Supermassive Black Hole Formation in Galatic Nuclei: The Role of Intermediate-mass Black Holes Abbas Askar Carl Tryggers Postdoctoral Fellow at Lund Observatory Department of Astronomy and Theoretical Physics Lund University In Collaboration with: Melvyn B. Davies & Ross P. Church Compact Objects For All, Lund, Sweden 10 th February, 2020
Galactic Nuclei: Nuclear Star Clusters and Massive Black Holes • Nuclear star clusters (NSCs) are extremely dense ( ) and massive star clusters ∼ 10 6 − 10 7 M ⊙ pc − 3 ( ) occupying the nucleus of most galaxies. ∼ 10 6 − 10 9 M ⊙ • Most frequent in galaxies with stellar masses in the range ∼ 10 8 − 10 10 M ⊙ • Many cases where NSCs and massive black holes (SMBH) are found to co-exist: ∼ 10 6 − 10 10 M ⊙ • Milky Way NSC Mass: SMBH Mass: 2.5 × 10 7 M ⊙ 4 × 10 6 M ⊙ • M31 NSC Mass: SMBH Mass: ∼ 5 × 10 7 M ⊙ ∼ 1.6 × 10 8 M ⊙ • Masses of both SMBHs and NSCs follow a tight relation with the masses of their host galaxies • Build-up of NSCs and the growth of massive black holes are closely related Neumayer et al. 2020 Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
M33: No Supermassive Black Hole • M33 contains a NSC but no SMBH! • NSC Mass: (Kormendy et al. 2010, McConnachie 2012) 2 × 10 6 M ⊙ • Upper limit on central black hole mass: 1500 M ⊙ Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
Key Question: What came first? • M33 contains a NSC but no SMBH! • NSC Mass: (Kormendy et al. 2010, McConnachie 2012) 2 × 10 6 M ⊙ • Upper limit on central black hole mass: 1500 M ⊙ Chicken or egg? Which comes first, a Supermassive Black Hole (SMBH) or a Nuclear Stellar Cluster (NSC)? Can a SMBH form AFTER NSC? Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
What we did: Central ideas • Make nuclear stellar cluster by merging globular clusters (Guillard, Emsellem & Renaud 2016) - Antonini et al. 2012; Mastrobuono-Battisti et al. 2014 - No pre-existing SMBH - Talk by Alessandra Mastrobuono-Battisti • Some of those globular clusters contain intermediate mass black holes (IMBHs) • What happens to the IMBHs? • Can we keep them? • How much must they grow to form SMBHs? Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
What we did: Making NSC from Merging Globular Clusters • Carried out direct N -body simulations of 3 merging globular clusters using NBODY6++GPU (Wang et al. 2015) - 3 merging cluster containing containing 50000, 30000 and 15000 stars - Containing up to 3 IMBH in different configurations 28.8 Myr 360 Myr Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
Flowchart for Possible Outcomes • Infalling globular clusters bring (in total): No One Two Three Many IMBH IMBH IMBHs IMBHs IMBHs Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
Flowchart for Possible Outcomes • Infalling globular clusters bring (in total): No One Two Three Many IMBH IMBH IMBHs IMBHs IMBHs No One Many SMBH Seed SMBH Seed SMBH Seeds? Go on to grow by tidal disruption of stars and gas accretion (i.e. wet growth with gas inflow) Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
Flowchart for Possible Outcomes • Infalling globular clusters bring (in total): No One Two Three Many IMBH IMBH IMBHs IMBHs IMBHs No One Many SMBH Seed SMBH Seed SMBH Seeds? Go on to grow by tidal disruption of stars and gas accretion (i.e. wet growth with gas inflow) Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
The 2 IMBH Case • Both IMBHs segregate to the center of the merged cluster and form a binary IMBH • IMBH binary hardens as it interacts with surrounding stars Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
IMBH Binary Merger due to Gravitational Wave Radiation • Eccentricity of binary IMBH increases as the binary hardens → gravitational wave radiation can efficiently merge the binary • Retention of merged BH depends on magnitude of gravitational recoil kick Wiseman 1992 Morawski et al. 2018 Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
Flowchart for Possible Outcomes • Infalling globular clusters bring (in total): No One Two Three Many IMBH IMBH IMBHs IMBHs IMBHs First grows, then Meet and merge meet and merge 1+1 = 0 1+1 = 1 No One Many SMBH Seed SMBH Seed SMBH Seeds? Go on to grow by tidal disruption of stars and gas accretion (i.e. wet growth with gas inflow) Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
3 IMBH Case: Diverse Outcomes • 2 most massive IMBHs form a binary • Less massive IMBH gets scattered away due to binary - single interaction • 2 + 1 = 2 • If IMBH binary is sufficiently hard at interaction time then all 3 IMBH can be ejected • 2 + 1 = 0 Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
Flowchart for Possible Outcomes • Infalling globular clusters bring (in total): No One Two Three Many IMBH IMBH IMBHs IMBHs IMBHs First grows, then Meet and merge meet and merge 1+1 = 0 1+1 = 1 No One Many SMBH Seed SMBH Seed SMBH Seeds? Go on to grow by tidal disruption of stars and gas accretion (i.e. wet growth with gas inflow) Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
Populating Galaxies with NSC and IMBH • Sample galaxies from a double-Schechter galaxy stellar mass function (Baldry 1.5 × 10 5 et al. 2012) • Find corresponding NSC Mass • Sample initial globular clusters masses from a log-normal distribution (Schaerer & Charbonnel 2011) until we can reproduce NSC Mass • Assign probability for a globular cluster to bring an IMBH • Estimate mass of IMBH brought in by globular cluster • Depends on initial on globular cluster mass Neumayer et al. 2020 • Based on results on results from Monte Carlo simulations of dense clusters (Askar et al. 2017, Morawski et al. 2018 and Arca Sedda et al. 2019) Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
Nuclear Star Clusters and Massive Black Holes Data from Neumayer et al. 2020 Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
SMBH Seed Population Synthesis Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
SMBH Seed Population Synthesis No Seed Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
SMBH Seed Population Synthesis One Seed No Seed Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
SMBH Seed Population Synthesis One Seed Many seeds but one remains No Seed Why BHs Matter in Globular Clusters - Abbas Askar SMBH formation in galactic nuclei: the role of IMBHs - Abbas Askar Compact Objects For All, Lund, Sweden 10 th February, 2020
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