LOFAR, the LOw-Frequency ARray, is a new-generation radio interferometer constructed in the north of the Netherlands and across europe. Utilizing a novel phased-array design, LOFAR covers the largely unexplored low-frequency range from 10-240 MHz and provides a number of unique observing capabilities. Spreading out from a core located near the village of Exloo in the northeast of the Netherlands, a total of 40 LOFAR stations are nearing completion. A further five stations have been deployed throughout Germany, and one station has been built in each of France, Sweden, and the UK. Digital beam-forming techniques make the LOFAR system agile and allow for rapid repointing of the telescope as well as the potential for multiple simultaneous observations. With its dense core array and long interferometric baselines, LOFAR achieves unparalleled sensitivity and angular resolution in the low-frequency radio regime. The LOFAR facilities are jointly operated by the International LOFAR Telescope (ILT) foundation, as an observatory open to the global astronomical community. LOFAR is one of the first radio observatories to feature automated processing pipelines to deliver fully calibrated science products to its user community. LOFAR's new capabilities, techniques and modus operandi make it an important pathfinder for the Square Kilometre Array (SKA). We give an overview of the LOFAR instrument, its major hardware and software components, and the core science objectives that have driven its design. In addition, we present a selection of new results from the commissioning phase of this new radio observatory.

Spitzer Space Telescope and Herschel Space Observatory imaging of M31 is used, with a physical dust model, to construct maps of dust surface density, dust-to-gas ratio, starlight heating intensity, and polycyclic aromatic hydrocarbon (PAH) abundance, out to R ≈ 25 kpc. The global dust mass is M d = 5.4 × 10 7 M , the global dust/H mass ratio is M d /M H = 0.0081, and the global PAH abundance is q PAH = 0.039. The dust surface density has an inner ring at R = 5.6 kpc, a maximum at R = 11.2 kpc, and an outer ring at R ≈ 15.1 kpc. The dust/gas ratio varies from M d /M H ≈ 0.026 at the center to ∼0.0027 at R ≈ 25 kpc. From the dust/gas ratio, we estimate the interstellar mediu (ISM) metallicity to vary by a factor ∼10, from Z/Z ≈ 3 at R = 0 to ∼ 0.3 at R = 25 kpc. The dust heating rate parameter U peaks at the center, with U ≈ 35, declining to U ≈ 0.25 at R = 20 kpc. Within the central kiloparsec, the starlight heating intensity inferred from the dust modeling is close to what is estimated from the stars in the bulge. The PAH abundance reaches a peak q PAH ≈ 0.045 at R ≈ 11.2 kpc. When allowance is made for the different spectrum of the bulge stars, q PAH for the dust in the central kiloparsec is similar to the overall value of q PAH in the disk. The silicate-graphite-PAH dust model used here is generally able to reproduce the observed dust spectral energy distribution across M31, but overpredicts 500µm emission at R ≈ 2-6 kpc, suggesting that at R = 2-6 kpc, the dust opacity varies more steeply with frequency (with β ≈ 2.3 between 200 and 600µm) than in the model. Subtraction of foreground and background emission has been carried out following methods described in Aniano et al. (2012), with automatic identification of background pixels and fitting of a "tilted plane" background model (with three parameters -zero point, tilt, and tilt orientation) for 3 IRAC images in bands 1-4 were multiplied by extended source calibration factors 0.91, 0.94, 0.66, 0.74 (Reach et al. 2005). 4 MIPS images were generated by the Mips enhancer v3.10 pipeline on 2007 Jul 3. 5 The PACS and SPIRE images were processed by HIPE v9, and the Level 1 HIPE images were then processed by Scanamorphos v18.0 (Roussel 2013). We used the calibration files in HIPE v9 (version 42 for PACS, and version 10.0 for SPIRE). Intensities in the SPIRE bands were obtained by dividing the HIPE v9 flux density per beam by effective beam solid angles Ω = (1.103, 1.944, 4.183) × 10 −8 sr for SPIRE250, 350, and 500, as recommended by Griffin et al. (2013).

No abstract

A variety of global kinetic models are reviewed, including first-order, nth-order, nucleation, and sequential models as well as models having Gaussian, Weibull, and discrete activation-energy distributions. The important characteristics of these various models are outlined, with guidance in how to select the correct model. Some of the models have similar characteristics, and the parameter relationships among similar models are discussed. The comparison includes the relationship between conversion-dependent parameters determined by modified Friedman and Coats−Redfern isoconversion methods and reactivity distribution parameters determined by nonlinear regression of rate or fraction-reacted profiles. A new method for deriving discrete activation-energy distribution parameters having ln(A) = a + bE is also presented. Data accuracy requirements are discussed briefly. Kinetic analyses are given for a variety of materials, including synthetic polymers (polyethylene, polystyrene, polydimethylenenaphthalene, polysulfone, and polyvinyl acetate), petroleum sources rocks (including well-preserved algal kerogens and the Bakken and Monterey shales), oil shales (including kukersite), and the Illinois and Pittsburgh Premium coal samples.

