1. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Interferometry at Millimeter and Submillimeter Wavelengths Michiel Hogeheijde Leiden Observatory michiel@strw.leidenuniv.nl

2. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Aims In addition to many similarities, the nature of the (sub)mm sky places unique requirements on the design and operation of interferometers at these wavelengths. This lecture aims to provide an overview of the arrays currently in operation, their characteristics, and the way observations are executed and analysed. It also looks ahead at the next generation instrument, the Atacama Millimeter Array, which wil radically alter how (sub)mm interferometry is done.

3. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Outline Location requirements Existing arrays –Properties –Operations A typical example: observing –> calibrating –> imaging –> analysis Mosaicing and addition of zero-spacing information ALMA –Specifications –Canfigurations and sensitivity –Science drivers –Calibration issues –Operations and data flow –Progress and time line Concluding remarks

4. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Location Requirements Atmosphere is partially transparent in (sub) millimeter wavelengths. Deep absorption by molecules (mostly water) separates various ‘windows’ or ‘bands’.

5. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Location requirements Need to find –A high place (above most atmospheric water) –A flat place (need space for baselines) –A place without much turbulence in the atmosphere (phase stability) –(phase fluctuations are caused by variable path length through the atmosphere. In the case of (sub)mm frequencies, this is due to the passing of ‘cells’ of humid air over the array.)

6. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Existing Arrays PdBI: Plateau de Bure, France Berkeley-Illinois-Maryland Array (BIMA): Hat Creek, Calif.) OVRO: Owens Valley, Calif. NMA: Nobeyama Millimeter Array, Japan SMA: Submillimeter Array, Hawaii ATCA: Australia Telescope Compact Array

7. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Existing Arrays PdBI: Plateau de Bure, France NMA: Nobeyama Millimeter Array, Japan SMA: Submillimeter Array, Hawaii BIMA + OVRO = CARMA: Combined Array for Millimeter Astronomy, Inyo Mountains, Calif. ATCA: Australia Telescope Compact Array

8. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Capabilities and Limitations With the possible exception of CARMA, none of these arrays have many elements –> poor uv filling; multiple tracks required for decent image quality

9. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Example for 3mm observations Obtained with OVRO Data calibration software: MMA –Other packages: miriad, aips, click… Imaging software: miriad

10. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Observing script (1/2) subfile SOURCECYC obs J0116-116 low_el=skip flags g t=1 int 3.0 reps=1 low_el=skip obs t7linear low_el=skip flags " " t=1 int 3.0 reps=5 low_el=skip endsubfile subfile LASTCAL obs/shortest_path J0116-116 low_el=skip flags g t=1 int 3.0 reps=1 low_el=skip endsubfile Loop: 3 min integration on gain calibrator (J0116-116) 5x3 min integration on source (t7linear) Last integration on calibrator

11. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Observing script (2/2) project 716 limits low_el=20.0 sch /mm/std/3c454point.sch start=12:40:00 stop=14:10:00 reps=100 sch/sub SOURCECYC start=14:10:00 stop=21:25:00 reps=100 sch/sub LASTCAL start=21:25:00 stop=22:20:00 reps=1 sch /mm/std/uranus.sch start=18:35:00 stop=01:25:00 reps=1 sch /mm/std/3c84point.sch start=21:25:00 stop=23:25:00 reps=100 limits low_el=20 endtrack Put these together in a script. Start/end with integrations on bright quasars. Also observe Uranus for flux calibration.

12. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Results from a track 3C454.3 source J0116-116 Uranus3C84

13. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Gain calibration (1/2)

14. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Gain calibration (2/2)

15. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Passband calibration (1/2)

16. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Passband calibration (2/2)

17. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Applying the calibrations

18. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Gain-calibrated data 3C454.3 source J0116-116 Uranus 3C84

19. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Flux calibration (1/2)

20. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Flux calibration (2/2)

21. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Data editing

22. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 (u,v) positions and beam shape

23. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 invert-clean-restor Detection of HCN J=1-0 line emission toward the Comet T7LINEAR

24. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Mosaicing What if emission extends beyond the array’s primary field of view? –> mosaic BIMA FOV Fields need to be Nyquist spaced

25. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006

26. Mosaicing Most, if not all, deconvolution routines can successfully deal with multiple pointings HCN J=1-0 HCO + N2H+N2H+

27. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Adding Zero-Spacing Information Even with mosaicing, one can still not measure flux distributed on scales larger than the shortest baseline. Solution –Obtain a nyquist sampled map with a single-dish telescope that has a diameter more than 2 times that of the array telescopes Sufficient overlap on uv-spacings –For example: 6 m BIMA –> Arizona 12 m, FCRAO 14 m 10 m OVRO –> IRAM 30 m Need to make sure that pointing and flux calibration of the single-dish data is excellent

28. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Adding zero-spacing information Combine data in uv-space,or use single-dish map as a ‘model’ for deconvolution of the interferometer data.

29. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Atacama Large Millimeter Array Need to bring (sub) millimeter interferometry at the same level as cutting edge facilities like HST and JWST: sensitivity and resolution –Large collecting area –Many baselines: imaging quality –Excellent site: access highest submm frequencies Europe + North-America + Japan

30. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Existing Arrays & ALMA PdBI: Plateau de Bure, France NMA: Nobeyama Millimeter Array, Japan SMA: Submillimeter Array, Hawaii BIMA + OVRO = CARMA: Combined Array for Millimeter Astronomy, Inyo Mountains, Calif. ALMA: Cajnantor, Chile ATCA: Australia Telescope Compact Array

31. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 ALMA: Science Drivers 1.The ability to detect spectral line emission from CO or CII in a normal galaxy like the Milky Way at a redshift of z = 3, in less than 24 hours of observation. 2. The ability to image the gas kinematics in protostars and in protoplanetary disks around young Sun-like stars at a distance of 150 pc (roughly the distance of the star-forming clouds in Ophiuchus or Corona Australis), enabling the study of their physical, chemical and magnetic field structures and to detect the tidal gaps created by planets undergoing formation in the disks. 3.The ability to provide precise images at an angular resolution of 0.1 arcsec. Here the term "precise image" means being able to represent, within the noise level, the sky brightness at all points where the brightness is greater than 0.1% of the peak image brightness.

32. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 ALMA: Specifications All atmospheric bands between 30 and 950 GHz 0.01 km/s resolution at 100 GHz: thermal line widths Spectral dynamic range 1:10,000; imaging dynamic range: 1:50,000 Detect <1 mJy in 10 min under median atmospheric conditions: 8 GHz bandwidth x 2 polarizations 50 antennas of 12m diameter 0.01” scales high fidelity imaging Baselines 150 m – 18.5 km Total power: 4 ants have nutating subreflectors Phase correction better than 1 rad at 950 GHz, amplitudes better than 3% at 300 GHz and 5% at higher freqs Full polarization capability (<0.1% polarized intensity, <6 deg PA) Can look at Sun at all freqs Software for proposal and observations preparation Software for pipeline calibration and reduction

33. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 ALMA bands Construction: 3,4,(5),6,7,8,9,(10)

34. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 ALMA: Configurations

35. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006

36. ALMA: Calibration Calibration strategy under development Hot & cold loads Suitable astrophysical calibrators Phase calibration may/will require continuous monitoring of the phases –Track water vapor at 22 GHz or 183 GHz –Derive path length variations –> phase correction –Developed for BIMA, OVRO, … –Still experimental, but essential for operations at higher frequencies

37. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Water Vapor Radiometers Observed phases of 3C273 (colors: individual baselines) Source: BIMA Memo 78 by Mel Wright

38. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Water Vapor Radiometers After WVR phase corrections have been applied

39. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Water Vapor Radiometers + apply selfcal to correct intermittent offsets

40. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 From proposal to observations user Phase I proposal Phase II proposal ESO TACNRAONAOJ JAO-Santiago OSF-San Pedro AOS-Chajnantor Science case Source(s) Lines/freqs Sensitivity Resolution Integration times Configurations Total power? –> script Minimally schedulable blocks Weather conditions

41. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Science quality image + raw visibilities From observations to images user European ALMA Regional CenterNAASCNAOJ JAO-Santiago OSF-San Pedro AOS-Chajnantor Archive Archive copy Pipeline calibration & reduction Archive copy Data quality control

42. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Progress and Time Line July–December 2005 –Antenna contracts signed 2007–2008 –Antenna construction and integration January 2009 –3-element array –commissioning and science verification March 2009 –call for early science proposals January 2010 –6-8 commissioned antennas –2 frequency bands –early operations April 2011 –automated pipeline available April 2012 –data archive operational December 2012 –Full science operations

43. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 Concluding Remarks Interferometry at (sub) millimeter wavelengths has progressed –~3 element arrays operating at 3 mm –6-10 element arrays operating at 3 and 1 mm –Submillimeter arrays of 10-15 elements ALMA: quantum leap to 50 element array that will make submillimeter interferometry a standard tools for all astronomers.

44. Interferometry at Millimeter and Submillimeter Wavelengths Interacademiaal College 1 maart 2006 ATCA: www.narrabri.atnf.csiro.au PdBI: iram.fr CARMA: www.mmarray.org SMA: sma-www.harvard.edu ALMA: www.eso.org/projects/alma