Brightest cluster galaxies (BCGs) lie deep within the largest gravitationally bound structures in existence. Though some cluster finding techniques identify the position of the BCG and use it as the cluster center, other techniques may not automatically include these coordinates. This can make studying BCGs in such surveys difficult, forcing researchers to either adopt oversimplified algorithms or perform cumbersome visual identification. For large surveys, there is a need for a fast and reliable way of obtaining BCG coordinates. We propose machine learning to accomplish this task and train a neural network to identify positions of candidate BCGs given no more information than multiband photometric images. We use both mock observations from The Three Hundred project and real ones from the Sloan Digital Sky Survey, and we quantify the performance. Training on simulations yields a squared correlation coefficient, R ^2 , between predictions and ground truth of R ^2 ≈ 0.94 when testing on simulations, which decreases to R ^2 ≈ 0.60 when testing on real data owing to discrepancies between data sets. Limiting the application of this method to real clusters more representative of the training data, such as those with a BCG r -band magnitude r _BCG ≤ 16.5, yields R ^2 ≈ 0.99. The method performs well up to a redshift of at least z ≈ 0.6. We find this technique to be a promising method to automate and accelerate the identification of BCGs in large data sets.

Clusters of galaxies host spectacular diffuse radio sources, extending over scales from 100 kpc to several Mpcs. These sources, with extremely faint surface brightness ( μ Jy/arcsec 2 level), are not tied to individual galaxies but trace synchrotron emission from large-scale magnetic fields and relativistic particles within the intracluster environment. Here, we report the discovery of a candidate radio minihalo in SpARCS104922.6+564032.5, the most distant cool-core galaxy cluster identified to date at z = 1.709, using deep LOFAR 120–168 MHz observations. We show that this emission originates from diffuse cluster-associated processes rather than unresolved active galactic nuclei or star-forming galaxies. The diffuse radio emission coincides spatially with the X-ray emission of the hot intracluster medium and has a radio power of P 150 MHz = 49 . 8 − 11.7 + 14.7 × 1 0 24 W Hz −1 , exhibiting striking similarities to low-redshift radio minihalos. This discovery doubles the redshift of previously known minihalos, challenging models of inverse Compton losses and indicating the presence of strong magnetic fields, enhanced turbulence in high-redshift clusters, or active hadronic processes that require a cosmic-ray-to-thermal-energy ratio of 0.07 within 200 kpc, assuming a clumped distribution with spatial correlations among the gas, cosmic rays, and magnetic field that partially compensate for cosmological redshift dimming. It further implies that magnetic fields are efficiently amplified to ∼10 μ G levels within an Mpc 3 volume during the epoch of cluster formation before z ∼ 2. These findings provide critical insights into high-redshift cluster physics and emphasize the transformative potential of next-generation radio surveys, such as those with the Square Kilometre Array and next-generation Very Large Array (ngVLA), in exploring the early evolution of galaxy clusters.

The changes in colors across a galaxy are intimately connected to the galaxy's formation, growth, quenching history, and dust content. A particularly important epoch in the growth of galaxies is near z similar to 2, often referred to as "cosmic noon," where galaxies on average reach the peak of their star formation. We study a population of 125 cluster galaxies at z similar to 1.6 in three Hubble Space Telescope filters, F475W, F625W, and F160W, roughly corresponding to the rest-frame far-ultraviolet, near-ultraviolet, and r band, respectively. By comparing to a control sample of 200 field galaxies at similar redshift, we reveal clear, statistically significant differences in the overall spatially resolved colors and color gradients in galaxies across these two different environments. On average, cluster galaxies have redder ultraviolet colors in both the inner and outer regions bounded by r 50, as well as an overall wider dispersion of outside-in color gradients. The presence of these observed differences, along with evidence from ancillary data from previous studies, strongly suggests that the environment drives these population-level color differences, by affecting the stellar populations and/or dust content.

