paper

Andromeda's Dust

arXiv:1306.2304 · doi:10.1088/0004-637X/780/2/172

Abstract

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 PAH abundance, out to R=25kpc. The global dust mass is M_d=5.4x10^7Msol, the global dust/H mass ratio is M_d/M_H=0.0081, and the global PAH abundance is <q_PAH>=0.039. The dust surface density has an inner ring at R=5.6kpc, a maximum at R=11.2kpc, and an outer ring at R=15.1kpc. The dust/gas ratio varies from M_d/M_H=0.026 at the center to ~0.0027 at R=25kpc. From the dust/gas ratio, we estimate the ISM metallicity to vary by a factor ~10, from Z/Zsol=3 at R=0 to ~0.3 at R=25kpc. The dust heating rate parameter <U> peaks at the center, with <U> approx 35, declining to <U> approx 0.25 at R=20kpc. Within the central kpc, 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 q_PAH=0.045 at R=11.2kpc. When allowance is made for the different spectrum of the bulge stars, q_PAH for the dust in the central kpc is similar to the overall value of q_PAH 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 500um emission at R=2-6kpc, suggesting that at R=2-6kpc, the dust opacity varies more steeply with frequency (with beta approx 2.3 between 200 and 600um) than in the model

Final version (corrected and revised), to appear in ApJ, 780, 172 (2014 Jan 10)

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