Other
Scientific paper
Sep 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006head....9.0713e&link_type=abstract
American Astronomical Society, HEAD meeting #9, #7.13; Bulletin of the American Astronomical Society, Vol. 38, p.351
Other
Scientific paper
We address the question of whether the AGNs found in nearby galaxies hosting LINERs can power their observed emission lines. To this end we study the spectral energy distributions of 35 objects which have been observed by Chandra with long exposure times. This sample is well suited for this study because the high spatial resolution of Chandra can isolate the AGN emission and the long exposure times result in high-S/N X-ray spectra. Of the 35 LINERs, 12 have also been observed with the HST in the near-UV band, allowing us to asses the contribution of UV photons to the energy budget. For objects not observed with the HST, we estimate the UV flux by adopting the most generous value of alpha_ox allowed by the HST measurements. We also consider carefully the effects of extinction on the observed ionizing spectrum. Balancing the enery budget depends sensitively on the fraction of ionizing photons, f, absorbed by the line-emitting gas. By comparing the ionizing luminosity (from 1 Ry to 100 keV) to the total luminosity of the strong optical emission lines we find that, for f=1, 11 percent of the AGNs do not provide enough power to match the observed emission line luminosity. This fraction becomes 49 percent for f=0.1. Comparing the number of ionizing photons to the number of H-alpha photons, we find that for f=1, 45 percent of the AGNs cannot provide enough photons to power the H-alpha emission. This fraction increases to 89 percent for f=0.1. In light of these results we discuss a number of other power sources for the optical emission lines, such as photoionization by young and intermediate-age stars in the nucleus, and mechanical heating of the emission-line gas by collimated outflows (radio jets).
Eracleous Michael
Flohic H. M.
Hwang Jason A.
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