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Measuring the environments of massive galaxies at high redshift is crucial to understanding galaxy evolution and the conditions that gave rise to the distribution of matter we see in the Universe today. While high- z radio galaxies (H z RGs) and quasars tend to reside in protocluster-like systems, the environments of their radio-quiet counterparts are relatively unexplored, particularly in the submillimetre, which traces dust-obscured star formation. In this study, we search for 850  μ m-selected submillimetre galaxies (SMGs) in the environments of massive (⁠|$M_{\star }$| |$\gt 10^{11}$| |${\rm M}_{\odot }$|⁠), radio-quiet (⁠|$L_{500 {\rm MHz}}$| |$\lesssim 10^{25}$|  WHz |$^{-1}$|⁠) galaxies at |$z \sim 1\!-\!3$| using data from the SCUBA-2 COSMOS (S2COSMOS) survey. By constructing number counts in circular regions of radius 1–6 arcmin and comparing with blank-field measurements, we find no significant overdensities of SMGs around massive radio-quiet galaxies at any of these scales, despite being sensitive down to overdensities of |$\delta \sim 0.4$|⁠. To probe deeper than the catalogue we also examine the distribution of peaks in the SCUBA-2 signal-to-noise (SNR) map, which reveals only tentative signs of any difference in the SMG densities of the radio-quiet galaxy environments compared to the blank field, and only on smaller scales (1 arcmin radii, corresponding to |$\sim 0.5$|  Mpc) and higher SNR thresholds. We conclude that massive, radio-quiet galaxies at cosmic noon are typically in environments with |$\delta \lesssim 0.4$|⁠ , which are either consistent with the blank field or contain only weak overdensities spanning sub-Mpc scales. The contrast between our results and studies of H z RGs with similar stellar masses and redshifts implies an intrinsic link between the wide-field environment and the radio luminosity of the active galactic nucleus at high redshift. [ABSTRACT FROM AUTHOR]

We present the results of our Keck /DEep Imaging Multi-Object Spectrograph spectroscopic follow-up of candidate galaxies of i -band-dropout protocluster candidate galaxies at z ∼ 6 in the COSMOS field. We securely detect Lyman α emission lines in 14 of the 30 objects targeted, 10 of them being at z  = 6 with a signal-to-noise ratio of 5–20; the remaining galaxies are either non-detections or interlopers with redshift too different from z  = 6 to be part of the protocluster. The 10 galaxies at z ≈ 6 make the protocluster one of the riches at z > 5. The emission lines exhibit asymmetric profiles with high skewness values ranging from 2.87 to 31.75, with a median of 7.37. This asymmetry is consistent with them being Ly α, resulting in a redshift range of z  = 5.85–6.08. Using the spectroscopic redshifts, we recalculate the overdensity map for the COSMOS field and find the galaxies to be in a significant overdensity at the 4σ level, with a peak overdensity of δ = 11.8 (compared to the previous value of δ = 9.2). The protocluster galaxies have stellar masses derived from Bagpipes spectral energy distribution fits of |$10^{8.29}\!-\!10^{10.28} \rm \, M_{\rm \odot }$| and star formation rates of |$2\!-\!39\, \rm M_{\rm \odot }\rm \, yr^{-1}$|⁠ , placing them on the main sequence at this epoch. Using a stellar-to-halo-mass relationship, we estimate the dark matter halo mass of the most massive halo in the protocluster to be |$\sim 10^{12}\rm M_{\rm \odot }$|⁠. By comparison with halo mass evolution tracks from simulations, the protocluster is expected to evolve into a Virgo- or Coma-like cluster in the present day. [ABSTRACT FROM AUTHOR]