We investigate the resolved kinematics of the molecular gas, as traced by the Atacama Large Millimeter/submillimeter Array in CO (2−1), of 25 cluster member galaxies across three different clusters at a redshift of z ∼ 1.6. This is the first large-scale analysis of the molecular gas kinematics of cluster galaxies at this redshift. By separately estimating the rotation curve of the approaching and receding sides of each galaxy via kinematic modeling, we quantify the difference in total circular velocity to characterize the overall kinematic asymmetry of each galaxy. 3/14 of the galaxies in our sample that we are able to model have similar degrees of asymmetry as that observed in galaxies in the field at similar redshift based on observations of mainly ionized gas. However, this leaves 11/14 galaxies in our sample with significantly higher asymmetry, and some of these galaxies have degrees of asymmetry of up to ∼50 times higher than field galaxies observed at similar redshift. Some of these extreme cases also have one-sided tail-like morphology seen in the molecular gas, supporting a scenario of tidal and/or ram pressure interaction. Such stark differences in the kinematic asymmetry in clusters versus the field suggest the evolutionary influence of dense environments, established as being a major driver of galaxy evolution at low redshift, is also active in the high-redshift universe.

We presentHerschel -PACS spectroscopy of the [OI]63 μm far-infrared cooling line from a sample of six unlensed and spectroscopically-confirmed 87 0μm-selected submillimetre (submm) galaxies (SMGs) at 1.1 < z < 1.6 from the LABOCA Extended Chandra Deep Field South (ECDFS) Submm Survey (LESS). This is the first sur vey of [OI]63μm, one of the main photodissociation region (PDR) cooling lines, i n SMGs. New high-resolution ALMA interferometric 870μm continuum imaging confirms that these six Herschel -targeted SMG counterparts are bona fide sources of submm emission. We d etect [OI]63μm in two SMGs with a SNR> ∼ 3, tentatively detect [OI]63μm in one SMG, and constrain the line flux for the non-detections. We also exploit the combination of s ubmm continuum photometry from 250–870μm and our new PACS continuum measurements to constrain the fa r-infr red luminosity, LFIR, in these SMGs to. 30per cent. We find that SMGs do not show a deficit in their [OI]63μm–to–far-infrared (FIR) continuum luminosity ratios (wit h ratios ranging from ≃ 0.5–1.5 per cent), similar to what was seen previously for the [C II]158μm–to–FIR ratios in SMGs. These observed ratios are about an order of magnitud e higher than what is seen typically for local ultra luminous infrared galaxies (ULIRGs) , which adds to the growing body of evidence that SMGs are not simply ‘scaled up’ versions of l oca ULIRGs. Rather, the PDR line–to–LFIR ratios suggest that the star formation modes of SMGs are like ly more akin to that of local normal (lower-luminosity) star-forming gala xies, with the bulk of the star formation occurring in extended galaxy-scale ( ∼kpc) regions. These observations represent the first step towards a census of the major PDR cooling lines in typica l SMGs that will be attainable with ALMA, enabling detailed modelling to probe the global p ro erties of the star formation and the evolutionary status of SMGs.

We present the first spatially resolved observations of molecular gas in a sample of cluster galaxies beyond z > 0.1. Using ALMA, we detect CO (2–1) in eight z ∼ 1.6 cluster galaxies, all within a single 70″ primary beam. The cluster, SpARCS-J0225, was discovered by the Spitzer Adaptation of the Red-sequence Cluster Survey, and is replete with gas-rich galaxies in close proximity, thus affording an efficient multiplexing strategy to amass the first sample of resolved CO in distant clusters. Mapping out the kinematic structure and morphology of molecular gas on ∼3.5 kpc scales reveals rotating gas disks in the majority of the galaxies, and some kinematic peculiarities, including a central gas void, a merger, and one-sided gas tails. We find that the extent of the molecular gas is slightly smaller than that of the optical HST stellar component; this is even more pronounced in low-redshift Virgo cluster galaxies. However, limited by small sample sizes of spatially resolved CO, we are unable to differentiate the distribution of stellar-to-gas radii between cluster and field environments at high redshift. Thus, at first glance, while the cluster galaxies generally look like galaxies infalling from the field, with typical main-sequence star formation rates and massive molecular gas reservoirs situated in rotating disks, they have potentially remarkable attributes, including elevated gas fractions, slightly smaller CO disks, and asymmetric gas tails. Taken in tandem, these signatures are tentative evidence for gas stripping in the z ∼ 1.6 cluster, though verification of these trends will require larger samples.

