I am using SExtractor (Source Extractor) to identify Star-Forming regions in a galaxy. The problem is I am unable to choose the parameters required for it. SExtractor is just a tool to identify the sources in a field. These can be point sources as well as extended diffuse sources. So it is not clear how to go about applying the sextractor and then isolating/identifying only the extended regions as the star-forming regions. Basically, why and how to choose the extent of 'X' pixels?
I need to calculate the Petrosian radius for each source as well. I can draw a histogram of the Petrosian radii for all the sources detected within the PSF of the instrument and use only those sources that have a radius larger than a certain value (say the FWHM or PSF of a bright Point source in the field). I think the histogram will be skewed towards larger radii as there are a large number of SF regions in the image and then set the size, like say 'X' pixels. And then I could do the photometry on the identified SF regions.
How do I find the Petrosian radius and proceed with using the SExtractor? Could someone tell me the inputs for this? Here are the default parameters.
Default configuration file for SExtractor 2.12.4
CATALOG_NAME FUV_BaF2_comp.txt # name of the output catalog CATALOG_TYPE ASCII_HEAD # NONE,ASCII,ASCII_HEAD, ASCII_SKYCAT, # ASCII_VOTABLE, FITS_1.0 or FITS_LDAC PARAMETERS_NAME default.param # name of the file containing catalog contents
DETECT_TYPE CCD # CCD (linear) or PHOTO (with gamma correction) DETECT_MINAREA 15 # min. # of pixels above threshold
DETECT_THRESH 5 # or , in mag.arcsec-2 ANALYSIS_THRESH 1.5 # or , in mag.arcsec-2
FILTER Y # apply filter for detection (Y or N)? FILTER_NAME gauss_4.0_7x7.conv # name of the file containing the filter
DEBLEND_NTHRESH 30 # Number of deblending sub-thresholds DEBLEND_MINCONT 0.18 # Minimum contrast parameter for deblending
CLEAN Y # Clean spurious detections? (Y or N)? CLEAN_PARAM 1.0 # Cleaning efficiency
WEIGHT_TYPE NONE # type of WEIGHTing: NONE, BACKGROUND, # MAP_RMS, MAP_VAR or MAP_WEIGHT WEIGHT_IMAGE weight.fits # weight-map filename
FLAG_IMAGE flag.fits # filename for an input FLAG-image FLAG_TYPE OR # flag pixel combination: OR, AND, MIN, MAX # or MOST
PHOT_APERTURES 5.0 # MAG_APER aperture diameter(s) in pixels PHOT_AUTOPARAMS 2.5, 1.5 # MAG_AUTO parameters: <Kron_fact>,<min_radius> PHOT_PETROPARAMS 2.0, 3.5 # MAG_PETRO parameters: <Petrosian_fact>, # <min_radius> PHOT_AUTOAPERS 0.0,0.0 # , minimum apertures # for MAG_AUTO and MAG_PETRO
SATUR_LEVEL 55000.0 # level (in ADUs) at which arises saturation SATUR_KEY SATURATE # keyword for saturation level (in ADUs)
MAG_ZEROPOINT 0.0 # magnitude zero-point MAG_GAMMA 4.0 # gamma of emulsion (for photographic scans) GAIN 1.00 # detector gain in e-/ADU GAIN_KEY GAIN # keyword for detector gain in e-/ADU PIXEL_SCALE 1.0 # size of pixel in arcsec (0=use FITS WCS info)
SEEING_FWHM 1.5 # stellar FWHM in arcsec STARNNW_NAME default.nnw # Neural-Network_Weight table filename
BACK_TYPE AUTO # AUTO or MANUAL BACK_VALUE 0.0 # Default background value in MANUAL mode BACK_SIZE 8 # Background mesh: or , BACK_FILTERSIZE 5 # Background filter: or ,
CHECKIMAGE_TYPE BACKGROUND,-OBJECTS # can be NONE, BACKGROUND, BACKGROUND_RMS, # MINIBACKGROUND, MINIBACK_RMS, -BACKGROUND, # FILTERED, OBJECTS, -OBJECTS, SEGMENTATION, # or APERTURES CHECKIMAGE_NAME Background_FUV_BaF2_comp.fits, Subtracted_FUV_BaF2_comp.fits # Filename for the check-image
Memory (change with caution!)
MEMORY_OBJSTACK 3000 # number of objects in stack MEMORY_PIXSTACK 300000 # number of pixels in stack MEMORY_BUFSIZE 1024 # number of lines in buffer
ASSOC_NAME sky.list # name of the ASCII file to ASSOCiate ASSOC_DATA 2,3,4 # columns of the data to replicate (0=all) ASSOC_PARAMS 2,3,4 # columns of xpos,ypos[,mag] ASSOC_RADIUS 2.0 # cross-matching radius (pixels) ASSOC_TYPE NEAREST # ASSOCiation method: FIRST, NEAREST, MEAN, # MAG_MEAN, SUM, MAG_SUM, MIN or MAX ASSOCSELEC_TYPE MATCHED # ASSOC selection type: ALL, MATCHED or -MATCHED
VERBOSE_TYPE NORMAL # can be QUIET, NORMAL or FULL HEADER_SUFFIX .head # Filename extension for additional headers WRITE_XML N # Write XML file (Y/N)? XML_NAME sex.xml # Filename for XML output XSL_URL file:///usr/local/share/sextractor/sextractor.xsl # Filename for XSL style-sheet