22 research outputs found
Molecular gas in the centre of nearby galaxies from VLT/SINFONI integral field spectroscopy - II. Kinematics(star)
We present an analysis of the H2 emission-line gas kinematics in the inner âČ4âarcsec radius of six nearby spiral galaxies, based on adaptive optics-assisted integral-field observations obtained in the K band with SINFONI/VLT. Four of the six galaxies in our sample display ordered H2 velocity fields, consistent with gas moving in the plane of the galaxy and rotating in the same direction as the stars. However, the gas kinematics is typically far from simple circular motion. We can classify the observed velocity fields into four different types of flows, ordered by increasing complexity: (1) circular motion in a disc (NGC 3351); (2) oval motion in the galaxy plane (NGC 3627 and NGC 4536); (3) streaming motion superimposed on circular rotation (NGC 4501); and (4) disordered streaming motions (NGC 4569 and NGC 4579). The H2 velocity dispersion in the galaxies is usually higher than 50âkmâsâ1 in the inner 1â2âarcsec radii. The four galaxies with ordered kinematics have v/Ï < 1 at radii less than 40â80âpc. The radius at which v/Ï = 1 is independent of the type of nuclear activity. While the low values of v/Ï could be taken as an indication of a thick disc in the innermost regions of the galaxies, other lines of evidence (e.g. H2 morphologies and velocity fields) argue for a thin disc interpretation in the case of NGC 3351 and NGC 4536. We discuss the implications of the high values of velocity dispersion for the dynamics of the gaseous disc and suggest caution when interpreting the velocity dispersion of ionized and warm tracers as being entirely dynamical. Understanding the nature and role of the velocity dispersion in the gas dynamics, together with the full 2D information of the gas, is essential for obtaining accurate black hole masses from gas kinematics
Three-integral multi-component dynamical models and simulations of the nuclear star cluster in NGC 4244
Adaptive optics observations of the flattened nuclear star cluster in the
nearby edge-on spiral galaxy NGC 4244 using the Gemini Near-Infrared Integral
Field Spectrograph (NIFS) have revealed clear rotation. Using these kinematics
plus 2MASS photometry we construct a series of axisymmetric two-component
particle dynamical models with our improved version of NMAGIC, a flexible
Chi^2-made-to-measure code. The models consist of a nuclear cluster disc
embedded within a spheroidal particle population. We find a mass for the
nuclear star cluster of M=1.6^+0.5_-0.2 x 10^7 M_sun within ~42.4 pc (2"). We
also explore the presence of an intermediate mass black hole and show that
models with a black hole as massive as M_bh = 5.0 x 10^5 M_sun are consistent
with the available data. Regardless of whether a black hole is present or not,
the nuclear cluster is vertically anisotropic (beta_z < 0), as was found with
earlier two-integral models. We then use the models as initial conditions for
N-body simulations. These simulations show that the nuclear star cluster is
stable against non-axisymmetric perturbations. We also explore the effect of
the nuclear cluster accreting star clusters at various inclinations. Accretion
of a star cluster with mass 13% that of the nuclear cluster is already enough
to destroy the vertical anisotropy, regardless of orbital inclination.Comment: Replaced with the version accepted for publication in MNRAS. 13
pages, 10 figures, 3 table
An expanded M_bh-sigma diagram, and a new calibration of active galactic nuclei masses
[Abridged] We present an updated and improved M_bh-sigma diagram containing
64 galaxies for which M_bh measurements (not just upper limits) are available.
Due to new and increased black hole masses at the high-mass end, and a better
representation of barred galaxies at the low-mass end, the "classical" (all
morphological type) M_bh-sigma relation for predicting black hole masses is
log(M_bh/M_Sun) = (5.13+/-0.34)log[sigma/200] + (8.13+/-0.05), with an rms
scatter of 0.43 dex. Modifying the regression analysis to correct for a
hitherto over-looked sample bias in which black holes with masses <10^6 M_Sun
are not (yet) detectable, the relation steepens further to give log(M_bh/M_Sun)
= (5.95+/-0.44)log[sigma/200] + (8.15+/-0.06). We have also updated the
"barless" and "elliptical-only" M_bh-sigma relations introduced by Graham and
Hu in 2008 due to the offset nature of barred/disc galaxies. These relations
have a total scatter as low as 0.34 dex and currently define the upper envelope
of points in the M_bh-sigma diagram. These relations also have a slope
consistent with the value 5, in agreement with the prediction by Silk & Rees
based on feedback from massive black holes in bulges built by
monolithic-collapse.
