221 research outputs found
Upper limits on the mass of supermassive black holes from HST/STIS archival data
The growth of supermassive black holes (SBHs) appears to be closely linked
with the formation of spheroids. There is a pressing need to acquire better
statistics on SBH masses, since the existing samples are preferentially
weighted toward early-type galaxies with very massive SBHs. With this
motivation we started a project aimed at measuring upper limits on the mass of
the SBHs in the center of all the nearby galaxies (D<100 Mpc) for which
STIS/G750M spectra are available in the HST archive. These upper limits will be
derived by modeling the central emission-line widths observed in the Halpha
region over an aperture of ~0.1''. Here we present our results for a subsample
of 20 S0-Sb galaxies within 20 Mpc.Comment: 2 pages, 1 figure. To appear in the proceedings of "Black Holes: from
Stars to Galaxies", IAU Symp. No. 238, V. Karas & G. Matt (eds.), Cambridge
University Pres
The SINFONI Black Hole Survey: The Black Hole Fundamental Plane revisited and the paths of (co-) evolution of supermassive black holes and bulges
We investigate the correlations between the black hole mass , the
velocity dispersion , the bulge mass , the bulge average
spherical density and its spherical half mass radius ,
constructing a database of 97 galaxies (31 core ellipticals, 17 power-law
ellipticals, 30 classical bulges, 19 pseudo bulges) by joining 72 galaxies from
the literature to 25 galaxies observed during our recent SINFONI black hole
survey. For the first time we discuss the full error covariance matrix. We
analyse the well known and relations and
establish the existence of statistically significant correlations between
and and anti-correlations between and . We
establish five significant bivariate correlations (,
, , ,
) that predict of 77 core and power-law ellipticals
and classical bulges with measured and intrinsic scatter as small as dex and dex respectively, or 0.26 dex when the subsample
of 45 galaxies defined by Kormendy and Ho (2013) is considered. In contrast,
pseudo bulges have systematically lower , but approach the predictions
of all the above relations at spherical densities or scale lengths kpc. These findings fit in a
scenario of co-evolution of BH and classical-bulge masses, where core
ellipticals are the product of dry mergers of power-law bulges and power-law Es
and bulges the result of (early) gas-rich mergers and of disk galaxies. In
contrast, the (secular) growth of BHs is decoupled from the growth of their
pseudo bulge hosts, except when (gas) densities are high enough to trigger the
feedback mechanism responsible for the existence of the correlations between
and galaxy structural parameters.Comment: Accepted for publication in ApJ, proofs correcte
The M-Sigma Relation Derived from Sphere of Influence Arguments
The observed relation between supermassive black hole (SMBH) mass (M) and
bulge stellar velocity dispersion (Sigma) is described by log(M) = alpha +
beta*log(Sigma/200 km/s). As this relation has important implications for
models of galaxy and SMBH formation and evolution, there continues to be great
interest in adding to the M catalog. The "sphere of influence" (r) argument
uses spatial resolution to exclude some M estimates and pre-select additional
galaxies for further SMBH studies. This Letter quantifies the effects of
applying the r argument to a population of galaxies and SMBHs that do not
follow the M-Sigma relation. All galaxies with known values of Sigma, closer
than 100 Mpc, are given a random M and selected when r is spatially resolved.
These random SMBHs produce an M-Sigma relation of alpha=8.3, beta=4.0,
consistent with observed values. Consequently, future proposed M estimates
should not be justified solely on the basis of resolving r. This Letter shows
the observed M-Sigma relation may simply be a result of available spatial
resolution. However, it also implies the observed M-Sigma relation defines an
upper limit. This potentially provides valuable new insight into the processes
of galaxy and SMBH formation and evolution.Comment: ApJ Letters, accepte
Numerical study of turbulent flow in eccentric annular pipe
An eccentric annular duct is a prototype element in many applications, for example
in close-packed tubular heat exchangers and coolant channels of nuclear reactors.
From a fundamental viewpoint, turbulent flow in eccentric annular ducts is an ideal
model for investigating inhomogeneous turbulence. It is also a convenient model to
study the laminar and turbulent interface and may serve as a test case for turbulence
modelling of flows with partly turbulent regimes. Based on the approach of direct
numerical simulation, numerical investigations of turbulent flow in eccentric annular
pipes are carried out in this thesis.
