Astronomy and Astrophysics – Astronomy
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007apj...660..346p&link_type=abstract
The Astrophysical Journal, Volume 660, Issue 1, pp. 346-362.
Astronomy and Astrophysics
Astronomy
63
Ism: Dust, Extinction, Ism: H Ii Regions, Infrared: Ism, Radio Continuum: Ism, Stars: Formation, X-Rays: Ism
Scientific paper
We combine diffuse emission photometry from GLIMPSE and several other Galactic plane surveys covering near-IR through radio wavelengths to synthesize a global spectral energy distribution (SED) for the M17 complex. By balancing the integrated flux in the SED with the total bolometric luminosity of all known O and early B stars in the ionizing cluster, we estimate a distance to M17 of 1.6+0.3-0.1 kpc. At this distance, the observed total flux in the SED corresponds to a luminosity of 2.4+/-0.3×106 Lsolar. We find that the SED from the H II region peaks at shorter wavelengths and has a qualitatively different shape than the SED from the photodissociation region (PDR). We find that polycyclic aromatic hydrocarbons (PAHs) are destroyed over a short distance or edge at the boundary of the H II region. We demonstrate that this PAH destruction edge can be located easily using GLIMPSE band-ratio images and confirm this using Spitzer IRS spectra. We investigate the relative roles of extreme ultraviolet (EUV) and X-ray photons in the destruction of PAHs, concluding that X-rays are not an important PAH destruction mechanism in M17 or, by extension, in any other Galactic H II region. Our results support the hypothesis that PAHs are destroyed by EUV photons within H II regions. PAHs dominate the mid-IR emission in the neutral PDR beyond the ionized gas.
Babler Brian L.
Churchwell Edward
Indebetouw Remy
Meade Marilyn R.
Povich Matthew S.
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