The Spectral Correlation Function (SCF) is a statistical tool for analyzing and inter-comparing spectral-line maps. The SCF was initially developed by our group to test the validity of theoretical models of molecular clouds (Rosolowsky et al. 1999). The main goal was to develop an algorithm that measured not just the distribution of line properties (e.g. centroid velocity analysis, autocorrelation functions, etc.), but the spatial distribution of line shapes as well.
There are two versions of the SCF in use today. Version 1.0 computes a number from 1 (perfect correlation) to 0 (no correlation) that measures, at every position in a map, how similar each spectrum is to all its nearest neighbors. SCF v1.0 was used by Rosolowsky, Goodman, Wilner & Williams (1999) to demonstrate the its ability to discriminate amongst various observed and simulated spectral-line maps (Data Page for this Paper). Ballesteros-Paredes, Vazquez-Semadeni & Goodman (2002) used the SCF to compare observed and simulated maps of the atomic ISM. The IDL code for SCF v1.0 is available here.
SCF Version 1.0
Another version of the SCF, v2.0, analyzes the correlation amongst spectra in a map as a function of spatial scale. The SCF v2.0 value for a spatial lag of 1 pixel is the same as for SCF v1.0, but the statistic is also computed for all possible spatial lags up to 1/3 the map size. The effects of noise and sampling on SCF v2.0 are discussed in detail by Padoan, Rosolowsky & Goodman (2001). Padoan, Kim, Goodman & Stavely-Smith (2001) used SCF v2.0 to map out the scale height of the the Large Magellanic Cloud, a nearly face-on galaxy. Padoan, Goodman & Juvela (2003) present an extensive SCF v2.0 analysis of observed and simulated 13CO maps of molecular clouds. The conclusion of their analysis is that existing MHD simulations are coming close to synthesizing "real" conditions for clouds with low Mach number, but that the simulations do not have enough dynamic range to accurately model high Mach number flows like those found in dense star-forming regions. The IDL code for SCF v2.0 is available here.
SCF Version 2.0
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Last modified on Monday, 30-Jun-2003 11:28:47 EDT