Low-luminosity active galaxies: Are they similar to Seyfert galaxies?

view Abstract Citations (73) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Low-Luminosity Active Galaxies: Are They Similar to Seyfert Galaxies? Koratkar, A. ; Deustua, S. E. ; Heckman, T. ; Filippenko, A. V. ; Ho, L. C. ; Rao, M. Abstract A careful X-ray study of five low-luminosity active galactic nuclei (LLAGNs) was conducted to address specifically the issue of whether the dominant X-ray production mechanism is the same at all luminosities in AGNs. The sample consists of three Seyfert 1 galaxies (NGC 4639, NGC 5033, and NGC 5273), and two low-ionization nuclear emission-line regions (NGC 3642 and NGC 4278) having a weak, broad component of Hα emission. We find that the X-ray emission (ROSAT HRI) is mostly or entirely nuclear (<~500 pc) despite the low X-ray luminosities (~9 x 10^40^ ergs s^-1^) of the sample. The correlation between X-ray luminosity and the broad Hα emission-line luminosity observed in high-luminosity active galaxies continues down to the low-luminosity range; the mean L_x_/L_Hα_ ratio of LLAGNs is approximately 14, while that of AGNs is approximately 29. ROSAT PSPC observations of three LLAGNs in our sample indicate that the 0.2-2.2 keV X-ray spectral energy distributions are similar to those seen in Seyfert nuclei but do not have high intrinsic absorbing columns. Using existing ultraviolet data for four LLAGNs, we find that the "optical" (2500 A) to X-ray spectral index (α_ox_) has an average upper limit of 1.6; for comparison, the measured value in AGNs is typically 1.4, while that in M81 (the prototypical LLAGN) is 1.0. Publication: The Astrophysical Journal Pub Date: February 1995 DOI: 10.1086/175255 Bibcode: 1995ApJ...440..132K Keywords: Active Galactic Nuclei; Active Galaxies; Emission Spectra; H Alpha Line; Seyfert Galaxies; Stellar Luminosity; X Ray Astronomy; X Ray Spectra; Astronomical Spectroscopy; Rosat Mission; Spaceborne Astronomy; Ultraviolet Astronomy; Ultraviolet Spectra; X Rays; Astronomy; GALAXIES: ACTIVE; GALAXIES: NUCLEI; GALAXIES: SEYFERT; X-RAYS: GALAXIES full text sources ADS | data products SIMBAD (5) NED (5) HEASARC (1)