We present ALMA CO (2-1) detections in 11 gas-rich cluster galaxies at z similar to 1.6, constituting the largest sample of molecular gas measurements in z > 1.5 clusters to date. The observations span three galaxy clusters, derived from the Spitzer Adaptation of the Red-sequence Cluster Survey. We augment the > 5 sigma detections of the CO (2-1) fluxes with multi-band photometry, yielding stellar masses and infrared-derived star formation rates, to place some of the first constraints on molecular gas properties in z similar to 1.6 cluster environments. We measure sizable gas reservoirs of 0.5-2 x 10(11) M circle dot in these objects, with high gas fractions (f(gas)) and long depletion timescales (tau), averaging 62% and 1.4 Gyr, respectively. We compare our cluster galaxies to the scaling relations of the coeval field, in the context of how gas fractions and depletion timescales vary with respect to the star-forming main sequence. We find that our cluster galaxies lie systematically off the field scaling relations at z = 1.6 toward enhanced gas fractions, at a level of similar to 4 sigma, but have consistent depletion timescales. Exploiting CO detections in lower-redshift clusters from the literature, we investigate the evolution of the gas fraction in cluster galaxies, finding it to mimic the strong rise with redshift in the field. We emphasize the utility of detecting abundant gas-rich galaxies in high-redshift clusters, deeming them as crucial laboratories for future statistical studies.

We report the detection of CO(2-1) emission coincident with the brightest cluster galaxy (BCG) of the high-redshift galaxy cluster SpARCS1049+56, with the Redshift Search Receiver (RSR) on the Large Millimeter Telescope (LMT). We confirm a spectroscopic redshift for the gas of z = 1.7091 +/- 0.0004, which is consistent with the systemic redshift of the cluster galaxies of z = 1.709. The line is well fit by a single-component Gaussian with an RSR-resolution-corrected FWHM of 569 +/- 63 km s(-1). We see no evidence for multiple velocity components in the gas, as might be expected from the multiple image components seen in near-infrared imaging with the Hubble Space Telescope. We measure the integrated flux of the line to be 3.6 +/- 0.3 Jy km s(-1), and using alpha(CO) = 0.8M(circle dot) (K km s(-1) pc(2))(-1), we estimate a total molecular gas mass of 1.1 +/- 0.1 x 10(11) M-circle dot and a M-H2/M-* similar to 0.4. This is the largest gas reservoir detected in a BCG above z > 1 to date. Given the infrared-estimated star formation rate of 860 +/- 130 M-circle dot yr(-1), this corresponds to a gas depletion timescale of similar to 0.1 Gyr. We discuss several possible mechanisms for depositing such a large gas reservoir to the cluster center-e.g., a cooling flow, a major galaxy-galaxy merger, or the stripping of gas from several galaxies-but conclude that these LMT data are not sufficient to differentiate between them.

We present a catalogue of ∼ 3000 submillimetre sources detected ( ≥ 3.5 σ ) at 850 µ m over ∼ 5 deg 2 surveyed as part of the James Clerk Maxwell Telescope (JCMT) SCUBA-2 Cosmology Legacy Survey (S2CLS). This is the largest survey of its kind at 850 µ m, increasing the sample size of 850 µ m selected submillimetre galaxies by an order of magnitude. The wide 850 µ m survey component of S2CLS covers the extragalactic fields: UKIDSS-UDS, COSMOS, Akari -NEP, Extended Groth Strip, Lockman Hole North, SSA22 and GOODS-North. The average 1 σ depth of S2CLS is 1.2 mJy beam − 1 , approaching the SCUBA-2 850 µ m confusion limit, which we determine to be σ c ≈ 0.8 mJy beam − 1 . We measure the 850 µ m number counts, reducing the Poisson errors on the differential counts to approximately 4 per cent at S 850 ≈ 3 mJy. With several independent fields, we investigate field-to-field variance, finding that the number counts on 0.5 ◦ –1 ◦ scales are generally within 50 per cent of the S2CLS mean for S 850 > 3 mJy, with scatter consistent with the Poisson and estimated cosmic variance uncertainties, although there is a marginal (2 σ ) density enhancement in GOODS-North. The observed counts are in reasonable agreement with recent phenomenological and semi-analytic models, although determining the shape of the faint-end slope ( S 850 < 3 mJy) remains a key test. The large solid angle of S2CLS allows us to measure the bright-end counts: at S 850 > 10 mJy there are approximately 10 sources per square and strongly lensed high-redshift galaxies. All calibrated maps and the catalogue are made publicly available.

