GNU Astronomy Utilities

7.4.5.4 MakeCatalog output file

When complete, MakeCatalog will store its measurements as a table. If an output filename is given (see --output in Input/Output options), the format of the table will be deduced from the name. When it isn’t given, the input name will be appended with a _cat suffix (see Automatic output) and its format will be determined from the --tableformat option, which is also discussed in Input/Output options. --tableformat is also necessary when the requested output name is a FITS table (recall that FITS can accept ASCII and binary tables, see Table).

By default only a single catalog/table will be created for “objects”, however, if --clumpscat is called, a secondary catalog/table will also be created. For more on “objects” and “clumps”, see Segment. In short, if you only have one set of labeled images, you don’t have to worry about clumps (they are deactivated by default). Here is a full description of MakeCatalog’s output options:

-C

--clumpscat

Do measurements on clumps and produce a second catalog (only devoted to clumps). When this option is given, MakeCatalog will also look for a secondary labeled dataset (identifying substructure) and produce a catalog from that. For more on the definition on “clumps”, see Segment.

When the output is a FITS file, the objects and clumps catalogs/tables will be stored as multiple extensions of one FITS file. You can use Table to inspect the column meta-data and contents in this case. However, in plain text format (see Gnuastro text table format), it is only possible to keep one table per file. Therefore, if the output is a text file, two output files will be created, ending in _o.txt (for objects) and _c.txt (for clumps).

--noclumpsort

Don’t sort the clumps catalog based on object ID (only relevant with --clumpscat). This option will benefit the performance¹⁴¹ of MakeCatalog when it is run on multiple threads and the position of the rows in the clumps catalog is irrelevant (for example you just want the number-counts).

MakeCatalog does all its measurements on each object independently and in parallel. As a result, while it is writing the measurements on each object’s clumps, it doesn’t know how many clumps there were in previous objects. Each thread will just fetch the first available row and write the information of clumps (in order) starting from that row. After all the measurements are done, by default (when this option isn’t called), MakeCatalog will reorder/permute the clumps catalog to have both the object and clump ID in an ascending order.

If you would like to order the catalog later (when its a plain text file), you can run the following command to sort the rows by object ID (and clump ID within each object), assuming they are respectively the first and second columns:

$ awk '!/^#/' out_c.txt | sort -g -k1,1 -k2,2

--sfmagnsigma=FLT

The median standard deviation (from a MEDSTD keyword in the Sky standard deviation image) will be multiplied by the value to this option and its magnitude will be reported in the comments of the output catalog. This value is a per-pixel value, not per object/clump and is not found over an area or aperture, like the common \(5\sigma\) values that are commonly reported as a measure of depth or the upper-limit measurements (see Quantifying measurement limits).

--sfmagarea=FLT

Area (in arcseconds squared) to convert the per-pixel estimation of --sfmagnsigma in the comments section of the output tables. Note that this is just a unit conversion using the World Coordinate System (WCS) information in the input’s header. It does not actually do any measurements on this area. For random measurements on any area, please use the upper-limit columns of MakeCatalog (see the discussion on upper-limit measurements in Quantifying measurement limits).

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GNU Astronomy Utilities 0.7 manual, August 2018.