A resolved analysis of cold dust and gas in the nearby edge-on spiral NGC 891
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.