Radio interferometry at millimetre and sub-millimetre wavelengths

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1 Radio interferometry at millimetre and sub-millimetre wavelengths Bojan Nikolic 1 & Frédéric Gueth 2 1 Cavendish Laboratory/Kavli Institute for Cosmology University of Cambridge 2 Institut de Radioastronomie Millimétrique Grenoble ERIS 2009 Oxford, September 2009 Rev 33 B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

2 Outline Introduction 1 Introduction Scientific differences from the cm/m-wave band Observational differences from the cm/w-wave band Science examples 2 Current and forthcoming mm and sub-mm arrays 3 Atmospheric effects/other calibration uncertainties Phase fluctuations Amplitude calibration uncertainties 4 Offline calibration/imaging 5 Summary B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

3 Introduction MM/sub-mm bands (ALMA site, 1mm water) The numbers shown are the ALMA band designations (+ band 1 at GHz) Band 8 Band 9 Band 10 Tx 0.4 Band 3 Band 4 Band Band 2 Band 5 Band B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave ν Interferometry (GHz) ERIS / 62

4 Introduction Scientific differences from the cm/m-wave band Some of the fundamental science from other bands Most science targets cool and close to thermal equilibrium Rotational lines of molecules, dust continuum, atomic carbon Emission mechanisms are energetically significant for star formation both on local and galaxy-wide scales Relatively low opacity except in the strongest molecular lines Strong positive cosmological K-correction Continuum from star-forming galaxies does not dim from z = 1 to z 8 B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

5 Introduction Scientific differences from the cm/m-wave band Some of the fundamental science from other bands Most science targets cool and close to thermal equilibrium Rotational lines of molecules, dust continuum, atomic carbon Emission mechanisms are energetically significant for star formation both on local and galaxy-wide scales Relatively low opacity except in the strongest molecular lines Strong positive cosmological K-correction Continuum from star-forming galaxies does not dim from z = 1 to z 8 B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

6 Introduction CO emission line ladder in Milky Way Fixsen et al. (1999) Scientific differences from the cm/m-wave band Lines show models S ν 4 exp[ E/kT ] B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

7 Introduction Scientific differences from the cm/m-wave band Some of the fundamental science from other bands Most science targets cool and close to thermal equilibrium Rotational lines of molecules, dust continuum, atomic carbon Emission mechanisms are energetically significant for star formation both on local and galaxy-wide scales Relatively low opacity except in the strongest molecular lines Strong positive cosmological K-correction Continuum from star-forming galaxies does not dim from z = 1 to z 8 B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

8 Introduction Scientific differences from the cm/m-wave band Spectral energy distribution of galaxies Lagache et al. (2005) B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

9 Introduction Scientific differences from the cm/m-wave band Some of the fundamental science from other bands Most science targets cool and close to thermal equilibrium Rotational lines of molecules, dust continuum, atomic carbon Emission mechanisms are energetically significant for star formation both on local and galaxy-wide scales Relatively low opacity except in the strongest molecular lines Strong positive cosmological K-correction Continuum from star-forming galaxies does not dim from z = 1 to z 8 B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

10 Introduction Dust extinction model: UV to near-ir Draine (2003) Scientific differences from the cm/m-wave band B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

11 Introduction Scientific differences from the cm/m-wave band Dust extinction model: near-ir to mm-wave Draine (2003) B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

12 Introduction Scientific differences from the cm/m-wave band Some of the fundamental science from other bands Most science targets cool and close to thermal equilibrium Rotational lines of molecules, dust continuum, atomic carbon Emission mechanisms are energetically significant for star formation both on local and galaxy-wide scales Relatively low opacity except in the strongest molecular lines Strong positive cosmological K-correction Continuum from star-forming galaxies does not dim from z = 1 to z 8 B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

13 Introduction Positive cosmological K-correction Lagache et al. (2005) Scientific differences from the cm/m-wave band B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

14 Outline Introduction Observational differences from the cm/w-wave band 1 Introduction Scientific differences from the cm/m-wave band Observational differences from the cm/w-wave band Science examples 2 Current and forthcoming mm and sub-mm arrays 3 Atmospheric effects/other calibration uncertainties Phase fluctuations Amplitude calibration uncertainties 4 Offline calibration/imaging 5 Summary B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

