ASTRO 6525 Lecture #18:! (Sub-)Millimeter Interferometry I!! October 27, 2015!

Transcription

1 ASTRO 6525 Lecture #18:! (Sub-)Millimeter Interferometry I!! October 27, 2015! Dominik A. Riechers Find me at office SSB

2 Schedule for this Section Today: Introduction to (Sub-)Millimeter Interferometry: OVRO/BIMA to ALMA Oct 29, 2015: ALMA Technical Details Dec 03, 2015: Proposal Panel Meeting

3 Homework: Proposal Exercise the homework of this section will be to write a (technically correct) proposal for ALMA instructions are posted on the class webpage you have 4 weeks to complete the proposal note that you will be required to read documentation and to learn how to use a number of tools to complete this process you will then be given 1.5 weeks to review the proposals of other participants (instructions for the review process will be provided) we will meet on the last day of class to have a review panel discussion, in which proposals will be ranked by scientific merit and technical feasibility based on the feedback you receive, you will be free to consider submission of the full proposal to ALMA in cycle-4 (spring 2016)

4 Overview (Sub)millimeter interferometry: path to ALMA Why the (sub)mm matters: Science with ALMA Specifics of (sub)millimeter interferometry How to use ALMA Summary 4

5 Overview (Sub)millimeter interferometry: path to ALMA Why the (sub)mm matters: Science with ALMA Specifics of (sub)millimeter interferometry How to use ALMA Summary 5

6 Radio Telescopes Around the World: >100

7 Why ALMA, why Atacama? What drives location? m/cm-wave RF quiet conditions e.g., the AU SKA site: 600 km into the WA desert mm/submm dry conditions Atacama, Greenland, Antarctica, Mauna Kea balloons, space absent/weak tropospheric O 2 line VLBI geographic distribution (diversity a/o filling) super-terrestrial baselines

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9 Tropospheric Opacity Depends on Altitude Models of atmospheric transmission from 0 to 1000 GHz for the ALMA site in Chile, and for the VLA site in New Mexico The difference is due primarily to the scale height of water vapor, not the dryness of the site. Atmospheric transmission not a problem for! > cm (most VLA bands)

10 History: OVRO & BIMA 1980s 2004: Caltech operates millimeter array at Owens Valley Radio Astronomy (OVRO) site in central California (Inyo mountains) six 10.4 m antennas operating at 3 mm & 1mm baselines up to 440 m : Berkeley-Illinois-Maryland Association (BIMA) operates BIMA array at Hat Creek Radio Observatory in northern California ten 6.1 m antennas operating at 3 mm & 1mm baselines 7 m - 2 km

11 History: CARMA : OVRO & BIMA are merged and moved to a better, higher site that allows more routine 1mm observing & long baselines (one BIMA antenna was scrapped)! CARMA (Combined Array for Research in Millimeter-wave Astronomy) 2008/2009: merger with Sunyaev-Zel dovich Array (SZA) of 3.5 m antennas; first used as radiometer on longest baselines, later adding routine 1 cm observing capabilities to the array 6x10.4 m, 9x6.1 m, 8x3.5 m antennas operating at 1 cm, 3 mm & 1mm; baselines up to 2 km 23 antennas: best image fidelity until ALMA

12 History: PdBI/NOEMA 1992-today: IRAM Plateau de Bure Interferometer (PdBI) in the french Alps Collaboration of Max-Planck-Society (Germany), CNRS (Centre National de la Recherche Scientifique, France) & IGN (Instituto Geográfico Nacional, Spain) Initially three 15 m antennas, later expanded to six 15 m antennas, operating at 3, 2, 1, and 0.8 mm baselines up to 760 m : major upgrade to NOEMA (Northern Extended Millimeter Array) up to twelve 15 m antennas (presently 7) baselines up to 1.6 km 32 GHz correlator (4x ALMA bandwidth)

