(range_file = "") Name of range file
(tmpl_image = "") Name of template image
(out_file = "") Name of output file
(sexroot = "") SExtractor file root name
(xgalroot = "") Extracted image root name
(reduce_cl = "") Name of output GIMFIT2D cl script
(imscale = ) Image scale (arcsecond/pixel)
(psftype = "") PSF type (delta|gaussian|tiny_wfpc|tiny_nic|tiny_stis|user)
(in_psf = "") Name of tinytim/user PSF image
(c_abs = 0.) Disk internal absorption coefficient (0-1)
(seeing = ) Seeing FWHM (arcseconds)
(egain = ) Effective gain (electrons/DU)
(earea = ) Extraction area in multiple of isophotal area
(ngal = ) Number of different galaxy simulations
(ngalbl = ) Number of galaxies for comparison baseline
(ngalfl = ) Number of galaxies per asymmetric flux level
(nHII = 0) Number of HII regions
(HIIrmax = ) Maximum galactocentric distance for HII regions
(HIIflux_leve = ) HII region flux levels
(seed = ) Random generator seed
(loggen = ) Generate flux and radius values in log (yes/no)
(osamp = 5) Core oversampling factor
(mode = "q")
GALIMAGE is used to create simulated PSF-convolved galaxy images. The galaxy light model is the sum of a de Vaucouleurs bulge and an exponential disk. GALIMAGE only uses in_image as a template for the output image size (NOTE: odd dimensions should be used) and header information, so in_image can even be a blank image. There are 11 parameters going into the galaxy light model: the total flux ltot, the bulge-to-total light ratio bt (bt = 1 for pure bulge systems), the bulge effective radius re, the exponential disk scale rd, the bulge ellipticity e, the disk inclination angle i in degrees (i = 0 for face-on disks), the bulge position angle phib, and the disk position angle phid. Position angles are measure clockwise from the positive y-axis of the image. The bulge ellipticity e is given by e = 1 - (b/a) where b = semi-minor axis length and a = semi-major axis length. The last three parameters are the x and y centroid pixel shifts dx and dy and a background level db in DU.
Four types of point-spread-function (PSF) are currently supported: Delta, gaussian, TINYTIM and user. The choice of PSF is specified by psftype and the PSF name is given by in_psf. If a Gaussian PSF is selected, its FWHM is given by seeing. The TINYTIM PSF type must be used when synthetic HST PSF's produced by the TINYTIM package are used. The volume of input TINYTIM PSF's need not be normalized to one. GALIMAGE takes care of it. The delta psftype simply means that no PSF convolution is applied to the model.
IMPORTANT: If the PSF image has dimensions nxpsf and nypsf, then the PSF should be centered at ((nxpsf-1)/2 +1, (nypsf-1)/2+1). TinyTim automatically performs the proper centering.
WFPC2 undersampling has been a major constraint on the way models are generated. First, a central core oversampled by a factor of 5 is generated. This central core is convolved with an oversampled (TinyTim) PSF, shifted by dx and dy through bilinear interpolation, and the result is rebinned to the detector resolution. Bilinear interpolation is performed on the logarithmic intensity values to minimize errors. Nonetheless, errors introduced by this interpolation scheme are at the 5% level which is a reasonable trade-off for speed. This is essentially the same procedure as the one used by Krist. Second, an outer model is generated and convolve with a PSF. The convolved outer model is then added to the core component, and the pixel scattering function (see TINYTIM manual) is applied if psftype = tinytim.
GALIMAGE also updates the image header of the output model with the parameter values used to create it.