No abstract

In the local Universe, most galaxies are dominated by stars, with less than ten per cent of their visible mass in the form of gas. Determining when most of these stars formed is one of the central issues of observational cosmology. Optical and ultraviolet observations of high-redshift galaxies (particularly those in the Hubble Deep Field) have been interpreted as indicating that the peak of star formation occurred between redshifts of 1 and 1.5. But it is known that star formation takes place in dense clouds, and is often hidden at optical wavelengths because of extinction by dust in the clouds. Here we report a deep submillimetre-wavelength survey of the Hubble Deep Field; these wavelengths trace directly the emission from dust that has been warmed by massive star-formation activity. The combined radiation of the five most significant detections accounts for 30-50 per cent of the previously unresolved background emission in this area. Four of these sources appear to be galaxies in the redshift range 2 < z < 4, which, assuming these objects have properties comparable to local dust-enshrouded starburst galaxies, implies a star-formation rate during that period about a factor of five higher than that inferred from the optical and ultraviolet observations. Recent years have seen the first meaningful attempts to determine the global star-formation history of the Universe, using the combined information provided by deep redshift surveys (for example, the Canada France Redshift Survey 1 ) reaching z Ϸ 1, and the statistics of Lyman-limit galaxies 2 at higher redshifts in, for example, the Hubble Deep Field (HDF) 3-5 . The results 6 imply that the starformation and metal-production rates were about 10 times greater at z Ϸ 1 than in the local Universe, that they peaked at a redshift in the range z Ϸ 1-1:5, and that they declined to values comparable to those observed at the present day at z Ϸ 4.These conclusions, derived from optical-ultraviolet data, may however be misleading, because the absorbing effects of dust within distant galaxies undergoing massive star-formation may have distorted our picture of the evolution of the high-redshift Universe in two ways. First, the star-formation rate (SFR) in known highredshift objects is inevitably underestimated unless some correction for dust obscuration is included in deriving the rest-frame ultraviolet luminosity. Second, it is possible that an entire population of heavily dust-enshrouded high-redshift objects, as expected in some models of elliptical galaxy formation 7 , have gone undetected in the optical-ultraviolet surveys. The extent of the former remains controversial 8-11 , while the possibility of the latter has until now been impossible to investigate. Submillimetre cosmologyAt high redshifts (z Ͼ 1), the strongly-peaked far-infrared radiation emitted by star-formation regions in distant galaxies is redshifted into the submillimetre waveband, and the steep spectral index of this emission on the long-wavelength side of the peak, at l Ϸ 100 m in the rest-frame, result...

We present total and polarized intensity images of 15 active galactic nuclei obtained with the Very Long Baseline Array at 7 mm wavelength at 17 epochs from 1998 March to 2001 April. At some epochs the images are accompanied by nearly simultaneous polarization measurements at 3 mm, 1.35/0.85 mm, and optical wavelengths. Here we analyze the 7 mm images to define the properties of the jets of two radio galaxies, five BL Lac objects, and eight quasars on angular scales 0.1 milliarcseconds. We determine the apparent velocities of 106