Using the First Light And Reionisation Epoch Simulations, a suite of hydrodynamical simulations, we explore the consequences of a realistic model for star–dust geometry on the observed properties of galaxies. We find that the ultraviolet (UV) attenuation declines rapidly from the central regions of galaxies, and bright galaxies have spatially extended star formation that suffers less obscuration than their fainter counterparts, demonstrating a non-linear relationship between the UV luminosity and the UV attenuation, giving a double power-law shape to the UVLF. Spatially distinct stellar populations within galaxies experience a wide range of dust attenuation due to variations in the dust optical depth along their line of sight, which can range from completely dust obscured to being fully unobscured. The overall attenuation curve of a galaxy is then a complex combination of various lines of sight within the galaxy. We explore the manifestation of this effect to study the reliability of line ratios to infer galaxy properties, in particular, the Balmer decrement and the Baldwin, Phillips, and Terlevich (BPT) diagram. We find the Balmer decrement predicted Balmer-line attenuation to be higher (factor of 1 to ≳ 10) than expected from commonly used attenuation curves. The observed BPT line ratios deviate from their intrinsic values [median difference of 0.08 (0.02) and standard deviation of 0.2 (0.05) for log10([N |${\small II}]\lambda 6585/$| Hα) (log10([O  iii ]λ5008/Hβ)]. Finally, we explore the variation in observed properties (UV attenuation, UV slope, and Balmer decrement) with viewing angle, finding average differences of ∼0.3 mag in the UV attenuation. [ABSTRACT FROM AUTHOR]

Detecting the line-intensity mapping (LIM) signal from the galaxies of the epoch of reionization is an emerging tool to constrain their role in reionization. Ongoing and upcoming experiments target the signal fluctuations across the sky to reveal statistical and astrophysical properties of these galaxies via signal statistics, e.g. the power spectrum. Here, we revisit the [C  ii ] |$_{158 \, \mu \text{m}}$| LIM power spectrum under non-uniform line–luminosity scatter, which has a halo-mass variation of statistical properties. Line–luminosity scatter from a cosmological hydrodynamic and radiative transfer simulation of galaxies at |$z$|  = 6 is considered in this study. We test the robustness of different model frameworks that interpret the impact of the line-luminosity scatter on the signal statistics. We use a simple power-law model to fit the scatter and demonstrate that the mean luminosity–halo mass correlation fit cannot preserve the mean intensity of the LIM signal (hence the clustering power spectrum) under non-uniform scatter. In our case, the mean intensity changes by ∼48 per cent compared to the mean correlation fit in contrast to the general case with semi-analytical scatter. However, we find that the prediction for the mean intensity from the most-probable fit can be modelled robustly, considering the generalized and more realistic non-uniform scatter. We also explore the possibility of diminishing luminosity bias under non-uniform scatter, affecting the clustering power spectrum, although this phenomenon might not be statistically significant. Therefore, we should adopt appropriate approaches that can consistently interpret the LIM power spectrum from observations. [ABSTRACT FROM AUTHOR]

We present the multiwavelength counterparts of 850- |$\mu$| m selected submillimetre sources over a 2-deg2 field centred on the North Ecliptic Pole. In order to overcome the large beam size (15 arcsec) of the 850- |$\mu$| m images, deep optical to near-infrared (NIR) photometric data and arcsecond-resolution 20-cm images are used to identify counterparts of submillimetre sources. Among 647 sources, we identify 514 reliable counterparts for 449 sources (69 per cent in number), based either on probabilities of chance associations calculated from positional offsets or offsets combined with the optical-to-NIR colours. In the radio imaging, the fraction of 850- |$\mu$| m sources having multiple counterparts is 7 per cent. The photometric redshift, infrared luminosity, stellar mass, star formation rate (SFR), and the active galactic nucleus (AGN) contribution to the total infrared luminosity of the identified counterparts are investigated through spectral energy distribution fitting. The SMGs are infrared-luminous galaxies at an average 〈 z 〉 = 2.5 with log10(L IR/L⊙) = 11.5–13.5, with a mean stellar mass of log10(M star/M⊙) = 10.90 and SFR of |$\mathrm{log}_{10} (\mathrm{SFR/M_\odot \, yr^{-1}})=2.34$|⁠. The submillimetre galaxies (SMGs) show twice as large SFR as galaxies on the star-forming main sequence, and about 40 per cent of the SMGs are classified as objects with bursty star formation. At z ≥ 4, the contribution of AGN luminosity to total luminosity for most SMGs is larger than 30 per cent. The FIR-to-radio correlation coefficient of SMGs is consistent with that of main-sequence galaxies at z ≃ 2. [ABSTRACT FROM AUTHOR]

