Herschel Sources Research Articles

MeerKAT observations of Herschel protocluster candidates

Abstract High-redshift protoclusters consisting of dusty starbursts are thought to play an important role in galaxy evolution. Their dusty nature makes them bright in the FIR/submm but difficult to find in optical/NIR surveys. Radio observations are an excellent way to study these dusty starbursts, as dust is transparent in the radio and there is a tight correlation between the FIR and radio emission of a galaxy. Here, we present MeerKAT 1.28 GHz radio imaging of 3 Herschel candidate protoclusters, with a synthesised beam size of ∼7.5″ × 6.6″ and a central thermal noise down to 4.35 μJy/beam. Our source counts are consistent with other radio counts with no evidence of overdensities. Around $95\%$ of the Herschel sources have 1.28 GHz IDs. Using the Herschel 250 μm primary beam size as the searching radius, we find $54.2\%$ Herschel sources have multiple 1.28 GHz IDs. Our average FIR-radio correlation coefficient q250μm is 2.33 ± 0.26. Adding q250μm as a new constraint, the probability of finding chance-aligned sources is reduced by a factor of ∼6, but with the risk of discarding true identifications of radio-loud/quiet sources. With accurate MeerKAT positions, we cross-match our Herschel sources to optical/NIR data followed by photometric redshift estimations. By removing z < 1 sources, the density contrasts of two of the candidate protoclusters increase, suggestive of them being real protoclusters at z > 1. There is also potentially a 0.9 < z < 1.2 overdensity associated with one candidate protocluster. In summary, photometric redshifts from radio-optical cross-identifications have provided some tentative evidence of overdensities aligning with two of the candidate protoclusters.

JWST’s PEARLS: Resolved study of the stellar and dust components in starburst galaxies at cosmic noon

Dusty star-forming galaxies (DSFGs) significantly contribute to the stellar buildup in galaxies during “cosmic noon,” the peak epoch of cosmic star formation. Major mergers and gas accretion are often invoked to explain DSFGs’ prodigious star formation rates (SFRs) and large stellar masses. We conducted a spatially resolved morphological analysis of the rest-frame ultraviolet/near-infrared (∼0.25–1.3 μm) emission in three DSFGs at z ≃ 2.5. Initially discovered as carbon monoxide (CO) emitters by NOrthern Extended Millimeter Array (NOEMA) observations of a bright (S350 μm = 111 ± 10 mJy) Herschel source, we observed them with the James Webb Space Telescope/NIRCam as part of the PEARLS program. The NIRCam data reveal the galaxies’ stellar populations and dust distributions on scales of 250 pc. Spatial variations in stellar mass, SFR, and dust extinction are determined in resolved maps obtained through pixel-based spectral energy distribution fitting. The CO emitters are massive (Mstar ≃ (3 − 30)×1010 M⊙), dusty starburst galaxies with SFRs ranging from 340 to 2500 M⊙ yr−1, positioning them among the most active star-forming galaxies at 2 < z < 3. Notably, they belong to the ∼1.5% of the entire JWST population with extremely red colors. Their morphologies are disk like (Sérsic index n ≃ 1), with effective radii of 2.0–4.4 kpc, and exhibit substructures such as clumps and spiral arms. The galaxies have dust extinctions up to AV = 5–7 mag extending over several kiloparsecs with asymmetric distributions that include off-center regions resembling bent spiral arms and clumps. The near-infrared dust-attenuation curve in these sources deviates from standard laws, possibly implying different dust–star geometries or dust grain properties than commonly assumed in starburst galaxies. The proximity (< 5″) of galaxies with consistent redshifts, strong color gradients, an overall disturbed appearance, asymmetric dust obscuration, and widespread star formation collectively favor interactions (minor mergers and flybys) as the mechanism driving the CO galaxies’ exceptional SFRs. The galaxies’ large masses and rich environment hint at membership in two proto-structures, as initially inferred from their association with a Planck-selected high-z source.

