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We present the molecular gas content and interstellar medium conditions of MACS J0717_Az9, a strong gravitationally lensed z = 4.273, M * ≃ 2 × 109 M ⊙ star-forming galaxy with an unusually high (∼80%) obscured star formation fraction. We detect CO (4–3) in two independent lensed images, as well as [N ii ] 205 μ m, with the Atacama Large Millimeter Array. We derive a molecular gas mass of log 10 [ M H 2 (M ⊙) ] = 9.77 , making it moderately deficient in molecular gas compared to the lower-redshift gas fraction scaling relation. Leveraging photodissociation region (PDR) models, we combine our CO (4–3) measurements with existing measurements of the [C ii ] 158 μ m line and total infrared luminosity to model the PDR conditions. We find PDR conditions similar to those in local star-forming galaxies, with a mean hydrogen density log10[ n H cm−3] = 4.80 ± 0.39 and a mean radiation field strength log10[ G 0 Habing] = 2.83 ± 0.26. Based on Band 3 continuum data, we derive an upper limit on the intrinsic dust mass of log10[ M dust(M ⊙)] < 7.73, consistent with existing estimates. We use the 3D tilted-ring model fitting code 3D-Barolo to determine the kinematic properties of the CO (4–3) emitting gas. We find that it is rotationally dominated, with a V / σ = 4.6 ± 1.7, consistent with the kinematics of the [C ii ]. With PDR conditions remarkably similar to those in normal dusty star-forming galaxies at z < 0.2 and a stable molecular disk, our observations of Az9 suggest that the dust-obscured phase for a low-mass galaxy at z ∼ 4 is relatively long. Thus, Az9 may be representative of a more widespread population that has been missed owing to insufficiently deep existing millimeter surveys. [ABSTRACT FROM AUTHOR]

As the progenitors of present-day galaxy clusters, protoclusters are excellent laboratories to study galaxy evolution. Since existing observations of protoclusters are limited to the detected constituent galaxies at UV and/or infrared wavelengths, the details of how typical galaxies grow in these young, pre-virialized structures remain uncertain. We measure the total stellar mass and star formation within protoclusters, including the contribution from faint undetected members by performing a stacking analysis of 211 z = 2–4 protoclusters selected as Planck cold sources. We stack Wide-field Infrared Survey Explorer and Herschel/SPIRE images to measure the angular size and the spectral energy distribution of the integrated light from the protoclusters. The fluxes of protoclusters selected as Planck cold sources can be contaminated by line-of-sight interlopers. Using the WebSky simulation, we estimate that a single protocluster contributes 33% ± 15% of the flux of a Planck cold source on average. After this correction, we obtain a total star formation rate of 7.3 ± 3.2 × 103 M ⊙yr−1 and a total stellar mass of 4.9 ± 2.2 × 1012 M ⊙. Our results indicate that protoclusters have, on average, 2× more star formation and 4× more stellar mass than the total contribution from individually detected galaxies in spectroscopically confirmed protoclusters. This suggests that much of the total flux within z = 2–4 protoclusters comes from galaxies with luminosities lower than the detection limit of SPIRE (L IR < 3 × 1012 L ⊙). Lastly, we find that protoclusters subtend a half-light radius of 2.′8 (4.2–5.8 cMpc), which is consistent with simulations. [ABSTRACT FROM AUTHOR]

