Friday, May 24, 2013

1305.5265 (Jonathan S. Brown et al.)

On the Offset of Barred Galaxies From the Black Hole M_BH-sigma Relationship    [PDF]

Jonathan S. Brown, Monica Valluri, Juntai Shen, Victor P. Debattista
We use collisionless N-body simulations to determine how the growth of a supermassive black hole (SMBH) influences the nuclear kinematics in both barred and unbarred galaxies. In the presence of a bar, the increase in the velocity dispersion sigma (within the effective radius) due to the growth of an SMBH is on average <= 10%, whereas the increase is only ~4% in an unbarred galaxy. In a barred galaxy, the increase results from a combination of three separate factors (a) orientation and inclination effects; (b) angular momentum transport by the bar that results in an increase in the central mass density; (c) an increase in the vertical and radial velocity anisotropy of stars in the vicinity of the SMBH. In contrast the growth of the SMBH in an unbarred galaxy causes the velocity distribution in the inner part of the nucleus to become less radially anisotropic. We argue that using an axisymmetric stellar dynamical modeling code to measure SMBH masses in barred galaxies could result in a slight overestimate of the derived M_BH. We conclude that the growth of a black hole in the presence of a bar could result in an offset in sigma, perhaps partially accounting for the claimed offset of barred galaxies and pseudo-bulges from the M_BH-sigma relation for unbarred galaxies. If the black hole grows significantly in a pre-existing barred galaxy, the resultant secular evolution would alter both the mass and velocity dispersion of the host bulge.
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