Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 483, Issue 4, Pages 4847-4865Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/sty3332
Keywords
galaxies: active; galaxies: ISM; galaxies: Seyfert
Categories
Funding
- Russian Science Foundation [17-12-01335]
- M. V. Lomonosov Moscow State University Program of Development
- Jim Gray Research Fund from Microsoft
- Leverhulme Trust
- National Science Foundation (NSF) Research at Undergraduate Institutions (RUI) [AST-1312296]
- Alfred P. Sloan Foundation
- National Aeronautics and Space Administration
- National Science Foundation
- U.S. Department of Energy
- Japanese Monbukagakusho
- Max Planck Society
- University of Chicago
- Fermilab
- Institute for Advanced Study
- Japan Participation Group
- Johns Hopkins University
- Los Alamos National Laboratory
- Max-Planck-Institute for Astronomy (MPIA)
- Max-Planck-Institute for Astrophysics (MPA)
- New Mexico State University
- Princeton University
- United States Naval Observatory
- University of Washington
- Russian Science Foundation [17-12-01335] Funding Source: Russian Science Foundation
- STFC [ST/S000488/1] Funding Source: UKRI
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We consider active galactic nucleus (AGN) photoionization of gas in companion galaxies (cross-ionization) as a way to sample the intensity of AGN radiation in both direction and time, independent of the gas properties of the AGN host galaxies. From an initial set of 212 AGN+companion systems, identified with the help of Galaxy Zoo participants, we obtained long-slit optical spectra of 32 pairs that were a priori likely to show cross-ionization based on projected separation or angular extent of the companion. From emission-line ratios, 10 of these systems are candidates for cross-ionization, roughly the fraction expected if most AGNs have ionization cones with 70 degrees opening angles. Among these, Was 49 remains the strongest nearby candidate. NGC 5278/9 and UGC 6081 are dual-AGN systems with tidal debris, complicating identification of cross-ionization. The two weak AGNs in the NGC 5278/9 system ionize gas filaments to a projected radius 14 kpc from each galaxy. In UGC 6081, an irregular high-ionization emission region encompasses both AGNs, extending more than 15 kpc from each. The observed AGN companion galaxies with and without signs of external AGN photoionization have similar distributions in estimated incident AGN flux, suggesting that geometry of escaping radiation or long-term variability controls this facet of the AGN environment. This parallels conclusions for luminous QSOs based on the proximity effect among Lyman a absorbers. In some galaxies, mismatch between spectroscopic classifications in the common BPT diagram and the intensity of weaker He II and [Ne V]emission lines highlights the limits of common classifications in low-metallicity environments.
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