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Title: Three-integral multi-component dynamical models and simulations of the nuclear star cluster in NGC 4244
Authors: F. De Lorenzi (1), M. Hartmann (2), V. P. Debattista (3,4), A. C. Seth (5), O. Gerhard (6) ((1) Zuercher Hochschule fuer Angewandte Wissenschaften, Switzerland, (2) Astronomisches Rechen-Institut, Zentrum fuer Astronomie der Universitaet Heidelberg, Germany, (3) Jeremiah Horrocks Institute, University of Central Lancashire, Preston, UK, (4) Visiting Lecturer, Department of Physics, University of Malta, (5) University of Utah, Salt Lake City, UT USA, (6) Max-Planck-Institut fuer Ex. Physik, Garching, Germany)

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 solar masses 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 solar masses 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.

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Title: Herschel/SPIRE Observations of the Dusty Disk of NGC 4244
Authors: B.W. Holwerda (ESA), S. Bianchi (INAF), T. Böker (ESA), D. Radburn-Smith (University of Washington), R. S. de Jong (AIP), M. Baes (University of Gent), P.C. van der Kruit (Kapteyn Institute), M.Xilouris (Athens Observatory), K.D. Gordon (STSCI), J.J. Dalcanton (University of Washington)

We present Herschel/SPIRE images at 250, 350, and 500 µm of NGC 4244, a typical low-mass, disk-only and edge-on spiral galaxy. The dust disk is clumpy and shows signs of truncation at the break radius of the stellar disk. This disk coincides with the densest part of the Hi disk. We compare the Spectral Energy Distribution, including the new SPIRE fluxes, to 3D radiative transfer models; a smooth model disk and a clumpy model with embedded heating. Each model requires a very high value for the dust scale-length (h(dust) = 2 - 5 h(stars)), higher dust masses than previous models of NGC 4244 (Md = 0.47 - 1.39 x 10e7 solar masses) and a face-on optical depth of {\tau}(V) = 0.4 - 1.12, in agreement with previous disk opacity studies. The vertical scales of stars and dust are similar. The clumpy model much better mimics the general morphology in the submm images and the general SED. The inferred gas-to-dust mass ratio is compatible with those of similar low-mass disks. The relatively large radial scale-length of the dust disk points to radial mixing of the dusty ISM within the stellar disk. The large vertical dust scale and the clumpy dust distribution of our SED model are both consistent with a scenario in which the vertical structure of the ISM is dictated by the balance of turbulence and self-gravity.

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A Rotating Compact Nuclear Stellar Cluster in NGC 4244
Based on laser guide star adaptive optics (LGS-AO) -fed integral field spectroscopy with the Near-Infrared Spectrograph (NIFS) at Gemini North, Anil C. Seth of the Harvard-Smithsonian Centre for Astrophysics and his collaborators demonstrate that the massive nuclear stellar cluster at the core of the spiral galaxy NGC 4244 is strongly rotating.
Most late-type spiral galaxies and early-type galaxies have prominent nuclear star clusters (NSCs), i.e. a significant conglomerate of stars about the same size (~ 5 parsecs) as normal globular clusters. Furthermore, the masses of NSCs are coupled to the mass of their host galaxy, following the similar mass vs. velocity dispersion relation known for massive black holes. This suggests that the formation of NSCs and black holes are linked to the formation of their host galaxy. However, unlike that of black holes, the assembly history of NSCs can be inferred from studies of their kinematics and stellar content.

fig1.jpg

SDSS g-r-i band image of the late-type spiral NGC 4244 seen edge-on. The NSC is visible as a small, almost point-like, white spot at the center.

NGC 4244 is beautiful edge-on galaxy located at 4.3 Megaparcecs (14 million light-years away). It harbours a tiny but impressive NSC that shows a clearly flattened shape in HST optical imaging  and the reconstructed K-band NIFS image.

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