1,435 research outputs found
A Correlation between Galaxy Light Concentration and Supermassive Black Hole Mass
We present evidence for a strong correlation between the concentration of
bulges and the mass of their central supermassive black hole (M_bh) -- more
concentrated bulges have more massive black holes. Using C_{r_e}(1/3) from
Trujillo, Graham & Caon (2001b) as a measure of bulge concentration, we find
that log (M_bh/M_sun) = 6.81(+/-0.95)C_{r_e}(1/3) + 5.03(+/-0.41). This
correlation is shown to be marginally stronger (Spearman's r_s=0.91) than the
relationship between the logarithm of the stellar velocity dispersion and log
M_bh (Spearman's r_s=0.86), and has comparable, or less, scatter (0.31 dex in
log M_bh), which decreases to 0.19 dex when we use only those galaxies whose
supermassive black hole's radius of influence is resolved and remove one well
understood outlying data point).Comment: 7 pages, 1 table, 2 figures. ApJ Letters, accepte
On the shape of the light profiles of early-type galaxies
We have obtained the best fit to the light profiles of a luminosity limited
sample of elliptical and S0 galaxies with a power law \rn, letting the exponent
remain free rather than keeping it fixed at as in the well known \GV
formula. The introduction of a free parameter in the fitting formula (ranging
from for kpc to for kpc) is justified by
the existence of a good correlation between and the global galaxian
parameters, such as total luminosity and scale-radius. This result seems to be
in line with the segregation of properties between the `ordinary' and `bright'
families of early-type galaxies, and has consequence for the claimed
independence of the shape of galaxy profiles with respect to the Fundamental
Plane parameters.Comment: 10 pages, postscript file including figures, PADOVA (archived file
truncated during email transfer
Galaxy Light Concentration. I. Index stability and the connection with galaxy structure, dynamics, and supermassive black holes
We explore the stability of different galaxy light concentration indices as a
function of the outermost observed galaxy radius. With a series of analytical
light-profile models, we show mathematically how varying the radial extent to
which one measures a galaxy's light can strongly affect the derived galaxy
concentration. The "mean concentration index", often used for parameterizing
high-redshift galaxies, is shown to be horribly unstable, even when modeling
one-component systems such as elliptical, dwarf elliptical and pure exponential
disk galaxies. The C_31 concentration index performs considerably better but is
also heavily dependent on the radial extent, and hence exposure depth, of any
given galaxy. We show that the recently defined central concentration index is
remarkably stable against changes to the outer radius, providing a meaningful
and reliable estimate of galaxy concentration. The index n from the r^(1/n)
models is shown to be monotonically related with the central concentration of
light, giving the index n a second and perhaps more tangible meaning. With a
sample of elliptical and dwarf elliptical galaxies, we present correlations
between the central light concentration and the global parameters: luminosity
(Pearson's r = -0.82), effective radius (r = 0.67), central surface brightness
(r = -0.88), and velocity dispersion (r = 0.80). The more massive elliptical
galaxies are shown to be more centrally concentrated. We speculate that the
physical mechanism behind the recently observed correlation between the central
velocity dispersion (mass) of a galaxy and the mass of its central supermassive
black hole may be connected with the central galaxy concentration. That is, we
hypothesize that it may not simply be the amount of mass in a galaxy but rather
how that mass is distributed that controls the mass of the central black hole.Comment: (aastex, 18 pages including 13 figures
On the estimation of galaxy structural parameters: the Sersic Model
This paper addresses some questions which have arisen from the use of the
S\'ersic r^{1/n} law in modelling the luminosity profiles of early type
galaxies. The first issue deals with the trend between the half-light radius
and the structural parameter n. We show that the correlation between these two
parameters is not only real, but is a natural consequence from the previous
relations found to exist between the model-independent parameters: total
luminosity, effective radius and effective surface brightness. We also define a
new galaxy concentration index which is largely independent of the image
exposure depth, and monotonically related with n. The second question concerns
the curious coincidence between the form of the Fundamental Plane and the
coupling between _e and r_e when modelling a light profile. We explain,
through a mathematical analysis of the S\'ersic law, why the quantity
r_e_e^{0.7} appears almost constant for an individual galaxy, regardless of
the value of n (over a large range) adopted in the fit to the light profile.
