Extragalactic Radio Astronomy from an Armchair: Continuum Spectral Shapes of 150 Faint Sources

Gonzalez-Perez, J. N.; Andernach, H.
Bibliographical reference

Astronomy Papers, Abstracts, XXII IAU General Assembly, ed. H. van Woerden, p. 276; abstracts of papers for Joint Discussion 20 ``The Status of Archiving Astronomical Data'', Twin Press, Sliedrecht, The Netherlands

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We have used all available radio-source surveys to construct the continuum spectra for sources in an area of 5 by 10 degrees near the North Ecliptic Pole (NEP), previously observed at 2.7 GHz with the Effelsberg telescope. Most of the surveys are of similar angular resolution (~3 to 5 arcmin) and cover a wide range of frequencies from 38 MHz to 5 GHz. We have developed a cross-identification algorithm that takes into account the dependence of source structure on observing frequency. This improved the number of true matches between the source catalogues. Spectra for 229 sources with flux measurements at two or more frequencies were constructed. For 124 of these we found data at four or more frequencies, allowing us to classify their spectral shape. In our rather faint sample (S_2.7GHz > 20 mJy) we find the fraction of sources with spectral curvature to be much lower than in samples of stronger sources previously studied by other authors. Preliminary optical identifications are being drawn from the digitized versions of the first Palomar Sky Survey prepared at STScI.