NAASC eNews Submissions for June 2013 Edition
ALMA Band 2 Workshop
- Orion-KL Spectral Line Survey 67-93.6 GHz (Frayer et al, in prep):
Twenty-five astronomers and students gathered at the North American ALMA Science Center for a workshop devoted to science which would be enabled by equipping ALMA with receivers covering 67-90 GHz, ALMA Band 2. The workshop was available via webcast; several others attended remotely. Presentations are available at the Workshop website (https://science.nrao.edu/facilities/alma/naasc-workshops/alma-band-2-science-workshop/facilities/alma/naasc-workshops/alma-band-2-science-workshop/program
) The excellent local support enabled distant participants to appreciate the science to be done should ALMA be equipped with Band 2 receivers. There are no radio interferometers currently operating in this band, although there has been a receiver at the Arizona Radio Observatory 12m antenna on Kitt Peak for many years. The Green Bank Telescope has recently been equipped with a very sensitive 4mm receiver. These receivers, and prospects for a similar design for ALMA, were reviewed in a discussion leading into science drivers for ALMA operation in that band.
One focus of 4mm science concentrates on the fundamental J=1-0 transitions of a number of deuterated molecules which fall into this band. Deuterium becomes enhanced over its cosmic abundance in molecules at low temperatures owing to exchange reactions in ion-molecule chemistry. These lines are therefore good probes of specific cold regions in astrophysical environments. They may be particularly useful when coupled with ALMA's high spatial resolution for identifying cold regions in the mid planes of protoplanetary disks. Similarly, the cold regions probed by these lines provide insights into the conditions in starless cores, which may subsequently evolve to star-centered cores. Of particular interest are those molecules which persist at low temperatures in the gas phase, such as N2D
+ and NH2D
, which were discussed by several speakers.
Important probes of the nearby Universe also lie in the 4mm band, among which the formaldehyde resonance transition figures prominently. Other lines migrate into the window as a function of the redshifts of their host galaxies; the window gives a view into an important period of evolution of the Universe. CO emission shifted to z~.6 provides a window into galaxies during the last ~5Gyr of evolution, a period in which the tremendous bursts of star formation began to quiet down*. ALMA's superior sensitivity and spatial resolution (up to 1" in Band 2, or about 6kpc) will be important to our understanding of galaxy evolution.