Consequently, Fundamental Planes of the form r_e_e^{0.7} propto sigma_0^x
(for any x, and where sigma_0 is the central galaxy velocity dispersion) are
insensitive to galaxy structure. Finally, we address the problematic issue of
the use of model-dependent galaxy light profile parameters versus
model-independent quantities for the half-light radii, mean surface brightness
and total galaxy magnitude. The former implicitly assume that the light profile
model can be extrapolated to infinity, while the latter quantities, in general,
are derived from a signal-to-noise truncated profile. We quantify
(mathematically) how these parameters change as one reduces the outer radius of
an r^{1/n} profile, and reveal how these can vary substantially when n>4.Comment: 10 pages, 10 figures, accepted for publication in MNRA
Context-aware gestural interaction in the smart environments of the ubiquitous computing era
A thesis submitted to the University of Bedfordshire in partial fulfilment of the requirements for the degree of Doctor of PhilosophyTechnology is becoming pervasive and the current interfaces are not adequate for the interaction with the smart environments of the ubiquitous computing era. Recently, researchers have started to address this issue introducing the concept of natural user interface, which is mainly based on gestural interactions. Many issues are still open in this emerging domain and, in particular, there is a lack of common guidelines for coherent implementation of gestural interfaces.
This research investigates gestural interactions between humans and smart environments. It proposes a novel framework for the high-level organization of the context information. The framework is conceived to provide the support for a novel approach using functional gestures to reduce the gesture ambiguity and the number of gestures in taxonomies and improve the usability.
In order to validate this framework, a proof-of-concept has been developed. A prototype has been developed by implementing a novel method for the view-invariant recognition of deictic and dynamic gestures. Tests have been conducted to assess the gesture recognition accuracy and the usability of the interfaces developed following the proposed framework. The results show that the method provides optimal gesture recognition from very different view-points whilst the usability tests have yielded high scores.
Further investigation on the context information has been performed tackling the problem of user status. It is intended as human activity and a technique based on an innovative application of electromyography is proposed. The tests show that the proposed technique has achieved good activity recognition accuracy.
The context is treated also as system status. In ubiquitous computing, the system can adopt different paradigms: wearable, environmental and pervasive. A novel paradigm, called synergistic paradigm, is presented combining the advantages of the wearable and environmental paradigms. Moreover, it augments the interaction possibilities of the user and ensures better gesture recognition accuracy than with the other paradigms
The Tilt of the Fundamental Plane: Three-quarters Structural Nonhomology, One-quarter Stellar Population
The variation of the mass-to-light ratios M/L of early type galaxies as
function of their luminosities L is investigated. It is shown that the tilt
beta=0.27 (in the B--band) of the fundamental plane relation M/L ~ L^{beta} can
be understood as a combination of two effects: about one-quarter (i.e. dbeta
=0.07) is a result of systematic variations of the stellar population
properties with increasing luminosity. The remaining three-quarters (i.e. dbeta
=0.2) can be completely attributed to nonhomology effects that lead to a
systematic change of the surface brightness profiles with increasing
luminosity. Consequently, the observed tilt in the K-band (beta=0.17) where
stellar population effects are negligible, is explained by nonhomology effects
alone. After correcting for nonhomology, the mean value of the mass-to-light
ratio of elliptical galaxies (M/L_B) is 7.1+-2.8 (1 sigma scatter).Comment: 8 pages, 3 figures, ApJL, 600, 39, minor changes made to match the
published versio
Color psychology and its application to advertising
openAn analysis of the link between color and consumer's buying impulses. Starting from an explanation of the general principles of color perception to an overview of how color psychology is applied in modern advertising today.An analysis of the link between color and consumer's buying impulses. Starting from an explanation of the general principles of color perception to an overview of how color psychology is applied in modern advertising today
Analytical Galaxy Profiles for Photometric and Lensing Analysis
This article introduces a family of analytical functions of the form x^{\nu}
K_{\nu}(x), where K_{\nu} is the incomplete Bessel function of the third kind.
This family of functions can describe the density profile, projected and
integrated light profiles and the gravitational potentials of galaxies. For the
proper choice of parameters, these functions accurately approximate Sersic
functions over a range of indices and are good fits to galaxy light profiles.
With an additional parameter corresponding to a galaxy core radius, these
functions can fit galaxy like M87 over a factor of 100,000 in radius. Unlike
Sersic profiles, these functions have simple analytical 2-dimensional and
3-dimensional Fourier transforms, so they are easily convolved with spatially
varying point spread function and are well suited for photometric and lensing
analysis. We use these functions to estimate the effects of seeing on lensing
measurements and show that high S/N measurements, even when the PSF is larger
than the galaxy effective radius, should be able to recover accurate estimates
of lensing distortions by weighting light in the outer isophotes that are less
effected by seeing
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