We compile a sample of spectroscopically and photometrically selected cluster galaxies from four high-redshift galaxy clusters (1.59 < z < 1.71) from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS), and a comparison field sample selected from the UKIDSS Deep Survey. Using near-infrared imaging from the Hubble Space Telescope, we classify potential mergers involving massive (M-* >= 3 x 10(10)M(circle dot)) cluster members by eye, based on morphological properties such as tidal distortions, double nuclei, and projected near neighbors within 20 kpc. With a catalog of 23 spectroscopic and 32 photometric massive cluster members across the four clusters and 65 spectroscopic and 26 photometric comparable field galaxies, we find that after taking into account contamination from interlopers, 11.0(-5.6)(+70) of the cluster members are involved in potential mergers, compared to 24.7(-4.6)(+5.3) of the field galaxies. We see no evidence of merger enhancement in the central cluster environment with respect to the field, suggesting that galaxy-galaxy merging is not a stronger source of galaxy evolution in cluster environments compared to the field at these redshifts.

We present the results of a Spitzer/Herschel infrared photometric analysis of the largest (716) and the highest-redshift (z = 1.8) sample of brightest cluster galaxies (BCGs), those from the Spitzer Adaptation of the Red-Sequence Cluster Survey Given the tension that exists between model predictions and recent observations of BCGs at z < 2, we aim to uncover the dominant physical mechanism(s) guiding the stellar mass buildup of this special class of galaxies, the most massive in the Universe and uniquely residing at the centres of galaxy clusters. Through a comparison of their stacked, broad-band, infrared spectral energy distributions (SEDs) to a variety of model templates in the literature, we identify the major sources of their infrared energy output, in multiple redshift bins between 0 < z < 1.8. We derive estimates of various BCG physical parameters from the stacked nu L-nu SEDs, from which we infer a star-forming, as opposed to a 'red and dead' population of galaxies, producing tens to hundreds of solar masses per year down to z = 0.5. This discovery challenges the accepted belief that BCGs should only passively evolve through a series of gas-poor, minor mergers since z similar to 4, but agrees with an improved semi-analytic model of hierarchical structure formation that predicts star-forming BCGs throughout the epoch considered. We attribute the star formation inferred from the stacked infrared SEDs to both major and minor 'wet' (gas-rich) mergers, based on a lack of key signatures (to date) of cooling-flow-induced star formation, as well as a number of observational and simulation-based studies that support this scenario.

We present a five-band Herschel study (100-500um) of three galaxy clusters at z 1.2 from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS). With a sample of 120 spectroscopically-confirmed cluster members, we investigate the role of environment on galaxy properties utilizing the projected cluster phase space (line-of-sight velocity versus clustercentric radius), which probes the time-averaged galaxy density to which a galaxy has been exposed. We divide cluster galaxies into phase-space bins of (r/r200) x (v/sigma_v), tracing a sequence of accretion histories in phase space. Stacking optically star-forming cluster members on the Herschel maps, we measure average infrared star formation rates, and, for the first time in high-redshift galaxy clusters, dust temperatures for dynamically distinct galaxy populations—namely, recent infalls and those that were accreted onto the cluster at an earlier epoch. Proceeding from the infalling to virialized (central) regions of phase space, we find a steady decrease in the specific star formation rate and increase in the stellar age of star-forming cluster galaxies. We perform a probability analysis to investigate all acceptable infrared spectral energy distributions within the full parameter space and measure a 4 sigma drop in the average dust temperature of cluster galaxies in an intermediate phase-space bin, compared to an otherwise flat trend with phase space. We suggest one plausible quenching mechanism which may be consistent with these trends, invoking ram-pressure stripping of the warmer dust for galaxies within this intermediate accretion phase.

