Merging of Source Lists after the Maximum Likelihood Detection

 

There are two ways of merging source lists,

1. either before (pre-merge) the maximum likelihood detection   or
2. after (post-merge)   the maximum likelihood detection.

The pre-merge is described in section 5.2.7. Here we introduce the post-merge.

The input lists to this command can be the result of a maximum likelihood detection (commands DETECT/MAXLIK or COMPUTE/UPPER_LIMITS). The merging is done if the overlap condition is satisfied. An overlap may be within the position error circle, the extent size circle and/or the FWHM size circle. The conditions can be set by flags specified in the parameter file. The scaling of the size of the circle is done by parameters as well. Two merge methods are available, either the source with the largest existence likelihood determines the merged source position or the merged position is the mean position of all sources fulfilling the merge criterion weighted with the existence likelihood of the contributing members.

The command

MERGE/ML_SOURCE_TABLES [parfil] [edit]

  works via a parameter file parfil (mppar.par in the default) which is offered to be edited (cf. Table 5.9) or which can be created by the command

  
Table 5.9: Parameter file for MERGE/ML_SOURCE_TABLES

 
CREATE/PARFIL MP mppar

The parameters of the parameter file mppar.par are described in more detail:

• NUM_OF_SOLST : number of source lists (ML_LIST_ACCEP or ML_LIST_ALL) from DETECT/MAXLIK or COMPUTE/UPPER_LIMITS.
• SOLSTN : name of the N-th (ML_LIST_ACCEP or ML_LIST_ALL) source table. Up to 8 tables can be merged.
• REF_IMAGE : name of the reference image. The merged coordinates will be given in this coordinate system.
• ERR_FLAG : determines whether (T) or not (F) the position errors :XERR and :YERR are used for the merging condition (see parameter ERR_FACTOR).
• ERR_FACTOR : multiplication factor for 1 -error radius determined from :XERR and :YERR. Sources lying closer together than this distance will be merged.
• EXT_FLAG : determines whether (T) or not (F) the source extension :EXT is used for the merging condition (see parameter EXT_FACTOR).
• EXT_FACTOR : multiplication factor for source extension determined from :EXT. Sources lying closer together than this distance will be merged.
• FWHM_FLAG : determines whether (T) or not (F) the FWHM of the point spread function of the source is used for the merging condition (see parameter FWHM_FACTOR).
• FWHM_FACTOR : multiplication factor for the FWHM of the point spread function determined from the column :FWHM. Sources lying closer together than this distance will be merged.
• MERGE_METHOD : Merge method. There are two methods, MERGE_METHOD =1, the source with the largest likelihood is taken as the merged source, MERGE_METHOD =2, from the sources to be merged a mean source weighted with the existence likelihood values is determined.
• INT_TAB_PRES_FLAG : specifies whether from previous merging the internal tables are still existing (T) or not (F).
• INT_TAB_KILL_FLAG : specifies if the internal tables will be deleted after the merging is finished (T) or not (F).
• TRANSP_SOLST_COL_FLAG : specifies if all (T) or only part (F) of the columns of the source lists will be transferred to the merged list.
• SORT_MRGLST_IN_Y_IMA : specifies if (T) or not (F) the merged list will be sorted at the end in ascending order in the :Y_IMA column
• MERGED_LIST : name of the merged source table.

The tables SOLST1, ..., SOLSTN must have at least the following columns: :X_IMA, :Y_IMA, :EXI_ML, :XERR, :YERR and :EXT. Further columns are mandatory (an index column :INDEX is recommended).

Columns :X_IMA and :Y_IMA will be calculated with reference to REF_IMAGE. In case TRANSP_SOLST_COL_FLAG is set to T, all further existing columns will be transferred. Columns containing coordinate information :X_SKY, :Y_SKY, :X_POS, :Y_POS still contain the old coordinates not related to the coordinates system of the reference image REF_IMAGE.

In case the flag TRANSP_SOLST_COL_FLAG is set to T, the columns :INDEX, :MRG and :LST will be put at the beginning of the table and the columns :RA_DEG, :DEC_DEG and :FWHM will be put at the end.

An existing column :INDEX in the source lists will be transferred into and renamed to a column :IND_O (old index).

In case the flag TRANSP_SOLST_COL_FLAG is set to F, the merged list contains the columns :INDEX, :MRG, :LST, :IND_O, :X_IMA, :Y_IMA, :EXI_ML, :XERR, :YERR, :EXT, :RA_DEG, :DEC_DEG and :FWHM.

The merged list contains besides the merged sources still the original sources contributing to the merged sources in continuation lines. The column :MRG shows if the entry is a merged entry. For :MRG = 0 it is the continuation line for an original source. For it is a merged source. :MRG gives the number of original sources contributing to the merged source (number of continuation lines).

The column :LST gives the number of the source lists from which the source is taken. The numbers 1,2,3, ... refer to the entries for the parameters SOLST1, SOLST2, SOLST3, ...

For the setting MERGE_METHOD = 2 (position weighting) :EXT and :FWHM is set to *. This means, no weighted source extension and :FWHM is determined.

It is recommended to check the MERGED_LIST for self consistency by merging with itself. Select the table with the condition :MRG.GT.0, copy it to a subtable (with COPY/TABLE) and merge this list with itself (NUM_OF_SOLST=1). If the number of merged sources reduces take this list as the relevant list.

Note:There is also a way to handle source lists coming from the local or map detection (commands DETECT/LOCAL or DETECT/MAP). These lists have first to be converted by the command

CONVERT/DETECTION_LISTS lslst1 solst_ls1

  for the local detection list lslst1.tbl e.g.