SIMDATA Simulation Shigehisa Takakuwa (ASIAA) ALMA Users Meeting 2011

Preparing for the ALMA Proposal What can you really get with ALMA observations ? Can ALMA provide you with what you want to see ? --> ALMA Observing Simulations

Theoretical model ALMA observing band ``Observed’’ Images Theoretical Physical Parameters of your favorite astronomical objects ``Observed’’ Physical Parameters  2 SED fitting ALMA Imaging Simulation Radiative Transfer Code Compare !!  Science Power of ALMA ALMA observing Simulation

ALMA Observation Data we obtain are ``Visibilities V (u,v)’’, V (u,v) = ∬ I (x,y) exp {-2πi (ux+vy)} dxdy x, y: Sky Spatial Coordinate u, v: Antenna Tracks projected on the sky V (u,v) consists of amplitude and phase Fourier-Transform of Source Images I (x,y)

ALMA Imaging --> To obtain I (x,y) Ideally: V (u,v) = ∬ I (x,y) exp {-2πi (ux+vy)} dxdy In reality: V obs (u,v) = S (u,v) ∬ I (x,y) exp {-2πi (ux+vy)} dxdy S(u,v): Sampling Function  Fourier-Transform of V obs (u,v) is NOT Real I(x, y), but we call it Dirty-Image I D (x,y) Methods to guess real I(x,y) from I D (x,y) ---> Clean, MEM, etc…

How to evaluate the imaging quantitatively ? ---> Introducing ``Fidelity’’ Fidelity (i, j) = abs[ Model (i, j) ] At each image pixel (i, j); abs[Model (i, j) - Simulated (i, j)] So Fidelity is an image. Pety et al. 2001

Model | Model - Simulation | Fidelity = Example of the ALMA Imaging Simulation: Debris Disk ACA is crucial to recover the flux from debris disks. (Takakuwa et al. 2008)

ALMA Observing Simulator Task ``simdata’’: One of the tasks in CASA, the ALMA data reduction software Create model visibilities from model images, with observing parameters such as the antenna location, specified by the user. Fourier-Transform the Visibility, and ``CLEAN’’ the image with the user-specified imaging parameters, such as weighting on the visibility sampling points.

Products from simdata  Synthetic visibilities  A synthesized CLEANed image  Image of the Difference between the model and simulated image, and Fidelity ALL you need is a model of the sky ALMA. (E)VLA, SMA simulations possible

Simdata Example: Forming Planets in Protoplanetary Disk

Proto-Planetary Disk Simulation Effects of the Different antenna configurations

demodemo

Hands-on Exercise: Read input fits image into CASA PC with CASA installed ＋ Input Image File (in FITS ）  casapy  default(‘importfits’)  fitsimage=‘input50pc_672GHz.fits’  imagename=‘input50pc_672GHz’  go  viewer();

 casapy  default(‘importfits’)  fitsimage=‘input50pc_672GHz.fits’  imagename=‘input50pc_672GHz’  go  viewer();  default(‘simdata’)  skymodel = ‘input50pc_672GHz’  project = ‘psim2’ (rm -rf psim2* for the 2nd time)  direction=‘center’  mapsize=‘0.76arcsec’  antennalist=‘/Applications/CASA.app/Contents/data/alma/simmos/alma.out20.cf g’ (Try different antenna configurations !)  imsize=[192,192]  threshold=‘1e-7Jy’  niter=10000  totaltime=‘1200s’  graphics=‘both’  image=True  analyze=True  go

Hands-on Exercise: simdata simulation, changing input model parameters  modifymodel=True  incenter=‘230GHz’  inwidth=‘2GHz’  incell=‘0.0155arcsec’  go