The eSMA: description and first results

The eSMA ("expanded SMA") combines the SMA, JCMT and CSO into a single facility, providing enhanced sensitivityand spatial resolution owing to the increased collecting area at the longest baselines. Until ALMA earlyscience observing (2011), the eSMA will be the facility capable of the highest angular resolution observations at345 GHz. The gain in sensitivity and resolution will bring new insights in a variety of fields, such as protoplanetary/transition disks, high-mass star formation, solar system bodies, nearby and high-z galaxies. Therefore theeSMA is an important facility to prepare the grounds for ALMA and train scientists in the techniques.Over the last two years, and especially since November 2006, there has been substantial progress towardmaking the eSMA into a working interferometer. In particular, (i) new 345-GHz receivers, that match thecapabilities of the SMA system, were installed at the JCMT and CSO; (ii) numerous tests have been performedfor receiver, correlator and baseline calibrations in order to determine and take into account the effects arisingfrom the differences between the three types of antennas; (iii) first fringes at 345 GHz were obtained on August30 2007, and the array has entered the science-verification stage.We report on the characteristics of the eSMA and its measured performance at 230 GHz and that expectedat 345 GHz. We also present the results of the commissioning and some initial science-verification observations,including the first absorption measurement of the C/CO ratio in a galaxy at z=0.89, located along the line of sight to the lensed quasar PKS 1830-211, and on the imaging of the vibrationally excited HCN line towards IRC+10216.