146 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
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
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
The ultraviolet flare at the center of the elliptical galaxy NGC 4278
A large fraction of otherwise normal galaxies shows a weak nuclear activity.
One of the signatures of the low-luminosity active galactic nuclei (LLAGNs) is
the ultraviolet variability which was serendipitously discovered in the center
of some low-ionization nuclear emission-line region (LINER) galaxies. There is
a pressing need to acquire better statistics about UV flaring and variability
in galaxy nuclei, both in terms of the number and monitoring of targets. The
Science Data Archive of the Hubble Space Telescope was queried to find all the
elliptical galaxies with UV images obtained in different epochs with the Wide
Field Planetary Camera 2 (WFPC2) and possibly with nuclear spectra obtained
with the Space Telescope Imaging Spectrograph (STIS) in the region of the
Halpha emission line. These data were found only for the elliptical radiogalaxy
NGC 4278. The UV flux of the nuclear source of NGC 4278 was measured by means
of aperture photometry on the WFPC2/F218W images obtained between June 1994 and
January 1995. The mass of the central supermassive black hole (SBH) was
estimated by measuring the broad components of the emission lines observed in
the STIS/G750M spectrum and assuming that the gas is uniformly distributed in a
sphere. The nucleus of NGC 4278 hosts a barely resolved but strongly variable
UV source. Its UV luminosity increased by a factor of 1.6 in a period of 6
months. The amplitude and scale time of the UV flare in NGC 4278 are remarkably
similar to those of the brightest UV nuclear transients which were earlier
found in other LLAGNs. The mass of the SBH was found to be in the range between
7x10^7 and 2x10^9 M_sun. This is in agreement with previous findings based on
different assumptions about the gas distribution and with the predictions based
on the galaxy velocity dispersion.Comment: 5 pages,3 figures, accepted for publication on A&
The KMOS^3D Survey: design, first results, and the evolution of galaxy kinematics from 0.7<z<2.7
We present the KMOS^3D survey, a new integral field survey of over 600
galaxies at 0.7<z<2.7 using KMOS at the Very Large Telescope (VLT). The KMOS^3D
survey utilizes synergies with multi-wavelength ground and space-based surveys
to trace the evolution of spatially-resolved kinematics and star formation from
a homogeneous sample over 5 Gyrs of cosmic history. Targets, drawn from a
mass-selected parent sample from the 3D-HST survey, cover the star
formation-stellar mass () and rest-frame planes uniformly. We
describe the selection of targets, the observations, and the data reduction. In
the first year of data we detect Halpha emission in 191
Msun galaxies at z=0.7-1.1 and z=1.9-2.7. In
the current sample 83% of the resolved galaxies are rotation-dominated,
determined from a continuous velocity gradient and , implying
that the star-forming 'main sequence' (MS) is primarily composed of rotating
galaxies at both redshift regimes. When considering additional stricter
criteria, the Halpha kinematic maps indicate at least ~70% of the resolved
galaxies are disk-like systems. Our high-quality KMOS data confirm the elevated
velocity dispersions reported in previous IFS studies at z>0.7. For
rotation-dominated disks, the average intrinsic velocity dispersion decreases
by a factor of two from 50 km/s at z~2.3 to 25 km/s at z~0.9 while the
rotational velocities at the two redshifts are comparable. Combined with
existing results spanning z~0-3, disk velocity dispersions follow an
approximate (1+z) evolution that is consistent with the dependence of velocity
dispersion on gas fractions predicted by marginally-stable disk theory.Comment: 20 pages, 11 figures, 1 Appendix; Accepted to ApJ November 2
Further evidence for large central mass-to-light ratios in early-type galaxies: the case of ellipticals and lenticulars in the Abell~262 cluster
We present radially resolved spectroscopy of 8 early-type galaxies in
Abell~262, measuring rotation, velocity dispersion, and
coefficients along three axes, and line-strength index profiles of Mg, Fe and
H. Ionized-gas velocity and velocity dispersion is included for 6
galaxies. We derive dynamical mass-to-light ratios and dark matter densities
from orbit-based dynamical models, complemented by the galaxies' ages,
metallicities, and -elements abundances. Four galaxies have significant
dark matter with halos about 10 times denser than in spirals of the same
stellar mass. Using dark matter densities and cosmological simulations,
assembly redshifts \zdm\approx 1-3, which we found earlier for Coma. The
dynamical mass following the light is larger than expected for a Kroupa stellar
IMF, especially in galaxies with high velocity dispersion \sigeff inside the
effective radius \reff. This could indicate a `massive' IMF in massive