We present a catalogue of ∼3000 submillimetre sources detected (≥3.5σ ) at 850 μm over ∼5 deg2 surveyed as part of the James Clerk Maxwell Telescope (JCMT) SCUBA-2 Cosmology Legacy Survey (S2CLS). This is the largest survey of its kind at 850 μm, increasing the sample size of 850 μm selected submillimetre galaxies by an order of magnitude. The wide 850 μm survey component of S2CLS covers the extragalactic fields: UKIDSS-UDS, COSMOS, Akari-NEP, Extended Groth Strip, Lockman Hole North, SSA22 and GOODS-North. The average 1σ depth of S2CLS is 1.2 mJy beam−1, approaching the SCUBA-2 850 μm confusion limit, which we determine to be σ c ≈ 0.8 mJy beam−1. We measure the 850 μm number counts, reducing the Poisson errors on the differential counts to approximately 4 per cent at S850 ≈ 3 mJy. With several independent fields, we investigate field-to-field variance, finding that the number counts on 0.5◦–1◦ scales are generally within 50 per cent of the S2CLS mean for S850 > 3 mJy, with scatter consistent with the Poisson and estimated cosmic variance uncertainties, although there is a marginal (2σ ) density enhancement in GOODS-North. The observed counts are in reasonable agreement with recent phenomenological and semi-analytic models, although determining the shape of the faint-end slope (S850 < 3 mJy) remains a key test. The large solid angle of S2CLS allows us to measure the bright-end counts: at S850 > 10 mJy there are approximately 10 sources per square degree, and we detect the distinctive up-turn in the number counts indicative of the detection of local sources of 850 μm emission, E-mail: j.geach@herts.ac.uk C © 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society D ow naded rom http/academ ic.p.com /m nras/article-at/465/2/1789/2454739 by O en U niersity Lrary (ER ) user on 31 M ay 2019 1790 J. E. Geach et al. and strongly lensed high-redshift galaxies. All calibrated maps and the catalogue are made publicly available.

We present the results of an MIPS-24 μm study of the brightest cluster galaxies (BCGs) of 535 high-redshift galaxy clusters. The clusters are drawn from the Spitzer Adaptation of the Red-Sequence Cluster Survey, which effectively provides a sample selected on total stellar mass, over 0.2 < z < 1.8 within the Spitzer Wide-Area Infrared Extragalactic (SWIRE) Survey fields. Twenty percent, or 106 clusters, have spectroscopically confirmed redshifts, and the rest have redshifts estimated from the color of their red sequence. A comparison with the public SWIRE images detects 125 individual BCGs at 24 μm ≳ 100 μJy, or 23%. The luminosity-limited detection rate of BCGs in similar richness clusters (Ngal > 12) increases rapidly with redshift. Above z ∼ 1, an average of ∼20% of the sample have 24 μm inferred infrared luminosities of LIR > 1012 L⊙, while the fraction below z ∼ 1 exhibiting such luminosities is <1%. The Spitzer-IRAC colors indicate the bulk of the 24 μm detected population is predominantly powered by star formation, with only 7/125 galaxies lying within the color region inhabited by active galactic nuclei (AGNs). Simple arguments limit the star formation activity to several hundred million years and this may therefore be indicative of the timescale for AGN feedback to halt the star formation. Below redshift z ∼ 1, there is not enough star formation to significantly contribute to the overall stellar mass of the BCG population, and therefore BCG growth is likely dominated by dry mergers. Above z ∼ 1, however, the inferred star formation would double the stellar mass of the BCGs and is comparable to the mass assembly predicted by simulations through dry mergers. We cannot yet constrain the process driving the star formation for the overall sample, though a single object studied in detail is consistent with a gas-rich merger.

We have discovered an optically rich galaxy cluster at z=1.7089 with star formation occurring in close proximity to the central galaxy. The system, SpARCS104922.6+564032.5, was detected within the Spitzer Adaptation of the red-sequence Cluster Survey, (SpARCS), and confirmed through Keck-MOSFIRE spectroscopy. The rest-frame optical richness of Ngal(500kpc) = 30+/-8 implies a total halo mass, within 500kpc, of ~3.8+/-1.2 x 10^14 Msun, comparable to other clusters at or above this redshift. There is a wealth of ancillary data available, including Canada-France-Hawaii Telescope optical, UKIRT-K, Spitzer-IRAC/MIPS, and Herschel-SPIRE. This work adds submillimeter imaging with the SCUBA2 camera on the James Clerk Maxwell Telescope and near-infrared imaging with the Hubble Space Telescope (HST). The mid/far-infrared (M/FIR) data detect an Ultra-luminous Infrared Galaxy spatially coincident with the central galaxy, with LIR = 6.2+/-0.9 x 10^12 Lsun. The detection of polycyclic aromatic hydrocarbons (PAHs) at z=1.7 in a Spitzer-IRS spectrum of the source implies the FIR luminosity is dominated by star formation (an Active Galactic Nucleus contribution of 20%) with a rate of ~860+/-30 Msun/yr. The optical source corresponding to the IR emission is likely a chain of of > 10 individual clumps arranged as beads on a string over a linear scale of 66 kpc. Its morphology and proximity to the Brightest Cluster Galaxy imply a gas-rich interaction at the center of the cluster triggered the star formation. This system indicates that wet mergers may be an important process in forming the stellar mass of BCGs at early times.

