[mmaimcal] Re: US-only ASAC meeting

[Al Wootten]

The minutes, with revisions received to date from the last whole ASAC
meeting, may be found at:
http://www.cv.nrao.edu/~awootten/mmaimcal/asac/asacmay01minutes.html

This says, in part:
"S. Guilloteau
noted the potential imact of a large future correlator. With a large
bandwidth and high sensitivity it will be possible to observe several
lines simultaneously, providing homogeneous data sets. The large bandwidth, 
higher sensitivity and larger number of channels will be
particularly important for high redshift galaxies surveys. Other projects
requiring simultaneous observations of several lines to provide homogeneous data
sets and planetary studies will also greatly benefit. M. Yun commented on the 
high data rates required."

In my opinion, the case for the future correlator is considerably overstated
here.  Several lines may be observed simultaneously with the baseline
correlator providing data sets of equal homogeneity.  The bandwidth of the
baseline correlator is equal to that of the future correlator.  There
is higher sensitivity in the future correlator in the broadest band modes
but the sensitivity is equal for spectral windows such as those which can
be achieved with existing correlators and which will be employed in at least
55% of observations, according to a pessimistic (my opinion) estimate by 
Guilloteau in his DSB/SSB memo.  The resolution of the baseline
correlator in its broadband mode is sufficient to provide good signal on
any known high redshift galaxy, with 25 km/s channels at 1.3mm.  
Confirmed detections of high reshift galaxies show linewidths much larger 
(400 k/s) than this.  A face-on quiescent spiral, if such a beast exists at high
redshift, would still cover several resolution elements.  Most high redshift
galaxies appear disturbed; an estimate of the 'turbulent velocity' in e.g.
Arp 220 by Scoville and Yun was 70 km/s, which we might adopt as a minimum
expectation.  Several 'redshift machines' operating on hi-z CO searches are
planned; the ALMA resolution matches that from either the UMass/LMT version
or the CSO version, the two with which I have some familiarity.

I have no doubt we will want a more capable correlator in the future.  I think
that the appropriate time for design of this is ca. 2006 for deployment after
ALMA construction.

Clear skies,
Al