Panic at the ISCO: time-varying double-peaked broad lines from evolving accretion disks are common amongst optically variable AGN

arXiv (Cornell University)

Abstract

About 3-10\% of Type I active galactic nuclei (AGN) have double-peaked broad Balmer lines in their optical spectra originating from the motion of gas in their accretion disk. Double-peaked profiles arise not only in AGN, but occasionally appear during optical flares from tidal disruption events and changing-state AGN. In this paper we identify 250 double-peaked emitters (DPEs) amongst a parent sample of optically variable broad-line AGN in the Zwicky Transient Facility (ZTF) survey, corresponding to a DPE fraction of 19\%. We model spectra of the broad H$α$ emission line regions and provide a catalog of the fitted accretion disk properties for the 250 DPEs. Analysis of power spectra derived from the 5 year ZTF light curves finds that DPE light curves have similar amplitudes and power law indices to other broad-line AGN. Follow-up spectroscopy of 12 DPEs reveals that $\sim$50\% display significant changes in the relative strengths of their red and blue peaks over long $10-20$ year timescales, indicating that broad-line profile changes arising from spiral arm or hotspot rotation are common amongst optically variable DPEs. Analysis of the accretion disk parameters derived from spectroscopic modeling provides evidence that DPEs are not in a special accretion state, but are simply normal broad-line AGN viewed under the right conditions for the accretion disk to be easily visible. We include inspiraling SMBH binary candidate SDSSJ1430+2303 in our analysis, and discuss how its photometric and spectroscopic variability is consistent with the disk-emitting AGN population in ZTF.

Authors 14

1. Charlotte Ward

   Princeton University

   Affiliation as printed

   Department of Astrophysical Sciences , Princeton University , Princeton , NJ 08544 , USA

2. Suvi Gezari

   Space Telescope Science Institute

   Affiliation as printed

   Space Telescope Science Institute , 3700 San Martin Dr. , Baltimore , MD 21218 , USA

3. P. Nugent

   Lawrence Berkeley National Laboratory · University of California, Berkeley

   Affiliation as printed

   Department of Astronomy , University of California , Berkeley , Berkeley , CA 94720 , USA

   Lawrence Berkeley National Laboratory , 1 Cyclotron Road , Berkeley , CA 94720 , USA

4. Matthew T. Kerr

   United States Naval Research Laboratory · Naval Research Laboratory Space Science Division

   Affiliation as printed

   Space Science Division , U.S. Naval Research Laboratory , Washington , DC 20375 , USA

5. Michael Eracleous
   Affiliation as printed

   Department of Astronomy & Astrophysics and Institute for Gravitation and the Cosmos , 525 Davey Laboratory , The Pennsylvania State University , University Park , PA 16802 , USA

6. Sara Frederick

   Vanderbilt University

   Affiliation as printed

   Department of Physics and Astronomy , Vanderbilt University , 6301 Stevenson Center , Nashville , TN 37235

7. Erica Hammerstein

   University of Maryland, College Park

   Affiliation as printed

   Department of Astronomy , University of Maryland , College Park , MD 20742 , USA

8. M. J. Graham

   California Institute of Technology

   Affiliation as printed

   Division of Physics, Mathematics, and Astronomy , California Institute of Technology , Pasadena , CA 91125 , USA

9. Sjoert van Velzen Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory , Leiden University , Postbus 9513 , 2300 RA , Leiden , the Netherlands

10. M. M. Kasliwal

    California Institute of Technology

    Affiliation as printed

    Division of Physics, Mathematics, and Astronomy , California Institute of Technology , Pasadena , CA 91125 , USA

11. Russ R. Laher

    California Institute of Technology · Infrared Processing and Analysis Center

    Affiliation as printed

    IPAC , California Institute of Technology , 1200 E. California Blvd , Pasadena , CA 91125 , USA

12. Frank J. Masci

    California Institute of Technology · Infrared Processing and Analysis Center

    Affiliation as printed

    IPAC , California Institute of Technology , 1200 E. California Blvd , Pasadena , CA 91125 , USA

13. Josiah N. Purdum

    California Institute of Technology

    Affiliation as printed

    Caltech Optical Observatories , California Institute of Technology , Pasadena , CA 91125 , USA

14. B. Racine

    Centre National de la Recherche Scientifique · Aix-Marseille Université · Centre de physique des particules de Marseille · Institut National de Physique Nucléaire et de Physique des Particules

    Affiliation as printed

    Aix Marseille Univ , CNRS/IN2P3 , CPPM , Marseille , France