Simulating the mass assembly history of Nuclear Star Clusters

Simulating the mass assembly history of Nuclear Star Clusters The imprints of cluster inspirals Alessandra Mastrobuono-Battisti Sassa Tsatsi Hagai Perets Nadine Neumayer Glenn vad de Ven Ryan Leyman David Merritt Roberto Capuzzo-Dolcetta Fabio Antonini Avi Loeb Stellar Aggregates, Bad Honnef, 8-12-2016

Nuclear Star Clusters (NSCs) are observed at the center of most galaxies 10 = 87pc 1.2kpc x 1.2kpc Neumayer et al 2011, Carollo et al. 1998, Matthews et al. 1999, Böker et al. 2002, 2003, 2004, Böker 2010, Côte et al. 2006

Nuclear Star Clusters (NSCs) are observed at the center of most galaxies 10 = 87pc NSC 1.2kpc x 1.2kpc Neumayer et al 2011, Carollo et al. 1998, Matthews et al. 1999, Böker et al. 2002, 2003, 2004, Böker 2010, Côte et al. 2006

The Milky Way has a NSC hosting a central Massive Black Hole

NSCs form through cluster infall and/or insitu star formation The in-situ star formation or gas model (Loose et al. 1982, Schinnerer et al. 2008, Milosavljevic 2004, Pflamm-Altenburg, Jan & Kroupa 2009), possibly in a disk like configuration. The cluster merger scenario (Tremaine et al. 1975, Ostriker 1988, Antonini, Capuzzo Dolcetta, MB & Merritt 2012, Antonini 2013, Gnedin et al. 2013 and references therein). Both processes can work in concert, and both could be important for the formation and evolution of NSCs.

We modelled NSC formation from cluster infalls using N-body simulations Initially: only the nuclear bulge of the galaxy; An MBH (4x10 6 M ) is at the center of the galaxy; The NSC is build up by consecutive infalls; Collisional evolution of the NSC. Antonini, Capuzzo-Dolcetta, Mastrobuono-Battisti & Merritt, 2012 ApJ; Perets & Mastrobuono- Battisti,2014, ApJ; Mastrobuono-Battisti, Perets & Loeb, 2016, ApJ; Tsatsi, Mastrobuono-Battisti et al., 2016, MNRAS

We modelled NSC formation from cluster infalls using N-body simulations 10 8 M Nuclear bulge Massive Black Hole 4 10 6 M (Milky Way-like) Initially: only the nuclear bulge of the galaxy; An MBH (4x10 6 M ) is at the center of the galaxy; The NSC is build up by consecutive infalls; Collisional evolution of the NSC. Antonini, Capuzzo-Dolcetta, Mastrobuono-Battisti & Merritt, 2012 ApJ; Perets & Mastrobuono- Battisti,2014, ApJ; Mastrobuono-Battisti, Perets & Loeb, 2016, ApJ; Tsatsi, Mastrobuono-Battisti et al., 2016, MNRAS

We modelled NSC formation from cluster infalls using N-body simulations 10 8 M Nuclear bulge Massive Black Hole 4 10 6 M (Milky Way-like) Initially: only the nuclear bulge of the galaxy; 12 GCs with random orientations An MBH (4x10 6 M ) is at the center of the galaxy; 1.1 The 10 6 MNSC is build up by consecutive infalls; Collisional evolution of the NSC. Antonini, Capuzzo-Dolcetta, Mastrobuono-Battisti & Merritt, 2012 ApJ; Perets & Mastrobuono- Battisti,2014, ApJ; Mastrobuono-Battisti, Perets & Loeb, 2016, ApJ; Tsatsi, Mastrobuono-Battisti et al., 2016, MNRAS

We modelled NSC formation from cluster infalls using N-body simulations 10 8 M Nuclear bulge Initially: only the nuclear bulge of the galaxy; 12 GCs with random orientations An MBH (4x10 6 M ) is at the center of the galaxy; ~12 Gyr Nuclear Star Cluster Massive Black Hole 4 10 6 M (Milky Way-like) 1.1 The 10 6 MNSC is build up by consecutive infalls; Collisional evolution of the NSC. 1.5 10 7 M Antonini, Capuzzo-Dolcetta, Mastrobuono-Battisti & Merritt, 2012 ApJ; Perets & Mastrobuono- Battisti,2014, ApJ; Mastrobuono-Battisti, Perets & Loeb, 2016, ApJ; Tsatsi, Mastrobuono-Battisti et al., 2016, MNRAS

GCs decay and merge, forming the NSC: models based on Milky Way data 40 40 30 30 20 20 10 10 y(pc) 0 z(pc) 0-10 -10-20 -20-30 -30-40 -40-40 -30-20 -10 0 10 20 30 40-40 -30-20 -10 0 10 20 30 40 x (pc) 12 GCs, initially at 20pc 1.1x10 6 M each ~800Myr between each infall x (pc) Antonini, Capuzzo-Dolcetta, Mastrobuono-Battisti & Merritt (2012); Perets & Mastrobuono-Battisti (2014)

GCs decay and merge, forming the NSC: snapshots 1st 2nd 3rd 4th 4th 6th 7th 8th 9th 10th 11th 12th Antonini, Capuzzo-Dolcetta, Mastrobuono-Battisti & Merritt 2012,

