The Origins of Off-Centre Massive Black Holes in Dwarf Galaxies

Bellovary, Jillian M.; Hayoune, Sarra; Chafla, Katheryn; Vincent, Donovan; Brooks, Alyson; Christensen, Charlotte; Munshi, Ferah; Tremmel, Michael; Quinn, Thomas R.; Van Nest, Jordan; Sligh, Serena K.; Luzuriaga, Michelle

doi:10.48550/arxiv.2102.09566

Cited by 8 publications

(10 citation statements)

References 63 publications

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“…For LMC ejections we assume the LMC MBH is coincident with our assumed LMC centre at α = 78.76 • , δ = −69.19 • (Zivick et al 2019). In at least a substantial fraction of dwarf galaxies, the MBH can be offset by the host dwarf centre by as much as a few kiloparsecs (see Reines et al 2020;Mezcua & Domínguez Sánchez 2020;Bellovary et al 2021). A modest deviation of the LMC MBH in position and velocity from the assumed LMC centre does not appreciably affect our predictions for the number of GC and LMC HVSs lurking in future surveys.…”

Section: Ejection Distribution and Ratementioning

confidence: 80%

Comparing hypervelocity star populations from the Large Magellanic Cloud and the Milky Way

Evans

Marchetti

Rossi

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We predict and compare the distributions and properties of hyper-velocity stars (HVSs) ejected from the centres of the Milky Way (MW) and the Large Magellanic Cloud (LMC). In our model, HVSs are ejected at a constant rate – equal in both galaxies – via the Hills mechanism and are propagated in a combined potential, where the LMC orbits the MW on its first infall. By selecting m > 2 M⊙ HVSs well-separated from the Magellanic Clouds and Galactic midplane, we identify mock HVSs which would stand out from ordinary stars in the stellar halo in future data releases from the Gaia satellite and the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST). We find that in these deep surveys, LMC HVSs will outnumber MW ones by a factor ∼2.5, as HVSs can more easily escape from the shallower potential of the LMC. At an assumed HVS ejection rate of 10−4 yr−1, HVSs detectable in the final Gaia data release and LSST from the LMC (MW) will number $125_{-12}^{+11}$ ($50_{-8}^{+7}$) and $140_{-11}^{+10}$ ($42_{-7}^{+6}$), respectively. The MW and LMC HVS populations show different kinematics and spatial distributions. While LMC HVSs have more modest total velocities and larger Galactocentric distances clustered around those of the LMC itself, HVSs from the MW show broader distributions, including a prominent high-velocity tail above 500 km s−1 that contains at least half of the stars. These predictions are robust against reasonable variation of the Galactic potential and of the LMC central black hole mass.

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Section: Ejection Distribution and Ratementioning

confidence: 80%

Comparing hypervelocity star populations from the Large Magellanic Cloud and the Milky Way

Evans

Marchetti

Rossi

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…A methodological note: in our model, efficient accretion occurs only for central BHs, as the compact object needs to be in the deepest section of the galactic potential well to have a large gas reservoir at its disposal. Recent studies (e.g., Bellovary et al 2019Bellovary et al , 2021Ricarte et al 2021) have suggested that a large fraction of MBHs in galaxies can be off-centered, with perhaps up to ∼ 50% of MBHs in low mass galaxies offcenter (Bellovary et al 2019). Although the observation of these compact objects is challenging (Bellovary et al 2021) due to paucity of available gas to accrete, the possibility that the off-nuclear MBHs are accreting cannot be ruled out and indeed several examples have recently been found in dwarf galaxies (see, e.g., Mezcua et al 2018c;Reines et al 2020;Mezcua & Domínguez Sánchez 2020).…”

Section: Theoretical Modelmentioning

confidence: 99%

“…Recent studies (e.g., Bellovary et al 2019Bellovary et al , 2021Ricarte et al 2021) have suggested that a large fraction of MBHs in galaxies can be off-centered, with perhaps up to ∼ 50% of MBHs in low mass galaxies offcenter (Bellovary et al 2019). Although the observation of these compact objects is challenging (Bellovary et al 2021) due to paucity of available gas to accrete, the possibility that the off-nuclear MBHs are accreting cannot be ruled out and indeed several examples have recently been found in dwarf galaxies (see, e.g., Mezcua et al 2018c;Reines et al 2020;Mezcua & Domínguez Sánchez 2020). In our fiducial model we do not include off-centered MBHs as they likely have very low accretion rates (Bellovary et al 2019).…”

