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
EB 2010-10-10
Catalog
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
Extraction
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
WEIGHTing
WEIGHT_TYPE NONE # type of WEIGHTing: NONE, BACKGROUND, # MAP_RMS, MAP_VAR or MAP_WEIGHT WEIGHT_IMAGE weight.fits # weight-map filename
FLAGging
FLAG_IMAGE flag.fits # filename for an input FLAG-image FLAG_TYPE OR # flag pixel combination: OR, AND, MIN, MAX # or MOST
Photometry
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)
Star/Galaxy Separation
SEEING_FWHM 1.5 # stellar FWHM in arcsec STARNNW_NAME default.nnw # Neural-Network_Weight table filename
Background
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 ,
Check Image
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
ASSOCiation
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
Miscellaneous
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