FLASH: Faint Lenses from Associated Selection with Herschel

ABSTRACT We report the ALMA Band 7 observations of 86 Herschel sources that likely contain gravitationally lensed galaxies. These sources are selected with relatively faint 500 μm flux densities between 15 and 85 mJy in an effort to characterize the effect of lensing across the entire million-source Herschel catalogue. These lensed candidates were identified by their close proximity to bright galaxies in the near-infrared VISTA Kilo-Degree Infrared Galaxy survey. Our high-resolution observations (0.15 arcsec) confirm 47 per cent of the initial candidates as gravitational lenses, while lensing cannot be excluded across the remaining sample. We find average lensing masses (log M/M⊙ = 12.9 ± 0.5) in line with previous experiments, although direct observations might struggle to identify the most massive foreground lenses across the remaining 53 per cent of the sample, particularly for lenses with larger Einstein radii. Our observations confirm previous indications that more lenses exist at low flux densities than expected from strong galaxy–galaxy lensing models alone, where the excess is likely due to additional contributions of cluster lenses and weak lensing. If we apply our method across the total 660 square degree H-ATLAS field, it would allow us to robustly identify 3000 gravitational lenses across the 660 square degree Herschel ATLAS fields.

Identifying and characterizing the most heavily dust-obscured galaxies at 1 ≤ z ≤ 4

ABSTRACT We present 65 extremely dust-obscured galaxies from the UltraVISTA DR3 survey of the COSMOS field at 1 < z < 4. In contrast to other studies of dusty galaxies, we select our sample based on dust attenuation measured by UV–MIR spectral energy distribution (SED) modelling that allows for extreme attenuation levels. We construct our sample by making cuts at 1 ≤ z ≤ 4, AV ≥ 3, and log(M*/M⊙) ≥ 10.5. This method reliably selects galaxies exhibiting independent indicators of significant dust content, including far-infrared detection rates. We perform panchromatic SED modelling with matched Herschel photometry and find stellar and dust properties that differ from typical submillimetre galaxy (SMG) samples as well as Herschel sources matched in redshift and stellar mass. Our sources have lower star formation rates and higher AV than SMGs, but comparable total infrared luminosities. Most of our sample falls on or near the star-forming main sequence for this redshift range. Finally, we perform a morphological analysis with galfit using the KS-band images and Hubble F814W and F160W imaging when available. Typical axial ratios of ∼0.4 suggest disc-like morphology for the majority of our sources, and we note only three apparent merging systems. Our sample generally agrees with the size–mass relation for star-forming galaxies, with a tail extending to smaller sizes. We conclude that the most heavily obscured galaxies in this redshift range share many characteristics with typical star-forming galaxies, forming a population of dusty galaxies that overlaps, but is not encompassed by, those selected through dust emission.