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 FROM AUTHOR]

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 FROM AUTHOR]

We present an 850- μ m mosaic map and extracted catalogue of submillimetre sources in the extended North Ecliptic Pole (NEP) region over about 2 deg2. The 850- μ m map is constructed using newly obtained observations by SCUBA-2 at the East Asian Observatory's James Clerk Maxwell Telescope, carried out using the observatory's large programme opportunities. The recent 850- μ m survey has extended the submillimetre data coverage by almost a factor of 4 compared to previous surveys, with a depth of |$\sigma _\text{rms}\, {=}\, 1.0$| – |$2.3\, {\rm mJy}\, {\rm beam}^{-1}$|⁠. The catalogue contains 549 sources selected above a significance level of 4σ, where the false-detection rate is 10 per cent; a higher threshold of 4.5σ is required in order to achieve a false-detection rate below 3 per cent, which results in 342 sources being selected. Despite the large spatial variation of the noise, the deboosted flux density of sources is comparable to results from the SCUBA-2 Cosmology Legacy Survey, which covered the central 0.6 deg2 of our survey area with better sensitivity. We construct the source counts at 850  μ m, finding results in agreement with other 850- μ m surveys in cosmological blank fields over S 850 = 4–15 mJy. We find a slight excess of bright galaxies (⁠|$S_{850}\, {\gt }\, 15$|  mJy), which can be considered to be at |$z_\text{phot}\, {=}\, 2$| –4. The 850- μ m data add valuable long-wavelength information to mid-infrared-selected sources from the AKARI NEP-deep and NEP-wide surveys, which will be helpful in preparing for future near-infrared to millimetre wavelength observations in the NEP region. Our 850- μ m mosaic map and source catalogue will be made publicly available. [ABSTRACT FROM AUTHOR]

To study the high-transition dense-gas tracers and their relationships to the star formation of the inner ∼2 kpc circumnuclear region of NGC 253, we present HCN J = 4−3 and HCO+ J = 4−3 maps obtained with the James Clerk Maxwell Telescope. Using the spatially resolved data, we compute the concentration indices r 90/ r 50 for the different tracers. HCN and HCO+ 4–3 emission features tend to be centrally concentrated, which is in contrast to the shallower distribution of CO 1–0 and the stellar component. The dense-gas fraction (f dense, traced by the velocity-integrated-intensity ratios of HCN/CO and HCO+/CO) and the ratio R 31 (CO 3–2/1–0) decline towards larger galactocentric distances, but increase with higher star formation rate surface density. The radial variation and the large scatter of f dense and R 31 imply distinct physical conditions in different regions of the galactic disc. The relationships of f dense versus Σstellar, and SFEdense versus Σstellar are explored. SFEdense increases with higher Σstellar in this galaxy, which is inconsistent with previous work that used HCN 1–0 data. This implies that existing stellar components might have different effects on the high-J HCN and HCO+ than their low-J emission. We also find that SFEdense seems to be decreasing with higher f dense which is consistent with previous works, and it suggests that the ability of the dense gas to form stars diminishes when the average density of the gas increases. This is expected in a scenario where only the regions with high-density contrast collapse and form stars. [ABSTRACT FROM AUTHOR]