The infall scenario forms an NSC with a large core-like structure 12 9 6 3 #infalls Antonini et al. 2012, Mastrobuono Battisti et al. 2014, Perets & MB 2014

The infall scenario forms an NSC with a large core-like structure 12 9 6 3 10Gyr #infalls Antonini et al. 2012, Mastrobuono Battisti et al. 2014, Perets & MB 2014

The infall scenario forms an NSC with a large core-like structure 12 9 6 20Gyr 3 10Gyr #infalls Antonini et al. 2012, Mastrobuono Battisti et al. 2014, Perets & MB 2014

The Milky Way s is the closest NSC MNSC ~10 7 M Schödel (2010) It hosts a massive BH: Sgr A* MBH = 4.3 10 6 M (Genzel et al. 2010; Ghez et al. 2008; Gillessen et al. 2009; Eisenhauer et al. 2005) Tangentially anisotropic, 0.1-10 : (Merritt 2010). Flattened with q = 0.71±0.02 (Schödel et al. 2014).

The Milky Way s is the closest NSC MNSC ~10 7 M It hosts a massive BH: Sgr A* MBH = 4.3 10 6 M (Genzel et al. 2010; Ghez et al. 2008; Gillessen et al. 2009; Eisenhauer et al. 2005) Tangentially anisotropic, 0.1-10 : (Merritt 2010). Flattened with q = 0.71±0.02 (Schödel et al. 2014).

The Milky Way s is the closest NSC MNSC ~10 7 M 10Gyr It hosts a massive BH: Sgr A* MBH = 4.3 10 6 M (Genzel et al. 2010; Ghez et al. 2008; Gillessen et al. 2009; Eisenhauer et al. 2005) Tangentially anisotropic, 0.1-10 : (Merritt 2010). Flattened with q = 0.71±0.02 (Schödel et al. 2014).

Simulations vs Observations: Direct comparison with the Milky Way NSC

What do we learn from observations? arcsec ν arcsec σ arcsec arcsec arcsec 1pc ~ 26 Feldmeier + 2014 arcsec

We can get similar maps for the simulated cluster

The real and simulated NSC look similar arcsec arcsec arcsec 1pc ~ 26 arcsec arcsec arcsec

The similarity is apparent from radial plots

The similarity is apparent from radial plots Feldmeier + 2014 arcsec arcsec

The similarity is apparent from radial plots Feldmeier + 2014 arcsec arcsec Tsatsi, Mastrobuono-Battisti et al. 2017

The similarity is apparent from radial plots

The similarity is apparent from radial plots Feldmeier + 2014 arcsec arcsec

The similarity is apparent from radial plots Feldmeier + 2014 arcsec arcsec Tsatsi, Mastrobuono-Battisti et al. 2017

Which role has the bulge?

Kinematic profiles are still consistent

Can we predict kinematic substructures? 60 V model 80 arcsec 40 20 0-20 60 40 arcsec -40-60 100 50 0-50 100 50 0-50 -100 arcsec V data -100-50 0 50 100 arcsec Velocity [km/s] 80 60 40 20 0-20 -40-60 -80 Velocity [km/s] 20 0-20 -40-60 -80 Fig. 8. Upper panel: kinemetric model velocity map of the cleaned data cube. Black dots denote Feldmeier the best fitting et ellipses. al. 2014 The model goes only to r 100 00 along the Galactic plane and to 60 00 perpendicular to it. The

Can we predict kinematic substructures? Feldmeier+2014 Tsatsi, Mastrobuono-Battisti et al., 2017

Can we predict kinematic substructures? Feldmeier+2014 Kinemetry (Krajnovic +2006) Tsatsi, Mastrobuono-Battisti et al., 2017

Can we predict kinematic substructures? Feldmeier+2014 Kinemetry (Krajnovic +2006) Created by a polar merger Tsatsi, Mastrobuono-Battisti et al., 2017

The effect of IMBHs on the formation and evolution of NSCs

IMBHs may be present in dense clusters and decay with them Silk & Arons (1975): massive clusters may host an IMBH at their center: The merging model implies the presence of IMBHs in NSCs. Orbital radius of the last IMBH to fall in The other 11 IMBHs We introduced an IMBH in each GC Mastrobuono-Battisti et al., 2014

The presence of IMBHs causes the NSC to have a steep cusp and to be strongly mass segregated without IMBHs with IMBHs Mastrobuono-Battisti et al., 2014

We can estimate the tidal disruption events rate Image credit: NASA/CXC/ M.Weiss

We can estimate the tidal disruption events rate Image credit: NASA/CXC/ M.Weiss Komossa 2012; Khabibullin & Sazonov 2014

We can estimate the tidal disruption events rate Image credit: NASA/CXC/ M.Weiss Komossa 2012; Khabibullin & Sazonov 2014 No IMBHs in NSCs?

Conclusions

Conclusions N-body simulations to study the merger scenario

Conclusions N-body simulations to study the merger scenario Direct comparison with the Milky Way NSC: mock observational maps

Conclusions N-body simulations to study the merger scenario Direct comparison with the Milky Way NSC: mock observational maps The infall scenario reproduces most of the properties of the MW NSC, including its rotation We also find kinematic substructures similar to the observed one: the infall scenario is really plausible!

Thank you!