NGC 5548 is a low-redshift (z=0.0174) Seyfert I
galaxy. In the radio band it shows a weak nuclear source surrounded by
two lobes wuth a total extent of 4.4 kpc. These is also an extended
emission line region roughly aligned with the radio structure. It has
been classified as a low-luminosity AGN.
NGC 5548 has been repeatedly observed with IUE. The figure below
shows the evolution of the IUE SWP spectra of NGC 5548 taken along
the period December 1988 to September 1989, during which it was regularly
observed every four days.
The emission lines correspond (from short to long wavelengths) to the Lyman alpha geocoronal line (emitted by the Earth atmosphere), the Lyman alpha line emitted by the galaxy (displaced from the geocoronal line due to the galaxy velocity), the weak SiIV line near 1400 A, the CIV line at 1550 A, and the weak CIII line at 1910 A.
The study of the changes of the intensity of the emission lines and the continuum revealed a displacement of twelve days in the case of Lyman alpha, as shown below. Click here to see why.
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