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Register a new userLimits on the Mass of the Central Black Hole in 16 Nearby Bulges
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We report upper limits on the masses of black holes that can be present in the centers of 16 nearby galaxy bulges. These limits for our statistically complete sample were derived from the modeling of the central emission-line widths ([N II] or [S II]), observed over a 0.25 X 0.2 (R < 9 pc) aperture. The experiment has a mean detection sensitivity of 3.9 X 10^6 solar masses. For three sample members with direct determinations of black hole masses our upper limits agree within the uncertainties, while in general our upper limits are found to be close to the masses measured in other bulges with global properties similar to ours. Remarkably, our limits lie quite closely to the recently derived relation between black hole mass and stellar velocity dispersion. These results support a picture wherein the black hole mass and overall galaxy structure are closely linked, as galaxies with exceptionally high black hole masses at a given velocity dispersion apparently are rare.
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[abridged] Theoretical investigations have suggested the presence of Intermediate Mass Black Holes (IMBHs, with masses in the 100-10000 Msun range) in the cores of some Globular Clusters (GCs). In this paper we present the first application of a new technique to determine the presence or absence of a central IMBH in globular clusters that have reached energy equipartition via two-body relaxation. The method is based on the measurement of the radial profile for the average mass of stars in the system, using the fact that a quenching of mass segregation is expected when an IMBH is present. Here we measure the radial profile of mass segregation using main-sequence stars for the globular cluster NGC 2298 from resolved source photometry based on HST-ACS data. The observations are compared to expectations from direct N-body simulations of the dynamics of star clusters with and without an IMBH. The mass segregation profile for NGC 2298 is quantitatively matched to that inferred from simulations without a central massive object over all the radial range probed by the observations, that is from the center to about two half-mass radii. Profiles from simulations containing an IMBH more massive than ~ 300-500 Msun (depending on the assumed total mass of NGC 2298) are instead inconsistent with the data at about 3 sigma confidence, irrespective of the IMF and binary fraction chosen for these runs. While providing a null result in the quest of detecting a central black hole in globular clusters, the data-model comparison carried out here demonstrates the feasibility of the method which can also be applied to other globular clusters with resolved photometry in their cores.
The mass estimator used to calculate black hole (BH) masses in broad-line active galactic nuclei (AGNs) relies on a virial coefficient (the $f$ factor) that is determined by comparing reverberation-mapped (RM) AGNs with measured bulge stellar velocity dispersions against the $M_{rm BH}-sigma_*$ relation of inactive galaxies. It has recently been recognized that only classical bulges and ellipticals obey a tight $M_{rm BH}-sigma_*$ relation; pseudobulges have a different zero point and much larger scatter. Motivated by these developments, we reevaluate the $f$ factor for RM AGNs with available $sigma_*$ measurements, updated H$beta$ RM lags, and new bulge classifications based on detailed decomposition of high-resolution ground-based and space-based images. Separate calibrations are provided for the two bulge types, whose virial coefficients differ by a factor of $sim 2$: $f=6.3pm1.5$ for classical bulges and ellipticals and $f = 3.2pm0.7$ for pseudobulges. The structure and kinematics of the broad-line region, at least as crudely encoded in the $f$ factor, seems to related to the large-scale properties or formation history of the bulge. Lastly, we investigate the bulge stellar masses of the RM AGNs, show evidence for recent star formation in the AGN hosts that correlates with Eddington ratio, and discuss the potential utility of the $M_{rm BH}-M_{rm bulge}$ relation as a more promising alternative to the conventionally used $M_{rm BH}-sigma_*$ relation for future refinement of the virial mass estimator for AGNs.
We investigate a mechanism for a super-massive black hole at the center of a galaxy to wander in the nucleus region. A situation is supposed in which the central black hole tends to move by the gravitational attractions from the nearby molecular clouds in a nuclear bulge but is braked via the dynamical frictions by the ambient stars there. We estimate the approximate kinetic energy of the black hole in an equilibrium between the energy gain rate through the gravitational attractions and the energy loss rate through the dynamical frictions, in a nuclear bulge composed of a nuclear stellar disk and a nuclear stellar cluster as observed from our Galaxy. The wandering distance of the black hole in the gravitational potential of the nuclear bulge is evaluated to get as large as several 10 pc, when the black hole mass is relatively small. The distance, however, shrinks as the black hole mass increases and the equilibrium solution between the energy gain and loss disappears when the black hole mass exceeds an upper limit. As a result, we can expect the following scenario for the evolution of the black hole mass: When the black hole mass is smaller than the upper limit, mass accretion of the interstellar matter in the circum-nuclear region, causing the AGN activities, makes the black hole mass larger. However, when the mass gets to the upper limit, the black hole loses the balancing force against the dynamical friction and starts spiraling downward to the gravity center. From simple parameter scaling, the upper mass limit of the black hole is found to be proportional to the bulge mass and this could explain the observed correlation of the black hole mass with the bulge mass.
Improved analysis of ultraviolet and optical monitoring data on the Seyfert 1 galaxy NGC 3783 provides evidence for the existence of a supermassive, (8.7+/-1.1)x10^6 M_sun, black hole in this galaxy. By using recalibrated spectra from the International Ultraviolet Explorer satellite and ground-based optical data, as well as refined techniques of reverberation mapping analysis, we have reduced the statistical uncertainties in the response of the emission lines to variations in the ionizing continuum. The different time lags in the emission line responses indicate a stratification in the ionization structure of the broad-line region and are consistent with the virial relationship suggested by the analysis of similar active galaxies.
In order to improve the reverberation-mapping based estimate of the mass of the central supermassive black hole in the Seyfert 1 galaxy NGC 4151, we have reanalyzed archival ultraviolet monitoring spectra from two campaigns undertaken with the International Ultraviolet Explorer. We measure emission-line time delays for four lines, C IV 1549, He II 1640, C III] 1909, and Mg II 2798, from both campaigns. We combine these measurements with the dispersion of the variable part of each respective emission line to obtain the mass of the central object. Despite the problematic nature of some of the data, we are able to measure a mass of 41.1 (+/- 7.3) million solar masses, although this, like all reverberation-based masses, is probably systematically uncertain by a factor of 3-4.
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