UNDER DEVELOPMENT

The software package is currently being dramatically improved and updated.
This is a (very) old version, potentially with bugs.

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Help for "simage_resample_pdf" routine:

Resamples a true population of galaxy shapes to generate a new object for a simulated image.

This routine smooths and Monte-Carlo resamples the PDF of galaxy morphologies from a real galaxy population in a real image, to create one new object. It is called many times by simage_generate_shapecat.pro to create an entire new galaxy catalogue. The size and magnitude of each object are incorporated as dimensions of the morphology PDF, to ensure that galaxies have the right morphological type for their depth. No redshift information is currently included, but this is the most likely place to add it!

The subroutine simage_pdf_kernel_width decides the amount of smoothing to perform upon the PDF of galaxy morphologies to genereate new objects. This amount is crucial: if it is too low, the new objects will not be significantly different. If it is too high, the new objects will not have realistic morphologies. If the flag /PAPER is set, the smoothing kernel from Massey et al. (2004) MNRAS 348, 214 is used, with an appropriate size to realistically morph objects from the HDFs. The subroutine simage_pair_separation calculates the nearest neighbour to a list of points, and can be used by simage_pdf_kernel_width to set the smoothing length in each direction. The subroutine simage_flag_pdf_topology flags each dimension of the PDF according to its topology. For example, an object's size can be any positive number. An object's magnitude can be any number. The phase of an object's polar shapelet coefficients can only lie between zero and two pi, and wraps around if it is extended beyond these limits. More information about the subroutines is available in their individual headers, within the source code for this routine.

See also the header below, which has been extracted from the source code for this routine.

; NAME: ; SIMAGE_RESAMPLE_PDF ; ; CATEGORY: ; Shapelets image simulation. ; ; PURPOSE: ; Generates a brand new object from a shapelet catalogue by drawing a ; bootstrapped sample from an (n_a+1)-dimensional probability space. This is ; smoothed using the Kernel method, where the widths of the kernels is decided ; by simage_pdf_kernel_width.pro and may even be adaptive to the local density. The new ; object is essentially the same as one of the originals, but perturbed by ; multivariate elliptical Gaussians in shapelet space. ; ; INPUTS: ; shapecat- A catalogue of objects read in by, eg: shapelets_read_shapeshapecat.pro or ; shapelets_read_shapecat_hdf.pro ; ; OPTIONAL INPUTS: ; width - size of kernel smoothing in each direction. This is slow to calculate, ; so is returned to speed up a second run. ; n_max - n_max to create new object up to (if catalogue goes that far) ; It is recommended that you go as far as the decompositions, because ; the size & magnitude of the objects are maintained. If, for example, ; an n_max=12 object is modelled by this code as an n_max=4 object, the ; output will be a large, bright version of the object`s nucleus. ; Default: whatever the catalogue goes up to. ; seed - Seed for random number generator. ; bs_obj - The catalogue number of an object to morph (bootstrap). ; Default: one picked at random. ; ; KEYWORD PARAMETERS: ; /PLOT - Plot newly generated object to screen at end. ; /SILENT - Operate silently. ; ; OUTPUTS: ; new_object - Cartesian decomp structure, representing a new, morphed galaxy. ; bs_obj - The catalogue number of the morphed object. ; ; NOTE: ; Covariance matrix and even errors of coefficients are ignored, but ; their existence does hint that some smoothing in shapelet space is ; philosophically justified. ; ; MODIFICATION HISTORY: ; Mar 04 - Tidied up by RM. ; May 02 - Complete rewrite by RM: renamed & now uses fast bootstrap method ; from Silverman (1984) rather than integrating the entire PDF. ; Apr 02 - RM - faithful size-magnitude plane ensured by fitting it by hand. ; Feb 02 - RM - now copes with polar shapelet decompositions. ; Dec 01 - Create.pro written by Richard Massey

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Last modified on 02nd May 2008 by Richard Massey.