THE 15-20 {mu}m EMISSION IN THE REFLECTION NEBULA NGC 2023

Journal Article · Thu Mar 01 04:00:00 EST 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/747/1/44· OSTI ID:22016319

Peeters, Els ^[1]; Allamandola, Louis J ^[2]

---

1. Department of Physics and Astronomy, University of Western Ontario, London, ON N6A 3K7 (Canada)
2. NASA-Ames Research Center, Space Science Division, Mail Stop 245-6, Moffett Field, CA 94035 (United States)

We present 15-20 {mu}m spectral maps toward the reflection nebula NGC 2023 obtained with the Infrared Spectrograph in short-wavelength, high-resolution mode on board the Spitzer Space Telescope. These spectra reveal emission from polycyclic aromatic hydrocarbons (PAHs), C{sub 60}, and H{sub 2} superposed on a dust continuum. These emission components exhibit distinct spatial distributions: with increasing distance from the illuminating star, we observe the PAH emission followed by the dust continuum emission and the H{sub 2} emission. The C{sub 60} emission is located closest to the illuminating star in the south, while in the north it seems to be associated with the H/H{sub 2} transition. Emission from PAHs and PAH-related species produces features at 15.8, 16.4, 17.4, and 17.8 {mu}m and the 15-18 {mu}m plateau. These different PAH features show distinct spatial distributions. The 15.8 {mu}m band and 15-18 {mu}m plateau correlate with the 11.2 {mu}m PAH band and with each other, and are attributed to large, neutral PAHs. Conversely, the 16.4 {mu}m feature correlates with the 12.7 {mu}m PAH band, suggesting that both arise from species that are favored by the same conditions that favor PAH cations. The PAH contribution to the 17.4 {mu}m band is displaced toward the illuminating star with respect to the 11.2 and 12.7 {mu}m emission and is assigned to doubly ionized PAHs and/or a subset of cationic PAHs. The spatial distribution of the 17.8 {mu}m band suggests that it arises from both neutral and cationic PAHs. In contrast to their intensities, the profiles of the PAH bands and the 15-18 {mu}m plateau do not vary spatially. Consequently, we conclude that the carrier of the 15-18 {mu}m plateau is distinct from that of the PAH bands.

• OSTI ID: 22016319
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 747; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ASTROPHYSICS
CATIONS
EMISSION
FULLERENES
HYDROGEN
NEBULAE
POLYCYCLIC AROMATIC HYDROCARBONS
SPATIAL DISTRIBUTION
STARS
TELESCOPES