14 January, 2006 - 11:45 AM
Beyond the Baselines: Detecting High-Redshift Molecular Emission with the GBT
Laura Hainline (California Institute of Technology) & Andrew Blain
The Robert C. Byrd Green Bank Telescope has opened to the astronomy community exciting new capabilities for the detection of molecular emission from high-redshift galaxies, offering an off-axis feed arm design for an unblocked aperture, active surface control, a large-bandwidth spectrometer, and receivers covering the radio window from below 1 GHz to nearly 100 GHz. These features, together with the ~100-m filled aperture of the GBT, have promise for minimizing some difficulties of single-dish radio spectroscopy that hamper attempts to observe the emission from low-J molecular rotational transitions from distant galaxies, such as spectral baseline shapes caused by reflections and scattering of light from more traditional feed structures. However, in attempting to use the K- and Ka-band receivers at the GBT we have found that the reality of the telescope's current performance does not yet match these high expectations. The observatory staff continue to smooth out the wrinkles and debug a complex new facility, putting forth considerable effort in shared-risk mode with the community, to find ways to calibrate GBT data on faint sources that produce useful scientific results. In this conference contribution we present the results of our efforts to calibrate and remove spectral baselines from our GBT observations, in which we use the K- and Ka-band receivers to search for CO(1-0) emission in several submillimeter-selected galaxies. With a likely detection of CO(1-0) emission from SMM J13120+4242 at z = 3.4, we show that despite the remaining systematic sources of error, we can still place useful constraints on the properties of interstellar gas in high-redshift systems.