arXiv subjects
Publications and source records attributed to D. Richstone.
This White Paper to the National Academy of Sciences Astro2010 Decadal Review Committee outlines some of the outstanding questions regarding the assembly history of Massive Black Holes in the nuclei of galaxies and the revolutionary contributions anticipated in this field from low-frequency gravitational wave astronomy.
This is the first of a series of papers dedicated to unveil the mass composition and dynamical structure of a sample of flattened early type galaxies in the Coma cluster. We describe our modifications to the Schwarzschild code of Richstone et al. (in preparation). Applying a Voronoi tessellation in the surface of section we are able to assign accurate phase-space volumes to individual orbits and to reconstruct the full three-integral phase-space distribution function (DF) of any axisymmetric orbit library. Two types of tests have been performed to check the accuracy with which DFs can be represented by appropriate orbit libraries. First, by mapping DFs of spherical gamma-models and flattened Plummer models on to the library we show that the resulting line-of-sight velocity distributions and internal velocity moments of the library match those directly derived from the DF to a precision better than that of present day observational errors. Second, by fitting libraries to the projected kinematics of the same DFs we show that the distribution function reconstructed from the fitted library matches the input DF to a rms of about 15 per cent over a region in phase-space covering 90 per cent of the mass of the library. The achieved accuracy allows us to implement effective entropy-based regularisation to fit real, noisy and spatially incomplete data.
Black holes, an extreme consequence of the mathematics of General Relativity, have long been suspected of being the prime movers of quasars, which emit more energy than any other objects in the Universe. Recent evidence indicates that supermassive black holes, which are probably quasar remnants, reside at the centers of most galaxies. As our knowledge of the demographics of these relics of a violent earlier Universe improve, we see tantalizing clues that they participated intimately in the formation of galaxies and have strongly influenced their present-day structure.
Recent surveys suggest that most or all normal galaxies host a massive black hole with 1/100 to 1/1000 of the visible mass of the spheroid of the galaxy. Various lines of argument suggest that these galaxies have merged at least once in our past lightcone, and that the black holes have also merged. This leads to a merger rate of massive black holes of about 1/\yrs.
We analyze the galaxy population and dynamics of the galaxy cluster Abell 576 using 281 redshifts (230 new), R band CCD galaxy photometry over a 2h^{-1} Mpc by 2h^{-1} Mpc region centered on the cluster, an Einstein IPC image, and an Einstein MPC spectrum. The cluster galaxies with emission lines in their spectra have a larger velocity dispersion and are significantly less clustered on this 2h^{-1} Mpc scale than galaxies without emission lines. We show that excluding the emission line galaxies decreases the velocity dispersion by 18% and the virial mass estimate by a factor of two. The central cluster region contains a non--emission galaxy population and an intracluster medium which are significantly cooler (sigma_{core}=387^{+250}_{-105}~km/s and T_X=1.6^{+0.4}_{-0.3}~keV at 90\% confidence) than the global populations (sigma=977^{+124}_{-96}~km/s for the non--emission population and T_X>4~keV at 90% confidence). Because (1) the low dispersion population is no more luminous than the global population and (2) the evidence for a cooling flow is weak, we suggest that the cluster core may contain the remnants of a lower mass subcluster. We examine the cluster mass, baryon fraction and luminosity function. The cluster virial mass varies significantly depending on the galaxy sample used. Consistency between the hydrostatic and virial estimators can be achieved if (1) the gas temperature at r\sim1h^{-1}~Mpc is T_X\sim8keV (the best fit value) and (2) several velocity outliers are excluded from the virial calculation. Although the best fit Schechter function parameters and the ratio of galaxy to gas mass are typical of other clusters, the baryon fraction is relatively low. Using a lower limit to the binding mass, we show that the gas mass fraction is \le3h^{-3/2}% and the baryon fraction is \le6%.
We present a set of structural parameters for the central parts of 57 early-type galaxies observed with the Planetary Camera of the Hubble Space Telescope. These parameters are based on a new empirical law that successfully characterizes the centers of early type galaxies. This empirical law assumes that the surface brightness profile is a combination of two power laws with different slopes gamma and beta for the inner and outer regions. Conventional structural parameters such as core radius and central surface brightness are replaced by break radius r_b, where the transition between power-law slopes takes place, and surface brightness mu_b at that radius. An additional parameter alpha describes the sharpness of the break. The structural parameters are derived using a chi-squared minimization process applied to the mean surface brightness profiles. The resulting model profiles generally give very good agreement to the observed profiles out to the radius of 10 arcseconds imaged by the Planetary Camera. Exceptions include galaxies which depart from pure power-laws at large radius, those with strong nuclear components, and galaxies partly obscured by dust. The uncertainties in the derived parameters are estimated using Monte-Carlo simulations which test the stability of solutions in the face of photon noise and the effects of the deconvolution process. The covariance of the structural parameters is examined by computing contours of constant chi squared in multi-dimensional parameter space.