Metal and dust evolution in ALMA REBELS galaxies: insights for future JWST observations

ALMA observations revealed the presence of significant amounts of dust in the first Gyr of Cosmic time. However, the metal and dust buildup picture remains very uncertain due to the lack of constraints on metallicity. JWST has started to reveal the metal content of high-redshift targets, which may lead to firmer constraints on high-redshift dusty galaxies evolution. In this work, we use detailed chemical and dust evolution models to explore the evolution of galaxies within the ALMA REBELS survey, testing different metallicity scenarios that could be inferred from JWST observations. In the models, we track the buildup of stellar mass by using non-parametric SFHs for REBELS galaxies. Different scenarios for metal and dust evolution are simulated by allowing different prescriptions for gas flows and dust processes. The model outputs are compared with measured dust scaling relations, by employing metallicity-dependent calibrations for the gas mass based on the [CII]158micron line. Independently of the galaxies metal content, we found no need for extreme dust prescriptions to explain the dust masses revealed by ALMA. However, different levels of metal enrichment will lead to different dominant dust production mechanisms, with stardust production dominant over other ISM dust processes only in the metal-poor case. This points out how metallicity measurements from JWST will significantly improve our understanding of the dust buildup in high-redshift galaxies. We also show that models struggle to reproduce observables such as dust-to-gas and dust-to-stellar ratios simultaneously, possibly indicating an overestimation of the gas mass through current calibrations, especially at high metallicities.Comment: 16 pages + appendices, 9 Figures, 1 Table. Resubmitted to MNRAS after moderate revisio

The VLA-COSMOS 3 GHz Large Project: Evolution of Specific Star Formation Rates out to z ~ 5

We provide a coherent, uniform measurement of the evolution of the logarithmic star formation rate(SFR)-stellarmass(M*)relation, called the main sequence(MS)of star-forming galaxies , for star-forming and all galaxies outto~z5. We measure the MS using mean stacks of 3 GHz radio-continuum images to derive average SFRs for∼200,000 mass-selected galaxies at z>0.3 in the COSMOSfield. We describe the MS relation by adopting anew model that incorporates a linear relation at low stellar mass(log(M*/Me)<10)and aflattening at high stellarmass that becomes more prominent at low redshift(z < 1.5).Wefind that the SFR density peaks at 1.5<z<2,and at each epoch there is a characteristic stellar mass(M*=1-4 x 1010Me)that contributes the most to theoverall SFR density. This characteristic mass increases with redshift, at least toz ∼ 2.5. Wefind no significant evidence for variations in the MS relation for galaxies in different environments traced by the galaxy numberdensity at 0.3<z<3, nor for galaxies in X-ray groups atz ∼ 0.75. We confirm that massive bulge-dominatedgalaxies have lower SFRs than disk-dominated galaxies at afixed stellar mass atz < 1.2. As a consequence, theincrease in bulge-dominated galaxies in the local star-forming population leads to aflattening of the MS at highstellar masses. This indicates that "mass quenching" is linked with changes in the morphological composition ofgalaxies at afixed stellar mass.B.G. acknowledges the support of the Australian Research Council as the recipient of a Future Fellowship (FT140101202). Y.P. acknowledges the National Key R&D Program of China, Grant 2016YFA0400702 and NSFC grant Nos. 11773001, 11721303, 1199105

The ALMA REBELS Survey: Dust Continuum Detections at z > 6.5

We report 18 dust continuum detections ($\geq 3.3\sigma$) at $\sim88{\rm \mu m}$ and $158{\rm \mu m}$ out of 49 ultraviolet(UV)-bright galaxies ($M_{\rm UV} 6.5$, observed by the Cycle-7 ALMA Large Program, 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 [CII]$_{\rm 158{\rm \mu m}}$ 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. The dust continuum detected sources in our sample tend to have a redder UV spectral slope than the ones without a dust continuum detection. We estimate that all of the sources have an infrared (IR) luminosity ($L_{\rm IR}$) in a range of $3-8 \times 10^{11} L_\odot$, except for one with $L_{\rm IR} = 1.5^{+0.8}_{-0.5} \times 10^{12}\,L_{\odot}$. Their fraction of obscured star formation is significant at $\gtrsim 50\%$. Some of the dust continuum detected galaxies show spatial offsets ($\sim 0.5-1.5''$) between the rest-UV and far-IR emission peaks. These separations appear to have an increasing trend against an indicator that suggests spatially decoupled phases of obscured and unobscured star formation. REBELS offers the best available statistical constraints on obscured star formation in UV-bright, massive galaxies at $z > 6.5$.Comment: 17 pages, 9 figures, submitted to MNRA

Gas conditions of a star-formation selected sample in the first billion years

We present Atacama Large Millimetre/submillimetre Array (ALMA) observations of the [O iii] 88 emission of a sample of thirteen galaxies at to 7.6 selected as [C ii]-emitting companion sources of quasars. To disentangle the origins of the luminous Oxygen line in the Universe, we looked at emission-line galaxies that are selected through an excellent star-formation tracer [C ii] with star-formation rates between 9 and 162. Direct observations reveal [O iii] emission in just a single galaxy (), and a stacked image shows no [O iii] detection, providing deep upper limits on the ratios in the Universe (at). While the fidelity of this sample is high, no obvious optical/near-infrared counterpart is seen in the JWST imaging available for four galaxies. Additionally accounting for low-z CO emitters, line stacking shows that our sample-wide result remains robust: The enhanced reported in the first billion years of the Universe is likely due to the selection towards bright, blue Lyman-break galaxies with high surface star-formation rates or young stellar populations. The deep upper limit on the rest-frame 90 μm continuum emission (Jy at), implies a low average dust temperature (K) and high-dust mass (). As more normal galaxies are explored in the early Universe, synergy between JWST and ALMA is fundamental to further investigate the ISM properties of the a broad range of samples of high-z galaxies