We present Early Science observations with the Large Millimeter Telescope, AzTEC 1.1 mm continuum images and wide bandwidth spectra (73–111 GHz) acquired with the Redshift Search Receiver, towards four bright lensed submillimetre galaxies identified through the Herschel Lensing Survey-snapshot and the Submillimetre Common-User Bolometer Array-2 Cluster Snapshot Survey. This pilot project studies the star formation history and the physical properties of the molecular gas and dust content of the highest redshift galaxies identified through the benefits of gravitational magnification. We robustly detect dust continuum emission for the full sample and CO emission lines for three of the targets. We find that one source shows spectroscopic multiplicity and is a blend of three galaxies at different redshifts (z = 2.040, 3.252, and 4.680), reminiscent of previous high-resolution imaging follow-up of unlensed submillimetre galaxies, but with a completely different search method, that confirm recent theoretical predictions of physically unassociated blended galaxies. Identifying the detected lines as 12CO (Jup = 2–5) we derive spectroscopic redshifts, molecular gas masses, and dust masses from the continuum emission. The mean H2 gas mass of the full sample is (2.0 ± 0.2) × 1011 M /μ, and the mean dust mass is (2.0 ± 0.2) × 109 M /μ, where μ ≈ 2–5 is the expected lens amplification. Using these independent estimations we infer a gas-to-dust ratio of δGDR ≈ 55–75, in agreement with other measurements of submillimetre galaxies. Our magnified high-luminosity galaxies fall on the same locus as other high-redshift submillimetre galaxies, extending the LCO–LFIR correlation observed for local luminous and ultraluminous infrared galaxies to higher far-infrared and CO luminosities.

We present Early Science observations with the Large Millimeter Telescope, AzTEC 1.1 mm continuum images and wide bandwidth spectra (73-111 GHz) acquired with the Redshift Search Receiver, towards four bright lensed submillimetre galaxies identified through the Herschel Lensing Survey-snapshot and the Submillimetre Common-User Bolometer Array-2 Cluster Snapshot Survey. This pilot project studies the star formation history and the physical properties of the molecular gas and dust content of the highest redshift galaxies identified through the benefits of gravitational magnification. We robustly detect dust continuum emission for the full sample and CO emission lines for three of the targets. We find that one source shows spectroscopic multiplicity and is a blend of three galaxies at different redshifts (z = 2.040, 3.252, and 4.680), reminiscent of previous high-resolution imaging follow-up of unlensed submillimetre galaxies, but with a completely different search method, that confirm recent theoretical predictions of physically unassociated blended galaxies. Identifying the detected lines as (CO)-C-12 (J(up) = 2-5) we derive spectroscopic redshifts, molecular gas masses, and dust masses from the continuum emission. The mean H-2 gas mass of the full sample is (2.0 +/- 0.2) x 10(11)M(circle dot)/mu, and the mean dust mass is (2.0 +/- 0.2) x 10(9) M-circle dot/mu, where mu approximate to 2-5 is the expected lens amplification. Using these independent estimations we infer a gas-to-dust ratio of delta(GDR) approximate to 55-75, in agreement with other measurements of submillimetre galaxies. Our magnified high-luminosity galaxies fall on the same locus as other high-redshift submillimetre galaxies, extending the L-CO'-L-FIR correlation observed for local luminous and ultraluminous infrared galaxies to higher far-infrared and CO luminosities.

