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Register a new userBlack Holes, Galaxy Formation, and the M_BH-sigma Relation
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Andrew King
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Recent X-ray observations of intense high-speed outflows in quasars suggest that supercritical accretion on to the central black hole may have an important effect on a host galaxy. I revisit some ideas of Silk and Rees, and assume such flows occur in the final stages of building up the black hole mass. It is now possible to model explicitly the interaction between the outflow and the host galaxy. This is found to resemble a momentum-driven stellar wind bubble, implying a relation M_BH = (f_g kappa/2 pi G^2) sigma^4 = 1.5 10^8 sigma_200^4 Msun between black hole mass and bulge velocity dispersion (f_g = gas fraction of total matter density, kappa = electron scattering opacity), without free parameters. This is remarkably close to the observed relation in both slope and normalization. This result suggests that the central black holes in galaxies gain most of their mass in phases of super-Eddington accretion, which are presumably obscured or at high redshift. Observed super-Eddington quasars are apparently late in growing their black hole masses.
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For galaxies hosting supermassive black holes (SMBHs), it has been observed that the mass of the central black hole (M_BH) tightly correlates with the effective or central velocity dispersion (sigma) of the host galaxy. The origin of this M_BH - sigma scaling relation is assumed to lie in the merging history of the galaxies but many open questions about its origin and the behavior in different mass ranges still need to be addressed. The goal of this work is to study the black-hole scaling relations for low black-hole masses, where the regime of intermediate-mass black holes (IMBHs) in globular clusters (GCs) is entered. We collect all existing reports of dynamical black-hole measurements in globular clusters, providing black-hole masses or upper limits for 14 candidates. We plot the black-hole masses versus different cluster parameters including total mass, velocity dispersion, concentration and half-mass radius. We search for trends and test the correlations in order to quantify their significance using a set of different statistical approaches. For correlations showing a large significance we perform a linear fit, accounting for uncertainties and upper limits. We find a clear correlation between the mass of the IMBH and the velocity dispersion of the globular cluster. As expected, the total mass of the globular cluster then also correlates with the mass of the IMBH. While the slope of the M_BH - sigma correlation differs strongly from the one observed for SMBHs, the other scaling relations M_BH - M_TOT, and M_BH - L are similar to the correlations in galaxies. Significant correlations of black-hole mass with other cluster properties were not found in the present sample.
We have studied the location of narrow-line Seyfert 1 (NLS1) galaxies and broad-line Seyfert 1 (BLS1) galaxies on the M_BH - sigma relation of non-active galaxies. We find that NLS1 galaxies as a class - as well as the BLS1 galaxies of our comparison sample - do follow the M_BH-sigma relation of non-active galaxies if we use the width of the [SII]6716,6731 emission lines as surrogate for stellar velocity dispersion, sigma_*. We also find that the width of [OIII]5007 is a good surrogate for sigma_*, but only after (a) removal of asymmetric blue wings, and, more important, after (b) excluding core [OIII] lines with strong blueshifts (i.e., excluding galaxies which have their [OIII] velocity fields dominated by radial motions, presumably outflows). The same galaxies which are extreme outliers in [OIII] still follow the M_BH - sigma relation in [SII]. We confirm previous findings that NLS1 galaxies are systematically off-set from the M_BH - sigma relation if the full [OIII] profile is used to measure sigma. We systematically investigate the influence of several parameters on the NSL1 galaxies location on the M_BH - sigma plane: [OIII]_core blueshift, L/L_Edd, intensity ratio FeII/H_beta, NLR density, and absolute magnitude. Implications for NLS1 models and for their evolution along the M_BH - sigma relation are discussed.
We utilize the local velocity dispersion function (VDF) of spheroids, together with their inferred age--distributions, to predict the VDF at higher redshifts (0<z<6), under the assumption that (i) most of the stars in each nearby spheroid formed in a single episode, and (ii) the velocity dispersion sigma remained nearly constant afterward. We assume further that a supermassive black hole (BH) forms concurrently with the stars, and within ~1 Gyr of the formation of the potential well of the spheroid, and that the relation between the mass of the BH and host velocity dispersion maintains the form M_BH ~ sigma^{beta} with beta~4, but with the normalization allowed to evolve with redshift as ~(1+z)^{alpha}. We compute the BH mass function associated with the VDF at each redshift, and compare the accumulated total BH mass density with that inferred from the integrated quasar luminosity function (LF; the so--called Soltan argument). This comparison is insensitive to the assumed duty cycle or Eddington ratio of quasar activity, and we find that the match between the two BH mass densities favors a relatively mild redshift evolution, with alpha ~ 0.26, with a positive evolution as strong as alpha>1.3 excluded at the 99% confidence level. A direct match between the characteristic BH mass in the VDF--based and quasar LF--based BH mass functions also yields a mean Eddington ratio of lambda ~ 0.5-1 that is roughly constant within 0<z<3. A strong positive evolution in the M_BH-sigma relation is still allowed by the data if galaxies increase, on average, their velocity dispersions since the moment of formation, due to dissipative processes. If we assume that the mean velocity dispersion of the host galaxies evolves as sigma(z)=sigma(0)*(1+z)^{-gamma}, we find a lower limit of gamma>0.23 for alpha>1.5. abridged
Stationary solutions of 5D supergravity with U(1) isometry can be efficiently studied by dimensional reduction to three dimensions, where they reduce to solutions to a locally supersymmetric non-linear sigma model. We generalize this procedure to 5D gauged supergravity, and identify the corresponding gauging in 3D. We pay particular attention to the case where the Killing spinor is non constant along the fibration, which results, even for ungauged supergravity in 5D, in an additional gauging in 3D, without introducing any extra potential. We further study SU(2)times U(1) symmetric solutions, which correspond to geodesic motion on the sigma model (with potential in the gauged case). We identify and study the algebra of BPS constraints relevant for the Breckenridge-Myers-Peet-Vafa black hole, the Gutowski-Reall black hole and several other BPS solutions, and obtain the corresponding radial wave functions in the semi-classical approximation.
We use hydrodynamical simulations to study the color transformations induced by star formation and active galactic nuclei (AGN) during major mergers of spiral galaxies. Our modeling accounts for radiative cooling, star formation, and supernova feedback. Moreover, we include a treatment of accretion onto supermassive black holes embedded in the nuclei of the merging galaxies. We assume that a small fraction of the bolometric luminosity of an accreting black hole couples thermally to surrounding gas, providing a feedback mechanism that regulates its growth. The encounter and coalescence of the galaxies triggers nuclear gas inflow which fuels both a powerful starburst and strong black hole accretion. Comparing simulations with and without black holes, we show that AGN feedback can quench star formation and accretion on a short timescale,particularly in large galaxies where the black holes can drive powerful winds once they become sufficiently massive. The color evolution of the remnant differs markedly between mergers with and without central black holes. Without AGN, gas-rich mergers lead to ellipticals which remain blue owing to residual star formation, even after more than 7 Gyrs have elapsed. In contrast, mergers with black holes produce ellipticals that redden much faster, an effect that is more pronounced in massive remnants where a nearly complete termination of star formation occurs, allowing them to redden to u-r ~ 2.3 in less than one Gyr. AGN feedback may thus be required to explain the population of extremely red massive early type-galaxies, and it appears to be an important driver in generating the observed bimodal color distribution of galaxies in the Local Universe.
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