A resolved analysis of cold dust and gas in the nearby edge-on spiral NGC 891
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abstract
We investigate the connection between dust and gas in the nearby edge-on
spiral galaxy NGC 891. High resolution Herschel PACS and SPIRE 70, 100, 160,
250, 350, and 500 $\mu$m images are combined with JCMT SCUBA 850 $\mu$m
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$\times$10$^{7}$ M$_{\odot}$ and an average temperature of 23$\pm$2 K. We
also fit the 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 $\mu$m emission. The derived dust temperature,
which ranges from approximately 17 to 24 K, is found to correlate with the 24
$\mu$m emission. Allowing the dust emissivity index to vary, we find an average
value of $\beta$ = 1.9$\pm$0.3. We confirm an inverse relation between the dust
emissivity spectral index and dust temperature, but do not observe any
variation of this relationship with vertical height from the mid-plane of the
disk. A comparison of the dust properties with the gaseous components of the
ISM reveals strong spatial correlations between the surface mass densities of
dust and the molecular hydrogen and total gas surface densities. Observed
asymmetries in the dust temperature, and the H$_{2}$-to-dust and total
gas-to-dust ratios 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 an enhancement in the star formation rate in the
NE side of the disk.
