Facilities > ALMA/NAASC > naasc-workshops > ALMA Band 2 Science Workshop

ALMA Band 2 Science Workshop

by Dong-Chan Kim last modified May 24, 2013 by Eric Bryerton

The 4mm wavelength region (67- 90 GHz), otherwise known as ALMA band 2, is a virtually unexplored region of the electromagnetic spectrum. Until the very recent addition of a 4mm receiver to the GBT, there has been only one telescope with a continuing operational receiver in this frequency region: the 12m on Kitt Peak, run by the Arizona Radio Observatory (ARO). Furthermore, unlike the 7mm (31-45 GHz) band, which is covered by the newly upgraded NRAO Karl G. Jansky Very Large Array (VLA), there are no radio interferometers in operation in the band 2 region.

However, in contrast to the lack of operational astronomical receivers, the expertise to construct and implement a sensitive and stable receiver in this frequency range currently exists. A nearly quantum-limited band receiver can be built for ALMA with very little technology development.

This workshop is part of an NRAO-funded ALMA design study to examine the scientific drivers for ALMA Band 2 and to demonstrate the technology readiness of the key receiver components.   The workshop will be available via video connection or local participation.  In this workshop, we welcome presentations addressing areas of science that would benefit from the addition of band 2 to ALMA, including but not limited to: astrochemistry, star formation, and galaxy evolution.  The outcome of these presentations and follow-on discussions will be a compelling science case for band 2.  This science case will be used to develop an ALMA development proposal for the full construction of band 2 receivers.

There is no registration fee for this workshop.


May 29, 2013


Conference Room 230
NRAO Headquarters & North American ALMA Science Center
520 Edgemont Road
Charlottesville, VA 22903-2475

Science with Band 2

The fundamental, J = 1→ 0 transitions of the deuterium analogs of common, abundant interstellar molecules are unique to this band, including DCO+, DCN, and N2D+. Studies of such species are crucial to our understanding of the evolution of cores in molecular clouds, and hence to star formation. Because such cores are often quite cold (T ~ 10 K), the J = 1→ 0 lines of these molecules that lie in band 2 are by far the most sensitive probes. The larger primary beam size in Band 2 (83" and 140" for 12m and 7m respectively at 73 GHz) is well-suited for imaging single cores with a single pointing or whole molecular clouds with mosaicing.  Furthermore, observations of such deuterated species are critical in evaluating chemical fractionation in interstellar material, and elucidating the pathways for ion-molecule chemistry.  Recently, Mathews et al. (in press) have demonstrated the utility of ALMA observations of the J=3-2 line of DCO+ for locating the CO 'snow line' in a protoplanetary disk; more suitable lower lying lines are not currently available with ALMA.

Band 2 also contains the fundamental transitions of H2CO and HCNH+, among other molecules. H2CO is an excellent tracer of galactic structure and an important pre-biotic molecule. HCNH+ is a cornerstone species in ion-molecule chemistry, and the precursor to both HCN and HNC. Further observations of both molecules would be insightful for astrochemistry, astrobiology, and the structure of molecular clouds. In addition, redshifted CO and HCN emission, critical to understanding galaxy evolution, fall in the 4mm window. At intermediate redshifts (z>0.34), CO(1→0) will not be available with ALMA band 3, and the key dense gas tracer HCN(1→0) will only be accessible with ALMA band 3 for the nearest galaxies (z<0.055).  These examples highlight what is currently known about band 2; as with most unexplored wavelength regions, new scientific discoveries will likely occur, provided a receiver/detector is available with sufficient sensitivity. In band 2, this sensitivity is virtually guaranteed.