Molecular gas properties of Planck-selected protocluster candidates at z ≃ 1.3–3

We report on IRAM 30-m/EMIR observations of 38 Herschel sources chosen as the brightest red submillimeter (submm) sources in 18 Planck-selected fields drawn from the Planck high-z (PHz) sample of protocluster candidates. These fields host overdensities of red Herschel sources, with high star formation rates (∼10 000 M⊙ yr−1), as obtained from the Planck measurements. The goals of these observations are to measure the spectroscopic redshifts of the Herschel sources in the PHz fields, investigate the origin of their bright submm emission, and find evidence of their association with high-z protoclusters. We detected 40 CO lines on a total of 24 bright (S​350 μm > 40 mJy) Herschel sources in 14 of the 18 PHz fields. The measured average redshift is ⟨zCO⟩ = 2.25 ± 0.09, spanning a range from 1.32 to 2.75. We measured the redshifts for multiple Herschel sources in projected proximity in eight PHz fields. In half of those fields, we detected between two and three objects at similar redshifts, supporting the idea that the PHz fields contain high-z protoclusters. The detection of sources at different redshifts in the same field demonstrates that foreground and background sources also contribute to the total submm emission. We compared the properties of the molecular gas and of the star formation activity of our sources with samples of normal star-forming galaxies (SFGs), submm galaxies (SMGs), and CO-detected cluster and protocluster galaxies drawn from the literature at similar redshifts. We find that the PHz-IRAM sources are mainly normal SFGs, with only ∼20% undergoing a starburst phase. The PHz-IRAM sources are characterized by star formation rates (⟨SFR⟩ = 1043 ± 157 M⊙ yr−1) and gas masses (⟨Mgas⟩ = (4.0 ± 0.7) × 1011 M⊙) that are, on average, eight and five times higher than those typical of normal SFGs at similar redshifts. Their dust temperatures (⟨Tdust⟩ = 29.2 ± 0.9 K) and depletion timescales (⟨τdep⟩ = 0.47 ± 0.07 Gyr) are instead consistent with those of normal SFGs. The analysis of the CO spectral line energy distribution, available for ten PHz-IRAM sources, peaks at a low quantum rotation number (Jup = 3) in most of the cases, implying low gas excitation. These properties imply that a significant number of PHz-IRAM sources contain extended and cold molecular gas reservoirs at low excitation and that their star formation is driven by secular processes. Multiplicity and moderate gravitational lensing might also play a role in producing the observed properties. Some of these properties are also observed in other CO-detected infrared-luminous protocluster galaxies at z ≃ 1.3 − 3. We find that the protoclusters with the highest level of star formation, drawn from the largest volume simulations available to date, exhibit similar SFRs as compared to the PHz protoclusters; however, they separate out into a higher number of star-forming galaxies. Millimeter and CO observations at higher spatial resolution than those presented here would be necessary to further elucidate the properties of our PHz-IRAM sources and determine which mechanisms drive star formation in infrared-luminous protocluster galaxies.

The bright extragalactic ALMA redshift survey (BEARS) – II. Millimetre photometry of gravitational lens candidates

ABSTRACT We present 101- and 151-GHz ALMA continuum images for 85 fields selected from Herschel observations that have 500-μm flux densities >80 mJy and 250–500-μm colours consistent with z > 2, most of which are expected to be gravitationally lensed or hyperluminous infrared galaxies. Approximately half of the Herschel 500-μm sources were resolved into multiple ALMA sources, but 11 of the 15 brightest 500-μm Herschel sources correspond to individual ALMA sources. For the 37 fields containing either a single source with a spectroscopic redshift or two sources with the same spectroscopic redshift, we examined the colour temperatures and dust emissivity indices. The colour temperatures only vary weakly with redshift and are statistically consistent with no redshift-dependent temperature variations, which generally corresponds to results from other samples selected in far-infrared, submillimetre, or millimetre bands but not to results from samples selected in optical or near-infrared bands. The dust emissivity indices, with very few exceptions, are largely consistent with a value of 2. We also compared spectroscopic redshifts to photometric redshifts based on spectral energy distribution templates designed for infrared-bright high-redshift galaxies. While the templates systematically underestimate the redshifts by ∼15 per cent, the inclusion of ALMA data decreases the scatter in the predicted redshifts by a factor of ∼2, illustrating the potential usefulness of these millimetre data for estimating photometric redshifts.

Herschel–ATLAS Data Release III: near-infrared counterparts in the South Galactic Pole field – another 100 000 submillimetre galaxies

ABSTRACT In this paper, we present the third data release (DR3) of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). We identify likely near-infrared counterparts to submillimetre sources in the South Galactic Pole (SGP) field using the VISTA VIKING survey. We search for the most probable counterparts within 15 arcsec of each Herschel source using a probability measure based on the ratio between the likelihood the true counterpart is found close to the submillimetre source and the likelihood that an unrelated object is found in the same location. For 110 374 (57.0 per cent) sources, we find galaxies on the near-infrared images where the probability that the galaxy is associated to the source is greater than 0.8. We estimate the false identification rate to be 4.8 per cent, with a probability that the source has an associated counterpart on the VIKING images of 0.835 ± 0.009. We investigate the effects of gravitational lensing and present 41 (0.14 deg−2) candidate lensed systems with observed flux densities >100 mJy at 500 μm. We include in the data release a probability that each source is gravitationally lensed and discover an additional 5923 sources below 100 mJy that have a probability greater than 0.94 of being gravitationally lensed. We estimate that ∼400–1 000 sources have multiple true identifications in VIKING based on the similarity of redshift estimates for multiple counterparts close to a Herschel source. The data described in this paper can be found at the H-ATLAS website.