We first investigated the case of fully turbulent flow. A detailed statistical analysis
of turbulent flow and heat transfer was performed. Simulation results, such
as friction factors, mean velocity profiles and the secondary-motion pattern, are in
overall qualitative and quantitative agreement with the existing experimental data.
The components of the Reynolds stress tensor, temperature-velocity correlations
and some others were obtained for the first time for such kind of a flow.
The study of the partly turbulent flow case was then carried out. Three approaches
for detecting interfaces between laminar and turbulent regimes in partly
turbulent flow in rotating eccentric pipes were compared and discussed. Positions of
laminar-turbulent and turbulent-laminar interfaces obtained from profiles of perturbation
enstrophy are the same as those obtained from production terms of enstrophy.
Using patterns of streaks defined by wall shear stresses to determine the locations
of interfaces showed similar results.
The growth rate of a small disturbance in partly turbulent flow case was also
analyzed. Small perturbations were introduced into the initial flow field in two different ways. Both cases show that the global growth rate of the small disturbance
normalized by the global viscous time scale is constant. This constant value is in
a good agreement with that obtained in channel flows and tube flows. A new
approach was proposed to distinguish the interface between laminar and turbulent
flow by introducing the global and local disturbance growth rate
Populating the galaxy velocity dispersion - supermassive black hole mass diagram: A catalogue of (M_bh, sigma) values
An updated catalogue of 76 galaxies with direct supermassive black hole mass
measurements (M_bh) plus, when available, their host bulge's central velocity
dispersion (sigma_0) is provided. Fifty of these mass measurements are
considered reliable, while the others remain somewhat uncertain at this time.
An additional eight stellar systems, including one stellar cluster and three
globular clusters, are listed as hosting potential intermediate mass black
holes < 10^6 M_solar.
With this larger data set, the demographics within the M_bh-sigma_0 diagram
are briefly explored. Many barred galaxies are shown to be offset from the
M_bh-sigma_0 relation defined by the non-barred galaxies, in the sense that
their velocity dispersions are too high. Furthermore, including 88 AGN with
black hole mass estimates from reverberation mapping studies, we speculate that
barred AGN may follow this same general trend. We also show that some AGN with
sigma_0 < 100 km/s tend to reside up to 0.6 dex above the "barless"
M_bh-sigma_0 relation. Finally, it is shown that ``core galaxies'' appear not
to define an additional subdivision of the M_bh-sigma_0 diagram, although
improved methods for measuring sigma_0-values will be valuable.Comment: To appear in PASA, accepted on the 4th of July, 200
First results from the VIRIAL survey: the stellar content of -selected quiescent galaxies at from KMOS
We investigate the stellar populations of 25 massive, galaxies
() at using data obtained with
the K-band Multi-Object Spectrograph (KMOS) on the ESO VLT. Targets were
selected to be quiescent based on their broadband colors and redshifts using
data from the 3D-HST grism survey. The mean redshift of our sample is , where KMOS YJ-band data probe age- and metallicity-sensitive
absorption features in the rest-frame optical, including the band, Fe I,
and high-order Balmer lines. Fitting simple stellar population models to a
stack of our KMOS spectra, we derive a mean age of Gyr.
We confirm previous results suggesting a correlation between color and age for
quiescent galaxies, finding mean ages of Gyr and
Gyr for the reddest and bluest galaxies in our sample.
