[mmaimcal] Re: [alma-site] location of terahertz array

[hliszt]

The points raised here are very similar if not identical to those
involved in using a singledish to recover the short spacings.  The
fundamental issue is whether a different instrument is needed or
whether the homogeneous array suffices.  Building another instrument
is just that; building another instrument.

regards, Harvey
------------
John Richer wrote:
> 
> Hi Simon,
> 
> The size and location of compact array for ALMA, or indeed if it
> should be built at all, are all important and interesting issues.  In
> the small number of meetings where I've heard this discussed, I've
> never seen a clear statement of the scientific goals of the ultra
> compact array.  I'm assuming the argument goes like this
> 
>   1) we need an array of small dishes because we are nervous about
>      'homogeneous mosaicing' producing complete spatial frequency
>      coverage, particularly at high submm frequencies and in the
>      continuum.
> 
>   2) So we build a small array of dishes to deal with this problem and
>      use ALMA receivers to make it relatively cheap.
> 
>   3) But the marginal cost of specifying this array for THz operations
>      is small, so let's do it; and similarly the marginal cost of the
>      high mountain site is small.
> 
> There is a logic to all this, but the key issues are obviously
> 
> - do we believe we need this array for the short spacing information?
>   I haven't seen the simulations yet to show this one way or another.
>   Of course, everyone has a different view on how effective
>   'homogeneous' mosaicing will be, but I think at low frequencies and
>   for narrow band signals it should be very good;  arguably, this will
>   cover most science goals which are probably line observations of
>   extended gas clouds.
> 
> - What is the science increment by going to >1THz at very high angular
>   resolution?  I know there are some lines out there, but what
>   specifically drives the need for super high resolution when so
>   little is known about these lines anyway?
> 
> I think this all needs looking at in the context of this wider debate,
> but they are fascinating issues to chew over.   Can anyone point me to
> the science cases for >1THz, or tell me about simulations involving
> the compact array?
> 
> Cheers,
> 
> John
> 
> --
> John Richer
> Astrophysics Group, Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE
> Tel: +44-1223-337246  Fax: +44-1223-354599  http://www.mrao.cam.ac.uk/~jsr/

-- 
Harvey Liszt                             phone:804.296.0344 fax 0278
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