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H. Calvani (JHU), A. Koratkar (STScI), S. Deustua (LBNL), I. Evans (SAO), A. V. Filippenko (UC Berkeley), T. Heckman (JHU), L. Ho (CfA)
Observations of activity in the nuclei of galaxies over a wide range of luminosities (from Seyfert galaxies and low-ionization nuclear emission-line regions [LINERs] to Quasars) suggest there is common energy source responsible for the activity and properties observed in these objects. It is of great interest to determine if the continuity of properties observed extends to moderate and lower luminosity active galaxies (Low-Luminosity Active Galactic Nuclei: LLAGNs) and thus, to explore how closely connected are LLAGNs to typical AGNs. Additionally, it is vital to ascertain if the level and properties of the activity merely scale with nuclear luminosity and if there is a lower limit where an underlying different physical process is needed to power the galactic nucleus. In this work we present an HST WFPC2 photometric study of a careful selected sample of LLAGNs: NGC4278, NGC4639, NGC5033 and NGC5273. We have taken advantage of the high spatial resolution and extensive selection of filters (F218W, F300W, F439W, F547M, F555W and F814W) of the WFPC2 PC to not only determine the spatial extent of the nuclear UV continuum source and investigate the dominant mechanism responsible for the ionizing radiation, but also to establish the spectral energy distribution of the nucleus for each source in the sample. The results are compared and coupled with previous observations taken from ROSAT and IUE to further explore and gain understanding on the issues addressed above.
The author(s) of this abstract have provided an email address for comments about the abstract: calvani@pha.jhu.edu