We have undertaken a deep, wide-field H I imaging survey of M31, reaching a maximum resolution of about 50 pc and 2 km s −1 across a 95×48 kpc region. The H I mass and brightness sensitivity at 100 pc resolution for a 25 km s −1 wide spectral feature is 1500 M ⊙ and 0.28 K. Our study reveals ubiquitous H I self-opacity features, discernible in the first instance as filamentary local minima in images of the peak H I brightness temperature. Local minima are organized into complexes of more than kpc length and are particularly associated with the leading edge of spiral arm features. Just as in the Galaxy, there is only patchy correspondence of self-opaque features with CO(1-0) emission. We have produced images of the best-fit physical parameters; spin temperature, opacity-corrected column density and non-thermal velocity dispersion, for the brightest spectral feature along each line-of-sight in the M31 disk. Spectroscopically opaque atomic gas is organized into filamentary complexes and isolated clouds down to 100 pc. Localized opacity corrections to the column density exceed an order of magnitude in many cases and add globally to a 30% increase in the atomic gas mass over that inferred from the integrated brightness under the usual assumption of negligible self-opacity. Opaque atomic gas first increases from 20 to 60 K in spin temperature with radius to 12 kpc but then declines again to 20 K beyond 25 kpc. We have extended the resolved star formation law down to physical scales more than an order of magnitude smaller in area and mass than has been possible previously. The relation between total-gas-mass-and star-formation-rate-density is significantly tighter than that with molecularmass and is fully consistent in both slope and normalization with the power law index of 1.56 found in the molecule-dominated disk of M51 at 500 pc resolution. Below a gas-mass-density of about 5 M ⊙ pc −2 , there is a down-turn in star-formation-rate-density which may represent a real local threshold for massive star formation at a cloud mass of about 5·10 4 M ⊙ .

A sample of large northern Spitzer Infrared Nearby Galaxies Survey (SINGS) galaxies has recently been observed with the Westerbork Synthesis Radio Telescope (WSRT). We present observations of the linearly polarized radio continuum emission in this WSRT-SINGS galaxy sample. Of the 28 galaxies treated in this paper, 21 are detected in polarized radio continuum at 18-and 22-cm wavelengths. We utilize the rotation measure synthesis (RM-Synthesis) method, as implemented by Brentjens & de Bruyn (2005, A&A, 441, 1217, to coherently detect polarized emission from a large fractional bandwidth, while simultaneously assessing the degree of Faraday rotation experienced by the radiation along each line-of-sight. This represents the first time that the polarized emission and its Faraday rotation have been systematically probed down to ∼10 μJy beam −1 RMs for a large sample of galaxies. Non-zero Faraday rotation is found to be ubiquitous in all of the target fields, from both the Galactic foreground and the target galaxies themselves. In this paper, we present an overview of the polarized emission detected in each of the WSRT-SINGS galaxies. The most prominent trend is a systematic modulation of the polarized intensity with galactic azimuth, such that a global minimum in the polarized intensity is seen toward the kinematically receding major axis. The implied large-scale magnetic field geometry is discussed in a companion paper. A second novel result is the detection of multiple nuclear Faraday depth components that are offset to both positive and negative RM by 100−200 rad m −2 in all targets that host polarized (circum-)nuclear emission.

Green Bank Telescope (GBT) λ21cm observations have revealed a faint, yet extensive H I cloud population surrounding the Andromeda Galaxy (M31). The newfound objects are likely analogs to the high-velocity H I clouds (HVCs) seen around the Milky Way. At least 20 discrete features are detected within 50 kpc of the M31 disk, with radial velocities that are comparable to those of outer disk rotation. In addition, a filamentary "halo" component of at least 30 kpc extent is concentrated at the M31 systemic velocity. Some of the discrete features are organized into elongated systems with velocity continuity, suggestive of tidal streams. The discrete population can be characterized by a steep power-law distribution of number versus H I mass in the range between 10 5 and 10 7 M ⊙ . The velocity line-width of discrete clouds is correlated with the cloud H I mass: such that if the clouds are gravitationally bound this implies a dark-to H I mass ratio of ∼ 100:1. Possible origins for the discrete and "halo" M31 features include: a Local Group "cooling flow", tidal debris from recent mergers or interactions, and the gaseous counterparts of low mass dark-matter halos.

The future of cm and m-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium of 17 countries. The SKA will be 50 times more sensitive than any existing radio facility. A majority of the key science for the SKA will be addressed through large-area imaging of the Universe at frequencies from 300 MHz to a few GHz. The Australian SKA Pathfinder (ASKAP) is aimed squarely in this frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phase-array feed systems on parabolic reflectors. This large field-of-view makes ASKAP an unprecedented synoptic telescope poised J. Wall is the overall editor.