A resolved analysis of cold dust and gas in the nearby edge-on spiral NGC 891
Résumé
We investigate the connection between dust and gas in the nearby edge-on spiral galaxy
NGC 891, a target of the Very Nearby Galaxies Survey. High resolution Herschel
PACS and SPIRE 70, 100, 160, 250, 350, and 500 μm images are combined with
JCMT SCUBA 850 μm observations to trace the
far-infrared/submillimetre spectral energy distribution (SED). Maps of the Hi 21
cm line and CO(J = 3−2) emission trace the atomic and molecular hydrogen gas, respectively.
We fit one-component modified blackbody models to the integrated SED, finding a global
dust mass of (8.5 ± 2.0)
× 107M⊙ and an
average temperature of 23 ± 2
K, consistent with results from previous far-infrared experiments. We also fit
one-component modified blackbody models to pixel-by-pixel SEDs to produce maps of the dust
mass and temperature. The dust mass distribution correlates with the total stellar
population as traced by the 3.6 μm emission. The derived dust temperature, which
ranges from approximately 17 to 24 K, is found to correlate with the 24 μm emission. Allowing the
dust emissivity index to vary, we find an average value of β = 1.9 ± 0.3. We confirm
an inverse relation between the dust emissivity spectral index and dust temperature, but
do not observe any variation of this relationship with vertical height from the mid-plane
of the disc. A comparison of the dust properties with the gaseous components of the ISM
reveals strong spatial correlations between the surface mass densities of dust
(Σdust) and the
molecular hydrogen (ΣH2) and total gas surface densities
(Σgas). These
observations reveal the presence of regions of dense, cold dust that are coincident with
peaks in the gas distribution and are associated with a molecular ring. Furthermore, the
observed asymmetries in the dust temperature, the H2-to-dust ratio and the total
gas-to-dust ratio hint that an enhancement in the star formation rate may be the result of
larger quantities of molecular gas available to fuel star formation in the NE compared to
the SW. Whilst the asymmetry likely arises from dust obscuration due to the geometry of
the line-of-sight projection of the spiral arms, we cannot exclude that there is also an
enhancement in the star formation rate in the NE part of the disc.
Origine : Publication financée par une institution
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