Massive galaxy clusters undergo strong evolution from z ∼ 1.6 to z ∼ 0.5, with overdense environments at high- z characterized by abundant dust-obscured star formation and stellar mass growth which rapidly give way to widespread quenching. Data spanning the near- to far-infrared (IR) can directly trace this transformation; however, such studies have largely been limited to the massive galaxy end of cluster populations. In this work, we present 'total light' stacking techniques spanning |$3.4\!-\!500\, \mu$| m aimed at revealing the total cluster emission, including low-mass members and potential intracluster dust. We detail our procedures for  WISE, Spitzer , and  Herschel imaging, including corrections to recover the total stacked emission in the case of high fractions of detected galaxies. We apply our techniques to 232 well-studied log |$\, M_{200}/\mathrm{M}_{\odot }\sim 13.8$| clusters in multiple redshift bins, recovering extended cluster emission at all wavelengths. We measure the averaged IR radial profiles and spectral energy distributions (SEDs), quantifying the total stellar and dust content. The near-IR profiles are well described by an NFW model with a high (c ∼ 7) concentration. Dust emission is similarly concentrated, albeit suppressed at  |$r\lesssim 0.3\,$| Mpc. The measured SEDs lack warm dust, consistent with the colder SEDs of low-mass galaxies. We derive total stellar masses consistent with the theoretical M halo− M ⋆ relation and specific star formation rates that evolve strongly with redshift, echoing that of log |$\, M_{\star }/\mathrm{M}_{\odot }\gtrsim 10$| cluster galaxies. Separating out the massive population reveals the majority of cluster far-IR emission (⁠|$\sim 70\!-\!80{{\ \rm per\ cent}}$|⁠) is provided by the low-mass constituents, which differs from field galaxies. This effect may be a combination of mass-dependent quenching and excess dust in low-mass cluster galaxies. [ABSTRACT FROM AUTHOR]

We present a new submm/mm galaxy counterpart identification technique which builds on the use of Spitzer Infrared Array Camera (IRAC) colours as discriminators between likely counterparts and the general IRAC galaxy population. Using 102 radio- and Submillimeter Array-confirmed counterparts to AzTEC sources across three fields [Great Observatories Origins Deep Survey-North, -South and Cosmic Evolution Survey (COSMOS)], we develop a non-parametric IRAC colour–colour characteristic density distribution, which, when combined with positional uncertainty information via likelihood ratios, allows us to rank all potential IRAC counterparts around submillimetre galaxies (SMGs) and calculate the significance of each ranking via the reliability factor. We report all robust and tentative radio counterparts to SMGs, the first such list available for AzTEC/COSMOS, as well as the highest ranked IRAC counterparts for all AzTEC SMGs in these fields as determined by our technique. We demonstrate that the technique is free of radio bias and thus applicable regardless of radio detections. For observations made with a moderate beam size (∼18 arcsec), this technique identifies ∼85 per cent of SMG counterparts. For much larger beam sizes (≳30 arcsec), we report identification rates of 33–49 per cent. Using simulations, we demonstrate that this technique is an improvement over using positional information alone for observations with facilities such as AzTEC on the Large Millimeter Telescope and Submillimeter Common User Bolometer Array 2 on the James Clerk Maxwell Telescope. [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 an analysis of the X-ray properties of 35 sub-mm galaxies (SMGs) in the Chandra Deep Field-North region. Using a sample of robust galaxies, with sub-arcsecond positions from Spitzer and/or radio counterparts, we find 16 objects ( per cent) with significant X-ray detections in the 2 Ms Chandra data. Six of these SMGs ( per cent) have measured X-ray luminosities or upper limits consistent with those expected based on the far-infrared or radio-derived star formation rate, and hence with the X-rays coming solely from star-forming processes. Extrapolating observed X-ray/star formation rate relations to the luminosity of the SMGs, we find that the X-ray-derived star formation rates are typically in the range of . In another seven sources ( per cent of the SMGs) a dominant active galactic nuclei (AGN) contribution to the X-ray emission is required, while in three more it is unclear whether the stellar process or accretion is responsible for the X-rays. Stacking of the X-ray-undetected SMGs reveals a highly significant (7σ) detection. Under the assumption that the stacked X-ray is due to star formation, this gives an average X-ray-derived star formation rate of around . We deduce that the AGN fraction in SMGs based on X-ray observations is per cent, which is towards the lower limit of previous estimates. Spectral analysis shows that in general, the SMGs are not heavily obscured in the X-ray but most of the SMGs classified as AGN show absorption with column densities in excess of . Of the secure AGN, the bolometric luminosity appears to be dominated by the AGN in only three cases. In around 85 per cent of the SMGs, the X-ray spectrum effectively rules out an AGN contribution that dominates the bolometric emission, even if the AGN is Compton thick. The evidence therefore suggests that intense star formation accounts for both the far-infrared and X-ray emission in most SMGs. We argue that, rather than having an especially high AGN fraction or duty cycle, SMGs have a high X-ray detection rate at very faint fluxes partly because of their high star formation rates and, in rarer cases, because the sub-mm emission is from an AGN. [ABSTRACT FROM AUTHOR]

