Measuring the physical proper2es of the Milky Way nuclear star cluster with 3D kinema2cs

Transcription

1 Measuring the physical proper2es of the Milky Way nuclear star cluster with 3D kinema2cs Tuan Do Dunlap Ins2tute, University of Toronto Dunlap Fellow Collaborators: A. Ghez (UCLA), J. Lu (IfA), G. Mar2nez (Oskar Klein Centre), Annika Peter (UCI), S. Yelda (UCLA), M. Morris (UCLA), M. Kaplinghat (UCI), J. Bullock (UCI), K. MaVhews (Caltech) IAU 303,

2 A massive black hole is predicted to substan2ally alter the structure of a stellar cluster MBH No BH n(r)= r 7/4 to r 3/2 Surface stellar density profile for a dynamically relaxed cluster e.g. Bahcall & Wolf 1977 (shown), Murphy et al. 1999, Alexander & Hopman 2008

3 Stellar cusps are important to simula2ons of black hole growth and dynamics around a supermassive black hole Feeding of supermassive black holes from stars assume a stellar cusp. Predic2ons of gravita2onal inspiral rates of compact objects depend on distribu2on of stars. Cusps has the poten2al for detec2ng massive black holes without kinema2cs. Tests will require: 1. A confirmed massive black hole. 2. A dynamically relaxed stellar system.

4 The MW nuclear star cluster is missing a stellar cusp of old stars Spectroscopic observa2ons of early and late- type stars within central 0.14 pc (Do et al. 2009) See also, Buchholz et al. 2009, Bartko et al. 2010

5 Surface density measurement only constrains the slope to be < 1.0 Volume density profile Projected surface density profile n(r) r γ (γ=7/4 from Bahcall & Wolf 1976) Σ(R) R Γ Need kinema3c informa3on to provide further constraints!

6 Current survey has spectral iden2fica2ons out to 0.5 pc Do et al. 2013

7 Proper mo2on measurements Mean velocity error: 4 km/s Dynamics can be used to further constrain the density profile

8 Dynamics can be used to further constrain the density profile 10 RV (km/s) DEC offset (arcsec) RA offset (arcsec) Line of sight velocity measurements, mean velocity error = 16 km/s

9 See also, Genzel et al. 1996, 2000; Trippe et al. 2008, Schoedel et al Jeans modeling can be used to constrain cluster proper2es with the inclusion of kinema2c measurements Observa2ons: x, y, vx, vy, vz Spherical Jeans Equa2on Parameteriza2on of the stellar density profile (broken power law model) d(? 2 r ) dr +2 (r)? 2 r r? / r 1+(r/r 0 ) = G? M(r) r 2 ( )/ Velocity anisotropy Gravita2onal poten2al due only to BH mass (r) = (r/r ) 1+(r/r ). M(r) =M BH Distance to the Galac2c center: R 0 Assumes spherical symmetry, no rota2on in inner 0.5 pc

10 Avoid binning by using the likelihoods of individual measurements to constrain model P(v,R M ) / parameters Probability distribu2on func2on for the measurement of an individual star 1 p exp (V V) C(R) 1 (V V)/2 C(R) Covariance matrix from Jean s equa2ons Combined likelihood of the whole sample: L(M )= Y i P(V i,r i M ) Mar2nez et al. 2011, Do et al. in prep

11 Probability distribu2ons from Jeans modeling places constraints on the inner slope and anisotropy Inner slope Inner anisotropy Central 1 sigma confidence intervals: = = Do et al. in prep

12 Joint probability distribu2ons shows the correla2ons with spa2al density profile Measured BH mass decreases with increasing slope Do et al. in prep

13 Velocity dispersions are in good agreement with Jeans modeling predic2ons 1 sigma probabili2es for each dispersion component from model

14 The core must be larger than > 0.5 pc in radius Projected surface density of the most probable space density profile The break radius is not well constrained at large radii because of the limited radial sampling in the current dataset

15 Resonant relaxa2on and collisions of giants can effec2vely remove stars within the central 0.1 pc Changes in spa2al density from resonant relaxa2on (Madigan et al. 2011) Collisions currently predicted to operate most efficiently in the inner 0.1 pc (Davies et al. 2008)

16 Infalling IMBH or binary SMBH will destroy the stellar cusp It takes at least 10 9 yrs to replenish cusp (see also, Gualandris & MerriV 2009, MerriV 2009) Stellar density profile aper the infall of IMBH (Baumgardt et al. 2006)

17 Observa2onal limits on IMBHs in this region allows 10 4 Msun at 0.5 pc 17 Gualandris & MerriV 2009

18 Measurement of BH mass and R o can be improved significantly using the stellar cluster With stellar cluster alone Combined Stellar cluster and orbit of S0-2: R o errors improve by 30% The dominant source of uncertainty is now systema2c errors Do et al. in prep

19 Use proper mo2ons out to 7 pc to constrain large scale physical proper2es Do et al. in prep HST F127M, F139M, F153M image from GO PI: T. Do, GO PI: A. Ghez