Systematic investigation of the expected gravitational wave signal from supermassive black hole binaries in the pulsar timing band

By A. Sesana. 2012

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In this letter we carry out the first systematic investigatio n of the expected gravitational wave (GW) background generated by supermassive black hole (SMBH) binaries in the nHz frequency band accessible to pulsar timing arrays (PTAs). We take from the literature several estimates of the redshift dependent galaxy mass function and of the fraction of close galaxy pairs to derive a wide range of galaxy merger rates. We then exploit empirical black holehost relations to populate merging galaxies with SMBHs. The result of our procedure is a collection of a large number of phenomenological SMBH binary merger rates consistent with current observational constraints on the galaxy assembly at z < 1.5. For each merger rate we compute the associated GW signal, eventually producing a large set of estimates of the nHz GW background that we use to infer confidence intervals of its expected amplitude. When considering the most recent SMBH-host relations, accounting for ultra-massive black holes in brightest cluster galaxies, we find that the nominal 1σ interval of the expected GW signal is only a factor of 3-to-10 below current PTA limits, implying a non negligible chance of detection in the next few years.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/8970e953316895b5863609d41579b8321126d508

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Citations in the corpus

The NANOGrav 11 Year Data Set: Pulsar-timing Constraints on the Stochastic Gravitational-wave Background (2018, background): “The discovery-space here is populated by GWs from supermassive black-hole binaries (SMBHBs) at galactic centers (see e.g. Sesana et al. 2004; Sesana 2013), and possibly from more speculative sources of cosmological origin, such as cosmic strings (Damour & Vilenkin 2001; Ölmez et al. 2010) and/or a…”
The NANOGrav 11-year Data Set: High-precision Timing of 45 Millisecond Pulsars (2017, background): “An expected signal in this band is the incoherent superposition of gravitational waves from the cosmic merger history of supermassive black hole binaries, i.e., a gravitational-wave background (Phinney 2001; Jaffe & Backer 2003; Sesana 2013).”
Massive Black Hole Binary Mergers in Dynamical Galactic Environments (2016, background): “The cutoff seen in the full LC case (Frefill = 1.0) is very similar to that found by Sesana (2013a) (with ours ∼ 5 times lower amplitude), who show that in the scattering-dominated regime the GWB turns into a hc ∝ f spectrum.”
Selection bias in dynamically measured supermassive black hole samples: its consequences and the quest for the most fundamental relation (2016, methodology): “…of theMbh-Mbulge relation is also a key ingredient in predicting what pulsar timing array searches (e.g., Sesana et al. 2008; Hobbs et al. 2010; Sesana2013; Kramer & Champion 2013; Rosado & Sesana 2014; Rosado et al. 2015) for gravitational radiation will see (Bonnor & Rotenberg 1961; Peres…”
Expected properties of the first gravitational wave signal detected with pulsar timing arrays (2015, methodology): “The realisations are produced following the prescriptions of Sesana (2013), employing, for this exploratory study, the simplifying assumption of circular, GW-driven binaries.”
Searching for the Nano-Hertz Stochastic Gravitational Wave Background with the Chinese Pulsar Timing Array Data Release I (2023, background): “It was predicted that the orbiting and merger of supermassive black hole binaries (SMBHBs) would create a stochastic nHz GW background (Sesana 2013), while alternative channels, including cosmic strings (Kibble 1976; Sanidas et al. 2012) and relic GWs from early universe processes (Grishchuk 2005;…”
The International Pulsar Timing Array: First Data Release (2016, background): “Traditionally, time-derivatives of DM were included in the timing model (e.g. by Cognard et al. 1995), but in case of sufficiently dense 10 Note that, depending on the GW source population, it has been shown that the GWB may peak at higher frequencies, too (Sesana et al. 2004; Enoki & Nagashima 2007”
European Pulsar Timing Array Limits On An Isotropic Stochastic Gravitational-Wave Background (2015, methodology): “13, we compare the expected range in hc predicted by the phenomenological models presented in Sesana (2013b) to the 95 per cent upper limit obtained in Section 5.1.”
Gravitational-wave sensitivity curves (2014, background): “of the stochastic background is h c = 2:7 10 15 at a frequency of f 0 = 1 yr 1 (Shannon et al., 2013). There is strong theoretical evidence that the actual background lies close to the current limit (Sesana, 2013). The distribution of source amplitudes with frequency is dependent on the chirp mass d”
The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave Background (2023, background): “…Cornish & Sesana 2013; Mingarelli & Sidery 2014; Mingarelli et al. 2017; Roebber & Holder 2017)—the HD template is effective for detecting even anisotropic GWBs in all but the most extreme scenarios (Cornish & Sesana 2013; Cornish & Sampson 2016; Taylor et al. 2020; Bécsy et al. 2022; Allen 2023).”
On the Evidence for a Common-spectrum Process in the Search for the Nanohertz Gravitational-wave Background with the Parkes Pulsar Timing Array (2021, background): “Sesana (2013) showed that background amplitudes of > 10−15 could be caused by the effect of overmassive black holes on black hole - host relations.”
European Pulsar Timing Array Limits on Continuous Gravitational Waves from Individual Supermassive Black Hole Binaries (2015, methodology): “More details on the simulations and the models employed to produce them can be found in Sesana (2013).”
THE NANOGRAV NINE-YEAR DATA SET: OBSERVATIONS, ARRIVAL TIME MEASUREMENTS, AND ANALYSIS OF 37 MILLISECOND PULSARS (2015, background): “A number of predictions for the expected strength of the SMBHB gravitational wave background have been made (e.g., Jaffe & Backer 2003; Sesana et al. 2008; Sesana 2013; McWilliams et al. 2014), with a = -2 3 and expected values for Agw ranging from ∼5 × 10−16 to 4 × 10−15.”