Spectroscopic observations of PHz G237.01+42.50: A galaxy protocluster at z = 2.16 in the Cosmos field

The Planck satellite has identified more than 2000 protocluster candidates with extreme star formation rates (SFRs). Here, we present the spectroscopic identification of a Planck-selected protocluster located in the Cosmos field, PHz G237.01+42.50. PHz G237.01+42.50 contains a galaxy overdensity of 31 spectroscopically identified galaxies at z ≃ 2.16 (significant at 5.4σ) in a 10′ × 11′ region. The overdensity contains two substructures or protoclusters at ⟨z⟩ ≃ 2.16 and 2.195 with estimated halo masses at z = 0 of ∼5–6 × 1014 M⊙, roughly consistent with Virgo-type clusters. The overdensity total SFR, ∼4000 M⊙ yr−1, is higher than predicted by simulations but much smaller than the SFR derived from the Planck data (i.e., 10 173 M⊙ yr−1). The analysis of the Herschel data in the field, in combination with the available ancillary data, shows that such a difference is due to an effect of source alignment along the line of sight that produces a 5σ overdensity of red Herschel sources in the field. We analyze the members’ ultraviolet (UV) spectra and UV-far-infrared spectral energy distributions to derive their SFR, stellar mass, and metallicity. Galaxy members include blue star-forming galaxies and Active galactic nuclei (AGN) with SFRs and stellar masses consistent with the main sequence. Active galactic nuclei, identified through optical spectroscopy or X-ray data, represent a significant fraction (20 ± 10%) of all members of the protocluster at z = 2.16, and they are powerful enough to produce radiative feedback. The core of this protocluster, besides being denser, includes members that are, on average, more massive and star-forming and contains a larger fraction of AGN and Herschel-detected galaxies than the full sample, suggesting an environmental effect on galaxy growth. A comparison between PHz G237.01+42.50 and other protoclusters in the literature at similar redshifts reveals some common traits and differences that reflect both observational biases and a diversity in intrinsic properties that is not yet fully understood.

The bright end of the infrared luminosity functions and the abundance of hyperluminous infrared galaxies

Aims. We provide the most accurate estimate yet of the bright end of the infrared (IR) luminosity functions (LFs) and the abundance of hyperluminous IR galaxies (HLIRGs) with IR luminosities >1013L⊙, thanks to the combination of the high sensitivity, angular resolution, and large area of the LOFAR Deep Fields, which probes an unprecedented dynamic range of luminosity and volume. Methods. We cross-match Herschel sources and LOFAR sources in Boötes (8.63 deg2), Lockman Hole (10.28 deg2), and ELAIS-N1 (6.74 deg2) with rms sensitivities of ~32, 22, and 20 μJy beam−1, respectively. We divide the matched samples into “unique” and “multiple” categories. For the multiple matches, we de-blend the Herschel fluxes using the LOFAR positions and the 150-MHz flux densities as priors. We perform spectral energy distribution fitting, combined with multi-wavelength counterpart identifications and photometric redshift estimates, to derive IR luminosities. Results. The depth of the LOFAR data allows us to identify highly complete (~92% completeness) samples of bright Herschel sources with a simple selection based on the 250 μm flux density (45, 40, and 35 mJy in Boötes, Lockman Hole, and ELAIS-N1, respectively). Most of the bright Herschel sources fall into the unique category (i.e. a single LOFAR counterpart). For the multiple matches, there is excellent correspondence between the radio emission and the far-IR emission. We find a good agreement in the IR LFs with a previous study out to z ~ 6 which used de-blended Herschel data. Our sample gives the strongest and cleanest indication to date that the population of HLIRGs has surface densities of ~5 to ~18/deg2 (with variations due to a combination of the applied flux limit and cosmic variance) and an uncertainty of a factor of ≲2. In comparison, the GALFORM semi-analytic model significantly under-predicts the abundance of HLIRGs.

