OPTICAL, INFRARED, RADIO AND POLARIZATION IMAGING OF THE HIGH-REDSHIFT GALAXY IRAS-F10214+4724

Optical and near-IR images of the extremely luminous high-redshift IRAS source F10214 + 4724 both show a compact core surrounded by diffuse emission. The diffuse emission contains approximately 12 per cent of the light at optical wavelengths and approximately 30 per cent at near-IR wavelengths, and is asymmetric, extending 4 arcsec at position angle approximately 30-degrees. Radio maps at 1.49 and 8.44 GHz show an elongated structure of size 0.6 x 0.3 arcsec2 roughly perpendicular to the diffuse optical-IR material, at position angle approximately 110-degrees; in other words, the alignment effect seen here is just the opposite of that seen in high-redshift radio galaxies. Imaging polarization through a broad-band optical filter shows that the unresolved core is polarized at a level p = 16.4 per cent, with E-vector at position angle 75-degrees. Such a large polarization suggests strongly that most or all of the optical-IR light we see arises from scattering, and that either the illumination or the scattering medium is highly anisotropic. However, the E-vector angle bears no obvious relation to the elongations seen at optical, IR and radio wavelengths, so the source geometry is unlikely to be very symmetrical. The scattering picture is analogous to that suggested for high-redshift radio galaxies, and nearby Type 2 Seyfert galaxies, so one might take this as indirect evidence that the hidden energy source is a quasar which is so luminous that even scattered light from it dominates the light from the parent galaxy. On the other hand, the diffuse nature of the radio source argues strongly for the presence of a starburst. There is no intrinsic reason why an enormous starburst might not also be subject to strongly anisotropic occultation and scattering, but no precedent is known. Overall ft seems likely that a burst of star formation and a quasar nucleus are both present.