1. Name of program and authors

A ultradeep galaxy survey through clusters using ALMA

Andrew Blain

   2. One short paragraph with science goal(s)

Clusters of galaxies are the most massive gravitationally relaxed
systems in the Universe, and the most powerful gravitational
lenses. Depending on the brightness distribution of faint background
galaxies, the surface density of their lensed images to a chosen flux
density limit can be increased by several times by a foreground
cluster. Furthermore, the magnification, by up to several 10's, allows
galaxies to be probed in more detail than possible without the
magnification. In order to determine the properties of the population
of galaxies at fainter levels than currently possible, benefiting from
the gravitational lensing, the typically ring-like 1-arcmin radius
`critical line' structures along which the greatest magnifications
will be found will be mapped, involving of order 20 pointings per
cluster.

An additional speculative investigation could image the central core
of the clusters to the same deep depth. If the potential of the
cluster is sufficiently is sufficienty steep at the center:
corresponding to a volume density of mass that depends on radius as
the -1.5 power or steeper, then de-magnified images of all the
background galaxies within the = approx.  1 arcmin radius of the
critical lines can be imaged within a few arcsec of the core of the
cluster. ALMA's exquisite resolution can be used to detect all of
these objects in a single additional pointing per cluster (Blain 2002
MNRAS 330 219).

Hence, the cluster images would have a `bullseye' structure. The
location of the fields within the clusters will be chosen carefully
based on the best models of the potential of the clusters available in
2012 from optical, X-ray and Sunyaev-Zeldovich (SZ) effect
observations.

It is likely that it would be productive to include the same targets in
a 90-GHz band-3 line survey, which could produce SZ effect images 
alongside.

   3. Number of sources

20 rich clusters at approximately z=0.2-0.4. Spread around the sky,
but mainly equatorial (based on the most complete cluster surveys
having been followed up by large telescopes in the North).

   4. Coordinates:

      4.1. Rough RA and DEC=20
		20 mostly equatorial and low-dec northern clusters,
avoiding 04-08 hours.
		Probably want to avoid 02hr, which is blessed with a
multitude of deep fields.

      4.2. Moving target: no  (e.g. comet, planet, ...)
      4.3. Time critical: no  (e.g. SN, GRB, ...)

   5. Spatial scales:
      5.1. Angular resolution (arcsec): 0.1"
      5.2. Range of spatial scales/FOV (arcsec): 0.1-10"          
           (optional: indicate whether single-field, small mosaic,
            wide-field mosaic...)
	Small mosaic. 20 fields at 280 GHz round critical lines in band-6/7
	      7 fields at 90GHz in a hexagonal pack to cover whole region. 
      5.3. Single dish total power data: YES (if ACA, then Single-Dish)
      5.4. ACA: yes - sensitivity crucial, and SZ signal from high 
frequency detection is possible in the cluster fields even at 280 GHz.
      5.5. Subarrays: no - sensitivity crucial

   6. Frequencies:
      6.1. Receiver band: Band 3, 6, 7, or 9
Edge of band 6/7: faint continuum surveys most promising at these 
frequencies.
Band-3: line surveys most promising here, and SZ effect
      6.2. Lines and Frequencies (GHz):
Continuum in band 6/7 single tuning.
3 line tunings in band 3.
      6.3. Spectral resolution (km/s): 50-300 km/s
      6.4. Bandwidth or spectral coverage (km/s or GHz): 8GHz

   7. Continuum flux density:

      7.1. Typical value (Jy):
Typical optical galaxies at 0.1mJy or less. Deep survey, so unknown.
SZ effect a few 100 mJy integrated over the cluster.

      7.2. Required continuum rms (Jy or K):
0.01 mJy - band 6/7 - to reach much deeper than any current survey:
detection limit is about 40 times deeper than current record.

      7.3. Dynamic range within image: 
Brightest continuum sources 20mJy.

   8. Line intensity:
      8.1. Typical value (K or Jy):
SG:		~1Jy km/s (SG: probably VERY optimistic... It corresponds to line flux of currently detected sources, i.e. fairly bright objects)
      8.2. Required rms per channel (K or Jy):
SG:		~3mJy  (SG: don't understand that value: seems to be the peak line flux...)
			 (SG: I'll assume 0.3 mJy (10 sigma))
      8.3. Spectral dynamic range:     
		Small

   9. Polarization:  no  (optional)
      9.1. Required Stokes
      9.2. Total polarized flux density (Jy)
      9.3. Required polarization rms and/or dynamic range
      9.4. Polarization fidelity

   10. Integration time for each observing mode/receiver setting (hr):
	Continuum rms is 0.016 mJy per hour => > 2.5 hour per pointing, 50 
hours per cluster.

SG:	Line rms is 0.12 mJy per hour for 50 km/s resolution. Need 0.14 hr =
per tuning per
	field, 4 tuning for band 3 coverage, total 0.54 hrs per field, 7 fields so 3.7 hrs...

   11. Total integration time for program (hr):

20 clusters (x54hr)= 1080 hours

   12. Comments on observing strategy (e.g. line surveys, Target of
       Opportunity, Sun, ...): (optional)
SG: SZ part not demonstrated here. Using low angular resolution (4" in 
compact array),	the brightness sensitivity in continuum at 3 mm is 1 mK per hour, which corresponds to	an SZ signal of 8.7 10^-4.  Is that sufficient ?


Review Chris Carilli: O.K., integration times checked.  This is large
proposal (1080 hrs). could cut it back by factor 2 to 4 (5 to 10
clusters instead of 20).

Comment Ewine: Time cut by factor of 2 to 10 clusters x 54 hrs = 540 hrs