International audienceMassive present-day early-type (elliptical and lenticular) galaxies probably gained the bulk of their stellar mass and heavy elements through intense, dust-enshrouded starbursts--that is, increased rates of star formation--in the most massive dark-matter haloes at early epochs. However, it remains unknown how soon after the Big Bang massive starburst progenitors exist. The measured redshift (z) distribution of dusty, massive starbursts has long been suspected to be biased low in z owing to selection effects, as confirmed by recent findings of systems with redshifts as high as ~5 (refs 2-4). Here we report the identification of a massive starburst galaxy at z = 6.34 through a submillimetre colour-selection technique. We unambiguously determined the redshift from a suite of molecular and atomic fine-structure cooling lines. These measurements reveal a hundred billion solar masses of highly excited, chemically evolved interstellar medium in this galaxy, which constitutes at least 40 per cent of the baryonic mass. A 'maximum starburst' converts the gas into stars at a rate more than 2,000 times that of the Milky Way, a rate among the highest observed at any epoch. Despite the overall downturn in cosmic star formation towards the highest redshifts, it seems that environments mature enough to form the most massive, intense starbursts existed at least as early as 880 million years after the Big Ban

The Herschel Multi‐tiered Extragalactic Survey (HerMES) is a legacy programme designed to map a set of nested fields totalling ∼380 deg2. Fields range in size from 0.01 to ∼20 deg2, using the Herschel‐Spectral and Photometric Imaging Receiver (SPIRE) (at 250, 350 and 500 μm) and the Herschel‐Photodetector Array Camera and Spectrometer (PACS) (at 100 and 160 μm), with an additional wider component of 270 deg2 with SPIRE alone. These bands cover the peak of the redshifted thermal spectral energy distribution from interstellar dust and thus capture the reprocessed optical and ultraviolet radiation from star formation that has been absorbed by dust, and are critical for forming a complete multiwavelength understanding of galaxy formation and evolution. The survey will detect of the order of 100 000 galaxies at 5σ in some of the best‐studied fields in the sky. Additionally, HerMES is closely coordinated with the PACS Evolutionary Probe survey. Making maximum use of the full spectrum of ancillary data, from radio to X‐ray wavelengths, it is designed to facilitate redshift determination, rapidly identify unusual objects and understand the relationships between thermal emission from dust and other processes. Scientific questions HerMES will be used to answer include the total infrared emission of galaxies, the evolution of the luminosity function, the clustering properties of dusty galaxies and the properties of populations of galaxies which lie below the confusion limit through lensing and statistical techniques. This paper defines the survey observations and data products, outlines the primary scientific goals of the HerMES team, and reviews some of the early results.

We present Herschel observations of six fine-structure lines in 25 Ultraluminous Infrared Galaxies at z < 0.27. The lines, [O III]52µm, [N III]57µm, [O I]63µm, [N II]122µm, [O I]145µm, and [C II]158µm, are mostly single gaussians with widths <600 km s −1 and luminosities of 10 7 − 10 9 L ⊙ . There are deficits in the [O I]63/L IR , [N II]/L IR , [O I]145/L IR , and [C II]/L IR ratios compared to lower luminosity systems. The majority of the line deficits are consistent with dustier H II regions, but part of the [C II] deficit may arise from an additional mechanism, plausibly charged dust grains. This is consistent with some of the [C II] originating from PDRs or the ISM. We derive relations between far-IR line luminosities and both IR luminosity and star formation rate. We find that [N II] and both [O I] lines are good tracers of IR luminosity and star formation rate. In contrast, [C II] is a poor tracer of IR luminosity and star formation rate, and does not improve as a tracer of either quantity if the [C II] deficit is accounted for. The continuum luminosity densities also correlate with IR luminosity and star formation rate. We derive ranges for the gas density and ultraviolet radiation intensity of 10 1 < n < 10 2.5 and 10 2.2 < G 0 < 10 3.6 , respectively. These ranges depend on optical type, the importance of star formation, and merger stage. We do not find relationships between far-IR line properties and several other parameters; AGN activity, merger stage, mid-IR excitation, and SMBH mass. We conclude that these far-IR lines arise from gas heated by starlight, and that they are not strongly influenced by AGN activity.