Combining our KMOS measurements with those obtained from previous studies at
we find evidence for a Gyr spread in the formation epoch of
massive galaxies. At the measured stellar ages are consistent with
passive evolution, while at they appear to saturate at
1 Gyr, which likely reflects changing demographics of the (mean)
progenitor population. By comparing to star-formation histories inferred for
"normal" star-forming galaxies, we show that the timescales required to form
massive galaxies at are consistent with the enhanced
-element abundances found in massive local early-type galaxies.Comment: 6 pages, 5 figures, accepted for publication in ApJ
The definition of environment and its relation to the quenching of galaxies at z=1-2 in a hierarchical Universe
A well calibrated method to describe the environment of galaxies at all
redshifts is essential for the study of structure formation. Such a calibration
should include well understood correlations with halo mass, and the possibility
to identify galaxies which dominate their potential well (centrals), and their
satellites. Focusing on z = 1 and 2 we propose a method of environmental
calibration which can be applied to the next generation of low to medium
resolution spectroscopic surveys. Using an up-to-date semi-analytic model of
galaxy formation, we measure the local density of galaxies in fixed apertures
on different scales. There is a clear correlation of density with halo mass for
satellite galaxies, while a significant population of low mass centrals is
found at high densities in the neighbourhood of massive haloes. In this case
the density simply traces the mass of the most massive halo within the
aperture. To identify central and satellite galaxies, we apply an
observationally motivated stellar mass rank method which is both highly pure
and complete, especially in the more massive haloes where such a division is
most meaningful. Finally we examine a test case for the recovery of
environmental trends: the passive fraction of galaxies and its dependence on
stellar and halo mass for centrals and satellites. With careful calibration,
observationally defined quantities do a good job of recovering known trends in
the model. This result stands even with reduced redshift accuracy, provided the
sample is deep enough to preserve a wide dynamic range of density.Comment: 19 pages, 12 figures, accepted for publication in MNRA
Fast and slow rotators in the densest environments: a FLAMES/GIRAFFE IFS study of galaxies in Abell 1689 at z=0.183
We present FLAMES/GIRAFFE integral field spectroscopy of 30 galaxies in the
massive cluster Abell 1689 at z = 0.183. Conducting an analysis similar to that
of ATLAS3D, we extend the baseline of the kinematic morphology-density relation
by an order of magnitude in projected density and show that it is possible to
use existing instruments to identify slow and fast rotators beyond the local
Universe. We find 4.5 +- 1.0 slow rotators with a distribution in magnitude
similar to those in the Virgo cluster. The overall slow rotator fraction of our
Abell 1689 sample is 0.15 +- 0.03, the same as in Virgo using our selection
criteria. This suggests that the fraction of slow rotators in a cluster is not
strongly dependent on its density. However, within Abell 1689, we find that the
fraction of slow rotators increases towards the centre, as was also found in
the Virgo cluster.Comment: Accepted by MNRA
Polar bulges and polar nuclear discs: the case of NGC 4698
The early-type spiral NGC 4698 is known to host a nuclear disc of gas and
stars which is rotating perpendicularly with respect to the galaxy main disc.
In addition, the bulge and main disc are characterised by a remarkable
geometrical decoupling. Indeed they appear elongated orthogonally to each
other. In this work the complex structure of the galaxy is investigated by a
detailed photometric decomposition of optical and near-infrared images. The
intrinsic shape of the bulge was constrained from its apparent ellipticity, its
twist angle with respect to the major axis of the main disc, and the
inclination of the main disc. The bulge is actually elongated perpendicular to
the main disc and it is equally likely to be triaxial or axisymmetric. The
central surface brightness, scalelength, inclination, and position angle of the
nuclear disc were derived by assuming it is infinitesimally thin and
exponential. Its size, orientation, and location do not depend on the observed
passband. These findings support a scenario in which the nuclear disc is the
end result of the acquisition of external gas by the pre-existing triaxial
bulge on the principal plane perpendicular to its shortest axis and
perpendicular to the galaxy main disc. The subsequent star formation either
occurred homogeneously all over the extension of the nuclear disc or through an
inside-out process that ended more than 5 Gyr ago.Comment: 6 pages, 3 figures. Accepted for publication in MNRAS Letter
SN Ia host galaxy properties from Sloan Digital Sky Survey-II spectroscopy
We study the stellar populations of Type Ia supernova (SN Ia) host galaxies using Sloan
Digital Sky Survey (SDSS)-II spectroscopy. The main focus is on the relationships of SN Ia
properties with stellar velocity dispersion and the stellar population parameters age, metallicity
and element abundance ratios. We concentrate on a sub-sample of 84 SNe Ia from the
SDSS-II Supernova Survey and find that SALT2 stretch factor values show the strongest dependence
on stellar population age. Hence, more luminous SNe Ia appear in younger stellar
progenitor systems. No statistically significant trends in the Hubble residual with any of the
stellar population parameters studied are found. Moreover, the method of photometric stellar
mass derivation affects the Hubble residualâmass relationship. For an extended sample (247
objects), including SNe Ia with SDSS host galaxy photometry only, the Hubble residualâmass
relationship behaves as a sloped step function. In the high-mass regime, probed by our host
spectroscopy sample, this relationship is flat. Below a stellar mass of âŒ2 Ă 1010M , i.e. close
to the evolutionary transition mass of low-redshift galaxies, the trend changes dramatically
such that lower mass galaxies possess lower luminosity SNe Ia after light-curve corrections.
The sloped step function of the Hubble residualâmass relationship should be accounted for
when using stellar mass as a further parameter for minimizing the Hubble residuals.Department of HE and Training approved lis
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