Section: Theoretical Modelmentioning

confidence: 99%

The Active Fraction of Massive Black Holes in Dwarf Galaxies

Pacucci,

Mezcua,

Regan

2021

Preprint

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The population of massive black holes (MBHs) in dwarf galaxies is elusive, but fundamentally important to understand the co-evolution of black holes with their hosts and the formation of the first collapsed objects in the Universe. While some progress was made in determining the X-ray detected fraction of MBHs in dwarfs, with typical values ranging from 0% to 6%, their overall active fraction, A, is still largely unconstrained. Here, we develop a theoretical model to predict the multi-wavelength active fraction of MBHs in dwarf galaxies starting from first principles and based on physical properties of the host, namely its stellar mass and angular momentum content. We find multi-wavelength active fractions for MBHs, accreting at typically low rates, ranging from 5% to 22%, and increasing with the stellar mass of the host as A ∼ (log 10 M ) 4.5 . If dwarfs are characterized by low-metallicity environments, the active fraction may reach ∼ 30% for the most massive hosts. For galaxies with stellar mass in the range 10 7 < M [ M ] < 10 10 , our predictions are in agreement with occupation fractions derived from simulations and semi-analytical models. Additionally, we provide a fitting formula to predict the probability of finding an active MBH in a dwarf galaxy from observationally-derived data. This model will be instrumental to guide future observational efforts to find MBHs in dwarfs. JWST, in particular, will play a crucial role in detecting MBHs in dwarfs, possibly uncovering active fractions ∼ 3 larger than current X-ray surveys.

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“…Unlike in the unified AGN model, IMBHs in dwarfs often wander within 1 kpc of the center due to the dwarfs' weak gravitational potential (Reines et al 2020, Bellovary et al 2021. Therefore, it is unclear whether the AGN and stellar radiation fields strike the same gas clouds, or spatially separated gas clouds, as the IMBH relocates or settles down in a particular location.…”

Section: Introductionmentioning

confidence: 99%

Optical and JWST Mid-IR Emission Line Diagnostics for Simultaneous IMBH and Stellar Excitation in z~0 Dwarf Galaxies

Richardson,

Simpson,

Polimera

et al. 2022

Preprint

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Current observational facilities have yet to conclusively detect 10 3 − 10 4 M intermediate mass black holes (IMBHs) that fill in the evolutionary gap between early universe seed black holes and z ∼ 0 supermassive black holes. Dwarf galaxies present an opportunity to reveal active IMBHs amidst persistent star formation. We introduce photoionization simulations tailored to address key physical uncertainties: coincident vs. non-coincident mixing of IMBH and starlight excitation, open vs. closed surrounding gas cloud geometries, and different AGN SED shapes. We examine possible AGN emission line diagnostics in the optical and mid-IR, and find that the diagnostics are often degenerate with respect to the investigated physical uncertainties. In spite of these setbacks, and in contrast to recent work, we are able to show that [O III]/Hβ typically remains bright for dwarf AGN powered by IMBHs down to 10 3 M . Dwarf AGN are predicted to have inconsistent star-forming and Seyfert/LINER classifications using the most common optical diagnostics. In the mid-IR, [O IV] 25.9µm and [Ar II] 6.98µm are less sensitive to physical uncertainties than are optical diagnostics. Based on these emission lines, we provide several mid-IR emission line diagnostic diagrams with demarcations for separating starbursts and AGN with varying levels of activity. The diagrams are valid over a wide range of

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The Origins of Off-Centre Massive Black Holes in Dwarf Galaxies

Cited by 8 publications

References 63 publications

Comparing hypervelocity star populations from the Large Magellanic Cloud and the Milky Way

Comparing hypervelocity star populations from the Large Magellanic Cloud and the Milky Way

The Active Fraction of Massive Black Holes in Dwarf Galaxies

Optical and JWST Mid-IR Emission Line Diagnostics for Simultaneous IMBH and Stellar Excitation in z~0 Dwarf Galaxies

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