http://arxiv.org/abs/1711.09936
We present observations of active galactic nuclei (AGN) with close companion galaxies, in search of regions of the companions whose gas is photoionized by the AGN (which we term cross-ionization). This phenomenon can trace patterns of escape of ionizing radiation from AGN, and their time histories. From an initial set of 212 candidates, identified with the help of Galaxy Zoo participants, we obtained long-slit optical spectra of 32 pairs most likely to show cross-ionization. Among these, 10 systems show evidence of such cross-ionization based on emission-line ratios, in broad agreement with expectations if most AGN have ionization cones with 60-degree opening angles. The distributions of companion galaxies with and without signs of cross-ionization are similar in estimated incident AGN flux, suggesting that such additional factors as geometry of escaping radiation and long-term variability control this facet of the AGN environment. This parallels conclusions for luminous QSOs based on the proximity effect among Lyman-alpha absorbers. In some galaxies, mismatch between spectroscopic classifications in the common BPT diagram and ratios of weaker emission lines highlights the limits of common classifications in low-metallicity environments. We highlight properties of several systems with particularly strong evidence for cross-ionization – Was 49, NGC 5278/9, and UGC 6081 – and find a potentially fading AGN in the NGC 5278/9 system. Finally, we provide guidelines for further examination of these systems.
W. Keel, V. Bennert, A. Pancoast, et. al.
Wed, 29 Nov 17
14/69
Comments: Submitted to MNRAS
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