1,384 research outputs found
Large scale kinematics and dynamical modelling of the Milky Way nuclear star cluster
Within the central 10pc of our Galaxy lies a dense nuclear star cluster
(NSC), and similar NSCs are found in most nearby galaxies. Studying the
structure and kinematics of NSCs reveals the history of mass accretion of
galaxy nuclei. Because the Milky Way (MW) NSC is at a distance of only 8kpc, we
can spatially resolve the MWNSC on sub-pc scales. This makes the MWNSC a
reference object for understanding the formation of all NSCs. We have used the
NIR long-slit spectrograph ISAAC (VLT) in a drift-scan to construct an
integral-field spectroscopic map of the central 9.5 x 8pc of our Galaxy. We use
this data set to extract stellar kinematics both of individual stars and from
the unresolved integrated light spectrum. We present a velocity and dispersion
map from the integrated light and model these kinematics using kinemetry and
axisymmetric Jeans models. We also measure CO bandhead strengths of 1,375
spectra from individual stars. We find kinematic complexity in the NSCs radial
velocity map including a misalignment of the kinematic position angle by 9
degree counterclockwise relative to the Galactic plane, and indications for a
rotating substructure perpendicular to the Galactic plane at a radius of 20" or
0.8pc. We determine the mass of the NSC within r = 4.2pc to 1.4 x 10^7 Msun. We
also show that our kinematic data results in a significant underestimation of
the supermassive black hole (SMBH) mass. The kinematic substructure and
position angle misalignment may hint at distinct accretion events. This
indicates that the MWNSC grew at least partly by the mergers of massive star
clusters. Compared to other NSCs, the MWNSC is on the compact side of the r_eff
- M_NSC relation. The underestimation of the SMBH mass might be caused by the
kinematic misalignment and a stellar population gradient. But it is also
possible that there is a bias in SMBH mass measurements obtained with
integrated light.Comment: 20 pages, 19 Figures, Accepted for publication in A&
Disentangling the Circumnuclear Environs of Centaurus A: III. An Inner Molecular Ring, Nuclear Shocks and the CO to warm H2 interface
We present the distribution and kinematics of the molecular gas in the
circumnuclear disk (CND, 400 pc x 200 pc) of Centaurus A with resolutions of ~5
pc (0.3 arcsec) and shed light onto the mechanism feeding the Active Galactic
Nucleus (AGN) using CO(3-2), HCO+(4-3), HCN(4-3), and CO(6-5) observations
obtained with ALMA. Multiple filaments or streamers of tens to a hundred parsec
scale exist within the CND, which form a ring-like structure with an
unprojected diameter of 9 x 6 arcsec (162pc x 108pc) and a position angle PA =
155deg. Inside the nuclear ring, there are two leading and straight filamentary
structures with lengths of about 30-60pc at PA = 120deg on opposite sides of
the AGN, with a rotational symmetry of 180deg and steeper position-velocity
diagrams, which are interpreted as nuclear shocks due to non-circular motions.
Along the filaments, and unlike other nearby AGNs, several dense molecular
clumps present low HCN/HCO+(4-3) ratios (~0.5). The filaments abruptly end in
the probed transitions at r = 20pc from the AGN, but previous near-IR H2
(J=1-0) S(1) maps show that they continue in an even ~1000 K), winding up in
the form of nuclear spirals, and forming an inner ring structure with another
set of symmetric filaments along the N-S direction and within r = 10pc. The
molecular gas is governed primarily by non-circular motions, being the
successive shock fronts at different scales where loss of angular momentum
occurs, a mechanism which may feed efficiently powerful radio galaxies down to
parsec scales.Comment: 46 pages. Accepted for publication in Ap
Donor characteristics and the allocation of aid to climate mitigation finance
We make use of a panel dataset of 22 donor countries from 1998 to 2009 to examine the links between donor characteristics and the share of overseas development assistance allocated to climate mitigation finance. We find that donors with a larger green domestic budget tend to allocate a smaller portion of overseas aid to mitigation finance (possibly as a result of a competing interest between spending on domestic environmental projects and international climate projects). The opposite holds for donor countries with better institutions (governance) that have ratified the Kyoto Protocol. We also find important discrepancies when comparing the effects of donor characteristics on committed versus disbursed mitigation finance (as a share of aid). For the latter, only commitment to the Kyoto Protocol appears to be of high statistical significance
Temperature dependence of viscosity, relaxation times (T1, T2) and simulated contrast for potential perfusates in post-mortem MR angiography (PMMRA).
Developments in post-mortem imaging increasingly focus on addressing recognised diagnostic weaknesses, especially with regard to suspected natural deaths. Post-mortem MR angiography (PMMRA) may offer additional diagnostic information to help address such weaknesses, specifically in the context of sudden cardiac death. Complete filling of the coronary arteries and acceptable contrast with surrounding tissue are essential for a successful approach to PMMRA. In this work, the suitability of different liquids for inclusion in a targeted PMMRA protocol was evaluated. Factors influencing cooling of paraffinum liquidum + Angiofil® (6 %) in cadavers during routine multiphase post-mortem CT angiography were investigated. The temperature dependence of dynamic viscosity (8-20 °C), longitudinal (T1) and transverse (T2) relaxation (1-23 °C) of the proposed liquids was quadratically modelled. The relaxation behaviour of these liquids and MR scan parameters were further investigated by simulation of a radiofrequency (RF)-spoiled gradient echo (GRE) sequence to estimate potentially achievable contrast between liquids and post-mortem tissue at different temperatures across a forensically relevant temperature range. Analysis of the established models and simulations indicated that based on dynamic viscosity (27-33 mPa · s), short T1 relaxation times (155-207 ms) and a minimal temperature dependence over the investigated range of these parameters, paraffin oil and a solution of paraffin oil + Angiofil® (6 %) would be most suitable for post-mortem reperfusion and examination in MRI
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