* Astronomy

Blobrana · L

RE: NGC 4244

Blobrana · L

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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Blobrana · L

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.

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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