Title  Imaging galaxy cluster mergers via the Sunyaev-Zel'dovich effect
Pi     K. Yamada
Time   400 hrs

1. Name of program and authors

Imaging galaxy cluster mergers via the Sunyaev-Zel'dovich effect

K. Yamada, N. Okabe, T. Kitayama, M. Hattori

2. One short paragraph with science goal(s)

We aim to reveal detailed structures around the merger sites and the
shock fronts in galaxy clusters via deep mapping observations of the
Sunyaev-Zel'dovich effect (SZE). The SZE provides a direct probe of
thermal pressure in the intracluster medium, complementary to the
X-ray observations which probes the emission measure.  The SZE is also
a unique tool for detecting the gas shock-heated to above 10 keV, for
which current X-ray spectrometers lose sensitivity. With the spatial
resolution of ALMA (2" at 90 GHz), we will be able to resolve the
substructures down to 10 kpc at z=0.3. These measurements will be
particularly useful in understanding the dynamical nature of the
mergers and their links to the thermal evolution of galaxy clusters.

3. Number of sources : 5 clusters with signatures of violent mergers
   and shock heating 

4. Coordinates:

4.1. Rough RA and DEC : 
     (13h, -10d), (06h, -50d), (20h, -60d), (02h, -40d), (16h, -10d) 

4.2. Moving target: no 

4.3. Time critical: no 

4.4. Scheduling constraints: (optional)


5. Spatial scales:

5.1. Angular resolution (arcsec): 2 arcsec (9 kpc at z=0.3)

5.2. Range of spatial scales/FOV (arcsec): 180 arcsec (800 kpc at
     z=0.3) diameter. Wide-field mosaic is necessary; e.g., 19 and 7 
     pointings in a hexagonal orientation for 12m and 7m antennas,
     respectively. 

5.3. Required pointing accuracy (arcsec): 1


6. Observational setup

6.1. Single dish total power data: required

     Observing modes for single dish total power: nutator switch or
     the on-the-fly mapping

6.2. Stand-alone ACA: yes 

6.3. Cross-correlation of 7m ACA and 12m baseline-ALMA antennas: required

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


7. Frequencies:

7.1. Receiver band: Band 3

7.2. Lines and Frequencies (GHz): 90 GHz

7.3. Spectral resolution (km/s):

7.4. Bandwidth or spectral coverage (km/s or GHz):


8. Continuum flux density:

8.1. Typical value (Jy): 0.02-0.06 mJy/ (2" beam) 

8.2. Required continuum rms (Jy or K): 0.004 mJy/ (2" beam) 

8.3. Dynamic range within image: 10-100.
      

8.4. Calibration requirements: absolute      (5%)  
                               repeatability (5%)
                               relative      (5%)


9. Line intensity: no 

9.1. Typical value (K or Jy):

     (take average value of set of objects)
     (optional: provide range of values for set of objects)

9.2. Required rms per channel (K or Jy):

9.3. Spectral dynamic range:

9.4. Calibration requirements: 

10. Polarization: no 

10.1. Required Stokes parameters:

10.2. Total polarized flux density (Jy):

10.3. Required polarization rms and/or dynamic range:

10.4. Polarization fidelity:

10.5. Required calibration accuracy:


11. Integration time for each observing mode/receiver setting (hr): 20
     hours per source for the ACA-baseline_ALMA cross-correlation, and
     additional 60 hours per source for the stand-alone ACA

12. Total integration time for program (hr): 100 hours for the 
    ACA-baseline_ALMA cross-correlation, and 300 hours for the stand
    alone ACA


13. Comments on observing strategy : 

    Major advantages of using Band 3 for the SZE observation are that
    the level of foreground/background contamination is expected to be
    minimal and the FOV is still adequate for covering compact
    (sub)clusters. In order to map the larger area and increase the
    number of feasible targets, Band 1 will be more suitable.

    We have checked that there are very few known luminous (>10mJy)
    source at 90GHz in our target fields. It may nevertheless be the
    case that there exist yet unknown or variable sources in the
    fields.  Detailed simulations will be helpful to clarify to what
    extent such sources can be removed using the long baseline data.
       
    An absolute calibration accuracy of 5% will be desirable and at
    least 10% will be necessary for performing detailed combined
    analysis with high sensitivity X-ray data to explore the physical
    status of the intracluster medium.