation in of more than two orders of magnitude. For the adopted dust model, dust masses can be estimated to within ∼0.2 dex accuracy using the f ₁₆₀/f ₅₀₀ flux ratio and the integrated dust luminosity, and to ∼0.07 dex accuracy using the 500 μm luminosity alone. There are additional systematic errors arising from the choice of dust model, but these are hard to estimate. These calibrated prescriptions for estimating starlight heating intensity and dust mass may be useful for studies of high-redshift galaxies.