ALMA’s Roots in Three Scientific Visions Paul Vanden Bout NRAO The Dusty & Molecular Universe – Paris 28/10/04

LSA (1988) MMA (1982) LMSA (19??) ALMA

The Millimeter Array MMA thinking was heavily influenced by the experience of the Very Large Array: rapid high- quality imaging at 230 GHz was the central performance characteristic of the MMA. The very first concept to be proposed (by F. Owen, 1982) was to build a 15 x 10m array at the VLA site at a cost of $36M. The MMA proposal (1992) was for a 40 x 8m array at a site to be chosen following a study; cost $120M The site study led NRAO to find the present ALMA site and to an interest in the submillimeter.

The Large Southern Array The first concept for what became the Large Southern Array was a 10 x 8m array to be located near Paranal – part of long term planning for SEST – cost ~$50M. The proposal (1991) for the LST itself was a 50 x 16m array at a cost of ~$250M. The huge collecting area of m 2 was needed (D. Downes) to gain sensitivity needed to observe unlensed high-z CO galaxies. (F10214 had just been detected in CO.) The LST was to work at 230 GHz and below and be located at a more modest elevation (~3500m) than the present ALMA site in Chile.

Merger of MMA and LSA 26 June 1997 Elements of the Agreement: a big array – 64x12m antennas; a high (submm) Chilean site; 50:50 deal between North America and Europe (+Japan as possibility); ESO and NRAO to do the job (no new international treaty organization like ESO or observatory like Gemini).

The Large Millimeter Submillimeter Array The first vision in Japan for the LMA was to expand the Nobeyama Interferometer to 30 antennas. Delayed by SUBARU, this plan was expanded to 50x10m antennas and submillimeter capability. The Large Millimeter Submillimeter Array (LMSA) was to operate to 950 GHz Following extensive site testing in Chile, the 10m ASTI telescope was installed at Pampa la Bola near the ALMA site. Plans for the LMSA evolved, following the European-North American partnership for ALMA, to joining ALMA with a contribution from Japan that added capabilities in brightness sensitivity (a compact array) and frequency coverage (additional receiver bands). The combination is known as Enhanced ALMA.

Enhanced ALMA 64x12m antennas in a large array 12x7m + 4x12m antenna compact array 7 receiver bands, 84 – 950 GHz Powerful correlators for both arrays Spatial frequency coverage from 12m single dish through compact array to 14km extent of the largest configuration of the large array. Excellent site

ALMA Observers In Europe, these functions will be conducted at ESO and several national institutes. In Japan at the NAOJ. In North America these functions will be located at NRAO, Charlottesville VA. Astronomers will see ALMA like a space mission, their point of contact from proposal submission to data analysis being an ALMA regional science center.

When? Interim operations are scheduled to begin in mid-2007 with 8 antennas Full operations are to begin in Antennas added to the array in sets of 8. Expect the level of support to begin modestly and grow, as the array is commissioned, de- bugged, and experience is gained in operations. Start to plan your science!

The Atacama Large Millimeter Array ALMA – A World Array