Using updated virial products and velocity dispersions from 28 active
galactic nuclei, we determine that the optimal scaling factor f - which brings
their virial products in line with the 64 directly measured black hole masses -
is 2.8^{+0.7}_{-0.5}. This is roughly half the value reported by Onken et al.
and Woo et al., and consequently halves the mass estimates of most
high-redshift quasars. We have explored the results after separating the
samples into barred and non-barred galaxies, and we have also developed a
preliminary corrective term to the velocity dispersion based on bar dynamics.Comment: 17 pages. MNRAS, in pres
Beitrïżœge zur Benennung, Bewertung und Verbreitung der Farn- und Blïżœtenpflanzen Deutschlands. III
Beitrïżœge zur Benennung, Bewertung und Verbreitung der Farn- und Blïżœtenpflanzen Deutschlands
Beitrïżœge zur Benennung, Bewertung und Verbreitung der Farn- und Blïżœtenpflanzen Deutschlands. II
The imprint of massive black hole mergers on the correlation between nuclear star clusters and their host galaxies
A literature compilation of nuclear star cluster (NSC) masses is used to study the correlation between global and NSC properties. A comparison of observational data to the predictions of semi-analytical galaxy formation models places constraints on the co-evolution of NSCs, massive black holes (MBHs), and host galaxies. Both data and theoretical predictions show an increased scatter in the NSC scaling correlations at high galaxy masses, and we show that this is due to the progressively more efficient ejection of stars from NSCs caused by MBH binaries in more massive stellar spheroids. Our results provide a natural explanation of why in nucleated galaxies hosting an MBH, the ratio (M-NSC + M-MBH) M-bulge (with M-bulge as the host spheroid's mass) shows significantly less scatter than M-NSC/M-bulge, and suggest that the formation of MBHs and NSCs are not mutually exclusive, as is also supported by observations of co-existing systems. Both MBHs and NSCs represent generic products of galaxy formation, with NSCs being destroyed or modified by the merger evolution of their companion MBHs
The HST/ACS Coma Cluster Survey â X. Nuclear star clusters in low-mass early-type galaxies: scaling relations
We present scaling relations between structural properties of nuclear star clusters and their host galaxies for a sample of early-type dwarf galaxies observed as part of the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) Coma Cluster Survey. We have analysed the light profiles of 200 early-type dwarf galaxies in the magnitude range 16.0 < mF814W < 22.6 mag, corresponding to â19.0 < MF814W < â12.4 mag. Nuclear star clusters are detected in 80 perâcent of the galaxies, thus doubling the sample of HST-observed early-type dwarf galaxies with nuclear star clusters. We confirm that the nuclear star cluster detection fraction decreases strongly towards faint magnitudes. The luminosities of nuclear star clusters do not scale linearly with host galaxy luminosity. A linear fit yields LnucâŒL0.57±0.05galLnucâŒLgal0.57±0.05. The nuclear star clusterâhost galaxy luminosity scaling relation for low-mass early-type dwarf galaxies is consistent with formation by globular cluster (GC) accretion. We find that at similar luminosities, galaxies with higher SĂ©rsic indices have slightly more luminous nuclear star clusters. Rounder galaxies have on average more luminous clusters. Some of the nuclear star clusters are resolved, despite the distance of Coma. We argue that the relation between nuclear star cluster mass and size is consistent with both formation by GC accretion and in situ formation. Our data are consistent with GC inspiralling being the dominant mechanism at low masses, although the observed trend with SĂ©rsic index suggests that in situ star formation is an important second-order effect