Overdensity of SMGs in fields containing z ∼ 0.3 galaxies: magnification bias and the implications for studies of galaxy evolution

ABSTRACT We report a remarkable overdensity of high-redshift submillimetre galaxies (SMG), 4–7 times the background, around a statistically complete sample of twelve 250 μm selected galaxies at z = 0.35, which were targeted by ALMA in a study of gas tracers. This overdensity is consistent with the effect of lensing by the haloes hosting the target z = 0.35 galaxies. The angular cross-correlation in this sample is consistent with statistical measures of this effect made using larger sub-mm samples. The magnitude of the overdensity as a function of radial separation is consistent with intermediate scale lensing by haloes of the order of $7\times 10^{13}\mbox{ $\rm M_{\odot }$ }$, which should host one or possibly two bright galaxies and several smaller satellites. This is supported by observational evidence of interaction with satellites in four out of the six fields with SMG, and membership of a spectroscopically defined group for a fifth. We also investigate the impact of these SMG on the reported Herschel fluxes of the z = 0.35 galaxies, as they produce significant contamination in the 350 and 500 μm Herschel bands. The higher than random incidence of these boosting events implies a significantly larger bias in the sub-mm colours of Herschel sources associated with z < 0.7 galaxies than has previously been assumed, with fboost = 1.13, 1.26, 1.44 at 250, 350, and 500 μm . This could have implications for studies of spectral energy distributions, source counts, and luminosity functions based on Herschel samples at z = 0.2–0.7.

The nature of 500 micron risers I: SMA observations

ABSTRACT We present SMA observations at resolutions from 0.35 to 3 arcsec of a sample of 34 candidate high redshift dusty star forming galaxies (DSFGs). These sources were selected from the HerMES Herschel survey catalogues to have SEDs rising from 250 to 350 to 500 μm, a population termed 500-risers. We detect counterparts to 24 of these sources, with four having two counterparts. We conclude that the remaining ten sources that lack detected counterparts are likely to have three or more associated sources which blend together to produce the observed Herschel source. We examine the role of lensing, which is predicted to dominate the brightest (F500 > 60 mJy) half of our sample. We find that while lensing plays a role, at least 35 per cent of the bright sources are likely to be multiple sources rather than the result of lensing. At fainter fluxes we find a blending rate comparable to, or greater than, the predicted 40 per cent. We determine far-IR luminosities and star formation rates for the non-multiple sources in our sample and conclude that, in the absence of strong lensing, our 500-risers are very luminous systems with LFIR > 1013 L⊙ and star formation rates >1000 M⊙ yr−1.

A search for the lenses in the Herschel Bright Sources (HerBS) sample

ABSTRACT Verifying that sub-mm galaxies are gravitationally lensed requires time-expensive observations with oversubscribed high-resolution observatories. Here, we aim to strengthen the evidence of gravitational lensing within the Herschel Bright Sources (HerBS) by cross-comparing their positions to optical (SDSS) and near-infrared (VIKING) surveys, in order to search for the foreground lensing galaxy candidates. Resolved observations of the brightest HerBS sources have already shown that most are lensed, and a galaxy evolution model predicts that ∼76 per cent of the total HerBS sources are lensed, although with the SDSS survey we are only able to identify the likely foreground lenses for 25 per cent of the sources. With the near-infrared VIKING survey, however, we are able to identify the likely foreground lenses for 57 per cent of the sources, and we estimate that 82 per cent of the HerBS sources have lenses on the VIKING images even if we cannot identify the lens in every case. We find that the angular offsets between lens and Herschel source are larger than that expected if the lensing is done by individual galaxies. We also find that the fraction of HerBS sources that are lensed falls with decreasing 500-micron flux density, which is expected from the galaxy evolution model. Finally, we apply our statistical VIKING cross-identification to the entire Herschel-ATLAS catalogue, where we also find that the number of lensed sources falls with decreasing 500-micron flux density.

