Constraints on black hole/host galaxy co-evolution and binary stalling using pulsar timing arrays

Journal Article · Wed Jul 20 04:00:00 EDT 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/826/1/11· OSTI ID:22868891

Simon, Joseph ^[1]; Burke-Spolaor, Sarah ^[2]

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1. Center for Gravitation, Cosmology and Astrophysics, University of Wisconsin Milwaukee, P.O. Box 413, Milwaukee, WI 53201 (United States)
2. National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville Rd, Socorro, NM 87801-0387 (United States)

Pulsar timing arrays are now setting increasingly tight limits on the gravitational wave background from binary supermassive black holes (SMBHs). But as upper limits grow more constraining, what can be implied about galaxy evolution? We investigate which astrophysical parameters have the largest impact on predictions of the strain spectrum and provide a simple framework to directly translate between measured values for the parameters of galaxy evolution and pulsar timing array (PTA) limits on the gravitational wave background of binary SMBHs. We find that the most influential observable is the relation between a host galaxy's central bulge and its central black hole, M{sub ∙}--M{sub bulge}, which has the largest effect on the mean value of the characteristic strain amplitude. However, the variance of each prediction is dominated by uncertainties in galaxy stellar mass functions. Using this framework with the best published PTA limit, we can set limits on the shape and scatter of the M{sub ∙}--M{sub bulge} relation. We find our limits to be in contention with strain predictions using two leading measurements of this relation. We investigate several possible reasons for this disagreement. If we take the M{sub ∙}--M{sub bulge} relations to be correct within a simple power-law model for the gravitational wave background, then the inconsistency is reconcilable by allowing for an additional “stalling” time between a galaxy merger and evolution of a binary SMBH to sub-parsec scales, with lower limits on this timescale of ∼1–2 Gyr.

• OSTI ID: 22868891
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 826; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BLACK HOLES
CARBON MONOXIDE
FORECASTING
GALACTIC EVOLUTION
GALAXIES
GRAVITATIONAL WAVES
MASS
PULSARS
QUASARS
SPECTRA