15 Introduction Observational differences from the cm/w-wave band Fundamental observational differences from cm/m wave Small field of view Finer resolution (yet to be fully realised) High cost per element of the array Lack of zero-spacing ( total-power ) and short-spacing information Sky has a small dynamic range, low surface brightness of typical sources Mechanical effects on antennas are important Troposphere gets seriously in the way, ionosphere not important Large absolute but small fractional bandwidths Current arrays do not have good instantaneous uv-coverage B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

16 Introduction Observational differences from the cm/w-wave band Contrast vs single dish Single dish continuum surveys are confusion limited interferometry essential for really deep surveys Much easier to integrate down: Atmospheric brightness fluctuations are rejected Standing waves are rejected Gain fluctuations of the receivers less important Better astrometry Good surface brightness sensitivity is expensive B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

17 Outline Introduction Science examples 1 Introduction Scientific differences from the cm/m-wave band Observational differences from the cm/w-wave band Science examples 2 Current and forthcoming mm and sub-mm arrays 3 Atmospheric effects/other calibration uncertainties Phase fluctuations Amplitude calibration uncertainties 4 Offline calibration/imaging 5 Summary B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

18 Introduction Science examples Identifying the sub-mm galaxies (LH850.02) Younger et al. (2009) Deep R-band SUBARU image with SCUBA centroid (dashed) and 2-σ position ellipsoid (dotted) B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

19 Introduction Science examples Identifying the sub-mm galaxies (LH850.02) Younger et al. (2009), SMA 890 µm and R-band SUBARU SMA (colour scale) SUBARU R-band image + SCUBA beam (dashed) + SMA position (yellow circle) + SCUBA position (dotted) B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

4 GHz + SMA position (yellow circle) + SMA position (yellow circle) B.

20 Introduction Science examples Identifying the sub-mm galaxies (LH850.02) Younger et al. (2009), Spitzer and VLA IRAC 3.6 µm VLA 1.4 GHz + SMA position (yellow circle) + SMA position (yellow circle) B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

21 Introduction Science examples Imaging of CO in a z = 6.42 quasar host Riechers et al. (2009) [detection of C I also presented in the paper] CO J 7 6 emission (contours) CO J 3 2 (colour scale) CO J 7 6 spectrum PdB λ 3 mm observations B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

22 Introduction Science examples Resolving the [C II] emission in the z = 6.42 host Walter et al. (2009) Continuum emission [CII] emission Red and blue shifted [CII] CO(3 2) [C II] rest-frame wavelength is 158 µm These PdB observations at λ 1.1 mm B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

23 Outline Current and forthcoming mm and sub-mm arrays 1 Introduction Scientific differences from the cm/m-wave band Observational differences from the cm/w-wave band Science examples 2 Current and forthcoming mm and sub-mm arrays 3 Atmospheric effects/other calibration uncertainties Phase fluctuations Amplitude calibration uncertainties 4 Offline calibration/imaging 5 Summary B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

24 Current and forthcoming mm and sub-mm arrays Existing (sub-)mm arrays IRAM PdB: 6 15-m antennas Funded by France, Germany and Spain Open to all EU countries via RadioNet TNA CARMA: m m m antennas SMA: 8 6-m antennas Nobeyama Millimetre Array: 6 10-m antenna Specialised array for cosmic background: CBI, VSA, DASI,... B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

25 Current and forthcoming mm and sub-mm arrays IRAM PdB array B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

26 Current and forthcoming mm and sub-mm arrays IRAM PdB array max baseline 800 m B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

27 Current and forthcoming mm and sub-mm arrays Current: Sub-Millimetre Array (SMA) B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

Current and forthcoming mm and sub-mm arrays Near Future: ALMA 50 12-m+ 12 7-m antennas, currently

28 Current and forthcoming mm and sub-mm arrays Near Future: ALMA m m antennas, currently being commissioned B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