We present results from a multiwavelength study of 29 sources (false detection probabilities <5 per cent) from a survey of the Great Observatories Origins Deep Survey-North (GOODS-N) field at 1.1 mm using the Astronomical Thermal Emission Camera (AzTEC). Comparing with existing 850 μm Submillimetre Common-User Bolometer Array (SCUBA) studies in the field, we examine differences in the source populations selected at the two wavelengths. The AzTEC observations uniformly cover the entire survey field to a 1σ depth of ∼1 mJy. Searching deep 1.4 GHz Very Large Array (VLA) and Spitzer 3–24 μm catalogues, we identify robust counterparts for 21 1.1 mm sources, and tentative associations for the remaining objects. The redshift distribution of AzTEC sources is inferred from available spectroscopic and photometric redshifts. We find a median redshift of , somewhat higher than for selected sources in the same field, and our lowest redshift identification lies at a spectroscopic redshift . We measure the 850 μm to 1.1 mm colour of our sources and do not find evidence for ‘850 μm dropouts’, which can be explained by the low signal-to-noise ratio of the observations. We also combine these observed colours with spectroscopic redshifts to derive the range of dust temperatures T, and dust emissivity indices β for the sample, concluding that existing estimates and are consistent with these new data. [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 explore the epoch dependence of number density and star formation rate for submillimetre galaxies (SMGs) found at 850 μm. The study uses a sample of 38 SMG in the Great Observatories Origins Deep Survey (GOODS)-N field, for which cross-waveband identifications have been obtained for 35/38 members together with redshift measurements or estimates. A maximum-likelihood analysis is employed, along with the ‘single-source-survey’ technique. We find a diminution in both space-density and star formation rate at z > 3, closely mimicking the redshift cut-offs found for quasi-stellar objects (QSOs) selected in different wavebands. The diminution in redshift is particularly marked at a significance level too small to measure. The data further suggest, at a significance level of about 0.001, that two separately evolving populations may be present, with distinct luminosity functions. These results parallel the different evolutionary behaviours of Luminous Infrared Galaxies and Ultra-Luminous Infrared Galaxies, and represent another manifestation of ‘cosmic down-sizing’, suggesting that differential evolution extends to the most extreme star-forming galaxies. [ABSTRACT FROM AUTHOR]

Bright submillimetre (sub-mm) galaxies are expected to arise in massive highly biased haloes, and hence exhibit strong clustering. We argue that a valuable tool for measuring these clustering properties is the cross-correlation of sub-mm galaxies with faint optically selected sources. We analyse populations of sub-mm detected and optical galaxies in the Great Observatories Origins Deep Survey-North (GOODS-N) survey area. Using optical/infrared photometric-redshift information, we search for correlations induced by two separate effects: (i) cosmic magnification of background sub-mm sources by foreground dark matter haloes traced by optical galaxies at lower redshifts and (ii) galaxy clustering due to sub-mm and optical sources tracing the same population of haloes where their redshift distributions overlap. Regarding cosmic magnification, we find no detectable correlation. Our null result is consistent with a theoretical model for the cosmic magnification, and we show that a dramatic increase in the number of sub-mm sources will be required to measure the effect reliably. Regarding clustering, we find evidence at the 3.5σ level for a cross-correlation between sub-mm and optical galaxies analysed in identical photometric redshift slices. The data hint that the sub-mm sources have an enhanced bias parameter compared to the optically selected population (with a significance of 2σ). The next generation of deep sub-mm surveys can potentially perform an accurate measurement of each of these cross-correlations, adding a new set of diagnostics for understanding the development of massive structure in the Universe. [ABSTRACT FROM AUTHOR]

