Abstract
ABSTRACT Obtaining a better understanding of intermediate-mass black holes (IMBHs) is crucial, as their properties could shed light on the origin and growth of their supermassive counterparts. Massive star-forming clumps, which are present in a large fraction of massive galaxies at z ∼ 1–3, are among the venues wherein IMBHs could reside. We perform a series of Fokker–Planck simulations to explore the occurrence of tidal disruption (TD) and gravitational wave (GW) events about an IMBH in a massive star-forming clump, modelling the latter so that its mass ($10^8 \, {\rm M}_{\odot}$) and effective radius (100 pc) are consistent with the properties of both observed and simulated clumps. We find that the TD and GW event rates are in the ranges of 10−6 to 10−5 and 10−8 to 10−7 yr−1, respectively, depending on the assumptions for the initial inner density profile of the system (ρ ∝ r−2 or ∝ r−1) and the initial mass of the central IMBH (105 or $10^3\, {\rm M}_{\odot}$). By integrating the GW event rate over z = 1–3, we expect that the Laser Interferometer Space Antenna will be able to detect ∼2 GW events per year coming from these massive clumps; the intrinsic rate of TD events from these systems amounts instead to a few 103 per year, a fraction of which will be observable by e.g. the Square Kilometre Array and the Advanced Telescope for High Energy Astrophysics. In conclusion, our results support the idea that the forthcoming GW and electromagnetic facilities may have the unprecedented opportunity of unveiling the lurking population of IMBHs.
Highlights
Black holes (BHs) are typically categorized into two different species: stellar-mass BHs (SBHs; e.g. Abbott et al 2016; Giesers et al 2018), whose mass spans from ∼10 to ∼100 M⊙, and supermassive BHs (SMBHs; e.g. Gillessen et al 2009; Event Horizon Telescope Collaboration 2019), with masses in the range of 106–1010 M⊙.In the last few decades, observational astronomers have been pointing to an apparent dearth of BHs with masses between the heaviest SBHs (∼100 M⊙) and the lightest SMBHs (∼106 M⊙): BHs inhabiting this loosely populated mass range have been named intermediate-mass BHs (IMBHs)
We find that the tidal disruption (TD) and gravitational wave (GW) event rates are in the ranges of 10−6 to 10−5 and 10−8 to 10−7 yr−1, respectively, depending on the assumptions for the initial inner density profile of the system (ρ ∝ r−2 or ∝ r−1) and the initial mass of the central intermediate-mass black holes (IMBHs) (105 or 103 M⊙)
By integrating the GW event rate over z = 1–3, we expect that the Laser Interferometer Space Antenna will be able to detect ∼2 GW events per year coming from these massive clumps; the intrinsic rate of TD events from these systems amounts instead to a few 103 per year, a fraction of which will be observable by e.g. the Square Kilometre Array and the Advanced Telescope for High Energy Astrophysics
Summary
Black holes (BHs) are typically categorized into two different species: stellar-mass BHs (SBHs; e.g. Abbott et al 2016; Giesers et al 2018), whose mass spans from ∼10 to ∼100 M⊙, and supermassive BHs (SMBHs; e.g. Gillessen et al 2009; Event Horizon Telescope Collaboration 2019), with masses in the range of 106–1010 M⊙.In the last few decades, observational astronomers have been pointing to an apparent dearth of BHs with masses between the heaviest SBHs (∼100 M⊙) and the lightest SMBHs (∼106 M⊙) (for a review, see Mezcua 2017): BHs inhabiting this loosely populated mass range have been named intermediate-mass BHs (IMBHs). 2010; Lützgendorf et al 2012, 2013; Lanzoni et al 2013; Haggard et al 2013; Reines et al 2013; Casares & Jonker 2014; Baldassare et al 2015; Kızıltan et al 2017; Perera et al 2017; Lin et al 2018; Mezcua et al 2018) and many of them remain debated. It is unclear whether the paucity of IMBH detections has to be interpreted as an intrinsic lack of these objects, or rather observational biases render their detection inherently more challenging It is unclear whether the paucity of IMBH detections has to be interpreted as an intrinsic lack of these objects, or rather observational biases render their detection inherently more challenging (e.g. Mezcua 2017)
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