We present SÍGAME (SImulator of GAlaxy Millimetre/submillimetre Emission), a new numerical code designed to simulate the 12CO rotational line spectrum of galaxies. Using sub-grid physics recipes to post-process the outputs of smoothed particle hydrodynamics (SPH) simulations, a molecular gas phase is condensed out of the hot and partly ionized SPH gas. The gas is subjected to far-UV radiation fields and cosmic ray ionization rates which are set to scale with the local star formation rate volume density. Level populations and radiative transport of the CO lines are solved with the 3D radiative transfer code LIME. We have applied SÍGAME to cosmological SPH simulations of three disc galaxies at z = 2 with stellar masses in the range ∼0.5-2 × 1011 M☉ and star formation rates ∼40-140 M☉ yr -1. Global CO luminosities and line ratios are in agreement with observations of disc galaxies at z ∼ 2 up to and including J = 3-2 but falling short of the few existing J=5-4 observations. The central 5 kpc regions of our galaxies have CO 3-2/1-0 and 7-6/1-0 brightness temperature ratios of ∼0.55-0.65 and ∼0.02-0.08, respectively, while further out in the disc the ratios drop to more quiescent values of ∼0.5 and <0.01. Global CO-to-H2 conversion (αCO) factors are ≃1.5M☉ pc-2(K km s -1)-1, i.e. ∼2-3 times below the typically adopted values for disc galaxies, and αCO increases with radius, in agreement with observations of nearby galaxies. Adopting a top-heavy Giant Molecular Cloud (GMC) mass spectrum does not significantly change the results. Steepening the GMC density profiles leads to higher global line ratios for Jup ≥ 3 and CO-to-H2 conversion factors [≃3.6M☉ pc-2 (K km s-1 )-1 ]. [ABSTRACT FROM AUTHOR]

We present a joint analysis of the overlapping Balloon-borne Large Aperture Submillimetre Telescope (BLAST) 250, 350, 500 m, and LABOCA 870 m observations [from the LABOCA ECDFS Submm Survey (LESS) survey] of the Extended Chandra Deep Field-South. Out to , the BLAST filters sample near the peak wavelength of thermal far-infrared (FIR) emission from galaxies (rest-frame wavelengths 60-200 m), primarily produced by dust heated through absorption in star-forming clouds. However, identifying counterparts to individual BLAST peaks is very challenging, given the large beams [full-width at half-maximum (FWHM) 36-60 arcsec]. In contrast, the ground-based 870 m observations have a significantly smaller 19 arcsec FWHM beam, and are sensitive to higher redshifts (-5, and potentially beyond) due to the more favourable negative -correction. We use the LESS data, as well as deep Spitzer and VLA imaging, to identify 118 individual sources that produce significant emission in the BLAST bands. We characterize the temperatures and FIR luminosities for a subset of 69 sources which have well-measured submillimetre (submm) spectral energy distributions (SEDs) and redshift measurements out to . For flux-limited sub-samples in each BLAST band, and a dust emissivity index , we find a median temperature K (all bands) as well as median redshifts: (interquartile range 0.2-1.9) for mJy; (interquartile range 0.6-2.1) for mJy; and (interquartile range 1.3-2.3) for mJy. Taking into account the selection effects for our survey (a bias towards detecting lower-temperature galaxies), we find no evidence for evolution in the local FIR-temperature correlation out to . Comparing with star-forming galaxy SED templates, about 8 per cent of our sample appears to exhibit significant excesses in the radio and/or mid-IR, consistent with those sources harbouring active galactic nuclei (AGN). Since our statistical approach differs from most previous studies of submm galaxies, we describe the following techniques in two appendices: our 'matched filter' for identifying sources in the presence of point-source confusion; and our approach for identifying counterparts using likelihood ratios. This study is a direct precursor to future joint FIR/submm surveys, for which we outline a potential identification and SED measurement strategy. [ABSTRACT FROM AUTHOR]

