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

We present Herschel SPIRE-FTS observations of Arp 220, a nearby ultraluminous infrared galaxy. The FTS provides continuous spectral coverage from 1 The SPIRE beam shapes are not gaussian; the effective beam solid angle can be found in the Herschel Observer's manual.

Massive galaxy clusters have been found that date to times as early as three billion years after the Big Bang, containing stars that formed at even earlier epochs. The high-redshift progenitors of these galaxy clusters-termed 'protoclusters'-can be identified in cosmological simulations that have the highest overdensities (greater-than-average densities) of dark matter. Protoclusters are expected to contain extremely massive galaxies that can be observed as luminous starbursts . However, recent detections of possible protoclusters hosting such starbursts do not support the kind of rapid cluster-core formation expected from simulations : the structures observed contain only a handful of starbursting galaxies spread throughout a broad region, with poor evidence for eventual collapse into a protocluster. Here we report observations of carbon monoxide and ionized carbon emission from the source SPT2349-56. We find that this source consists of at least 14 gas-rich galaxies, all lying at redshifts of 4.31. We demonstrate that each of these galaxies is forming stars between 50 and 1,000 times more quickly than our own Milky Way, and that all are located within a projected region that is only around 130 kiloparsecs in diameter. This galaxy surface density is more than ten times the average blank-field value (integrated over all redshifts), and more than 1,000 times the average field volume density. The velocity dispersion (approximately 410 kilometres per second) of these galaxies and the enormous gas and star-formation densities suggest that this system represents the core of a cluster of galaxies that was already at an advanced stage of formation when the Universe was only 1.4 billion years old. A comparison with other known protoclusters at high redshifts shows that SPT2349-56 could be building one of the most massive structures in the Universe today.

We use the Atacama Large Millimeter/submillimeter Array (ALMA) in Cycle 1 to determine spectroscopic redshifts of high-redshift dusty star-forming galaxies (DSFGs) selected by their 1.4 mm continuum emission in the South Pole Telescope (SPT) survey. We present ALMA 3 mm spectral scans between 84-114 GHz for 15 galaxies and targeted ALMA 1 mm observations for an additional eight sources. Our observations yield 30 new line detections from CO, [C I], [N II], H 2 O and NH 3 . We further present APEX [C II] and CO mid-J observations for seven sources for which only a single line was detected in spectral-scan data from ALMA Cycle 0 or Cycle 1. We combine the new observations with previously published and new mm/submm line and photometric data of the SPT-selected DSFGs to study their redshift distribution. The combined data yield 39 spectroscopic redshifts from molecular lines, a success rate of >85%. Our sample represents the largest data set of its kind today and has the highest spectroscopic completeness among all redshift surveys of high-z DSFGs. The median of the redshift distribution is z=3.9 ± 0.4, and the highest-redshift source in our sample is at z=5.8. We discuss how the selection of our sources affects the redshift distribution, focusing on source brightness, selection wavelength, and strong gravitational lensing. We correct for the effect of gravitational lensing and find the redshift distribution for 1.4 mm-selected sources with a median redshift of z=3.1 ± 0.3. Comparing to redshift distributions selected at shorter wavelengths from the literature, we show that selection wavelength affects the shape of the redshift distribution.

We present [CII] observations of 20 strongly lensed dusty star forming galaxies at 2.1 < z < 5.7 using APEX and Herschel. The sources were selected on their 1.4 mm flux (S 1.4 mm > 20 mJy) from the South Pole Telescope survey, with far-infrared (FIR) luminosities determined from extensive photometric data. The [CII] line is robustly detected in 17 sources, all but one being spectrally resolved. Eleven out of 20 sources observed in [CII] also have low-J CO detections from ATCA. A comparison with midand high-J CO lines from ALMA reveals consistent [CII] and CO velocity profiles, suggesting that there is little differential lensing between these species. The [CII], low-J CO and FIR data allow us to constrain the properties of the interstellar medium. We find [CII] to CO(1-0) luminosity ratios in the SPT sample of 5200 ± 1800, with significantly less scatter than in other samples. This line ratio can be best described by a medium of [CII] and CO emitting gas with a higher [CII] than CO excitation temperature, high CO optical depth τ CO (1-0) 1, and low to moderate [CII] optical depth τ [CII] 1. The geometric structure of photodissociation regions allows for such conditions.

