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ABSTRACT We present new observations of 16 bright (r = 19–21) gravitationally lensed galaxies at z ≃ 1–3 selected from the CASSOWARY survey. Included in our sample is the z = 1.42 galaxy CSWA-141, one of the brightest known reionization-era analogues at high redshift (g = 20.5), with a large specific star formation rate (31.2 Gyr−1) and an [O iii]+H β equivalent width (EW[O iii] + H β = 730 Å) that is nearly identical to the average value expected at z ≃ 7–8. In this paper, we investigate the rest-frame UV nebular line emission in our sample with the goal of understanding the factors that regulate strong C iii] emission. Although most of the sources in our sample show weak UV line emission, we find elevated C iii] in the spectrum of CSWA-141 (EWC iii] = 4.6 ± 1.9 Å) together with detections of other prominent emission lines (O iii], Si iii], Fe ii⋆, Mg ii). We compare the rest-optical line properties of high-redshift galaxies with strong and weak C iii] emission, and find that systems with the strongest UV line emission tend to have young stellar populations and nebular gas that is moderately metal-poor and highly ionized, consistent with trends seen at low and high redshift. The brightness of CSWA-141 enables detailed investigation of the extreme emission line galaxies which become common at z > 6. We find that gas traced by the C iii] doublet likely probes higher densities than that traced by [O ii] and [S ii]. Characterization of the spectrally resolved Mg ii emission line and several low-ionization absorption lines suggests neutral gas around the young stars is likely optically thin, potentially facilitating the escape of ionizing radiation. 

Abstract We present JWST and Atacama Large Millimeter/submillimeter Array (ALMA) imaging for the lensing system SPT0418−47, which includes a strongly lensed, dusty, star-forming galaxy at redshiftz= 4.225 and an associated multiply imaged companion. The JWST NIRCam and MIRI imaging observations presented in this paper were acquired as part of the Early Release Science program Targeting Extremely Magnified Panchromatic Lensed Arcs and Their Extended Star formation (TEMPLATES). This data set provides robust mutiwavelength detections of stellar light in both the main (SPT0418A) and companion (SPT0418B) galaxies, while the ALMA detection of [Cii] emission confirms that SPT0418B lies at the same redshift as SPT0418A. We infer that the projected physical separation of the two galaxies is 4.42 ± 0.05 kpc. We derive total magnifications ofμ= 29 ± 1 andμ= 4.1 ± 0.7 for SPT0418A and SPT0418B, respectively. We use bothprospectorandcigaleto derive stellar masses. We find that SPT0418A has a stellar mass of $M_{*}={3.4}_{-0.6}^{+1.1}\times {10}^{10}{M}_{\odot }$fromprospector orM_*= 1.5 ± 0.3 × 10¹⁰M_⊙fromcigale. The stellar mass ratio of SPT0418A and SPT0418B is roughly between 4 and 7 ( ${4.2}_{-1.6}^{+1.9}$forprospectorand 7.5 ± 3.7 forcigale). We see evidence of extended structure associated with SPT0418A that is suggestive of a tidal feature. These features, along with the close projected proximity, imply that the system is interacting. Interestingly, the star formation rates and stellar masses of both galaxies are consistent with the main sequence of star-forming galaxies at this epoch, indicating that this ongoing interaction has not noticeably elevated the star formation levels. 

ABSTRACT We present APEX-LABOCA 870-μm observations of the fields surrounding the nine brightest high-redshift unlensed objects discovered in the South Pole Telescope’s (SPT) 2500 deg2 survey. Initially seen as point sources by SPT’s 1-arcmin beam, the 19-arcsec resolution of our new data enables us to deblend these objects and search for submillimetre (submm) sources in the surrounding fields. We find a total of 98 sources above a threshold of 3.7σ in the observed area of 1300 arcmin2, where the bright central cores resolve into multiple components. After applying a radial cut to our LABOCA sources to achieve uniform sensitivity and angular size across each of the nine fields, we compute the cumulative and differential number counts and compare them to estimates of the background, finding a significant overdensity of $$\delta \, {\approx }\,$$10 at $$S_{870}= 14$$ mJy. The large overdensities of bright submm sources surrounding these fields suggest that they could be candidate protoclusters undergoing massive star formation events. Photometric and spectroscopic redshifts of the unlensed central objects range from $z= $3 to 7, implying a volume density of star-forming protoclusters of approximately 0.1 Gpc−3. If the surrounding submm sources in these fields are at the same redshifts as the central objects, then the total star formation rates of these candidate protoclusters reach 10 000 M⊙ yr−1, making them much more active at these redshifts than seen so far in either simulations or observations. 