We present a study of the cosmic infrared background, which is a measure of the dust-obscured activity in all galaxies in the Universe. We venture to isolate the galaxies responsible for the background at 1 mm; with spectroscopic and photometric redshifts we constrain the redshift distribution of these galaxies. We create a deep 1.16 mm map (mJy) by combining the AzTEC 1.1 mm and MAMBO 1.2 mm data sets in the Great Observatories Origins Deep Survey North (GOODS-N) region. This combined map contains 41 secure detections, 13 of which are new. By averaging the 1.16 mm flux densities of individually undetected galaxies with flux densities Jy, we resolve 31-45 per cent of the 1.16 mm background. Repeating our analysis on the SCUBA map, we resolve a higher percentage (40-64 per cent) of the background. A majority of the background resolved (attributed to individual galaxies) at both wavelengths comes from galaxies at . If the ratio of the resolved submillimetre to millimetre background is applied to a reasonable scenario for the origins of the unresolved submillimetre background, 60-88 per cent of the total 1.16 mm background comes from galaxies at . [ABSTRACT FROM AUTHOR]

We present a 1200-μm image of the Great Observatories Origin Deep Survey North (GOODS-N) field, obtained with the Max Planck Millimetre Bolometer array (MAMBO) on the IRAM 30-m telescope. The survey covers a contiguous area of 287 arcmin2 to a near-uniform noise level of . After Bayesian flux deboosting, a total of 30 sources are recovered (≥3.5σ). An optimal combination of our 1200-μm data and an existing 850-μm image from the Submillimetre Common-User Bolometer Array (SCUBA) yielded 33 sources (≥4σ). We combine our GOODS-N sample with those obtained in the Lockman Hole and ELAIS N2 fields ( Scott et al. 2002 ; Greve et al. 2004 ) in order to explore the degree of overlap between 1200- and 850-μm-selected galaxies (hereafter SMGs), finding no significant difference between their distributions. However, a noise-weighted stacking analysis yields a significant detection of the 1200-μm-blank SCUBA sources, , whereas no significant 850-μm signal is found for the 850-μm-blank MAMBO sources . The hypothesis that the distribution of SCUBA sources is also representative of the MAMBO population is rejected at the ∼4σ level, via Monte Carlo simulations. Therefore, although the populations overlap, galaxies selected at 850 and 1200 μm are different, and there is compelling evidence for a significant 1200-μm-detected population which is not recovered at 850 μm. These are submillimetre dropouts (SDOs), with , requiring very cold dust or unusual spectral energy distributions , unless SDOs reside beyond the redshift range observed for radio-identified SMGs, i.e. at . [ABSTRACT FROM AUTHOR]

We present an 850- μ m mosaic map and extracted catalogue of submillimetre sources in the extended North Ecliptic Pole (NEP) region over about 2 deg2. The 850- μ m map is constructed using newly obtained observations by SCUBA-2 at the East Asian Observatory's James Clerk Maxwell Telescope, carried out using the observatory's large programme opportunities. The recent 850- μ m survey has extended the submillimetre data coverage by almost a factor of 4 compared to previous surveys, with a depth of |$\sigma _\text{rms}\, {=}\, 1.0$| – |$2.3\, {\rm mJy}\, {\rm beam}^{-1}$|⁠. The catalogue contains 549 sources selected above a significance level of 4σ, where the false-detection rate is 10 per cent; a higher threshold of 4.5σ is required in order to achieve a false-detection rate below 3 per cent, which results in 342 sources being selected. Despite the large spatial variation of the noise, the deboosted flux density of sources is comparable to results from the SCUBA-2 Cosmology Legacy Survey, which covered the central 0.6 deg2 of our survey area with better sensitivity. We construct the source counts at 850  μ m, finding results in agreement with other 850- μ m surveys in cosmological blank fields over S 850 = 4–15 mJy. We find a slight excess of bright galaxies (⁠|$S_{850}\, {\gt }\, 15$|  mJy), which can be considered to be at |$z_\text{phot}\, {=}\, 2$| –4. The 850- μ m data add valuable long-wavelength information to mid-infrared-selected sources from the AKARI NEP-deep and NEP-wide surveys, which will be helpful in preparing for future near-infrared to millimetre wavelength observations in the NEP region. Our 850- μ m mosaic map and source catalogue will be made publicly available. [ABSTRACT FROM AUTHOR]