According to the current understanding of cosmic structure formation, the precursors of the most massive structures in the Universe began to form shortly after the Big Bang, in regions corresponding ...to the largest fluctuations in the cosmic density field. Observing these structures during their period of active growth and assembly-the first few hundred million years of the Universe-is challenging because it requires surveys that are sensitive enough to detect the distant galaxies that act as signposts for these structures and wide enough to capture the rarest objects. As a result, very few such objects have been detected so far. Here we report observations of a far-infrared-luminous object at redshift 6.900 (less than 800 million years after the Big Bang) that was discovered in a wide-field survey. High-resolution imaging shows it to be a pair of extremely massive star-forming galaxies. The larger is forming stars at a rate of 2,900 solar masses per year, contains 270 billion solar masses of gas and 2.5 billion solar masses of dust, and is more massive than any other known object at a redshift of more than 6. Its rapid star formation is probably triggered by its companion galaxy at a projected separation of 8 kiloparsecs. This merging companion hosts 35 billion solar masses of stars and has a star-formation rate of 540 solar masses per year, but has an order of magnitude less gas and dust than its neighbour and physical conditions akin to those observed in lower-metallicity galaxies in the nearby Universe. These objects suggest the presence of a dark-matter halo with a mass of more than 100 billion solar masses, making it among the rarest dark-matter haloes that should exist in the Universe at this epoch.
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.
Galaxies grow inefficiently, with only a small percentage of the available gas converted into stars each free-fall time. Feedback processes, such as outflowing winds driven by radiation pressure, ...supernovae, or supermassive black hole accretion, can act to halt star formation if they heat or expel the gas supply. We report a molecular outflow launched from a dust-rich star-forming galaxy at redshift 5.3, 1 billion years after the Big Bang. The outflow reaches velocities up to 800 kilometers per second relative to the galaxy, is resolved into multiple clumps, and carries mass at a rate within a factor of 2 of the star formation rate. Our results show that molecular outflows can remove a large fraction of the gas available for star formation from galaxies at high redshift.
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 . 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 (2-1), and subsequently was confirmed by detections of CO(3-2) with the Australia Telescope Compact Array and 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 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 . Its large mass and intense star formation is very rare for a source well into the epoch of reionization.
Using the Australia Telescope Compact Array, we conducted a survey of CO J = 1 − 0 and J = 2 − 1 line emission towards strongly lensed high-redshift dusty star-forming galaxies (DSFGs) previously ...discovered with the South Pole Telescope (SPT). Our sample comprises 17 sources that had CO-based spectroscopic redshifts obtained with the Atacama Large Millimeter/submillimeter Array and the Atacama Pathfinder Experiment. We detect all sources with known redshifts in either CO J = 1 − 0 or J = 2 − 1. 12 sources are detected in the 7-mm continuum. The derived CO luminosities imply gas masses in the range (0.5–11) × 1010 M⊙ and gas depletion time-scales t
dep < 200 Myr, using a CO to gas mass conversion factor αCO = 0.8 M⊙ (K km s−1 pc2)−1. Combining the CO luminosities and dust masses, along with a fixed gas-to-dust ratio, we derive αCO factors in the range 0.4–1.8 M⊙ (K km s−1 pc2)−1, similar to what is found in other starbursting systems. We find small scatter in αCO values within the sample, even though inherent variations in the spatial distribution of dust and gas in individual cases could bias the dust-based αCO estimates. We find that lensing magnification factors based on the CO linewidth to luminosity relation (μCO) are highly unreliable, but particularly when μ < 5. Finally, comparison of the gas and dynamical masses suggest that the average molecular gas fraction stays relatively constant at z = 2–5 in the SPT DSFG sample.
Massive 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 Bang.
