Paul J Francis , Matthew T. Whiting , Rachel L. Webster, PASA, 17 (1), 56.
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Title/Abstract Page: The Optical/Near-IR Colours of
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Multicolour Selection of Red Quasars
Could there be a population of radio-quiet QSOs with the same colours as our radio-loud red quasars? Webster et al. showed that it is virtually impossible to find such QSOs in any sample with a blue optical magnitude limit. In this section we ask whether red QSOs could be identified by colour selection in the red optical and near-IR.
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In Fig 12, we compare the optical and near-IR colours of the Parkes sources against the colours of high galactic latitude point sources drawn from the Two-Micron All Sky Survey (2MASS, K<15) and ESO Imaging Survey (EIS, K<22). The `Main Sequence' sources, both red and blue, are clearly separated from the foreground objects. This separation is due to their power-law spectral energy distributions: as compared to the convex spectral energy distributions of stars and galaxies, the quasars have excess flux in B and/or K. This selection technique is similar to the `KX' technique proposed by Warren, Hewett & Foltz (1999). Unfortunately, the very red sources lying below the `main sequence' have colours within the stellar locus and will be hard to find.
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Can red quasars be identified purely on the basis of their near-IR colours? In Fig 13, we show that most of the Parkes quasars lie in regions of the near-IR colour-colour plot with substantial stellar contamination, but that the reddest move away from the stellar locus, and could be detectable in the IR alone. Fig 14 shows that purely optical colour selection is not likely to be effective.
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