期刊
ASTROPHYSICAL JOURNAL
卷 834, 期 2, 页码 -出版社
IOP Publishing Ltd
DOI: 10.3847/1538-4357/834/2/129
关键词
accretion, accretion disks; galaxies: active; galaxies: nuclei; quasars: emission lines; quasars: general
资金
- NSF [AST-1409524, AST-1515763]
- NASA [14-ATP14-0059, 15-XRP15-2-0139]
- Ambrose Monell Foundation
- National Science Foundation [1310405]
- Science and Technology Facilities Council [ST/P000673/1, ST/L000636/1] Funding Source: researchfish
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [1310405] Funding Source: National Science Foundation
- STFC [ST/P000673/1, ST/L000636/1] Funding Source: UKRI
Supermassive black hole binaries (SMBHs) are expected to result from galaxy mergers, and thus are natural byproducts (and probes) of hierarchical structure formation in the universe. They are also the primary expected source of low-frequency gravitational wave emission. We search for binary BHs using time-variable velocity shifts in broad Mg II emission lines of quasars with multi-epoch observations. First, we inspect velocity shifts of the binary SMBH candidates identified in Ju et al., using Sloan Digital Sky Survey spectra with an additional epoch of data that lengthens the typical baseline to similar to 10 yr. We find variations in the line of sight velocity shifts over 10 yr that are comparable to the shifts observed over 1-2 yr, ruling out the binary model for the bulk of our candidates. We then analyze 1438 objects with eight-year median time baselines, from which we would expect to see velocity shifts > 1000 km s(-1) from sub-parsec binaries. We find only one object with an outlying velocity of 448 km s-1, indicating-based on our modeling-that less than or similar to 1% (the value varies with different assumptions) of SMBHs that are active as quasars reside in binaries with similar to 0.1 pc separations. Binaries either sweep rapidly through these small separations or stall at larger radii.
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