galaxies. Alternatively, some dark matter in massive galaxies could follow the
light closely. Combining with our comparison sample of Coma early-types, we now
have 5 of 24 galaxies where (1) mass follows light to 1-3\,\reff, (2) the
dynamical mass-to-light ratio {of all the mass that follows the light is large
( in the Kron-Cousins band), (3) the dark matter fraction is
negligible to 1-3\,\reff. Unless the IMF in these galaxies is particularly
`massive' and somehow coupled to the dark matter content, there seems a
significant degeneracy between luminous and dark matter in some early-type
galaxies. The role of violent relaxation is briefly discussed.Comment: 62 pages, 13 figures, 8 tables, accepted for publication in A
On the Correlations between Galaxy Properties and Supermassive Black Hole Mass
We use a large sample of upper limits and accurate estimates of supermassive
black holes masses coupled with libraries of host galaxy velocity dispersions,
rotational velocities and photometric parameters extracted from Sloan Digital
Sky Survey i-band images to establish correlations between the SMBH and host
galaxy parameters. We test whether the mass of the black hole, MBH, is
fundamentally driven by either local or global galaxy properties. We explore
correlations between MBH and stellar velocity dispersion sigma, bulge
luminosity, bulge mass Sersic index, bulge mean effective surface brightness,
luminosity of the galaxy, galaxy stellar mass, maximum circular velocity Vc,
galaxy dynamical and effective masses. We verify the tightness of the MBH-sigma
relation and find that correlations with other galaxy parameters do not yield
tighter trends. We do not find differences in the MBH-sigma relation of barred
and unbarred galaxies. The MBH-sigma relation of pseudo-bulges is also coarser
and has a different slope than that involving classical bulges. The MBH-bulge
mass is not as tight as the MBH-sigma relation, despite the bulge mass proving
to be a better proxy of MBH than bulge luminosity. We find a rather poor
correlation between MBH and Sersic index suggesting that MBH is not related to
the bulge light concentration. The correlations between MBH and galaxy
luminosity or mass are not a marked improvement over the MBH sigma relation. If
Vc is a proxy for the dark matter halo mass, the large scatter of the MBH-Vc
relation then suggests that MBH is more coupled to the baryonic rather than the
dark matter. We have tested the need for a third parameter in the MBH scaling
relations, through various linear correlations with bulge and galaxy
parameters, only to confirm that the fundamental plane of the SMBH is mainly
driven by sigma, with a small tilt due to the effective radius. (Abridged)Comment: 32 pages, 18 figures, 6 tables, accepted for publication in MNRA
Spectroscopic evidence of distinct stellar populations in the counter-rotating stellar disks of NGC 3593 and NGC 4550
We present the results of integral-field spectroscopic observations of the
two disk galaxies NGC 3593 and NGC 4550 obtained with VIMOS/VLT. Both galaxies
are known to host 2 counter-rotating stellar disks, with the ionized gas
co-rotating with one of them. We measured in each galaxy the ionized gas
kinematics and metallicity, and the surface brightness, kinematics, mass
surface density, and the stellar populations of the 2 stellar components to
constrain the formation scenario of these peculiar galaxies. We applied a novel
spectroscopic decomposition technique to both galaxies, to separate the
relative contribution of the 2 counter-rotating stellar and one ionized-gas
components to the observed spectrum. We measured the kinematics and the line
strengths of the Lick indices of the 2 counter-rotating stellar components. We
modeled the data of each stellar component with single stellar population
models that account for the alpha/Fe overabundance. In both galaxies we
successfully separated the main from the secondary stellar component that is
less massive and rotates in the same direction of the ionized-gas component.
The 2 stellar components have exponential surface-brightness profiles. In both
galaxies, the two counter-rotating stellar components have different stellar
populations: the secondary stellar disk is younger, more metal poor, and more
alpha-enhanced than the main galaxy stellar disk. Our findings rule out an
internal origin of the secondary stellar component and favor a scenario where
it formed from gas accreted on retrograde orbits from the environment fueling
an in situ outside-in rapid star formation. The event occurred ~ 2 Gyr ago in
NGC 3593, and ~ 7 Gyr ago in NGC 4550. The binary galaxy merger scenario cannot
be ruled out, and a larger sample is required to statistically determine which
is the most efficient mechanism to build counter-rotating stellar disks
(abridged).Comment: 13 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
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