13 History: NMA & SMA : Nobeyama Millimeter Array (NMA) in Japan six 10 m antennas, operating at 3 mm (some 2/1 mm) baselines up to 560 m could be linked to NRO 45 m rarely used 2004-today: Submillimeter Array (SMA) on Mauna Kea, Hawai i, operated by Smithsonian Astrophysical Observatory (SAO) & Academia Sinica (Taiwan) eight 6 m antennas, operating at 1.3 and 0.8 mm baselines up to 509 m could be linked to CSO 10.4 m and JCMT 15 m (780 m max baseline) rarely used

14 ALMA Basics Global partnership (shared cost ~$1.3 billion, ~30 yr in planning): North America (US, Canada) Europe (ESO) East Asia (Japan,Taiwan, South Korea) In collaboration with Chile Unique high, dry site: 5000m (16,500 ft) in Chilean Atacama desert At least 66 submillimeter/millimeter telescopes:! 12-m Array 50 x 12-m Atacama Compact Array (ACA) - 12x7-m, 4x12-m (TP)

15 ALMA Antennas

16 Full Science Capabilities! better sensitivity and resolution than current mm arrays. ALMA Baselines to ~15 km (0.015 at 300 GHz) in zoom lens configurations Sensitive, precision imaging 84 to 950 GHz! (3.6 mm to 315 µm) State-of-the-art low-noise, wide-band SIS receivers (8 GHz bandwidth per polarization) Flexible correlator with high spectral resolution at wide bandwidth Full polarization capabilities Est. 1TB/day data rate

17 Frequency Coverage ALMA Early Science (now) Full Operations!#$%#&'()*+,-.) /00) 100) 200) 34560) 74560) 84560) /4560) O 2 H 2 O H 2 O H 2 O H 2 O O 3

18 !-*)% *+,($% $#&$'(($)%!#$% cm/mm: rich in line + continuum diagnostics Cosmic Eyelash model SED CNO fine structure lines ISM gas coolant! PAHs + SiL!#$%&!' Thermal dust (young stars) star formation! CO ladder total gas masses! excitation, dynamics! phys. conditions Smail et al Swinbank et al Synchrotron + Free-Free (AGN+SNR) star formation!

19 Sensitivity & Resolution ALMA will match best observatories at other wavelengths in sensitivity and spatial resolution first sharp images at (sub)mm wavelengths

20 Telescope Diameter: Source Confusion 25m 3.5m ALMA vs. Herschel Bussmann, Riechers et al Single-dish (sub)mm to radio telescopes are limited in resolution due to!/d scaling - best current resolution at 350 µm: ~30 (3.5m) - best current resolution at 1mm: ~10 (30m) - best current resolution at 1cm: ~15 (100m) Difficult to resolve, or at high z, even tell apart galaxies

21 An Interferometer

22 What Does an Interferometer Measure?

23 What Does an Interferometer Measure? Amplitudes and Phases Visibility! - Each pair of antennas (=baseline) will generate a visibility (amplitude and phase) - every integration (time interval) - every correlator channel (frequency interval)

24 Separation of slits / projected baseline

25 Visibility and Sky Brightness

26 We measure the source brightness distribution convolved with the dirty beam. The dirty beam size and structure is a direct representation of the baseline distribution and coverage due to Earth rotation synthesis The image fidelity has two major components: - sensitivity - baseline coverage Interferometric Imaging

27 Collecting Area & Baselines CARMA 23 (253) 8 (28) ALMA ALMA Full Science ( ) Cycle I ( ) 6 (15) Circles Show Collecting Area (sensitivity) Captions give # of antennas and # of baselines (fidelity)

28 Sensitivity+Baselines=Image Fidelity

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31 Quick Reminder on 2D Fourier Transforms Small spatial structure translates to large scales in Fourier space, and thus are best sampled by large separations of telescopes/long baselines Large-scale structure is best sampled by telescopes close together/short baselines

32 Limitations of Interferometry

33 ALMA vs. ACA+ALMA *./ %47%5829:;%<212=;% % % 12-M ARRAY ONLY MODEL 12-M + 7-M ACA Image reconstruction artifact ( bowls ) Not present when 7-m antennas included