Frossie Economou

Scuba-2: The 10 000 pixel bolometer camera on the james clerk maxwell telescope

SCUBA-2 is an innovative 10000 pixel bolometer camera operating at submillimetre wavelengths on the James Clerk Maxwell Telescope (JCMT). The camera has the capability to carry out wide-field surveys to unprecedented depths, addressing key questions relating to the origins of galaxies, stars and planets. With two imaging arrays working simultaneously in the atmospheric windows at 450 and 850µm, the vast increase in pixel count means that SCUBA-2 maps the sky 100–150 times faster than the previous SCUBA instrument. In this paper we present an overview of the instrument, discuss the physical characteristics of the superconducting detector arrays, outline the observing modes and data acquisition, and present the early performance figures on the telescope. We also showcase the capabilities of the instrument via some early examples of the science SCUBA-2 has already undertaken. In February 2012, SCUBA-2 began a series of unique legacy surveys for the JCMT community. These surveys will take 2.5years and the results are already providing complementary data to the shorter wavelength, shallower, larger-area surveys from Herschel. The SCUBA-2 surveys will also provide a wealth of information for further study with new facilities such as ALMA, and future telescopes such as CCAT and SPICA.

Measurement of the star formation rate from Halpha in field galaxies at z=1

We report the results of J-band infrared spectroscopy of a sample of 13 z=1 field galaxies drawn from the Canada-France Redshift Survey, targeting galaxies whose redshifts place the rest frame H-alpha line emission from HII regions in between the bright night sky OH lines. As a result we detect emission down to a flux limit of ~10^{-16} ergs cm^{-2} s^{-1} corresponding to a luminosity limit of ~10^{41} ergs at this redshift for a H_0=50 km s^{-1} Mpc,^{-1} q_0=0.5 cosmology. From these luminosities we derive estimates of the star-formation rates in these galaxies which are independent of previous estimates based upon their rest-frame ultraviolet (2800A) luminosity. The mean star-formation rate at z=1, from this sample, is found to be at least three times as high as the ultraviolet estimates. The standard dust extinction in these galaxies is inferred to be A_V=0.5-1.0 mags, comparable to local field galaxies, suggesting that the bulk of star-formation is not heavily obscured unless one uses greyer extinction laws. Star-forming galaxies have the bluest colours and a preponderance of disturbed/interacting morphologies. We also investigate the effects of particular star-formation histories, in particular the role of bursts vs continuous star-formation in changing the detailed distribution of UV to H-alpha emission. Generally we find that models dominated by short, overlapping, bursts at typically 0.2 Gyr intervals provide a better model for the data than a constant rate of star-formation. The star-formation history of the Universe from Balmer lines is compiled and found to be typically 2--3\times higher than that inferred from the UV {\em at all redshifts}. It can not yet be clearly established whether the star-formation rate falls off or remains constant at high-redshift.

SCUBA-2: iterative map-making with the Sub-Millimetre User Reduction Facility

The Submillimetre Common User Bolometer Array 2 (SCUBA-2) is an instrument operating on the 15-m James Clerk Maxwell Telescope, nominally consisting of 5120 bolometers in each of two simultaneous imaging bands centred over 450 and 850 um. The camera is operated by scanning across the sky and recording data at a rate of 200 Hz. As the largest of a new generation of multiplexed kilopixel bolometer cameras operating in the (sub)millimetre, SCUBA-2 data analysis represents a significant challenge. We describe the production of maps using the Sub-Millimetre User Reduction Facility (SMURF) in which we have adopted a fast, iterative approach to map-making that enables data reduction on single, modern, high-end desktop computers, with execution times that are typically shorter than the observing times. SMURF is used in an automated setting, both at the telescope for real-time feedback to observers, as well as for the production of science products for the JCMT Science Archive at the Canadian Astronomy Data Centre. Three detailed case studies are used to: (i) explore convergence properties of the map-maker using simple prior constraints (Uranus -- a point source); (ii) achieve the white-noise limit for faint point-source studies (extragalactic blank-field survey of the Lockman Hole); and (iii) demonstrate that our strategy is capable of recovering angular scales comparable to the size of the array footprint (approximately 5 arcmin) for bright extended sources (star-forming region M17).

Towards the automated reduction and calibration of SCUBA data from the James Clerk Maxwell Telescope

The Submillimetre Common User Bolometer Array (SCUBA) instrument has been operating on the James Clerk Maxwell Telescope (JCMT) since 1997. The data archive is now sufficiently large that it can be used to investigate instrumental properties and the variability of astronomical sources. This paper describes the automated calibration and reduction scheme used to process the archive data with particular emphasis on ‘jiggle-map’ observations of compact sources. We demonstrate the validity of our automated approach at both 850- and 450-µm and apply it to several of the JCMT secondary flux calibrators. We determine light curves for the variable sources IRC+10216 and OH 231.8. This automation is made possible by using the ORAC-DR data reduction pipeline, a flexible and extensible data reduction pipeline that is used on UKIRT and the JCMT.

