SEARCH task

BBarolo’s search algorithm is derived from Duchamp, a 3D source finder for spectral-line data developed by Matthew Whiting. BBarolo adds a few new functionalities and parallelization. For a comprehensive description of the algorithm and the input parameters, see Duchamp’s main paper and user guide.

Parameters

  • SEARCH [false]. This flag enables the source finding algorithm. Can be true or false.

  • FLAGROBUSTSTATS [true]. Whether to use to robust estimators (median and MADFM) instead of normal estimators (mean and standard deviation) when calculating cube statistics.

  • ITERNOISE [false]. Whether to use an iterative algorithm to estimate the noise level. If true, it will reiterate over the array, masking pixels above 3sigma and re-calculating noise statistics until convergence.

  • SORTSOURCES [NVOX]. This parameter specifies how to sort detections. Accepted values are XVALUE, YVALUE, ZVALUE, RA, DEC, VEL, IFLUX (integrated flux), PFLUX (peak flux), NPIX (number of pixels), NVOX (number of voxels), W20 (width at 20% peak flux), W50 (width at 50% peak flux) and SNR (average signal-to-noise). By default, sorting is descending, but it can be done ascending by adding a - (e.g. -VEL).

  • CUBELETS [false]. If true, it produces individual cubelets and sub-images for each detected source.

  • SEARCHTYPE [spatial]. How the search is performed. Accepted values are spatial and spectral. Spatial search is done in 2D channel maps, spectral search along 1D spectra.

  • SNRCUT [5]. The primary S/N cut (number of σ above the mean/median).

  • THRESHOLD [none]. Alternatively to SNRCUT, the primary threshold can be given in the same flux units of the input datacube. This overrides SNRCUT.

  • FLAGGROWTH [true]. Whether to grow detected sources to a secondary threshold.

  • GROWTHCUT [3]. Secondary S/N cut used when growing objects (number of σ above the mean/median).

  • GROWTHTHRESHOLD [none]. Alternatively to GROWTHCUT, the secondary threshold can be given in the same flux units of the input datacube. This overrides GROWTHCUT.

  • MINPIX [beam area]. The minimum number of spatial pixels for a detection to be accepted. Default is the area covered by the observational beam.

  • MINCHANNELS [2]. The minimum number of channels for a detection to be accepted.

  • MINVOXELS [none]. The minimum number of voxels for a detection to be accepted. If not set, MINVOXELS = MINPIX*MINCHANNELS.

  • MAXCHANNELS [none]. The maximum number of channels for a detection to be accepted. Default is no limits.

  • MAXANGSIZE [none]. The maximum angular size of a detection to be accepted in arcmin. Default is no limits.

  • FLAGADJACENT [true]. Whether to use the adjacent criterion to merge objects. If false, the next two parameters are used to determine whether objects are to be merged.

  • THRESHSPATIAL [2]. The maximum minimum spatial separation in pixels for two objects to be merged into a single one. Ignored if FLAGADJACENT is true.

  • THRESHVELOCITY [3]. The maximum minimum channel separation in channels for two objects to be merged into a single one. Ignored if FLAGADJACENT is true.

  • REJECTBEFOREMERGE [true]. Whether to reject sources before merging them.

  • TWOSTAGEMERGING [true]. Whether to do a partial merge during search.

Outputs

The task produces the following outputs. Here NAME is the name of the galaxy.

  • A FITS file detections.fits, a datacube with just the detections.

  • A FITS file DetectMap.fits, containing a 2D map telling how many channels are detected in each spaxel.

  • FITS files of the moment maps for the detections (NAME_mom0th.fits, NAME_mom1st.fits, NAME_mom2nd.fits).

  • A text file detections.txt, containinig a list of detections and their properties.

Example

With the following parameter file, the datacube of NGC2403 is searched. Unsurprisingly, the galaxy is detected…

FITSFILE    ngc2403.fits
THREADS     4

/////////// SEARCH parameters /////////////
SEARCH      true
// Searching map by map
SEARCHTYPE  spatial
// Primary and secondary cut
SNRCUT      10
GROWTHCUT   3 
// Setting some criteria for rejection    
MINPIX      30
MINCHANNELS 5
///////////////////////////////////////////