GSC2 Matches with the FIRST and SDSS Catalogs

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GSC-2 Matches with the FIRST and SDSS Catalogs
Rick White 2001 October 23 Torino, Italy
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The FIRST Survey

• The FIRST Survey is a large-area, high-resolution
  radio survey using the VLA.
• 20 cm wavelength
• 5.4 FWHM resolution (B-configuration)
• 1 mJy detection limit
• 10,000 sq deg of north Galactic Cap
• Matches SDSS current coverage 8600 sq deg

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Current FIRST Sky Coverage
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Southern Sky Coverage
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The FIRST Source Catalog

• First wide-area radio survey with the one arcsec
  positions needed for optical identifications
• 1 positions (90 confidence) at flux limit
• FIRST catalog and images are online
• http//sundog.stsci.edu
• Current catalog contains 771,000 sources
• 90 sources per sq deg

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FIRST/Optical IDs
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FIRST/GSC-2 Match

• Matched FIRST catalog to GSC 2.2
• Used web interface (www-gsss.stsci.edu
  /cgi-bin/gsc22query.exe) via Python script
• 722,354 FIRST catalog sources
• 326,384 GSC-2.2 counterparts within 24
• Wide match separation allows estimate of
  background coincidence rate
• 65,336 GSC-2.2 counterparts within 2

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FIRST/GSC-2 Separation Distribution
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Star Separation Distribution
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Galaxy Separation Distribution
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DRA vs. DDec - All Matches
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DRA vs. DDec - GSC-2 Stars
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Sky DistributionFIRST/GSC-2 Matches lt 2
65,336 FIRST/GSC2.2 matches
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Match Magnitude Distribution
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Magnitude Log Distribution
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Comparison with SDSS Catalog

• GSC-2.2 was matched against SDSS Early Data
  Release Catalog
• Two random samples of 10000 sources selected from
  SDSS EDR
• 10000 random objects with 15 lt r lt 20
• 5000 stars, 5000 galaxies forced to have uniform
  distribution in each 0.2 magnitude bin from r15
  to r20
• In total, 12000 SDSS/GSC-2 matches

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GSC-2/SDSS Magnitudes for SDSS Stars
GSC-2 F vs. SDSS r
GSC-2 J vs. SDSS g
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GSC-2/SDSS Magnitudes for SDSS Galaxies
GSC-2 F vs. SDSS r
GSC-2 J vs. SDSS g
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GSC-2/SDSS Magnitudes for SDSS Stars
GSC-2 F vs. SDSS r
GSC-2 J vs. SDSS g
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SDSS/GSC-2 Colors
J-g vs. F-r
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SDSS/GSC-2 Classifications
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SDSS/GSC-2 Classifications
Stars
Combined
Galaxies
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SDSS/GSC-2 Classifications
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Science with FIRST/GSC-2

• APM catalog has some limitations
• Classifications inaccurate for fainter objects
• Old POSS-I positions have too much proper motion
  to find radio stars
• FIRST/GSC-2 used to push beyond APM
• E.g., search for red quasars

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FIRST/2MASS 07382750
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FIRST/2MASS 07382750
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SDSS 1044-0125
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Summary

• 65,000 FIRST matches in GSC 2.2
• Positions look good
• Stars have 0.33 arcsec RMS with FIRST (including
  FIRST errors)
• FIRST/GSC-2 matches useful for magnitude test
  (faint, good astrometry)
• F 15-18.5 classification accuracy is excellent,
  95 agreement with SDSS
• Magnitudes accurate to 0.13 mag compared with
  SDSS (without color terms!)

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