We analyse new SCUBA-2 submillimeter and archival SPIRE far-infrared imaging of a z=1.62 cluster, Cl0218.3-0510, which lies in the UKIDSS/UDS field of the SCUBA-2 Cosmology Legacy Survey. Combining these tracers of obscured star formation activity with the extensive photometric and spectroscopic information available for this field, we identify 31 far-infrared/submillimeter-detected probable cluster members with bolometric luminosities >1e12 Lo and show that by virtue of their dust content and activity, these represent some of the reddest and brightest galaxies in this structure. We exploit Cycle-1 ALMA submillimeter continuum imaging which covers one of these sources to confirm the identification of a SCUBA-2-detected ultraluminous star-forming galaxy in this structure. Integrating the total star-formation activity in the central region of the structure, we estimate that it is an order of magnitude higher (in a mass-normalised sense) than clusters at z~0.5-1. However, we also find that the most active cluster members do not reside in the densest regions of the structure, which instead host a population of passive and massive, red galaxies. We suggest that while the passive and active populations have comparable near-infrared luminosities at z=1.6, M(H)~-23, the subsequent stronger fading of the more active galaxies means that they will evolve into passive systems at the present-day which are less luminous than the descendants of those galaxies which were already passive at z~1.6 (M(H)~-20.5 and M(H)~-21.5 respectively at z~0). We conclude that the massive galaxy population in the dense cores of present-day clusters were already in place at z=1.6 and that in Cl0218.3-0510 we are seeing continuing infall of less extreme, but still ultraluminous, star-forming galaxies onto a pre-existing structure.

We present a study of the infrared properties for a sample of seven spectroscopically confirmed submillimeter galaxies (SMGs) at z > 4.0. By combining ground-based near-infrared, Spitzer IRAC and MIPS, Herschel SPIRE, and ground-based submillimeter/millimeter photometry, we construct their spectral energy distributions (SEDs) and a composite model to fit the SEDs. The model includes a stellar emission component at lambda(rest) < 3.5 mu m ot dust component peaking at lambda(rest) similar to 5 mu m and cold dust component which becomes significant for lambda(rest) > 50 mu m. Six objects in the sample are detected at 250 and 350 mu m. The dust temperatures for the sources in this sample are in the range of 40-80 K, and their LFIR similar to 10(13) L circle dot qualifies them as hyper-luminous infrared galaxies. The mean FIR-radio index for this sample is around q = 2.2 indicating no radio excess in their radio emission. Most sources in the sample have 24 mu m detections corresponding to a rest-frame 4.5 mu m luminosity of Log(10)(L-4.5/L circle dot) = 11 similar to 11.5. Their L4.5/L-FIR ratios are very similar to those of starburst-dominated SMGs at z similar to 2. The LCO -LFIR relation for this sample is consistent with that determined for local ULIRGs and SMGs at z similar to 2. We conclude that SMGs at z > 4 are hotter and more luminous in the FIR but otherwise very similar to those at z similar to 2. None of these sources show any sign of the strong QSO phase being triggered.

We present an infrared study of a z=0.872 cluster, SpARCS J161314+564930, with the primary aim of distinguishing the dynamical histories of spectroscopically confirmed star-forming members to assess the role of cluster environment. We utilize deep MIPS imaging and a mass-limited sample of 85 spectroscopic members to identify 16 24um-bright sources within the cluster, and measure their 24um star formation rates (SFRs) down to 6 Msolar/year. Based on their line-of-sight velocities and stellar ages, MIPS cluster members appear to be an infalling population that was recently accreted from the field with minimal environmental dependency on their star formation. However, we identify a double-sequenced distribution of star-forming galaxies amongst the members, with one branch exhibiting declining specific SFRs with mass. The members along this sub-main sequence contain spectral features suggestive of passive galaxies. Using caustic diagrams, we kinematically identify these galaxies as a virialized and/or backsplash population. Moreover, we find a mix of dynamical histories at all projected radii, indicating that standard definitions of environment (i.e., radius and density) are contaminated with recently accreted interlopers, which could contribute to a lack of environmental trends for star-forming galaxies. A cleaner narrative of their dynamical past begins to unfold when using a proxy for accretion histories through profiles of constant (r/r_200)x(Delta v/sigma_v); galaxies accreted at earlier times possess lower values of (r/r_200)x(Delta v/sigma_v) with minimal contamination from the distinct infalling population. Therefore, adopting a time-averaged definition for density (as traced by accretion histories) rather than an instantaneous density yields a depressed specific SFR within the dynamical cluster core.