We present the results of analysis of direct imaging data of the galaxy NGC 5548. This galaxy hosts a time-variable active nucleus which has been the focus of intensive spectroscopic monitoring. We focus here on data obtainable from direct imaging of the object. First, we use an image modeling program to derive an image of the galaxy component alone, with the AGN removed, and use such images to study the structure and color of the galaxy. The host galaxy appears to be a relatively normal bulge-dominated (Sa type) spiral, with no evidence of current star formation in the bulge. The derived " AGN-free " images are useful for deriving corrections for the galaxian light that is an inevitable contaminant in spectroscopic and photometric measurements of this object. We discuss how to measure the flux from the nucleus from direct images, and in particular describe a method to obtain photometrically calibrated nuclear flux measurements from less than optimum images. We present nuclear flux values from images contributed by the coauthors, and present flux measurements, corrected for host galaxy light, derived from published photoelectric aperture photometry. We discuss the contamination of the standard spectroscopic aperture by galaxy light. The galaxy flux contamination in the standard spectroscopic aperture derived from the AGN-free images agrees extremely well with that derived from a totally independent spectroscopic method.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science