29 Outline Atmospheric effects/other calibration uncertainties 1 Introduction Scientific differences from the cm/m-wave band Observational differences from the cm/w-wave band Science examples 2 Current and forthcoming mm and sub-mm arrays 3 Atmospheric effects/other calibration uncertainties Phase fluctuations Amplitude calibration uncertainties 4 Offline calibration/imaging 5 Summary B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

Atmospheric effects/other calibration uncertainties Troposphere (Sub-)mm radiation is predominantly affected by the troposphere (Sub-)mm telescopes are sited at high elevations

30 Atmospheric effects/other calibration uncertainties Troposphere (Sub-)mm radiation is predominantly affected by the troposphere (Sub-)mm telescopes are sited at high elevations (Mauna Kea, Chajnator, SP), airborne observatories (SOFIA) or space Little effect on polarisation B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

31 Atmospheric effects/other calibration uncertainties Two molecular species most significant: H 2 O and O 2 Atmospheric transmission broken down into contributions from: H 2 O (blue) and O 2 (red), and total (black) Tx ν (GHz) B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

32 Atmospheric effects/other calibration uncertainties H 2 O is not well mixed B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

33 Atmospheric effects/other calibration uncertainties Atmospheric transparency Model of atmospheric conditions at summit of Mauna Kea 1 Sky Transparency Sky brightness (in K) Tx 0.4 TB (K) ν (GHz) Loss of astronomical signal + Additional noise ν (GHz) B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

34 Atmospheric effects/other calibration uncertainties Phase fluctuations Atmospheric path fluctuations Refractive index n 1: n [ α P d T + β P w T + γ P w T 2 ] P w : Partial pressure of the water vapour T : Temperature of the water vapour Furthermore, the refractive index is a function of frequency (i.e., the atmosphere is dispersive), especially at sub-mm frequencies and close to the edges of the bands Horizontal and line of sight variation in atmospheric properties lead to phase errors and phase fluctuations B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

35 Atmospheric effects/other calibration uncertainties Example of path fluctuations SMA, Mauna Kea, Hawaii Phase fluctuations 750 p (µm) t (hours UT) Measured path while observing a quasar 200 m baseline About 3.5 mm line-of-sight water σ φ = 207 µm. B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

36 Atmospheric effects/other calibration uncertainties Phase fluctuations Correlation between baseline length and fluctuation The phase fluctuation measured at 22 GHz at the VLA by observing a quasar for about thirty minutes. Correlations along one arm of the VLA only shown. 100 Phase fluctuation (deg) baseline length (m) B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

37 Atmospheric effects/other calibration uncertainties Phase fluctuations Effect of uncorrected phase errors From simulations in ALMA Memo # Point-source sensitivity 1 Gaussian beam size S D (arcsecs) φrms (rad) φrms (rad) Decorrelation Limit on possible resolution B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

38 Atmospheric effects/other calibration uncertainties Phase fluctuations Effect of uncorrected phase errors on snapshots From simulations in ALMA Memo # Positional error 1 Fractional flux error P 2 (arcsecs) S 2 S 2 / S φrms (rad) φrms (rad) Astrometric errors Flux calibration errors B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

39 Atmospheric effects/other calibration uncertainties Phase fluctuations Correcting the phase fluctuations (Wait for stable weather) The magnitude of fluctuations can vary by a factor of five Switch to a quasar and measure the phase, apply to science Essentially the same as normal phase calibration To be effective v t 2 < B Correction with Water Vapour Radiometers (WVRs) Measure water vapour along line of sight of each antenna Infer the path fluctuation on one second timescale Correct for the resulting phase errors Self-calibration Small field of view, small dynamic range of sky only possible in specialised projects Example: quasar absorption lines Paired-antenna technique: Dedicated antennas continuously monitoring a quasar B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

40 Atmospheric effects/other calibration uncertainties IRAM PdB 22 GHz WVRs Phase fluctuations B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

41 Atmospheric effects/other calibration uncertainties Phase fluctuations ALMA 183 GHz WVRs Blue rectangles are the WVR filters Tb (K) ν (GHz) B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

42 Atmospheric effects/other calibration uncertainties Phase fluctuations How WVR phase correction works ALMA WVRs + SMA: Channel 3 data from two telescopes TB,3 (K) t (hours UT) B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

