Download 05_CASCA_band3 - Astronomy Research Centre

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
CO Lines in ALMA
4
Observing
Windows
5-4
Redshift Z
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.
10-9
Upgrade
adapted from the ALMA Design Reference Science Plan
4-3
2
Definitive Science with Band 3
Day 1
3-2
(www.strw.leidenuniv.nl/~joergens/alma/)
1
2-1
CO 1-0
100
200
300
Observing Frequency GHz
400
For Z = 0.5,1,2,3,4 Age of Universe is 55%,35%,19%,12%,9%
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
Receiver Band 3 Main Specifications
Search for dense gas tracers - for example HCN
Molecular line absorption studies - using background radio galaxies to probe ISM in intervening systems
•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.
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:
Broad band 4-8 GHz
USB0
LSB0
USB1
LSB1
60
Cartridge #1
Pol 0 USB LO=92 GHz
70
System Noise Temperature (K)
70
System Noise Temperature (K)
Small scale structure in molecular clouds - characterising the threshold for self-similar hierarchy in GMCs
80
80
50
40
30
20
10
0
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
60
Infall velocity structure of starless cores - understanding the process of collapse
50
High angular resolution required to map the infall motions across the core using N2H+ or HCO+
40
30
Depletion of molecules in low-mass cores - searching for evidence of freeze-out or chemistry
20
Comparison of tracer molecules and their isotopomers such as CO, HCO+, CS, CCS, N2H+
10
Unbiased Line surveys of Star-forming regions - searching for new and exotic molecules
0
92
94
96
98
100
102
LO Frequency (GHz)
104
106
108
4
5
6
7
Absorption line studies toward background bright point sources - detecting diffuse and translucent clouds
8
Intermediate Frequency (GHz)
Molecular gas in disks around young stars
4 K Assembly
Feedhorn
OMT
2SB Mixer assembly
Pol 0
4 Low Noise
Amplifiers
& isolators
Pol 1
DSB Mixer Unit
4 K stage