David Naylor and Brad Gom

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FTS-2 A Fourier Transform Spectrometer for use
with SCUBA-2

• David Naylor and Brad Gom
• University of Lethbridge
• On behalf of the Canadian SCUBA-2 Consortium

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Outline

• Review of Fourier transform spectroscopy at the
  JCMT
• Science goals of FTS-2
• Challenges of ground-based submm FTS
• Design of FTS-2

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Project Milestones
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Andromeda Galaxy
In optical light
In infrared light
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FTS-2 Science Goals
To determine the Spectral Energy Distributions
(SED) of a wide range of astronomical objects
through low resolution imaging spectroscopy. FTS-2
fills a niche between the SCUBA-2 continuum
images and the higher spectral resolution, but
limited size images, produced by HARP.

• Interstellar Medium - offers both a rich
  spectrum, with continuum and line components, and
  a rich field. The FTS will allow for the spectral
  index mapping of molecular clouds and in
  particular identify those sources where a
  significant contribution to the total band flux
  arises from line emission.
• Extra galactic objects although challenging it
  may be possible to measure the SED of some higher
  Z objects across the 850 µm band.
• Images are great, but the science is revealed
  through spectroscopy.

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Spectral Energy Distribution
The continuum emission can be expressed as
??
850 and 450 µm photometry can provide estimates
of ? but a knowledge of the dust temperature is
required to determine ß.
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Comparison of methods to determine SEDs

• 850 and 450 µm photometry
• best sensitivity
• requires knowledge of source size and coupling to
  850 and 450 µm beams
• requires estimate of temperature to get ß
• 450 µm observations difficult
• FTS-2 850 and 450 µm spectroscopy
• less sensitive than photometry
• requires knowledge of source size and coupling to
  850 and 450 µm beams
• can use spectra to determine temperature
• 450 µm observations difficult
• FTS-2 850 µm spectroscopy
• less sensitive than photometry
• essentially same beam for all observations
• low dependence on assumed temperature
• does not require 450 µm observations

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Comparison of methods to determine SEDs
Measurement Retrieved Beta Assuming known T30K Retrieved Beta Error Assuming T40K (add to second column) Retrieved Beta Error Assuming T20K (add to second column)
Photometry 1.503 0.122 -0.263
Photometry 2.005 0.122 -0.263
FTS 2 band 1.5002 0.0149 -0.0242
FTS 2 band 2.0003 0.0152 -0.0245
FTS 1 band 1.4995 0.0136 -0.0212
FTS 1 band 1.9995 0.0136 -0.0212
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The challenge
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KL
S
Bar
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Poor S/N is not always a showstopper
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HCl doublets
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SO 98 - 87
SO 88 - 77
H13CN 4 - 3
SiO 8 - 7
CS 7 - 6
SO 78 - 67
CO 3 - 2
SO2 164,12 163,13
SO2 191,19 180,18
CH3CN 19 - 18
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SCUBA-2 FTS Features
FTS-2 design

• Hyperspectral imaging FTS-2 in conjunction with
  SCUBA-2, will provide an unprecedented
  spectroscopic imaging capability in the
  submillimetre.
• Mach-Zehnder Design - The innovative FTS-2 design
  provides high efficiency and differential
  measurements of source and background regions.
• Dual wavelength operation FTS-2 will take
  advantage of the unique simultaneous dual
  wavelength capability of SCUBA-2.
• Variable spectral resolution - The resolving
  power of FTS-2 can be selected instantly within a
  range of 10 to 5000.
• Novel observing modes In addition to the
  baseline stare mode, the potential exists to
  exploit novel observing modes (aliasing and
  DREAM) to minimize variations in atmospheric
  transmission.

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SCUBA-2 Feed Optics
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FTS-2 JCMT Installation
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FTS-2 Operations
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FTS-2 observing planning tool
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SCUBA 2 Ports Observing Orion KL
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SCUBA 2 Ports Observing W 31 D
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Predicted performance of FTS-2
850 ?m 850 ?m 450 ?m 450 ?m
FTS Optical Efficiency i 43.7 43.7 43.7 43.7
System Transmission ii 23 23 23 23
Resolution (MHz) 150 3000 150 3000
Resolution (cm -1) 0.005 0.1 0.005 0.1
1-? Flux sensitivity in one hour integration (mJy) 255 13 2524 126
1-? ?T sensitivity in one hour integration (mK) 15 0.7 106 5
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Acknowledgements

• Brad Gom
• Dan Handford
• John Lindner
• Jamil Shariff
• Locke Spencer
• Jeremy Svendsen
• Greg Tompkins
• Dave Triomphe
• Brandon Wong
• Baoshe Zhang
• CFI, NSERC, CSA, ASRA

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FTS-2 Time estimator
In terms of dT
In terms of Flux
Where Tnumber of 16-hr nights ? mapping
efficiency 0.6 ?f spectral resolution in MHz A
survey area in square degrees FOV FTS-2
field of view (2.8 X 10-3 sq deg) NEP noise
equivalent power 7 X 10-17 W Hz 1/2 at
850 ?m 5 X 10-16 W Hz
1/2 at 450 ?m?T survey noise temperature in
K (1-?) x 8.8 X 104 at 850 ?m 8.4 X 105 at 450
?m NEFD SCUBA-2 NEFD per pixel (1-s, 1-?) 25
mJy at 850 ?m 80 mJy at 450 ?m D survey
photometric depth in mJy (1-?)