astro 6525 lecture #18: (sub-)millimeter interferometry...
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ASTRO 6525 Lecture #18: !(Sub-)Millimeter Interferometry I!
!October 27, 2015!
Dominik A. Riechers"Find me at office SSB 220"
E-mail: dr@astro.cornell.edu"
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"
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)"
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
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
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 O2 line"
– VLBI"• geographic distribution (diversity a/o filling)"• super-terrestrial baselines"
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)"
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"
1996 – 2004: 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"
History: CARMA"
2006 – 2015: 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"
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""2014-2019: 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)"
History: NMA & SMA"
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"
1983-2010: 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"
ALMA Basics"
• Global partnership (shared cost ~$1.3 billion, ~30 yr in planning):"North America (US, Canada)"Europe (ESO)"East Asia (Japan,Taiwan, South Korea)"In collaboration with Chile"
• Unique high, dry site:"5000m (16,500 ft) in Chilean Atacama desert""
• At least 66 submillimeter/millimeter telescopes: ! 12-m Array – 50 x 12-m"" Atacama Compact Array (ACA) - 12x7-m, 4x12-m (TP)""
ALMA Full Science Capabilities"!10-100" better sensitivity and resolution than current mm arrays."
• Baselines to ~15 km (0.015” at 300 GHz) in “zoom lens” configurations"
• Sensitive, precision imaging 84 to 950 GHz!(3.6 mm to 315 µm)"
• State-of-the-art low-noise, wide-band SIS receivers (8 GHz bandwidth per polarization)""• Flexible correlator with high spectral resolution
at wide bandwidth""• Full polarization capabilities"
• Est. 1TB/day data rate"
ALMA Full Operations
Early Science (now)
Frequency Coverage"
!"#$%#&'()*+,-.)
3 6 7 9
/00)
100)
200)
3456
0)
7456
0)
8456
0)
/456
0)
H2O"
H2O"
H2O"
H2O"
O3"
O2"
cm/mm: rich in line + continuum diagnostics"
CO ‘ladder’" total gas masses! excitation, dynamics! phys. conditions"
CNO fine structure lines" ISM gas coolant!
Synchrotron + Free-Free (AGN+SNR) star formation!
Thermal dust(young stars) star formation!
!"#$%$#&$'(($)%
PAHs + SiL"
*+,($%!-*)%
Smail et al. 2011 Swinbank et al. 2011"
Cosmic Eyelash model SED
!"#$%&!'
Sensitivity & Resolution"
ALMA will match best observatories at other wavelengths in sensitivity and spatial resolution " first “sharp” images at (sub)mm wavelengths
Telescope Diameter: Source Confusion"25m" 3.5m"
ALMA vs. Herschel"
Bussmann, Riechers et al. 2015"
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"
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)"
What Does an Interferometer Measure?"
Interferometric Imaging"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"
ALMA 8 (28)
CARMA
23 (253)
6 (15)
ALMA Full Science
50+12+4 (1225+66)
Cycle I 32+9+2 (496+36.)
Collecting Area & Baselines"
Circles Show Collecting Area (sensitivity) Captions give # of antennas and # of baselines (fidelity)
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"
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