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

Radio Telescopes Around the World: >100"

www.astro.uni-bonn.de/~rcbruens/links/world_map.html

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 Antennas"

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

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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"

An Interferometer"

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)"

What Does an Interferometer Measure?"

Separation of “slits” / projected baseline"

Visibility and Sky Brightness"

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)

Sensitivity+Baselines=Image 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"

Limitations of Interferometry"

ALMA vs. ACA+ALMA"•  *./0123456%47%5829:;%<212=;%

>?@*AB"AC%$%&?DA#%?E%F?GB%)$BHA)%-,)I%JKL&%$MD%JKL&'$($N%(?&+$BA%%%

12-M ARRAY ONLY MODEL 12-M + 7-M ACA

Image reconstruction

artifact (“bowls”)

Not present when 7-m antennas included