Multifrequency filter search for high redshift sources and lensing systems in Herschel-ATLAS

We present a new catalog of high-redshift candidate Herschel sources. Our sample is obtained after applying a multifrequency filtering method (“matched multifilter”), which is designed to improve the signal-to-noise ratio of faint extragalactic point sources. The method is tested against already-detected sources from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) and used to search for new high-redshift candidates. The multifilter technique also produces an estimation of the photometric redshift of the sources. When compared with a sample of sources with known spectroscopic redshift, the photometric redshift returned from the multifilter is unbiased in the redshift range 0.8 < z < 4.3. Using simulated data we reproduced the same unbiased result in roughly the same redshift range and determined the error (and bias above z ≈ 4) in the photometric redshifts. Based on the multifilter technique, and a selection based on color, flux, and agreement of fit between the observed photometry and assumed SED, we find 370 robust candidates to be relatively bright high-redshift sources. A second sample with 237 objects focuses on the faint end at high-redshift. These 237 sources were previously near the H-ATLAS detection limit but are now confirmed with our technique as high significance detections. Finally, we look for possible lensed Herschel sources by cross-correlating the first sample of 370 objects with two different catalogs of known low-redshift objects, the redMaPPer Galaxy Cluster Catalog and a catalog of galaxies with spectroscopic redshift from the Sloan Digital Sky Survey Data Release 14. Our search renders a number of candidates to be lensed systems from the SDSS cross-correlation but none from the redMaPPeR confirming the more likely galactic nature of the lenses.

Spitzer Planck Herschel Infrared Cluster (SPHerIC) survey: Candidate galaxy clusters at 1.3 < z < 3 selected by high star-formation rate

There is a lack of large samples of spectroscopically confirmed clusters and protoclusters at high redshifts, z > 1.5. Discovering and characterizing distant (proto-)clusters is important for yielding insights into the formation of large-scale structure and on the physical processes responsible for regulating star-formation in galaxies in dense environments. The Spitzer Planck Herschel Infrared Cluster (SPHerIC) survey was initiated to identify these characteristically faint and dust-reddened sources during the epoch of their early assembly. We present Spitzer/IRAC observations of 82 galaxy (proto-)cluster candidates at 1.3 < zp < 3.0 that were vetted in a two step process: (1) using Planck to select by color those sources with the highest star-formation rates, and (2) using Herschel at higher resolution to separate out the individual red sources. The addition of the Spitzer data enables efficient detection of the central and massive brightest red cluster galaxies (BRCGs). We find that BRCGs are associated with highly significant, extended and crowded regions of IRAC sources which are more overdense than the field. This result corroborates our hypothesis that BRCGs within the Planck–Herschel sources trace some of the densest and actively star-forming proto-clusters in the early Universe. On the basis of a richness-mass proxy relation, we obtain an estimate of their mean masses which suggests our sample consists of some of the most massive clusters at z ≈ 2 and are the likely progenitors of the most massive clusters observed today.

Cosmic happenstance: 24-µm selected, multicomponent Herschel sources are line-of-sight projections

In this paper, we investigate the physical associations between blended far-infrared (FIR)-emitting galaxies, in order to identify the level of line-of-sight projection contamination in the single-dish Herschel data. Building on previous work, and as part of the Herschel Extragalactic Legacy Project (HELP), we identify a sample of galaxies in the COSMOS field which are found to be both FIR-bright (typically $\sim 15$ mJy) and blended within the Herschel 250 $\mu$m beam. We identify a spectroscopic or photometric redshift for each FIR-bright source. We conduct a joint probability distribution analysis on the redshift probability density functions to determine the fraction of the FIR sources with multiple FIR-bright counterparts which are likely to be found at consistent ($\Delta z$ $< 0.01$) redshifts. We find that only 3 (0.4 per cent) of the pair permutations between counterparts are $>50$ per cent likely to be at consistent redshifts. A majority of counterparts (72 per cent) have no overlap in their redshift probability distributions whatsoever. This is in good agreement with the results of recent simulations, which indicate that single-dish observations of the FIR sky should be strongly contaminated by line of sight projection effects. We conclude that for our sample of 3.6- and 24-$\mu$m selected, FIR-bright objects in the COSMOS field, the overwhelming majority of multi-component FIR systems are line of sight projections within the 18.1 arcsec Herschel beam, rather than physical associations.

