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Submillimeter Array Advisory Committee Report

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Submillimeter Array Advisory Committee Report October 12, 2007 1 Introduction The Submillimeter Array (SMA) Advisory Committee met at the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA, on September 4 and 5, 2007. Committee members P. Cox, R. Crutcher, E. van Dishoeck, B. Draine, A. Harris (Chair), K. Menten, and T. Phillips were present; R. Genzel was unable to attend. Presentations informed the Committee of progress in scientific, technical, and operational areas in addition to an extensive discussion of the SMA’s future plans. 2 Overview The Committee was very pleased to see that the SMA has hit its scientific stride and is producing a substantial amount of high-quality scientific results. Results at 350 GHz are impressive and unmatched by any other observatory. Star and planet formation is a visible area, with the polarization work in star forming regions and SgrA* unique and especially noteworthy. Observations within the Solar System are impressive. The strength of high-z work in combination with Spitzer is exciting and quite unexpected. The SMA’s impact, measured by publications (one per week this year) and presence in the field, is high. As part of its success and increase in visibility, the SMA’s user base is expanding modestly, a clear sign of relevance to communities inside and outside of the SMA’s parent institutions. It was clear that there is a strong and mutually beneficial partnership between CfA and ASIAA. The operations model of splitting work between Hawaii, Cambridge, and Taipei is a success. Presentations showed that operations in Hawaii have been maintained despite the loss of key personnel, although the present arrangement is unsustainable in the long run. Instrumental development has slowed as personnel have left or taken other positions. Staffing is the Committee’s main concern for the SMA’s continued health. There are a variety of options for the future of the SMA. In a practical sense they will be viable only if funding is available, and to some degree that depends on exciting science results in the near term. It also depends on a positive view by the community, developed both from publication, where large data sets carry high impact, and by observing with the SMA. The scientific productivity of the SMA is good and improving, but would be significantly enhanced by interaction with other members of the SAO and particularly theorists. This may naturally occur as papers are published and talks given. The SMA can certainly have a place in the ALMA era if it can exploit its flexibility to compensate for its relatively small collecting area. The Committee endorses the plans to form a task force immediately that will investigate science cases for different possible future courses. Whatever the future path, maintaining strong and vigorous scientific and technical staffs will be key to future plans.2A brief summary of the Committee’s main recommendations is: • Continue to focus strongly on o Observations in the 350 GHz atmospheric window o Polarimetry in the 350 and 650 GHz windows o Studying small samples of sources in a coherent program rather than dissecting individual targets one-by-one o Phase correction using stratospheric ozone as a beacon for tropospheric water vapor absorption o Sensitivity and ease-of-use improvements • Foster collaborative projects o Within the CfA; the connection with Spitzer is an outstanding example, and collaborations with ASIAA theorists would be valuable o With Herschel and SOFIA science teams o With scientists and engineers at CARMA, IRAM, and other observatories o With high-frequency mixer fabricators • Move quickly on three key staff hires • Continue eSMA work at moderate priority, and VLBI at low priority. • Form a task force to thoroughly explore the cases that will carry the SMA into the ALMA era. 3 Science highlights 3.1 Star and Planet Formation Unraveling the physical and chemical processes during star and planet formation has been one of the main science drivers of the SMA from its conception. The high densities and column densities make star-forming clouds a natural target for submillimeter line and dust continuum observations, providing distinct diagnostics from those available at other millimeter arrays. Indeed, as shown by the strongly increasing publication rate and presentations at conferences world-wide, the SMA is starting to have a significant impact on the field. Highlights in the area of low-mass star formation include the first direct imaging of the hourglass shape magnetic field geometry in protostars (see below); characterizing disks and envelopes in the earliest embedded stages when the star is still being assembled; quantitative studies of protoplanetary disk sizes, temperature, density, and kinematic structures; exciting images of gaps and holes in the newly discovered population of transitional disks; and resolving knotty jets in outflow sources showing increasing evidence for episodic accretion, precession and bending. In the area of high-mass star formation, impressive subarcsec continuum images reveal Trapezium-like clusters in formation whereas the kinematics of a wide variety of molecular lines stimulate a lively debate in the community whether or not high-mass stars have disks and outflows and whether they form by similar processes as their low-mass counterparts.3In both low- and high-mass star-formation, the most successful projects have involved close interactions with theorists and modelers. The committee strongly encourages SMA observers to strengthen these interactions. Star formation was an area where the power of studying small samples of sources in coherent programs, rather than dissecting individual targets one-by-one, was especially evident. 3.2 Polarimetry The SMA has made unique and outstanding contributions in polarimetry of star forming regions and of the Galactic center. Especially noteworthy are the clear evidence for an hourglass morphology magnetic field in NGC1333 IRAS4A and an estimate of the field strength. Results for IRAS16293 are equally impressive, while studies of other star forming sources are less advanced, due at least partly to limited sensitivity. These results add significant new evidence in the investigation of the role of magnetic fields in the star formation process. The polarization studies of Sgr A* have yielded unexpected and astonishing results: intraday


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