Unstructured thoughts AOfed dIFUs

1
Unstructured thoughts _at_AO-fed d-IFUs

• Keith Taylor
• TMT (AOI)WG
• 19 March 2004

2
Required input to the d-IFUInstrument Design
Process

• The Hard Bit
• What do we need from the SAC ?
• What class of objects need spatially resolved
  (3-d) spectroscopy ?
• When is 3-d spectroscopy absolutely essential,
  rather than wouldnt it be nice ?
• What is the likely (rest-frame) spatio-spectral
  (x,y,?) morphology of these sources ?
• Limiting surface brightness requirements
• What fraction are emission-line sources with
  known z ?
• What is the volume density (as fn of z) of each
  class of
• d-IFU(able) objects ?
• Sensitivities to cosmological model assumptions
• Sensitivities to evolutionary assumptions
• Is there an argument for building a d-IFU system,
  because we
• know how to (or think we do) ? or
• Should we actually be defining its (presently
  perceived) purpose (quantitatively) ?

3
Required input to the d-IFUInstrument Design
Process

• The Easy Bit
• What do we need from the AOWG ?
• MCAO vs- MOAO
• What are the FoV implications ?
• What are the PSF implications ?
• What are the throughput implications ?
• What are the relative risks ?
• What is the delivered PSF as function of
  (x,y,?,t) ?
• What is the realizable duty cycle for a
  particular PSF(x,y,?) ?
• Why is GLAO off the menu ?

4
Why do we need this information ?

• .. to answer the following (fundamental) design
  questions
• What is the optimum spatial sampling ?
• Unlikely to a have a selector knob for dialing
  up a preferred value.
• What is the required resolving power and ?-range
  ?
• How many d-IFU buttons are required ?
• How big a spectrograph (and how many) do we
  require ?
• What is the required minimum separation between
  individual d-IFUs ?
• When can we get away with multi-slit (or
  multi-fiber) spectroscopy ?
• MOS will often win over d-IFU for high surface
  density targets

5
Crisis of Confidence

• in the AOWG
• The SAC (and the PS ?) dont believe you can
  deliver good science.
• in the IWG
• The PM (and the PS ?) doesnt believe (may be
  required to be convinced that) we can manage a
  piss-up in a brewary.
• The consequence
• Lets build a Telescope NOT an Observatory