What is Millimetre-Wave Astronomy and why is it different? Michael Burton University of New South Wales

Some Millimetre Basics MM: 1–~12mm, Sub-MM: 0.3–1mm CMBR (T = 2.7K  = 1mm) Molecular rotational lines –Polar molecules (have dipole moment) eg CO (E 1 = 5K), HCN, CS, HCO + Cold thermal continuum (dust) –Thermal processes: F ~ B  ~ 2kT 2 /c 2. x Problem: Atmosphere (O 2, H 2 O)……

The Millimetre Advantage Thermal Processes  B Decay Rates (linear molecules) 3 Doppler Widths 0.5 [?] Level Population (T>>T J ; g J  J) Number of Photons -1 Energy Spatial Resolution -1

Transparancies Electromagnetic Spectrum MM transmission for 4mm H 2 O MM transmission for 11mm H 2 O Some bright MM-lines

Brightness Temperature

Atmospheric Transmission

The 3mm Millimetre Spectrum

Physical Parameters you can derive! Temperature: T ex, T Brightness Density: n H2 (~n crit  range of densities present!) Column Density: N (when optically thin) Optical Depth: (use isotope ratios) Mass (with scale length) Abundances: different species Velocities: line widths, centres, shapes Infall, outflow, mass transfer rates  Constrain the properties of your source!!

SEST molecular line survey –Gradient: T rot = 27 ± 4 K –Intercept: N(H 2 ) = 1 x cm -2 (  comes in as well) – Size + Column: n(H 2 ) = 6 x 10 5 cm -3 – With Volume: Mass = 6 x 10 3 M  Garay et al, 2002

: SEST kinematical studies – Evidence for infall (profile of optically thick lines) - Modelling: V infall ~ 0.5 km s -1 - Speed + Density + Size: dM infall /dt ~10 -2 M  yr -1 – Evidence for outflow from wings - Extent: V outflow = 15 km s -1 Brooks et al, 2002 Optically Thick Optically Thin Wide Wings

Mopra: Current Capabilities 22-m Telescope for > ~3mm 85–115 GHz SIS receiver (2.6 – 3.5 mm) 35” 100 GHz T sys ~ – 300K Beam Efficiency: –  mb (86 GHz) = 0.49,  mb (115 GHz) = 0.42 –  xb (86 GHz) = 0.65,  xb (115 GHz) = 0.55 Bandwidth 64, 128 or 256 MHz ( km/s) 1024 Channels ( km/s per channel) 2 Polarizations –1 frequency or 1 polarization + SiO 86 GHz Must Nod – No chopping OTF Mapping

Methanol Maser-selected Hot Molecular Core Survey CH 3 CN CH 3 OH HCO + H 13 CO + N 2 H + HCN HNC 7 lines; 86 Sources Purcell

‘On the Fly’ Mapping with Mopra: The Horsehead Nebula Optical 12 CO 13 CO 6 arcmin Tony Wong

0.17 km/s channel spacing

OTF Mapping Specifications For a 300” x 300” map: –~1400 spectra (31 x 46) –~35” resolution –0.17 km/s resolution –120 km/s bandwidth –Dual polarization –  ~ 0.3K per channel, per beam –~70 minutes / grid –Upto 7 grids / transit –Processed with LIVEDATA + GRIDZILLA packages

The DQS in 13 CO: Mopra OTF Mapping

How many photons have we lost (or gained)? 00  0 sec(z) z Signal on-source: T rec T sou T atm

Sky (Reference, Off) Source (On) Difference

Some Radiative Transfer Radiative TransferdI /ds = -  I +  Kirchoff (LTE)  /  = B (T)  Radiative TransferdI /d  = I + B (T) SolutionI (s)= I (0)e -  (s) + B (T)(1 - e -  (s) ) Source Atmosphere

Obtaining Data: Signal from Source and Reference T Sig = C{T R +T A (1-e -  0 secz )+T S e -  0 secz } T Ref = C{T R +T A (1-e -  0 secz )} [T Sig -T Ref ]/[T Ref ] = T S e -  0 secz / {T R +T A (1-e -  0 secz )} Show Plots of Opacity + Brightness Temperature T BB = C{T R +T A } [T Sig -T Ref ]/[T BB - T Ref ] = T S /T A

Calibrating Data: Gated Total Power GTP Ref = C’ T Ref GTP Paddle = C’{T A + T R } [GTP Paddle - GTP Ref ] / GTP Ref = T A e -  0 secz / {T R +T A (1-e -  0 secz )} GTP Hot - GTP Cold = C’{T Hot - T Cold } Atmosphere Liquid Nitrogen

Calibrating Data: {[T Sig -T Ref ]/[T Ref ]} / {[GTP Paddle - GTP Ref ] / GTP Ref } = T Source / T Atmosphere Actually T Source = T’ Source / Efficiency –Usually written as T MB = T A * /  (note the different notation)

Mopra Upgrades 8 GHz Digital Filter Bank –Zoom modes –4(?) lines simultaneously MMIC receiver –Easier tuning –Higher T sys –May loose 115 GHz end? 7 mm receiver –New ATNF project? Focal Plane Array??? Ultra-wide band correlator??? –Needs source of funds……

Australia’s MM–Wave Radio Telescopes 3 mm 12 mm

Australia Telescope Compact Array National Facility –Built for 1–10 GHz operation MM-upgrades –3 mm (85-~105 (115) GHz) 5 x 22m antennas EW-array + NS-spur –Currently GHz –12 mm (22-25 GHz) 6 x 22m antennas 2 GHz bandwidth upgrade 7 mm (45 GHz) upgrade planned –6 antennas FPAs??? –With ultra-wide-band correlators??

Water Vapour and Phase Fluctuations

Millimetre Interferometry Poses special challenges: Significant atmospheric opacity, mostly due to H 2 O Fluctuations in H 2 O produce phase shifts These increase with both baseline and frequency Instrumental requirements (e.g. surface, pointing, baseline accuracy) are more severe Need more bandwidth to cover same velocity range (1 MHz  (mm) km/s) R Sault Desai 1998 Brightness Temperature H 2 O Turbulence  Seeing

ALMA Atacama Large Millimetre Array

Antarctica??