ANDROMEDA'S DUST

By B. Draine, G. Aniano, O. Krause, B. Groves, K. Sandstrom, R. Braun, A. Leroy, U. Klaas, H. Linz, Hans-Walter Rix and 3 more. 2013

161 citations recorded by the source corpus.

Spitzer Space Telescope and Herschel Space Observatory imaging of M31 is used, with a physical dust model, to construct maps of dust surface density, dust-to-gas ratio, starlight heating intensity, and polycyclic aromatic hydrocarbon (PAH) abundance, out to R ≈ 25 kpc. The global dust mass is Md = 5.4 × 107 M☉, the global dust/H mass ratio is Md/MH = 0.0081, and the global PAH abundance is 〈qPAH〉 = 0.039. The dust surface density has an inner ring at R = 5.6 kpc, a maximum at R = 11.2 kpc, and an outer ring at R ≈ 15.1 kpc. The dust/gas ratio varies from Md/MH ≈ 0.026 at the center to ∼0.0027 at R ≈ 25 kpc. From the dust/gas ratio, we estimate the interstellar medium metallicity to vary by a factor ∼10, from Z/Z☉ ≈ 3 at R = 0 to ∼0.3 at R = 25 kpc. The dust heating rate parameter 〈U〉 peaks at the center, with 〈U〉 ≈ 35, declining to 〈U〉 ≈ 0.25 at R = 20 kpc. Within the central kiloparsec, the starlight heating intensity inferred from the dust modeling is close to what is estimated from the stars in the bulge. The PAH abundance reaches a peak qPAH ≈ 0.045 at R ≈ 11.2 kpc. When allowance is made for the different spectrum of the bulge stars, qPAH for the dust in the central kiloparsec is similar to the overall value of qPAH in the disk. The silicate–graphite–PAH dust model used here is generally able to reproduce the observed dust spectral energy distribution across M31, but overpredicts 500 μm emission at R ≈ 2–6 kpc, suggesting that at R = 2–6 kpc, the dust opacity varies more steeply with frequency (with β ≈ 2.3 between 200 and 600 μm) than in the model.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/e01a86d613c04394dd8c2c7c5157caf25771c8b8