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28 March 2024 |
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Article overview
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Cross-ionization of gas in AGN companion galaxies as a probe of AGN radiation in time and angle | William C. Keel
; Vardha N. Bennert
; Anna Pancoast
; Chelsea E. Harris
; Anna Nierenberg
; S. Drew Chojnowaki
; Chris J. Lintott
; Kevin Schawinski
; Graham Mitchell
; Claude Cornen
; | Date: |
27 Nov 2017 | Abstract: | 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. | Source: | arXiv, 1711.9936 | Services: | Forum | Review | PDF | Favorites |
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