37,826 research outputs found
Active Galaxies and the Study of Black Hole Demographics
We discuss the critical importance of black hole mass indicators based on
scaling relations in active galaxies. We highlight outstanding uncertainties in
these methods and potential paths to substantial progress in the next decade.Comment: 4 pages, 1 figure, Invited review to appear in PAS
X-ray Properties of Intermediate-mass Black Holes in Active Galaxies. III. Spectral Energy Distribution and Possible Evidence for Intrinsically X-ray-weak AGNs
We present a systematic X-ray study, the third in a series, of 49 active
galactic nuclei with intermediate-mass black holes (IMBH; ~10^5-10^6 M_sun)
using Chandra observations. We detect 42 out of 49 targets with a 0.5-2 keV
X-ray luminosity 10^41-10^43 erg/s. We perform spectral fitting for the 10
objects with enough counts (>200), and they are all well fit by a simple
power-law model modified by Galactic absorption, with no sign of significant
intrinsic absorption. While we cannot fit the X-ray spectral slope directly for
the rest of the sample, we estimate it from the hardness ratio and find a range
of photon indices consistent with those seen in more luminous and massive
objects. The X-ray-to-optical spectral slope (alphaox) of our IMBH sample is
systematically flatter than in active galaxies with more massive black holes,
consistent with the well-known correlation between alphaox and UV luminosity.
Thanks to the wide dynamic range of our sample, we find evidence that alphaox
increases with decreasing M_BH as expected from accretion disk models, where
the UV emission systematically decreases as M_BH decreases and the disk
temperature increases. We also find a long tail toward low alphaox values.
While some of these sources may be obscured, given the high L_bol/L_Eddington
values in the sample, we argue that some may be intrinsically X-ray-weak,
perhaps owing to a rare state that radiates very little coronal emission.Comment: 13 pages (double columns), 2 tables, 9 figures, ApJ accepte
Intermediate-mass Black Holes in Galactic Nuclei
We present the first homogeneous sample of intermediate-mass black hole
candidates in active galactic nuclei. Starting with broad-line active nuclei
from the Sloan Digital Sky Survey, we use the linewidth-luminosity-mass scaling
relation to select a sample of 19 galaxies in the mass range M_BH ~ 8 x 10^4 -
10^6 solar masses. In contrast to the local active galaxy population, the host
galaxies are ~1 mag fainter than M* and thus are probably late-type systems.
The active nuclei are also faint, with M_g ~ -15 to -18 mag, while the
bolometric luminosities are close to the Eddington limit. The spectral
properties of the sample are compared to the related class of objects known as
narrow-line Seyfert 1 galaxies. We discuss the importance of our sample as
observational analogues of primordial black holes, contributors to the
integrated signal for future gravitational wave experiments, and as a valuable
tool in the calibration of the M-sigma relation.Comment: 4 pages, 4 figures. To appear in "The Interplay among Black Holes,
Stars and ISM in Galactic Nuclei," Proc. IAU 222 (Gramado, Brazil), eds Th.
Storchi Bergmann, L.C. Ho, H.R. Schmit
A Relation Between the Kauffman and the HOMFLY Polynomials for Torus Knots
Polynomial invariants corresponding to the fundamental representation of the
gauge group are computed for arbitrary torus knots in the framework of
Chern-Simons gauge theory making use of knot operators. As a result, a formula
which relates the Kauffman and the HOMFLY polynomials for torus knots is
presented.Comment: 47 pages, macropackage phyzzx.tex, minor corrections made, version to
appear in Journal of Mathematical Physic
Off-diagonal hyperfine interaction between the 6p1/2 and 6p3/2 levels in 133Cs
The off-diagonal hyperfine interaction between the 6p1/2 and 6p3/2 states in
133Cs is evaluated in third-order MBPT giving 37.3 Hz and 48.3 Hz,
respectively, for second-order energies of the 6p3/2 F=3 and F=4 levels. This
result is a factor of 10 smaller than one obtained from an uncorrelated
first-order Dirac-Hartree-Fock calculation and used in the analysis of a recent
high-precision (< 2 kHz) measurement of the 6p3/2 hyperfine structure [Gerginov
et al. Phys. Rev. Lett. 91, 72301 (2003)]. The factor of 10 difference has
negligible effect on the conclusions of the recent experiment but will become
important for experiments carried out at a precision of better than 1 kHz
"Low-state" Black Hole Accretion in Nearby Galaxies
I summarize the main observational properties of low-luminosity AGNs in
nearby galaxies to argue that they are the high-mass analogs of black hole
X-ray binaries in the "low/hard" state. The principal characteristics of
low-state AGNs can be accommodated with a scenario in which the central engine
is comprised of three components: an optically thick, geometrically accretion
disk with a truncated inner radius, a radiatively inefficient flow, and a
compact jet.Comment: 8 pages. To appear in From X-ray Binaries to Quasars: Black Hole
Accretion on All Mass Scales, ed. T. J. Maccarone, R. P. Fender, and L. C. Ho
(Dordrecht: Kluwer
Physical Properties of the Narrow-Line Region of Low-Mass Active Galaxies
We present spectroscopic observations of 27 active galactic nuclei (AGN) with
some of the lowest black hole (BH) masses known. We use the high spectral
resolution and small aperture of our Keck data, taken with the Echellette
Spectrograph and Imager, to isolate the narrow-line regions (NLRs) of these
low-mass BHs. We investigate their emission-line properties and compare them
with those of AGN with higher-mass black holes. While we are unable to
determine absolute metallicities, some of our objects plausibly represent
examples of the low-metallicity AGN described by Groves et al. (2006), based on
their [N II]/H_alpha ratios and their consistency with the Kewley & Ellison
(2008) mass-metallicity relation. We find tentative evidence for steeper far-UV
spectral slopes in lower-mass systems. Overall, NLR emission lines in these
low-mass AGN exhibit trends similar to those seen in AGN with higher-mass BHs,
such as increasing blueshifts and broadening with increasing ionization
potential. Additionally, we see evidence of an intermediate line region whose
intensity correlates with L/L_Edd, as seen in higher-mass AGN. We highlight the
interesting trend that, at least in these low-mass AGN, the [O III] equivalent
width (EW) is highest in symmetric NLR lines with no blue wing. This trend of
increasing [O III] EW with line symmetry could be explained by a high covering
factor of lower ionization gas in the NLR. In general, low-mass AGN preserve
many well-known trends in the structure of the NLR, while exhibiting steeper
ionizing continuum slopes and somewhat lower gas-phase metallicities.Comment: 46 pages, 14 figures, 7 table
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