Completion of a Survey and Detailed Study of Double-peaked Emission Lines in Radio-loud Active Galactic Nuclei

By M. Eracleous, J. Halpern. 2003

214 citations recorded by the source corpus.

We report the completion of a survey of radio-loud active galactic nuclei (AGNs) begun in an earlier paper with the main goal of finding and studying broad, double-peaked Balmer lines. We present Hα spectra of 13 more broad-lined objects, including three with double-peaked Hα profiles. The final sample includes 106 radio-loud AGNs. In our final census 20% of objects have Hα lines with double peaks or twin shoulders (the "double-peaked emitters"), and of these 60% (the disklike emitters) can be fitted quite well with a model attributing the emission to a circular, relativistic, Keplerian disk. In four objects where broad Hβ and Mg II lines have been observed, we compare the profiles with models of photoionized accretion disks and find them to be in reasonable agreement. We reaffirm the conclusion of Paper I that double-peaked emitters stand out among radio-loud AGNs on the basis of a number of additional properties that they possess: (1) an unusually large contribution of starlight to the optical continuum around Hα, (2) unusually large equivalent widths of low-ionization lines ([O I] and [S II]), (3) unusually large [O I]/[O III] ratios, and (4) Balmer lines that are on average twice as broad as those of other radio-loud AGNs and preferentially redshifted. We consider and evaluate models for the origin of the lines, and we find accretion disk emission to be the most successful one because it can explain the double-peaked line profiles and it also offers an interpretation of the additional spectroscopic properties of these objects. We find the alternative suggestions (binary broad-line regions, bipolar outflows, anisotropically illuminated spherical broad-line regions) unsatisfactory because (1) they fail direct observational tests, (2) they cannot explain all of the unusual properties of disklike emitters self-consistently, or (3) in one case the physical foundations appear to be unsound. We suggest that double-peaked emitters and accretion-powered LINERs are the segment of the AGN population in which the accretion rate is considerably lower than the Eddington rate, with the consequence that the inner accretion disk takes the form of an ion torus and the wind that normally enshrouds the disk proper is absent.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/46d13ac306f94930256b964342326f3291d9454a

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. J. Newman
2. S. Faber
3. D. Koo
4. Christopher J. Conselice
5. A. Coil
6. P. Hopkins
7. R. Yan
8. M. Cooper

Citations in the corpus

• Evolution of broad-line emission from active galactic nuclei (2013, background): “The other approach, motivated by the double-peaked profiles observed in some AGNs, invoked emission from the Keplerian accretion disk (Chen & Halpern 1989; Eracleous & Halpern 2003; Eracleous et al. 2009).”
• A LARGE SYSTEMATIC SEARCH FOR CLOSE SUPERMASSIVE BINARY AND RAPIDLY RECOILING BLACK HOLES (2011, unknown): “…studies of about two dozen double-peaked emitters (Gezari et al. 2007; Lewis et al. 2010) do not show the signature of orbital motion and a number of arguments suggest that broad double-peaked lines are much more likely to originate in an accretion disk (see discussion in Eracleous & Halpern 2003).”
• Broad-line Balmer decrements in blue active galactic nuclei (2007, background): “In these kinds of AGN the physical conditions related to accretion/jet may be different (Blandford et al. 1990, Falcke et al. 1996, Eracleous & Halpern 2003), e.g., with additional X-ray ionizing radiation from the jet base.”
• INSPIRALLING SUPERMASSIVE BLACK HOLES: A NEW SIGNPOST FOR GALAXY MERGERS (2008, result): “…we also note that although some analyses of double-peaked broad lines in quasar spectra conclude they are caused by binary black holes (e.g., Gaskell 1984, 1988, 1996), most such lines are now understood to be caused by accretion discs (e.g., Eracleous et al. 1997; Eracleous & Halpern 2003).”
• What broad emission lines tell us about how active galactic nuclei work (2009, background): “A subsequent comprehensive survey of radiogalaxies by Eracleous & Halpern (1994, 2003) revealed many disk-like Balmer line profiles.”