Molecular Tracers of Embedded Star Formation in Ophiuchus

In this paper we analyze nine SCUBA cores in Ophiuchus using the second-lowest rotational transitions of four molecular species (12CO, 13CO, C18O, and C17O) to search for clues to the evolutionary state and star-formation activity within each core. Specifically, we look for evidence of outflows, infall, and CO depletion. The line wings in the CO spectra are used to detect outflows, spectral asymmetries in 13CO are used to determine infall characteristics, and a comparison of the dust emission (from SCUBA observations) and gas emission (from C18O) is used to determine the fractional CO freeze-out. Through comparison with Spitzer observations of protostellar sources in Ophiuchus, we discuss the usefulness of CO and its isotopologues as the sole indicators of the evolutionary state of each core. This study is an important pilot project for the JCMT Legacy Survey of the Gould Belt (GBS) and the Galactic Plane (JPS), which intend to complement the SCUBA-2 dust continuum observations with HARP observations of 12CO, 13CO, C18O, and C17O J = 3 - 2 in order to determine whether or not the cold dust clumps detected by SCUBA-2 are protostellar or starless objects. Our classification of the evolutionary state of the cores (based on molecular line maps and SCUBA observations) is in agreement with the Spitzer designation for six or seven of the nine SCUBA cores. However, several important caveats exist in the interpretation of these results, many of which large mapping surveys like the GBS may be able to overcome to provide a clearer picture of activity in crowded fields.Comment: 43 pages including 19 postscript figures. Accepted for publication in the PAS

Modeling the electromagnetic properties of the SCUBA-2 detectors

SCUBA-2 is the next-generation replacement for SCUBA (Sub-millimetre Common User Bolometer Array) on the James Clerk Maxwell Telescope. Operating at 450 and 850 microns, SCUBA-2 fills the focal plane of the telescope with fully-sampled, monolithic bolometer arrays. Each SCUBA-2 pixel uses a quarter-wave slab of silicon with an implanted resistive layer and backshort as an absorber and a superconducting transition edge sensor as a thermometer. In order to verify and optimize the pixel design, we have investigated the electromagnetic behaviour of the detectors, using both a simple transmission-line model and Ansoft HFSS, a finite-element electromagnetic simulator. We used the transmission line model to fit transmission measurements of doped wafers and determined the correct implant dose for the absorbing layer. The more detailed HFSS modelling yielded some unexpected results which led us to modify the pixel design. We also verified that the detectors suffered little loss of sensitivity for off-axis angles up to about 30 degrees.Comment: 13 pages, 14 figures, SPIE Glasgow 21-25 June 2004, Conference 549

SCUBA - A submillimetre camera operating on the James Clerk Maxwell Telescope

The Submillimetre Common-User Bolometer Array (SCUBA) is one of a new generation of cameras designed to operate in the submillimetre waveband. The instrument has a wide wavelength range covering all the atmospheric transmission windows between 300 and 2000 microns. In the heart of the instrument are two arrays of bolometers optimised for the short (350/450 microns) and long (750/850 microns) wavelength ends of the submillimetre spectrum. The two arrays can be used simultaneously, giving a unique dual-wavelength capability, and have a 2.3 arc-minute field of view on the sky. Background-limited performance is achieved by cooling the arrays to below 100 mK. SCUBA has now been in active service for over a year, and has already made substantial breakthroughs in many areas of astronomy. In this paper we present an overview of the performance of SCUBA during the commissioning phase on the James Clerk Maxwell Telescope (JCMT).Comment: 14 pages, 13 figures (1 JPEG), Proc SPIE vol 335

Precise Identifications of Submillimeter Galaxies: Measuring the History of Massive Star-Forming Galaxies to z>5

We carried out extremely sensitive Submillimeter Array (SMA) 340 GHz (860 micron) continuum imaging of a complete sample of SCUBA 850 micron sources (>4 sigma) with fluxes >3 mJy in the GOODS-N. Using these data and new SCUBA-2 data, we do not detect 4 of the 16 SCUBA sources, and we rule out the original SCUBA fluxes at the 4 sigma level. Three more resolve into multiple fainter SMA galaxies, suggesting that our understanding of the most luminous high-redshift dusty galaxies may not be as reliable as we thought. 10 of the 16 independent SMA sources have spectroscopic redshifts (optical/infrared or CO) to z=5.18. Using a new, ultradeep 20 cm image obtained with the Karl G. Jansky Very Large Array (rms of 2.5 microJy), we find that all 16 of the SMA sources are detected at >5 sigma. Using Herschel far-infrared (FIR) data, we show that the five isolated SMA sources with Herschel detections are well described by an Arp 220 spectral energy distribution template in the FIR. They also closely obey the local FIR-radio correlation, a result that does not suffer from a radio bias. We compute the contribution from the 16 SMA sources to the universal star formation rate (SFR) per comoving volume. With individual SFRs in the range 700-5000 solar masses per year, they contribute ~30% of the extinction-corrected ultraviolet-selected SFR density from z=1 to at least z=5. Star formation histories determined from extinction-corrected ultraviolet populations and from submillimeter galaxy populations only partially overlap, due to the extreme ultraviolet faintness of some submillimeter galaxies.Comment: 26 pages, minor changes to match published versio