Seyfert galaxies (especially type 1 Seyferts) can have nuclei which stand out, even at the eyepiece, as unusually bright and compact. This is illustrated by comparing a well-known type 1 Seyfert galaxy, NGC 5548 (to the left), with a normal spiral galaxy of similar distance and type, NGC 3277 (on the right). The images are both displayed with the same brightness mapping over a logarithmic intensity scale to allow direct comparison. The brilliant nucleus of NGC 5548 has saturated the detector, and produces the prominent diffraction spikes caused by the secondary-mirror supports, plus charge-bleeding lines above and below the nucleus, while no such source is present in NGC 3277.
NGC 5548 has figured prominently in attempts to understand active nuclei through their variability. The International AGN Watch has produced an unparalleled series of measurements for NGC 5548, including optical spectroscopy, ultraviolet, and X-ray measurements.
These images were produced from data retrieved from the HST archive. Both were in the F606W filter (between the traditional V and R filters), and most of the PC chip is shown; to be specific, a region of sky 25 by 30 arcseconds is depicted. The NGC 5548 image is from Matt Malkan's snapshot survey of AGN, and NGC 3277 is from a survey program by Carollo, Stiavelli, and Mack. Total exposure times were 500 and 600 seconds respectively. The image is shown above half-size; click on it to get the full-resolution version.
Last changes: July 1999