The Nature of the Extended Blue Continuum in Cygnus-A

Details The Nature of the Extended Blue Continuum in Cygnus-A The Nature of the Extended Blue Continuum in Cygnus-A

Apr 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994mnras.267..589s&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Vol. 267, NO. 3/APR1, P. 589, 1994

Astronomy and Astrophysics

Astronomy

14

Scientific paper

We have used long-slit spectra to derive spatial continuum profiles at UV, optical and near-IR wavelengths in the central region of Cygnus A. The line-free continuum colour distributions derived from these are used to identify the spatial distribution of, and relative contribution from, the featureless blue continuum (FBC) in each of the principal nuclear subcomponents in this object. The FBC is spatially extended, covering a region ~4-4.5 arcsec in extent along a P.A. of 105^deg^. Beyond this, the emission is predominantly that of the old stellar population in the underlying galaxy. In addition, the core region is markedly redder than the adjacent northwest and southeast nuclear subcomponents, suggesting considerable reddening/extinction. This is strong evidence in favour of the presence of a nuclear dust lane within the central region of Cygnus A. The fractional contribution of the FBC has been estimated as a function of wavelength in each nuclear subregion. A striking UV excess is seen in our data, the FBC contributing ~60-90 per cent of the total continuum flux at λ < 3800 A (the range reflecting the degree of reddening within the intrinsic old stellar population). The continuum shape of the FBC possesses a break at ~4100 A, exactly as observed in some steep-spectrum radio quasars (and quite different from the spectra of young star clusters). Whilst our observations are most consistent with a scattering origin for the FBC, a definitive solution will only be provided by spectropolarimetric observations in the blue.

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