We present C ii observations of 20 strongly lensed dusty star-forming galaxies at 2.1 < z < 5.7 using Atacama Pathfinder EXperiment and Herschel. The sources were selected on their 1.4 mm flux (S
1.4 ...mm > 20 mJy) from the South Pole Telescope (SPT) survey, with far-infrared (FIR) luminosities determined from extensive photometric data. The C ii line is robustly detected in 17 sources, all but one being spectrally resolved. 11 out of 20 sources observed in C ii also have low-J CO detections from Australia Telescope Compact Array. A comparison with mid- and high-J CO lines from Atacama Large Millimeter/submillimeter Array reveals consistent C ii and CO velocity profiles, suggesting that there is little differential lensing between these species. The C ii, low-J CO and FIR data allow us to constrain the properties of the interstellar medium. We find C ii 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 C ii and CO emitting gas with a higher C ii than CO excitation temperature, high CO optical depth τCO(1–0) ≫ 1, and low to moderate C ii optical depth
$\tau _{{\rm C\,\small {II}}}$
≲ 1. The geometric structure of photodissociation regions allows for such conditions.
Abstract
We present Atacama Large Millimeter Array C i(1 − 0) (rest frequency 492 GHz) observations for a sample of 13 strongly lensed dusty star-forming galaxies (DSFGs) originally discovered at ...1.4 mm in a blank-field survey by the South Pole Telescope (SPT). We compare these new data with available C i observations from the literature, allowing a study of the interstellar medium (ISM) properties of ∼30 extreme DSFGs spanning a redshift range 2 < z < 5. Using the C i line as a tracer of the molecular ISM, we find a mean molecular gas mass for SPT-DSFGs of 6.6 × 1010 M⊙. This is in tension with gas masses derived via low-J
12CO and dust masses; bringing the estimates into accordance requires either (a) an elevated CO-to-H2 conversion factor for our sample of αCO ∼ 2.5 and a gas-to-dust ratio ∼200, or (b) an high carbon abundance
$X_{\rm C\,\small {I}} \sim 7\times 10^{-5}$
. Using observations of a range of additional atomic and molecular lines (including C i, C iiand multiple transitions of CO), we use a modern photodissociation region code (3d-pdr) to assess the physical conditions (including the density, UV radiation field strength and gas temperature) within the ISM of the DSFGs in our sample. We find that the ISM within our DSFGs is characterized by dense gas permeated by strong UV fields. We note that previous efforts to characterize photodissociation region regions in DSFGs may have significantly under-estimated the density of the ISM. Combined, our analysis suggests that the ISM of extreme dusty starbursts at high redshift consists of dense, carbon-rich gas not directly comparable to the ISM of starbursts in the local Universe.
Stellar archaeology shows that massive elliptical galaxies formed rapidly about ten billion years ago with star-formation rates of above several hundred solar masses per year. Their progenitors are ...probably the submillimetre bright galaxies at redshifts z greater than 2. Although the mean molecular gas mass (5 × 10(10) solar masses) of the submillimetre bright galaxies can explain the formation of typical elliptical galaxies, it is inadequate to form elliptical galaxies that already have stellar masses above 2 × 10(11) solar masses at z ≈ 2. Here we report multi-wavelength high-resolution observations of a rare merger of two massive submillimetre bright galaxies at z = 2.3. The system is seen to be forming stars at a rate of 2,000 solar masses per year. The star-formation efficiency is an order of magnitude greater than that of normal galaxies, so the gas reservoir will be exhausted and star formation will be quenched in only around 200 million years. At a projected separation of 19 kiloparsecs, the two massive starbursts are about to merge and form a passive elliptical galaxy with a stellar mass of about 4 × 10(11) solar masses. We conclude that gas-rich major galaxy mergers with intense star formation can form the most massive elliptical galaxies by z ≈ 1.5.
Pink-beam serial crystallography Meents, A; Wiedorn, M O; Srajer, V ...
Nature communications,
11/2017, Letnik:
8, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Serial X-ray crystallography allows macromolecular structure determination at both X-ray free electron lasers (XFELs) and, more recently, synchrotron sources. The time resolution for serial ...synchrotron crystallography experiments has been limited to millisecond timescales with monochromatic beams. The polychromatic, "pink", beam provides a more than two orders of magnitude increased photon flux and hence allows accessing much shorter timescales in diffraction experiments at synchrotron sources. Here we report the structure determination of two different protein samples by merging pink-beam diffraction patterns from many crystals, each collected with a single 100 ps X-ray pulse exposure per crystal using a setup optimized for very low scattering background. In contrast to experiments with monochromatic radiation, data from only 50 crystals were required to obtain complete datasets. The high quality of the diffraction data highlights the potential of this method for studying irreversible reactions at sub-microsecond timescales using high-brightness X-ray facilities.
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