The Spectral and Photometric Imaging REceiver (SPIRE), is the Herschel Space Observatory's submillimetre camera and spectrometer. It contains a three-band imaging photometer operating at 250, 350 and 500 μm, and an imaging Fourier-transform spectrometer (FTS) which covers simultaneously its whole operating range of 194-671 μm (447-1550 GHz). The SPIRE detectors are arrays of feedhorn-coupled bolometers cooled to 0.3 K. The photometer has a field of view of 4 × 8 , observed simultaneously in the three spectral bands. Its main operating mode is scan-mapping, whereby the field of view is scanned across the sky to achieve full spatial sampling and to cover large areas if desired. The spectrometer has an approximately circular field of view with a diameter of 2.6 . The spectral resolution can be adjusted between 1.2 and 25 GHz by changing the stroke length of the FTS scan mirror. Its main operating mode involves a fixed telescope pointing with multiple scans of the FTS mirror to acquire spectral data. For extended source measurements, multiple position offsets are implemented by means of an internal beam steering mirror to achieve the desired spatial sampling and by rastering of the telescope pointing to map areas larger than the field of view. The SPIRE instrument consists of a cold focal plane unit located inside the Herschel cryostat and warm electronics units, located on the spacecraft Service Module, for instrument control and data handling. Science data are transmitted to Earth with no on-board data compression, and processed by automatic pipelines to produce calibrated science products. The in-flight performance of the instrument matches or exceeds predictions based on pre-launch testing and modelling: the photometer sensitivity is comparable to or slightly better than estimated pre-launch, and the spectrometer sensitivity is also better by a factor of 1.5-2. Key words. instrumentation: photometers -instrumentation: spectrographs -space vehicles: instruments -submillimeter: generalHerschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Blazars are the most extreme active galactic nuclei. They possess oppositely directed plasma jets emanating at near light speeds from accreting supermassive black holes. According to theoretical models, such jets are propelled by magnetic fields twisted by differential rotation of the black hole's accretion disk or inertial-frame-dragging ergosphere. The flow velocity increases outward along the jet in an acceleration and collimation zone containing a coiled magnetic field. Detailed observations of outbursts of electromagnetic radiation, for which blazars are famous, can potentially probe the zone. It has hitherto not been possible to either specify the location of the outbursts or verify the general picture of jet formation. Here we report sequences of high-resolution radio images and optical polarization measurements of the blazar BL Lacertae. The data reveal a bright feature in the jet that causes a double flare of radiation from optical frequencies to TeV gamma-ray energies, as well as a delayed outburst at radio wavelengths. We conclude that the event starts in a region with a helical magnetic field that we identify with the acceleration and collimation zone predicted by the theories. The feature brightens again when it crosses a standing shock wave corresponding to the bright 'core' seen on the images.

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.

The external region of a cell membrane, known as the glycocalyx, is dominated by glycosylated molecules, which direct specific interactions such as cell-cell recognition and contribute to the steric repulsion that prevents undesirable non-specific adhesion of other molecules and cells. Mimicking the non-adhesive properties of a glycocalyx provides a potential solution to the clinical problems, such as thrombosis, that are associated with implantable devices owing to non-specific adsorption of plasma proteins. Here we describe a biomimetic surface modification of graphite using oligosaccharide surfactant polymers, which, like a glycocalyx, provides a dense and confluent layer of oligosaccharides. The surfactant polymers consist of a flexible poly(vinyl amine) with dextran and alkanoyl side chains. We show that alkanoyl side chains assemble on graphite through hydrophobic interaction and epitaxial adsorption. This constrains the polymer backbone to lie parallel to the substrate, with solvated dextran side chains protruding into the aqueous phase, creating a glycocalyx-like coating. The resulting biomimetic surface is effective in suppressing protein adsorption from human plasma protein solution.

We present the first results of a deep unbiased submillimetre survey carried out at 450 and 850µm. We detected 12 sources at 850 µm, giving a surface density of sources with S 850µm > 2.8 mJy of 0.49 ± 0.16 arcmin −2 . The sources constitute 20-30% of the background radiation at 850µm and thus a significant fraction of the entire background radiation produced by stars. This implies, through the connection between metallicity and background radiation, that a significant fraction of all the stars that have ever been formed were formed in objects like those detected here. The combination of their large contribution to the background radiation and their extreme bolometric luminosities make these objects excellent candidates for being proto-ellipticals. Optical astronomers have recently shown that the UV -luminosity density of the universe increases by a factor of ≃10 between z = 0 and z = 1 − 2 and then decreases again at higher redshifts. Using the results of a parallel submillimetre survey of the local universe, we show that both the submillimetre source density and background can be explained if the submillimetre luminosity density evolves in a similar way to the UV -luminosity density. Thus, if these sources are ellipticals in the process of formation, they may be forming at relatively modest redshifts.