43 Atmospheric effects/other calibration uncertainties Phase fluctuations How WVR phase correction works ALMA WVRs + SMA: Channel 3 difference & phase 3 4 TB,3 (K) L(µm) t (hours UT) B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

44 Atmospheric effects/other calibration uncertainties Phase fluctuations How WVR phase correction works ALMA WVRs + SMA: Channel 3 phase prediction and residual Uncorrected path fluctuation: 157 µm RMS Estimated Optimum p(µm) 0 p(µm) p(µm) 0 p(µm) t (hours UT) t (hours UT) Residual RMS 74 µm Residual RMS 71 µm B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

45 Atmospheric effects/other calibration uncertainties Phase fluctuations WVR correction in practice at the PdB B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

Atmospheric effects/other calibration uncertainties Phase fluctuations WVR correction in practice at the PdB Example of point source observation Turbulent conditions, 4.

46 Atmospheric effects/other calibration uncertainties Phase fluctuations WVR correction in practice at the PdB Example of point source observation Turbulent conditions, 4.4 mm precipitable water vapour, long baselines No WVR correction With WVR correction 2.5 improvement in signal/noise B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

47 Atmospheric effects/other calibration uncertainties Amplitude calibration uncertainties Amplitude calibration uncertainties Fundamental uncertainties 1 Atmospheric transparency varies with time and with frequency 2 Receiver gain is variable 3 Antenna gain is difficult to measure and sometimes variable Difficult to inject a signal of known strength Quasars are highly variable at (sub-)mm wavelengths Solar system bodies (e.g., Mars, Neptune) also variable, but can be modelled Accurate models for the radiometric brightness are required May be resolved, especially at sub-mm wavelengths A calibration chain is required B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

48 Atmospheric effects/other calibration uncertainties Amplitude calibration uncertainties Flux calibration chain Build reasonably stable receiver systems Calibrate receiver gain using hot and ambient load every few to tens of minutes Calibrate atmospheric absorption through a combination of: Tipping scans (once 1 hour) Atmospheric models and WVRs (could go as short as 1 second) Total power atmospheric emission [Quasar observations (once 3 mins)] Calibrate antenna gains using primary calibration standards once per session once a year at short wavelengths only planets may be suitable Calibrate antenna primary beam shape through direct interferometric measurement B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

49 Outline Offline calibration/imaging 1 Introduction Scientific differences from the cm/m-wave band Observational differences from the cm/w-wave band Science examples 2 Current and forthcoming mm and sub-mm arrays 3 Atmospheric effects/other calibration uncertainties Phase fluctuations Amplitude calibration uncertainties 4 Offline calibration/imaging 5 Summary B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

50 Offline calibration/imaging Bandpass calibration Principle: Frequency-dependence of gain is independent of time Calibration steps: Observe a strong quasar at beginning of each session (Need high SNR since can not combine the channels) Fit (complex) gain vs frequency If SNR is high solve for each channel individually Otherwise fit a smooth function of frequency Apply this bandpass solution to all other data in the session B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

51 Offline calibration/imaging Bandpass calibration: PdB example amplitude B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

52 Offline calibration/imaging Bandpass calibration: PdB example phase B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

53 Channel Velocity (km/s) Channel Velocity (km/s) Offline calibration/imaging Channel Velocity (km/s) Channel Velocity (km/s) Channel Velocity (km/s) Bandpass calibration: SMA Data + CASA Amplitude two out of 24 spectral windows shown Antennas 1&2 Antennas 1&3 Antennas 1&4 Vector Average Amplitude Vector Average Amplitude Vector Average Amplitude Antennas 1&5 Antennas 1&6 Vector Average Amplitude Vector Average Amplitude B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

54 Channel Velocity (km/s) Channel Velocity (km/s) Offline calibration/imaging Channel Velocity (km/s) Channel Velocity (km/s) Channel Velocity (km/s) Bandpass calibration: SMA Data + CASA Phase two out of 24 spectral windows shown Antennas 1&2 Antennas 1&3 Antennas 1&4 Phase Average Phase Average Phase Average Antennas 1&5 Antennas 1&6 Phase Average Phase Average B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