Context. Deep far-infrared (FIR) cosmological surveys are known to be affected by source confusion, causing issues when examining the main sequence (MS) of star forming galaxies. In the past this has typically been partially tackled by the use of stacking. However, stacking only provides the average properties of the objects in the stack. Aims. This work aims to trace the MS over 0.2 ≤ z < 6.0 using the latest de-blended Herschel photometry, which reaches ≈ 10 times deeper than the 5σ confusion limit in SPIRE. This provides more reliable star formation rates (SFRs), especially for the fainter galaxies, and hence a more reliable MS. Methods. We built a pipeline that uses the spectral energy distribution (SED) modelling and fitting tool CIGALE to generate flux density priors in the Herschel SPIRE bands. These priors were then fed into the de-blending tool XID+ to extract flux densities from the SPIRE maps. In the final step, multi-wavelength data were combined with the extracted SPIRE flux densities to constrain SEDs and provide stellar mass (M ) and SFRs. These M and SFRs were then used to populate the SFR-M plane over 0.2 ≤ z < 6.0. Results. No significant evidence of a high-mass turn-over was found; the best fit is thus a simple two-parameter power law of the form log(SFR) = α[log(M ) − 10.5] + β. The normalisation of the power law increases with redshift, rapidly at z 1.8, from 0.58 ± 0.09 at z ≈ 0.37 to 1.31 ± 0.08 at z ≈ 1.8. The slope is also found to increase with redshift, perhaps with an excess around 1.8 ≤ z < 2.9. Conclusions. The increasing slope indicates that galaxies become more self-similar as redshift increases. This implies that the specific SFR of high-mass galaxies increases with redshift, from 0.2 to 6.0, becoming closer to that of low-mass galaxies. The excess in the slope at 1.8 ≤ z < 2.9, if present, coincides with the peak of the cosmic star formation history.

Context. Since the mid-1990s, the sample of Lyman break galaxies (LBGs) has been growing thanks to the increasing sensitivities in the optical and in near-infrared telescopes for objects at z > 2.5. However, the dust properties of the LBGs are poorly known because the samples are small and/or biased against far-infrared or sub-mm observations. Aims. This work explores from a statistical point of view the far-infrared (far-IR) and sub-millimeter (sub-mm) properties of a large sample of LBGs at z ∼ 3 that cannot be individually detected from current far-infrared observations. Methods. We select a sample of 22, 000 LBGs at 2.5 < z < 3.5 in the COSMOS field using the dropout technique. The large number of galaxies included in the sample allows us to split it in several bins as a function of UV luminosity (L FUV ), UV continuum slope (β UV ) and stellar mass (M * ) to better sample their variety. We stack in PACS (100 and 160 µm) images from PACS Evolution Probe survey (PEP), SPIRE (250, 350 and 500µm) images from the Herschel Multi-tied Extragalactic Survey (HerMES) programs and AzTEC (1.1 mm) images from the Atacama Submillimetre Telescope Experiment (ASTE). Our stacking procedure corrects the biases induced by galaxy clustering and incompleteness of our input catalogue in dense regions. Results. We obtain the full infrared spectral energy distributions (SED) of subsamples of LBGs and derive the mean IR luminosity as a function of L FUV , β UV and M * . The average IRX (or dust attenuation) is roughly constant over the L FUV range, with a mean of 7.9 (1.8 mag). However, it is correlated with β UV , A FUV = (3.15 ± 0.12) + (1.47 ± 0.14) β UV , and stellar mass, log (IRX) = (0.84 ± 0.11) log M * /10 10.35 + 1.17 ± 0.05. We investigate using a statistically-controlled stacking analysis as a function of (M * , β UV ) the dispersion of the IRX-β UV and IRX-M * plane. On the one hand, the dust attenuation shows a departure by up to 2.8 mag above the mean IRX-β UV relation, when log(M * [M ]) increases from 9.75 to 11.5 in the same β UV bin. That strongly suggests that M * plays an important role in shaping the IRX-β UV plane. On the other hand, the IRX-M * plane is less dispersed for variation in the β UV . However, the dust attenuation shows a departure by up to 1.3 mag above the mean IRX-M * relation, when β UV increases from -1.7 to 0.5 in the same M * bin. The low stellar mass LBGs (log(M * [M ]) < 10.5) and red β UV (β UV > −0.7), 15% of the total sample, present a large dust attenuation than the mean IRX-M * , but they still are in agreement with the mean IRX-β UV relation. We suggest that we have to combine both, IRX-β UV and IRX-M * , relations to obtain the best estimation of the dust attenuation from the UV and NIR properties of the galaxies (L FUV , β UV , M * ). Our results enable us to study the average relation between star-formation rate (SFR) and stellar mass, and we show that our LBG sample lies on the main sequence of star formation at z ∼ 3. we demonstrate that the SFR is underestimate for LBGs with hig...