TY - JOUR
T1 - SEARCHING for BINARY SUPERMASSIVE BLACK HOLES VIA VARIABLE BROAD EMISSION LINE SHIFTS
T2 - LOW BINARY FRACTION
AU - Wang, Lile
AU - Greene, Jenny E.
AU - Ju, Wenhua
AU - Rafikov, Roman R.
AU - Ruan, John J.
AU - Schneider, Donald P.
N1 - Publisher Copyright:
© 2017. The American Astronomical Society. All rights reserved.
PY - 2017/1/10
Y1 - 2017/1/10
N2 - 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 ∼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 ≲1% (the value varies with different assumptions) of SMBHs that are active as quasars reside in binaries with ∼0.1 pc separations Binaries either sweep rapidly through these small separations or stall at larger radii.
AB - 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 ∼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 ≲1% (the value varies with different assumptions) of SMBHs that are active as quasars reside in binaries with ∼0.1 pc separations Binaries either sweep rapidly through these small separations or stall at larger radii.
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U2 - 10.3847/1538-4357/834/2/129
DO - 10.3847/1538-4357/834/2/129
M3 - Article
AN - SCOPUS:85010424944
SN - 0004-637X
VL - 834
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 129
ER -