Title  Background quasars and the chemistry of the ISM
Pi     Black
Time   396 hrs

1. Name: Background quasars and the chemistry of the ISM
         in the Magellanic Clouds
   Authors: Black, Aalto et al
    
2. Science goal: More than 60 quasars are known to lie behind the
Magellanic Clouds (Geha, Alcock, Allsman, et al. 2003; Dobrzycki
et al. 2003).  A subset of these will have flat spectra with
sufficient flux at mm and submm wavelengths to permit absorption
spectroscopy that will probe the molecular component of the
interstellar gas in the MC. 
High abundances of molecules like HCO+, H_2CO, HCN, HNC have been
found in the diffuse gas of the Galaxy. From  HI emission/absorption
measurements it is known that the diffuse ISM is colder in the 
Magellanic Clouds and it is expected that the diffuse gas abundances
and physical conditions are different from those in our Galaxy's high
metallicity environment.

The fact that most of these quasars
have been identified by their variability in databases from microlensing
surveys is a reminder that ALMA studies of lensed quasars will be
of considerable interest. The identification of background quasars
via optical variability selects against highly reddened sources
occulted by dense molecular gas; however, X-ray-selected AGN include
some highly obscured sources Haberl et al. 2001).
Quasars behind the MC also provide astrometric reference for
measurements of proper motion (see prop on stars and proper motion).






3. Number of sources: 	5
	

4. Coordinates:

  4.1. LMC      (RA=05h40m, DEC=-69d)
       SMC (RA=01h, DEC=-73d)
       
 
  4.2. Moving target: no

  4.3. Time critical: no


5.  Spatial scales:

  5.1. Angular resolution: 0.1"=0.025 pc linear

  5.2. Range of spatial scales/FOV: 
				   
  5.3. Required pointing accuracy: (arcsec)
  
  6. Observational setup

6.1. Single dish total power data: no

     Observing modes for single dish total power: 

     (e.g., nutator switch; frequency switch; position switch;
     on-the-fly mapping; and combinations of the above)

6.2. Stand-alone ACA: no

6.3. Cross-correlation of 7m ACA and 12m baseline-ALMA antennas: 
     no

6.4. Subarrays of 12m baseline-ALMA antennas: no



7. Frequencies: 345 GHz

  7.1. Receiver band: 	Bands 7



  7.2. Lines: For example: 1mm and 3mm transitions of 
  CO, 13CO, HCO+, HCN, HNC, CN, CS, C2H, C3H2 - that have
  been observed in Galactic absorption studies.

  7.3. Spectral resolution (km/s):0.2
  

  7.4. Spectral coverage (km/s or GHz): 20 km/s


8. Continuum flux density: 

  8.1. Typical value: 10 mJy

  8.2. Continuum peak value:

  8.3. Required continuum rms:0.1 mJy

  8.4. Dynamic range in image:


9. Line intensity:

  9.1. Typical value: 0-10 mJy

  9.2. Required rms per channel:1-2 mJy

  9.3. Spectral dynamic range: 
  
  9.4. Calibration requirements: as good as possible
  

10. Polarization: no


11. Integration time per setting: 

3mm: 4 hrs x number of molecular species (rms 1.17 mJy)
1mm: 7 hrs x number of molecular species (rms 1.4 mJy)
 
9 species, two transitions, 4 QSOs = 99x4

11. Total integration time for program: 396 hrs

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Review v2.0:
 
1.8.3 background quasars and the chemistry of the ISM in the MC Black
    396 hours

proposal is to do 5 sources. Potentially very interesting, but.. I
would start with just one.