Optical identification of radio sources with the I band CCD catalogue
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positions limit of the I band catalogue used for the cross correlation:
35.8051 < RA < 37.1931 -4.97655 < DEC < -4.02486
02 23 13.22 < RA < 02 28 46.34 -04 58 35.58 < DEC < -04 01 29.5
Area covered : about 1.31 deg2
(extremely approsimated value obtained from
the RA and DEC limit of the I band catalogue)
Optical sources in the catalogue : 170488 (~130000 sources/deg2)
Radio sources within I band CCD area : 1060
Histogram of the number of optical sources
within a radius of
10 arcsec around each radio position
- As first step we used 2 arcsec for the radio-optical associations.
Using r=2arcsec we have 832 associations
Using these 832 associations we have :
Mean offsets (arcsec)
RADIO - I Band position RA, DEC: 0.09 , 0.30
Median offsets (arcsec)
RADIO - I Band position RA, DEC: 0.12 , 0.32
Standard deviation RA, DEC: 0.56 , 0.63
Position offset between radio and optical position
- As second step we applied the median offset values to the
radio positions (i.e. we corrected the radio position of RA : -0.12 arcsec
and DEC : -0.32) and we cross-correlated again the radio and optical
catalogues.
Here there is the histogram of the number of optical sources
again within a radius of
10 arcsec around each radio position (offset corrected)
- Finally we used a radius of 1.5 arcsec around each radio position
to find the optical counterparts. Using r=1.5 arcsec we have
755 associations, 78 of which (9.9 per cent)
are expected to be spurious associations
Click here for the list of the 755 associations
So.. as preliminary results we have : 755 - 78 = 677 likely associations
( ==> 677 / 1060 = 64 % of the radio sources within CCD area)
Position offset between radio (offset corrected) and optical position
I band magnitude distribution of the whole catalogue and of the 755
optical counterparts of the radio sources
I band magnitude distribution of the 755
optical counterparts of the radio sources and the expected magnitude
distribution of the spurious sources
Radio flux distribution of the whole radio catalogue and of the radio sources
with an optical id
