AN IN-DEPTH VIEW OF THE MID-INFRARED PROPERTIES OF POINT SOURCES AND THE DIFFUSE ISM IN THE SMC GIANT H II REGION, N66
- Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904 (United States)
- Laboratoire AIM, CEA, Universite Paris Diderot, IRFU/Service d'Astrophysique, Bat. 709, F-91191 Gif-sur-Yvette (France)
- Service d'Astrophysique-Laboratoire AIM, CEA/Saclay, L'Orme des Merisiers, F-91191 Gif-sur-Yvette (France)
- Department of Physics and Astronomy, University of Western Ontario, 1151 Richmond Street, London, ON N6A 3K7 (Canada)
- IAS, Universite Paris-Sud 11, Bat. 121, F-91405 Orsay (France)
The focus of this work is to study mid-infrared point sources and the diffuse interstellar medium (ISM) in the low-metallicity ({approx}0.2 Z{sub Sun }) giant H II region N66 in order to determine properties that may shed light on star formation in these conditions. Using the Spitzer Space Telescope's Infrared Spectrograph, we study polycyclic aromatic hydrocarbon (PAH), dust continuum, silicate, and ionic line emission from 14 targeted infrared point sources as well as spectra of the diffuse ISM that is representative of both the photodissociation regions (PDRs) and the H II regions. Among the point source spectra, we spectroscopically confirm that the brightest mid-infrared point source is a massive embedded young stellar object, we detect silicates in emission associated with two young stellar clusters, and we see spectral features of a known B[e] star that are commonly associated with Herbig Be stars. In the diffuse ISM, we provide additional evidence that the very small grain population is being photodestroyed in the hard radiation field. The 11.3 {mu}m PAH complex emission exhibits an unexplained centroid shift in both the point source and ISM spectra that should be investigated at higher signal-to-noise and resolution. Unlike studies of other regions, the 6.2 {mu}m and 7.7 {mu}m band fluxes are decoupled; the data points cover a large range of I{sub 7.7}/I{sub 11.3} PAH ratio values within a narrow band of I{sub 6.2}/I{sub 11.3} ratio values. Furthermore, there is a spread in PAH ionization, being more neutral in the dense PDR where the radiation field is relatively soft, but ionized in the diffuse ISM/PDR. By contrast, the PAH size distribution appears to be independent of local ionization state. Important to unresolved studies of extragalactic low-metallicity star-forming regions, we find that emission from the infrared-bright point sources accounts for only 20%-35% of the PAH emission from the entire region. These results make a comparative data set to other star-forming regions with similarly hard and strong radiation fields.
- OSTI ID:
- 22140230
- Journal Information:
- Astrophysical Journal, Vol. 771, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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