Title   The GMC Scale Chemical Anatomy of Nearby Galaxies
Pi     D. Meier
Time   144 hrs

   1. Name: The GMC Scale Chemical Anatomy of Nearby Galaxies 
   		D. Meier, J. Turner

   2. One short paragraph with science goal(s):

Little is known about the chemistry applicable on scales larger than a
few parsecs, for example over galactic-scale structures such as spiral
arms.  Chemical surveys of nearby galaxies are important for
understanding this large-scale chemistry.  Beyond providing physical
conditions and abundances for molecular clouds in specific galaxies,
it will also provide insights into interesting astrochemical
questions, such as what is the cosmic ray rate versus galactocentric
distance?  What is the ionization fraction at different galactocentric
distances?  Does the chemical structure of the ISM differ
significantly between regions where the clouds are expected to be
young (eg. nuclei, spiral arms) versus those not (eg.  outer galaxy,
interarm regions) and if so can this be used to ``clock'' the chemical
ages of molecular clouds across the galaxy?  Over what physical scale
do bars, spiral arms, AGNs, and massive star forming regions (AKA
"starbursts") influence the chemistry and physics of their
surroundings?  Can we see the chemical signature of shocks associated
with galaxy dynamics?  Must grain surface processing be invoked to
explain the rich, molecular complexity seen, particularly in the
center of galaxies, or can normal ion-molecule chemistry in especially
dense or warm gas suffice?  What is the molecular complexity reached
in diffuse clouds and what constraint does this impose on basic
chemical formation pathways?  Comparisons with the study of
astrochemistry in the LMC and SMC should also provide important clues
on the dependence of molecular abundances to abundances of the atomic
pools.

   3. Number of sources: 

	3: 1 AGN (Centarus A, Circinus --class galaxy)
	   1 Starburst (NGC 253, N4945 --class galaxy)
 	   1 "Normal Spiral" (M 83 --class galaxy)

   4. Coordinates:

      4.1. Distributed Across the Sky

      4.2. Moving target: no

      4.3. Time critical: no

1 MM BAND Line Survey:
---------------------

   5. Spatial scales:

      5.1. Angular resolution (arcsec): 1" = 10-30 pc

      5.2. Range of spatial scales/FOV (arcsec): 
		6 pointing distributed in galactocentric radius.

      5.3. Single dish total power data: yes

      5.4. ACA: yes

      5.5. Subarrays: no


   6. Frequencies:

      6.1. Receiver band: Band 6

      6.2. Lines and Frequencies (GHz):
           4 x (1 GHz*8 basebands) = 32 GHz distributed across 
	   218 - 270 GHz

      6.3. Spectral resolution (km/s): 5 km/s

      6.4. Bandwidth or spectral coverage (km/s or GHz):
		8 GHz (as wideband as possible)		


   8. Line intensity:

      8.1. Typical value (K or Jy): 0.03 - 10 K

      8.2. Required rms per channel (K or Jy): 0.01 K

      8.3. Spectral dynamic range: 3 - 1000

   9. Polarization: no

   10. Integration time for each observing mode/receiver setting (hr):
		2 hrs per receiver setting per pointing per galaxy


   11. Total integration time for program (hr): 
	(6 pnts * 4 corr. set. * 3 gals.) * 2 hrs = 144 hrs
			=~ 10% of sub-theme

   12. Comments on observing strategy (e.g. line surveys, Target of
       Opportunity, Sun, ...): (optional)


Three galaxies will be selected at distances of ~5 Mpc.  One AGN
(eg. NGC 4945, Centarus A -like galaxy), one starburst (eg. NGC 253,
N4945 -like galaxy) and one "normal" spiral (eg. M83 -like galaxy) 
will be selected in order to assess the impacts of starbursts, AGNs 
and bars/spiral arms on the chemistry.  Six pointings will be 
distributed across each galaxy, one nuclear, one inner disk, and one 
outer disk (~solar radius) and three others distributed to sample 
particularly interesting regions (eg. spiral arms, bar ends, massive 
star forming regions).

Four 1 GHz x 8 baseband correlator configurations will be distributed
throughout Band 6 (218 - 270 GHz), making sure to catch important
molecular transitions.  Based on the sensitivity achieved in 2 hrs, it
is conservatively estimated to be possible to detect all transitions 2
K and brighter in the Nummelin et al. 1998 Sgr B2 survey (given
similar chemistries).  This equates to ~100 molecular transitions over
the 32 total GHz of bandwidth.  Deep 1 mm continuum observations will
also be obtained for free, providing measurements of N(H_2) to derive
fractional abundances.  Moreover, the wide bandwidth of spectral 
line observations will provide an opportunity to assess the line 
contamination of the continuum data.

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Review Chris Carilli: OK
--------------------------------------------------
Review v2.0:
 
The GMC scale...
Meier & Turner 

This line survey proposal on specific local galaxies is a must-do, but
modest program. Choosing to make discrete pointings in only 3 targets
is reasonable. It would be interesting to get the authors' estimate of
whether they're holding down the time request at the expense of
getting better sampling.

It would also be interesting to know what additional science results
could come from coordinating targets, fields and analysis with
localgal_3 `Calibrating the I_CO...'

Is the ACA needed if the fields are not within a primary beam of each
other?