Space Telescope and Optical Reverberation Mapping Project. IX. Velocity–Delay Maps for Broad Emission Lines in NGC 5548

Author Info

Keith Horne, University of St. Andrews
G. De Rosa, Space Telescope Science Institute
B. M. Peterson, The Ohio State University
A. J. Barth, University of California, Irvine
Vardha N. Bennert, California Polytechnic State University, San Luis ObispoFollow
Y. Zu, The Ohio State University

Author ORCID Identifier

https://orcid.org/0000-0003-2064-0518

Recommended Citation

Postprint version. Published in The Astrophysical Journal, Volume 907, Issue 2, February 1, 2021.

Please note: Only the first four authors, Cal Poly affiliated authors, and the last author are listed above. For the complete list of authors, please download the article using the download button at the top of the page.

The definitive version is available at https://doi.org/https://doi.org/10.3847/1538-4357/abce60.

Abstract

In this contribution, we achieve the primary goal of the active galactic nucleus (AGN) STORM campaign by recovering velocity–delay maps for the prominent broad emission lines (Lyα, C IV, He II, and Hβ) in the spectrum of NGC 5548. These are the most detailed velocity–delay maps ever obtained for an AGN, providing unprecedented information on the geometry, ionization structure, and kinematics of the broad-line region. Virial envelopes enclosing the emission-line responses show that the reverberating gas is bound to the black hole. A stratified ionization structure is evident. The He II response inside 5–10 lt-day has a broad single-peaked velocity profile. The Lyα, CIV, and Hβ responses extend from inside 2 to outside 20 lt-day, with double peaks at ±2500 km s⁻¹ in the 10–20 lt-day delay range. An incomplete ellipse in the velocity–delay plane is evident in Hβ. We interpret the maps in terms of a Keplerian disk with a well-defined outer rim at R = 20 lt-day. The far-side response is weaker than that from the near side. The line-center delay t = (R/c)(1 - sin i) ≈ 5 days gives the inclination i ≈ 45°. The inferred black hole mass is M_BH ≈ 7 x 10⁷ M_e. In addition to reverberations, the fit residuals confirm that emission-line fluxes are depressed during the “BLR Holiday” identified in previous work. Moreover, a helical “Barber-Pole” pattern, with stripes moving from red to blue across the C IV and Lyα line profiles, suggests azimuthal structure rotating with a 2 yr period that may represent precession or orbital motion of inner-disk structures casting shadows on the emission-line region farther out.

Disciplines

Physics

Copyright

© 2021. The American Astronomical Society. All rights reserved.

Number of Pages

19