The FIRSTGSC2 Match

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The FIRST/GSC-2 Match
Rick White 2000 October 20 Stevensville, MD
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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 (C-configuration)
• 1 mJy detection limit
• 10,000 sq deg of north Galactic Cap
• Matches SDSS current coverage 8000 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 720,000 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 2.1.1
• Used chart.stsci.edu web interface
• 720,000 FIRST catalog sources
• 980,000 GSC-2 counterparts within 24
• Wide match separation allows estimate of
  background coincidence rate
• 120,000 GSC-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
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Match Magnitude Distribution
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Magnitude Log Distribution
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Comparison with APM Catalog

• Previous FIRST optical matches have used APM
  catalog of POSS-I (McMahon, Irwin et al.)
• FIRST team has improved APM astrometry and
  photometry
• APM catalog used for FIRST Bright Quasar Survey
  (White et al. 2000), etc.
• FIRST/APM/GSC-2 can be used as test

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GSC-2/APM Magnitudes
E(APM) vs. F(GSC-2)
O(APM) vs. J(GSC-2)
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E(APM) vs. F(GSC-2)
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APM/GSC-2 Classifications
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APM/GSC-2 Classifications
Galaxies
Combined
Stars
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Magnitude Log Distribution
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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

• 120,000 FIRST matches in GSC 2.1.1
• Positions look good on average
• FIRST/GSC-2 matches useful for magnitude test
  (faint, good astrometry)
• Classification limitations bright galaxies
  classified as stars
• Good addition to bright training set
• Already valuable for science

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