The atomic CII fine-structure line is one of the brightest lines in a typical star-forming galaxy spectrum with a luminosity ∼ 0.1% to 1% of the bolometric luminosity. It is potentially a reliable tracer of the dense gas distribution at high redshifts and could provide an additional probe to the era of reionization. By taking into account of the spontaneous, stimulated and collisional emission of the CII line, we calculate the spin temperature and the mean intensity as a function of the redshift. When averaged over a cosmologically large volume, we find that the CII emission from ionized carbon in individual galaxies is larger than the signal generated by carbon in the intergalactic medium (IGM). Assuming that the CII luminosity is proportional to the carbon mass in dark matter halos, we also compute the power spectrum of the CII line intensity at various redshifts. In order to avoid the contamination from CO rotational lines at low redshift when targeting a CII survey at high redshifts, we propose the cross-correlation of CII and 21-cm line emission from high redshifts. To explore the detectability of the CII signal from reionization, we also evaluate the expected errors on the CII power spectrum and CII-21 cm cross power spectrum based on the design of the future milimeter surveys. We note that the CII-21 cm cross power spectrum contains interesting features that captures physics during reionization, including the ionized bubble sizes and the mean ionization fraction, which are challenging to measure from 21-cm data alone. We propose an instrumental concept for the reionization CII experiment targeting the frequency range of ∼ 200 to 300 GHz with 1, 3 and 10 meter apertures and a bolometric spectrometer array with 64 independent spectral pixels with about 20,000 bolometers. Subject headings: cosmology: theory -diffuse radiation -intergalactic medium -large scale structure of universe

We report observations of the CO J = 7 → 6 transition toward the starburst nucleus of NGC 253. This is the highest-excitation CO measurement in this source to date, and allows an estimate of the molecular gas excitation conditions. Comparison of the CO line intensities with a large velocity gradient, escape probability model indicates that the bulk of the 2-5×10 7 M ⊙ of molecular gas in the central 180 pc is highly excited. A model with T ∼ 120 K, n H 2 ∼ 4.5 × 10 4 cm −3 is consistent with the observed CO intensities as well as the rotational H 2 lines observed with ISO.The inferred mass of warm, dense molecular gas is 10-30 times the atomic gas mass as traced through its [C II] and [O I] line emission. This large mass ratio is inconsistent with photodissociation region models where the gas is heated by far-UV starlight. It is also not likely that the gas is heated by shocks in outflows or cloud-cloud collisions. We conclude that the best mechanism for heating the gas is cosmic rays, which provide a natural means of uniformly heating the full volume of molecular clouds. With the tremendous supernova rate in the nucleus of NGC 253, the CR heating rate is at least ∼ 800 times greater than in the Galaxy, more than sufficient to match the cooling observed in the CO lines.

We report the discovery and constrain the physical conditions of the interstellar medium of the highest-redshift millimeter-selected dusty star-forming galaxy to date, SPT-S J031132−5823.4 (hereafter SPT0311−58), at z 6.900 0.002 =  . SPT0311−58 was discovered via its 1.4 mm thermal dust continuum emission in the South Pole Telescope (SPT)-SZ survey. The spectroscopic redshift was determined through an Atacama Large Millimeter/submillimeter Array 3 mm frequency scan that detected CO(6-5), CO(7-6), and C I [ ](2-1), and subsequently was confirmed by detections of CO(3-2) with the Australia Telescope Compact Array and C II [ ]with APEX. We constrain the properties of the ISM in SPT0311−58 with a radiative transfer analysis of the dust continuum photometry and the CO and C I [ ] line emission. This allows us to determine the gas content without ad hoc assumptions about gas mass scaling factors. SPT0311−58 is extremely massive, with an intrinsic gas mass of M M 3.3 1.9 10 gas 11 = ´. Its large mass and intense star formation is very rare for a source well into the epoch of reionization.