55 Offline calibration/imaging Phase calibration Principles: Observed phase of a point source at phase centre should be zero The phase response of telescope will change very little for small angular changes on the sky Most causes of errors are antenna-based and independent of baseline Calibrations steps: Observe quasars every 10 seconds to 20 minutes Fit (complex) gain vs time to estimate phase variation If SNR is low and you think phase should be varying slowly, fit smooth functions If SNR is high or there are jumps, use linear interpolation Apply phase solution to science data B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

56 Offline calibration/imaging Phase calibration: PdB Example smooth phase variation B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

57 Offline calibration/imaging Phase calibration: PdB Example jump ignored by smooth fit B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

58 Offline calibration/imaging Phase calibration: PdB Example function use higher order B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

59 Offline calibration/imaging Phase transfer Principles: Low frequency receivers are more sensitive, atmosphere more transparent, telescopes more efficient Quasar spectra often roughly ν 0.7 easier to make phase calibration observations at lower frequency Calibration steps: Observe phase calibration targets at 3 mm Scale phase solutions to science bands and apply to data B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

60 Offline calibration/imaging Phase transfer: PdB Example B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

61 Offline calibration/imaging Phase transfer: PdB Example with transferred correction B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

62 Offline calibration/imaging Amplitude/Flux calibration B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

63 Offline calibration/imaging Amplitude/Flux calibration B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

64 Offline calibration/imaging Amplitude/Flux calibration B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

65 Offline calibration/imaging Imaging Imaging generally tractable with established techniques Adding short/zero-spacing one important challenge but now almost routine in some systems Comparison (sub-)mm observations vs cm/m Science Imaging Resolution ( λ/b) (current arrays) Field of View ( λ/d) Few pixels in image ( B/D) (current arrays) Many spectral channels Low signal-to-noise B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

66 Offline calibration/imaging Short-spacing information Belloche & André (2004), Class 0 proto-star observations PdB only dashed circle is the primary beam B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

67 Offline calibration/imaging Short-spacing information Belloche & André (2004), Class 0 proto-star observations PdB + short spacing from IRAM 30-m B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

68 Outline Summary 1 Introduction Scientific differences from the cm/m-wave band Observational differences from the cm/w-wave band Science examples 2 Current and forthcoming mm and sub-mm arrays 3 Atmospheric effects/other calibration uncertainties Phase fluctuations Amplitude calibration uncertainties 4 Offline calibration/imaging 5 Summary B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

69 Summary Summary The physics of (sub-)mm emission means observing it allows unique science Interferometers open the possibility of high-resolution and deep observations Troposphere has a big effect on (sub-)mm radiation but combination of excellent sites and new techniques can/will resolve most of these Many of the techniques are the same as traditional cm-wave interferometry IRAM mm-interferometry summer schools: next year B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

70 Summary Resources on the web Brogan et al: CASA training pages: IRAM MM-Interferometry Summer School: Schilke, P: Interferometric Calibration & Imaging http: // bertoldi/wiki/radiointerferometry B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

71 Summary References Belloche A., André P., 2004, A&A, 419, L35 Draine B. T., 2003, ARA&A, 41, 241 Fixsen D. J., Bennett C. L., Mather J. C., 1999, ApJ, 526, 207 Lagache G., Puget J.-L., Dole H., 2005, ARA&A, 43, 727 Riechers D. A., Walter F., Bertoldi F., Carilli C. L., Aravena M., Neri R., Cox P., Weiss A., Menten K. M., 2009, ArXiv e-prints Walter F., Riechers D., Cox P., Neri R., Carilli C., Bertoldi F., Weiss A., Maiolino R., 2009, Nature, 457, 699 Younger J. D., Omont A., Fiolet N., Huang J.-S., Fazio G. G., Lai K., Polletta M., Rigopoulou D., Zylka R., 2009, MNRAS, 394, 1685 B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS / 62

Atmospheric phase correction for ALMA with water-vapour radiometers

Atmospheric phase correction for ALMA with water-vapour radiometers B. Nikolic Cavendish Laboratory, University of Cambridge January 29 NA URSI, Boulder, CO B. Nikolic (University of Cambridge) WVR phase