Definitive Science with Band 3 adapted from the ALMA Design Reference Science Plan

1. The 3 Millimetre (Band 3) Receivers for ALMA Jim Hesser, Doug Johnstone, Stephane Claude, Keith Yeung, Lewis Knee, and the Band 3 Receiver Team The Role of Band 3 The Atacama Large Millimetre Array (ALMA) will be one of astronomy's most powerful telescopes, providing unprecedented imaging capabilities and sensitivity many orders of magnitude greater than anything of its kind today. The largest Canadian contribution will be the 3-millimetre wavelength band (Band 3) receivers for each of ALMA's antennas. The millimetre instrumentation laboratory of NRC's Herzberg Institute of Astrophysics (HIA) in Victoria, BC, is one of the few facilities in the world with expertise in superconducting detector technology for millimetre waves. Operating at temperatures of -269 °C, these receivers will detect and amplify the incredibly faint whispers of radiation that reach earth from the remotest parts of the cosmos. These receivers are of paramount importance to the project because they will be used not only for many science applications but also for final adjustment of the antenna panels and for regular calibration of the array during operations. The first Band 3 cartridge (cartridge #1) has been assembled at HIA and cartridge #2 will be assembled shortly. This first cartridge has gone through an exhaustive series of acceptance tests at HIA and is scheduled for shipment to the North American Front End Integration Centre at NRAO in Summer 2005. • Definitive Science with Band 3 • adapted from the ALMA Design Reference Science Plan • (www.strw.leidenuniv.nl/~joergens/alma/) • EXTRA-GALACTIC: • Unbiased surveys of sub-millimetre galaxies - understanding the process of cosmic star formation • Of order 50% of star formation in the cosmos occurs in galaxies highly obscured by dust, and this fraction may rise with redshift • Dust continuum observations will constrain SED of the galaxy - sensitivity in the µJy range @ 3mm • Molecular line observations will constrain the redshift of the galaxy - predominantly using CO • Molecular line studies of sub-millimetre galaxies - constraining dust obscured galaxy formation • High resolution imaging of CO - ALMA’s 0.2 arcsecond resolution corresponds to approximately 1 kpc • Search for dense gas tracers - for example HCN • Molecular line absorption studies - using background radio galaxies to probe ISM in intervening systems • Full spectral scan through Band 3 range will provide evidence for rare or low-excitation molecules • Sunyaev-Zel’dovich Effect of Proto Clusters -measuring the fine scale structure of high redshift clusters • These observations require two receiver bands (3 and 6) and can be obtained in continuum or lines • Calibration of the CO to molecular hydrogen ratio • Surveying the free-free emission in nearby galaxies • Gas content and dynamics of Elliptical Galaxies GALACTIC: • Small scale structure in molecular clouds - characterising the threshold for self-similar hierarchy in GMCs • High resolution (0.1 arcseconds) imaging of several nearby molecular clouds using the CO (1-0) line • Searching for the scale on which turbulent or magnetic energy is dissipated • Infall velocity structure of starless cores - understanding the process of collapse • High angular resolution required to map the infall motions across the core using N2H+ or HCO+ • Depletion of molecules in low-mass cores - searching for evidence of freeze-out or chemistry • Comparison of tracer molecules and their isotopomers such as CO, HCO+, CS, CCS, N2H+ • Unbiased Line surveys of Star-forming regions - searching for new and exotic molecules • Absorption line studies toward background bright point sources - detecting diffuse and translucent clouds • Molecular gas in disks around young stars • Receiver Band 3 Main Specifications • Receiving frequency range is 84-116 GHz (converted down to 6 GHz for processing) • Receiving signal amplified by 60 dB (that is a gain of 1 million) • Receiver noise temperature of 37 K (equivalent to the sky noise temperature at the ALMA site) • Simultaneous reception of two orthogonal polarizations • Simultaneous reception of both side-bands (2SB mode) • Total IF output bandwidth of 8 GHz per polarization • Superconductor-Isolator-Superconductor (SIS) cryogenic detector and low noise amplifier operating at 4K.