ABSTRACT The protocluster SPT2349−56 at $z = 4.3$ contains one of the most actively star-forming cores known, yet constraints on the total stellar mass of this system are highly uncertain. We have therefore carried out deep optical and infrared observations of this system, probing rest-frame ultraviolet to infrared wavelengths. Using the positions of the spectroscopically confirmed protocluster members, we identify counterparts and perform detailed source deblending, allowing us to fit spectral energy distributions in order to estimate stellar masses. We show that the galaxies in SPT2349−56 have stellar masses proportional to their high star formation rates, consistent with other protocluster galaxies and field submillimetre galaxies (SMGs) around redshift 4. The galaxies in SPT2349−56 have on average lower molecular gas-to-stellar mass fractions and depletion time-scales than field SMGs, although with considerable scatter. We construct the stellar-mass function for SPT2349−56 and compare it to the stellar-mass function of $z = 1$ galaxy clusters, finding consistent shapes between the two. We measure rest-frame galaxy ultraviolet half-light radii from our HST-F160W imaging, finding that on average the galaxies in our sample are similar in size to typical star-forming galaxies at these redshifts. However, the brightest HST-detected galaxy in our sample, found near the luminosity-weighted centre of the protocluster core, remains unresolved at this wavelength. Hydrodynamical simulations predict that the core galaxies will quickly merge into a brightest cluster galaxy, thus our observations provide a direct view of the early formation mechanisms of this class of object. 

Abstract The SPT 0311–58 system atz= 6.900 is an extremely massive structure within the reionization epoch and offers a chance to understand the formation of galaxies at an extreme peak in the primordial density field. We present 70 mas Atacama Large Millimeter/submillimeter Array observations of the dust continuum and [Cii] 158μm emission in the central pair of galaxies and reach physical resolutions of ∼100–350 pc, among the most detailed views of any reionization-era system to date. The observations resolve the source into at least a dozen kiloparsec-size clumps. The global kinematics and high turbulent velocity dispersion within the galaxies present a striking contrast to recent claims of dynamically cold thin-disk kinematics in some dusty galaxies just 800 Myr later atz∼ 4. We speculate that both gravitational interactions and fragmentation from massive parent disks have likely played a role in the overall dynamics and formation of clumps in the system. Each clump individually is comparable in mass to other 6 <z< 8 galaxies identified in rest-UV/optical deep field surveys, but with star formation rates elevated by a factor of ~3-5. Internally, the clumps themselves bear close resemblance to greatly scaled-up versions of virialized cloud-scale structures identified in low-redshift galaxies. Our observations are qualitatively similar to the chaotic and clumpy assembly within massive halos seen in simulations of high-redshift galaxies. 

ABSTRACT We present an extensive ALMA spectroscopic follow-up programme of the $$z\, {=}\, 4.3$$ structure SPT2349–56, one of the most actively star-forming protocluster cores known, to identify additional members using their [C ii] 158 μm and CO(4–3) lines. In addition to robustly detecting the 14 previously published galaxies in this structure, we identify a further 15 associated galaxies at $$z\, {=}\, 4.3$$, resolving 55$$\, {\pm }\,$$5 per cent of the 870 μm flux density at 0.5 arcsec resolution compared to 21 arcsec single-dish data. These galaxies are distributed into a central core containing 23 galaxies extending out to 300 kpc in diameter, and a northern extension, offset from the core by 400 kpc, containing three galaxies. We discovered three additional galaxies in a red Herschel-SPIRE source 1.5 Mpc from the main structure, suggesting the existence of many other sources at the same redshift as SPT2349–56 that are not yet detected in the limited coverage of our data. An analysis of the velocity distribution of the central galaxies indicates that this region may be virialized with a mass of (9$$\pm 5)\, {\times }\, 10^{12}$$  M⊙, while the two offset galaxy groups are about 30 and 60 per cent less massive and show significant velocity offsets from the central group. We calculate the [C ii] and far-infrared number counts, and find evidence for a break in the [C ii] luminosity function. We estimate the average SFR density within the region of SPT2349–56 containing single-dish emission (a proper diameter of 720 kpc), assuming spherical symmetry, to be roughly 4$$\, {\times }\, 10^4$$ M⊙ yr−1 Mpc−3; this may be an order of magnitude greater than the most extreme examples seen in simulations.