Properties of the SCUBA-2 850 μm Sources in the Akari NEP-Deep Field

Author(s): Seo, H; Jeong, WS; Kim, M; Kim, SJ; Ko, J; Pyo, J; Kim, MG; Pearson, C; Barrufet, L; Varillas, MDCC; Matsuhara, H; Malkan, M; Kim, HK; Takagi, T; Miyaji, T; Tello, JD; Goto, T; Oi, N | Abstract: We carry out a study of Sub-Millimeter Galaxies (SMGs) in the AKARI NEP-Deep field using the James Clerk Maxwell Telescope (JCMT) SCUBA-2 850 µm source catalog, released as part of the SCUBA-2 Cosmology Legacy Survey (S2CLS) program. The SCUBA-2 850 µm map has a root mean square (rms) noise of 1.2 mJy beam−1 and covers an area of 0.60 degree2. We find four SMGs which have counterparts to Herschel sources with spectroscopic redshifts in the literature. In addition, three dust obscured galaxies (DOGs) detected in Herschel bands are selected as a comparison sample. We derive IR luminosities of SMGs using the CIGALE code, which are similar to those of high redshift SMGs from previous studies. The contribution of AGN to the total IR luminosity in SMGs (2%–11%) is smaller than the lower limit for the one in DOGs (19%–35%), which is consistent with the expectation from the evolutionary scenario of massive galaxies. We search for SMGs in overdense regions as protocluster candidates and investigate four regions, including candidates around three DOGs. Finally, we argue that follow-up spectroscopic observation for the NEP-Deep field will provide crucial information to understand the role of SMGs in the evolution of massive galaxies.

Red, redder, reddest: SCUBA-2 imaging of colour-selected Herschel sources

High-redshift, luminous, dusty star forming galaxies (DSFGs) constrain the extremity of galaxy formation theories. The most extreme are discovered through follow-up on candidates in large area surveys. Here we present 850 $\mu$m SCUBA-2 follow-up observations of 188 red DSFG candidates from the \textit{Herschel} Multi-tiered Extragalactic Survey (HerMES) Large Mode Survey, covering 274 deg$^2$. We detected 87 per cent with a signal-to-noise ratio $>$ 3 at 850~$\mu$m. We introduce a new method for incorporating the confusion noise in our spectral energy distribution fitting by sampling correlated flux density fluctuations from a confusion limited map. The new 850~$\mu$m data provide a better constraint on the photometric redshifts of the candidates, with photometric redshift errors decreasing from $\sigma_z/(1+z)\approx0.21$ to $0.15$. Comparison spectroscopic redshifts also found little bias ($\langle (z-z_{\rm spec})/(1+z_{\rm spec})\rangle = 0.08 $). The mean photometric redshift is found to be 3.6 with a dispersion of $0.4$ and we identify 21 DSFGs with a high probability of lying at $z > 4$. After simulating our selection effects we find number counts are consistent with phenomenological galaxy evolution models. There is a statistically significant excess of WISE-1 and SDSS sources near our red galaxies, giving a strong indication that lensing may explain some of the apparently extreme objects. Nevertheless, our sample should include examples of galaxies with the highest star formation rates in the Universe ($\gg10^3$ M$_\odot$yr$^{-1}$).

The impact of clustering and angular resolution on far-infrared and millimeter continuum observations

