The optical/near-IR colours of red quasars

Paul J. Francis*, Matthew T. Whiting, Rachel L. Webster

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    51 Citations (Scopus)


    We present quasi-simultaneous multi-colour optical/near-IR photometry for 157 radio selected quasars, forming an unbiassed sub-sample of the Parkes Flat-Spectrum Sample. Data are also presented for 12 optically selected QSOs, drawn from the Large Bright QSO Survey. The spectral energy distributions of the radio- and optically-selected sources are quite different. The optically selected QSOs are all very similar: they have blue spectral energy distributions curving downwards at shorter wavelengths. Roughly 90% of the radio-selected quasars have roughly power-law spectral energy distributions, with slopes ranging from Fν ∝ ν0 to Fν, ∝ ν-2. The remaining 10% have spectral energy distributions showing sharp peaks: these are radio galaxies and highly reddened quasars. Four radio sources were not detected down to magnitude limits of H ∼ 19 · 6. These are probably high redshift (z > 3) galaxies or quasars. We show that the colours of our red quasars lie close to the stellar locus in the optical: they will be hard to identify in surveys such as the Sloan Digital Sky Survey. If near-IR photometry is added, however, the red power-law sources can be clearly separated from the stellar locus: IR surveys such as 2MASS should be capable of finding these sources on the basis of their excess flux in the K-band.

    Original languageEnglish
    Pages (from-to)56-71
    Number of pages16
    JournalPublications of the Astronomical Society of Australia
    Issue number1
    Publication statusPublished - 2000


    Dive into the research topics of 'The optical/near-IR colours of red quasars'. Together they form a unique fingerprint.

    Cite this