We present radio, optical and X-ray-detected counterparts to the submillimetre sources found using SCUBA in theHubble Deep FieldNorth region (GOODS-N). A new counterpart identification statistic is developed to identify properties of galaxies detected at other wavelengths that can be used to aid counterpart identification. We discriminate between criteria that can use used to pre-select submillimetre bright objects, and those that identify the counterpart to a known submillimetre object. Optically faint galaxies detected in the deepest 1.4-GHz radio continuum maps are the only effective way of pre-selecting SCUBA galaxies, and radio sources are the best way to identify counterparts to known submillimetre detections. Looking at radio spectral indices, only the steeper sources (indicative of star formation) are detected in the submillimetre range. Although we find several X-ray identifications, we show that deepChandraimages do not contribute to counterpart identifications, as in all cases they are already detected in the more easily obtained VLA radio maps. We also find no evidence for clustering betweenChandraand SCUBA sources in this field. For a known SCUBA position, the reddest source tends to be the correct association, although we can find no cut on colour, magnitude or clustering property that efficiently pre-selects for SCUBA sources. 15-μmISOsources are statistically detected by SCUBA, but the limiting mid-infrared flux is not low enough to provide useful constraints. We present postage stamp strips for each SCUBA detection in separate bands from X-ray to radio bands, providing direct visual evidence that approximately half of the submillimetre sources in this field remain unidentified, despite an abundance of deep multiwavelength data. [ABSTRACT FROM AUTHOR]

Dusty galaxies at z ∼ 2 span a wide range of relative brightness between rest-frame mid-infrared (8 μm) and ultraviolet wavelengths. We attempt to determine the physical mechanism responsible for this diversity. Dust-obscured galaxies (DOGs), which have rest-frame mid-IR to UV flux density ratios ≳ 1000, might be abnormally bright in the mid-IR, perhaps due to prominent emission from active galactic nuclei and/or polycyclic aromatic hydrocarbons, or abnormally faint in the UV. We use far-infrared data from the GOODS-Herschel survey to show that most DOGs with 1012L☼ ≲ LIR ≲ 1013L☼ are not abnormally bright in the mid-IR when compared to other dusty galaxies with similar IR (8-1000 μm) luminosities. We observe a relation between the median IR to UV luminosity ratios and the median UV continuum power-law indices for these galaxies, and we find that only 24% have specific star formation rates that indicate the dominance of compact star-forming regions. This circumstantial evidence supports the idea that the UV- and IR-emitting regions in these galaxies are spatially coincident, which implies a connection between the abnormal UV faintness of DOGs and dust obscuration. We conclude that the range in rest-frame mid-IR to UV flux density ratios spanned by dusty galaxies at z ∼ 2 is due to differing amounts of UV obscuration. Of galaxies with these IR luminosities, DOGs are the most obscured. We attribute differences in UV obscuration to either (1) differences in the degree of alignment between the spatial distributions of dust and massive stars or (2) differences in the total dust content. [ABSTRACT FROM AUTHOR]

Using a sample of BzK-selected galaxies at z ∼ 2 identified from the CFHT/WIRCAM near-infrared survey of GOODS-North, we discuss the relation between star formation rate (SFR), specific star formation rate (SSFR), and stellar mass (M*), and the clustering of galaxies as a function of these parameters. For star-forming galaxies (sBzKs), the UV-based SFR, corrected for extinction, scales with the stellar mass as SFR∝Mα* with α = 0.74 ± 0.20 down to M* ∼ 109M☼, indicating a weak dependence on the stellar mass of the SFR efficiency, namely, SSFR. We also measure the angular correlation function and hence infer the correlation length for sBzK galaxies as a function of M*, SFR, and SSFR, as well as K-band apparent magnitude. We show that passive galaxies (pBzKs) are more strongly clustered than sBzK galaxies at a given stellar mass, mirroring the color-density relation seen at lower redshifts. We also find that the correlation length of sBzK galaxies ranges from 4 to 20 h–1 Mpc, being a strong function of MK, M*, and SFR. On the other hand, the clustering dependence on SSFR changes abruptly at 2 × 10–9 yr–1, which is the typical value for “main-sequence” star-forming galaxies at z ∼ 2. We show that the correlation length reaches a minimum at this characteristic value, and is larger for galaxies with both smaller and larger SSFRs; a dichotomy that is only marginally implied from the predictions of the semi-analytical models. Our results suggest that there are two types of environmental effects at work at z ∼ 2. Stronger clustering for relatively quiescent galaxies implies that the environment has started to play a role in quenching star formation. At the same time, stronger clustering for galaxies with elevated SSFRs (“starbursts”) might be attributed to an increased efficiency for galaxy interactions and mergers in dense environments. [ABSTRACT FROM AUTHOR]