Follow-up observations at high-angular resolution of bright submillimeter galaxies selected from deep extragalactic surveys have shown that the single-dish sources are comprised of a blend of several galaxies. Consequently, number counts derived from low- and high-angular-resolution observations are in tension. This demonstrates the importance of resolution effects at these wavelengths and the need for realistic simulations to explore them. We built a new 2 deg2 simulation of the extragalactic sky from the far-infrared to the submillimeter. It is based on an updated version of the 2SFM (two star-formation modes) galaxy evolution model. Using global galaxy properties generated by this model, we used an abundance-matching technique to populate a dark-matter lightcone and thus simulate the clustering. We produced maps from this simulation and extracted the sources, and we show that the limited angular resolution of single-dish instruments has a strong impact on (sub)millimeter continuum observations. Taking into account these resolution effects, we are reproducing a large set of observables, as number counts and their evolution with redshift and cosmic infrared background power spectra. Our simulation consistently describes the number counts from single-dish telescopes and interferometers. In particular, at 350 and 500 μm, we find that the number counts measured by Herschel between 5 and 50 mJy are biased towards high values by a factor ~2, and that the redshift distributions are biased towards low redshifts. We also show that the clustering has an important impact on the Herschel pixel histogram used to derive number counts from P(D) analysis. We find that the brightest galaxy in the beam of a 500 μm Herschel source contributes on average to only ~60% of the Herschel flux density, but that this number will rise to ~95% for future millimeter surveys on 30 m-class telescopes (e.g., NIKA2 at IRAM). Finally, we show that the large number density of red Herschel sources found in observations but not in models might be an observational artifact caused by the combination of noise, resolution effects, and the steepness of color- and flux density distributions. Our simulation, called Simulated Infrared Dusty Extragalactic Sky (SIDES), is publicly available.

Far-infrared observations of a massive cluster forming in the Monoceros R2 filament hub⋆.

We present far-infrared observations of Monoceros R2 (a giant molecular cloud at approximately 830 pc distance, containing several sites of active star formation), as observed at 70 μm, 160 μm, 250 μm, 350 μm, and 500 μm by the Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging Receiver (SPIRE) instruments on the Herschel Space Observatory as part of the Herschel imaging survey of OB young stellar objects (HOBYS) Key programme. The Herschel data are complemented by SCUBA-2 data in the submillimetre range, and WISE and Spitzer data in the mid-infrared. In addition, C18O data from the IRAM 30-m Telescope are presented, and used for kinematic information. Sources were extracted from the maps with getsources, and from the fluxes measured, spectral energy distributions were constructed, allowing measurements of source mass and dust temperature. Of 177 Herschel sources robustly detected in the region (a detection with high signal-to-noise and low axis ratio at multiple wavelengths), including protostars and starless cores, 29 are found in a filamentary hub at the centre of the region (a little over 1% of the observed area). These objects are on average smaller, more massive, and more luminous than those in the surrounding regions (which together suggest that they are at a later stage of evolution), a result that cannot be explained entirely by selection effects. These results suggest a picture in which the hub may have begun star formation at a point significantly earlier than the outer regions, possibly forming as a result of feedback from earlier star formation. Furthermore, the hub may be sustaining its star formation by accreting material from the surrounding filaments.

The Herschel Bright Sources (HerBS): sample definition and SCUBA-2 observations

We present the Herschel Bright Sources (HerBS) sample, a sample of bright, high-redshift Herschel sources detected in the 616.4 square degree H-ATLAS survey. The HerBS sample contains 209 galaxies, selected with a 500 {\mu}m flux density greater than 80 mJy and an estimated redshift greater than 2. The sample consists of a combination of HyLIRGs and lensed ULIRGs during the epoch of peak cosmic star formation. In this paper, we present SCUBA-2 observations at 850 ${\mu}$m of 189 galaxies of the HerBS sample, 152 of these sources were detected. We fit a spectral template to the Herschel-SPIRE and 850 ${\mu}$m SCUBA-2 flux densities of 22 sources with spectroscopically determined redshifts, using a two-component modified blackbody spectrum as a template. We find a cold- and hot-dust temperature of 21.29 K and 45.80 K, a cold-to-hot dust mass ratio of 26.62 and a $\beta$ of 1.83. The poor quality of the fit suggests that the sample of galaxies is too diverse to be explained by our simple model. Comparison of our sample to a galaxy evolution model indicates that the fraction of lenses is high. Out of the 152 SCUBA-2 detected galaxies, the model predicts 128.4 $\pm$ 2.1 of those galaxies to be lensed (84.5%). The SPIRE 500 ${\mu}$m flux suggests that out of all 209 HerBS sources, we expect 158.1 $\pm$ 1.7 lensed sources, giving a total lensing fraction of 76 per cent.