Is there a disc in the superluminal quasars

We look for the expected signature of an accretion disc by examining the properties of the Hα emission line versus viewing angle in a sample of 22 superluminal (SL) quasars. The Doppler factor δ, jet velocity γ and viewing angle θ towards the jet are derived from published radio and X-ray data. Most of the Hα spectra (14) have been observed at the United Kingdom Infrared Telescope (UKIRT) and are reported here. About a quarter of the SL objects have weak or absent Hα emission lines, with small equivalent widths (EW). These have high optical polarization, radio core dominance and Doppler factor, and most of them have high apparent SL velocity and low viewing angles. Therefore these weak-EW objects almost certainly have relativistically beamed optical continua. The strong-EW objects also show a clear beaming effect, but a much weaker one, with line EW varying by only a factor of 3 while radio core dominance varies by a factor of several hundred. The correlation of EW with θ is quantitatively in good agreement with the prediction of a flat accretion disc with limb darkening. The weakand strong-EW sources also show an anticorrelation of line velocity width with the various beaming indicators. Again, the correlation with the derived viewing angle θ shows a quantitative agreement with the effect expected for an axisymmetric structure with velocity dominated by rotation. The line emission cannot come from the surface of the disc, or the line beaming would cancel the continuum beaming. However, it could come from an axisymmetric system of clouds corotating with the accretion disc.

Learning from 25 years of the extensible N-Dimensional Data Format ☆

The extensible N-Dimensional Data Format (NDF) was designed and developed in the late 1980s to provide a data model suitable for use in a variety of astronomy data processing applications supported by the UK Starlink Project. Starlink applications were used extensively, primarily in the UK astronomical community, and form the basis of a number of advanced data reduction pipelines today. This paper provides an overview of the historical drivers for the development of NDF and the lessons learned from using a defined hierarchical data model for many years in data reduction software, data pipelines and in data acquisition systems.

Learning from FITS: Limitations in use in modern astronomical research

The Flexible Image Transport System (FITS) standard has been a great boon to astronomy, allowing observatories, scientists and the public to exchange astronomical information easily. The FITS standard, however, is showing its age. Developed in the late 1970s, the FITS authors made a number of implementation choices that, while common at the time, are now seen to limit its utility with modern data. The authors of the FITS standard could not anticipate the challenges which we are facing today in astronomical computing. Difficulties we now face include, but are not limited to, addressing the need to handle an expanded range of specialized data product types (data models), being more conducive to the networked exchange and storage of data, handling very large datasets, and capturing significantly more complex metadata and data relationships. There are members of the community today who find some or all of these limitations unworkable, and have decided to move ahead with storing data in other formats. If this fragmentation continues, we risk abandoning the advantages of broad interoperability, and ready archivability, that the FITS format provides for astronomy. In this paper we detail some selected important problems which exist within the FITS standard today. These problems may provide insight into deeper underlying issues which reside in the format and we provide a discussion of some lessons learned. It is not our intention here to prescribe specific remedies to these issues; rather, it is to call attention of the FITS and greater astronomical computing communities to these problems in the hope that it will spur action to address them.

ORAC-DR: A generic data reduction pipeline infrastructure

Abstract ORAC-DR is a general purpose data reduction pipeline system designed to be instrument and observatory agnostic. The pipeline works with instruments as varied as infrared integral field units, imaging arrays and spectrographs, and sub-millimeter heterodyne arrays and continuum cameras. This paper describes the architecture of the pipeline system and the implementation of the core infrastructure. We finish by discussing the lessons learned since the initial deployment of the pipeline system in the late 1990s.

Observatory/data centre partnerships and the VO-centric archive: The JCMT Science Archive experience

We present, as a case study, a description of the partnership between an observatory (JCMT) and a data centre (CADC) that led to the development of the JCMT Science Archive (JSA). The JSA is a successful example of a service designed to use Virtual Observatory (VO) technologies from the start. We describe the motivation, process and lessons learned from this approach.

ORAC: a modern observing system for UKIRT

The steady improvement in telescope performance at UKIRT and the increase in data acquisition rates led to a strong desired for an integrated observing framework that would meet the needs of future instrumentation, as well as providing some support for existing instrumentation. Thus the Observatory Reduction and Acquisition Control (ORAC) project was created in 1997 with the goals of improving the scientific productivity in the telescope, reducing the overall ongoing support requirements, and eventually supporting the use of more flexibly scheduled observing. The project was also expected to achieve this within a tight resource allocation. In October 1999 the ORAC system was commissioned at the United Kingdom Infrared Telescope.