SPIRE spectroscopy of the prototypical Orion Bar photodissociation region

Habart, E.; Dartois, E.; Abergel, A.; Baluteau, J.-P.; Naylor, D.; Polehampton, E.; Joblin, C.; Ade, P.; Anderson, L. D.; André, P.; Arab, H.; Bernard, J.-P.; Blagrave, K.; Bontemps, S.; Boulanger, F.; Cohen, M.; Compiegne, M.; Cox, P.; Davis, G.; Emery, R.; Fulton, T.; Gry, C.; Huang, M.; Jones, S. C.; Kirk, J.; Lagache, G.; Lim, T.; Madden, S.; Makiwa, G.; Martin, P.; Miville-Deschênes, M.-A.; Molinari, S.; Moseley, H.; Motte, F.; Okumura, K.; Pinheiro Gonçalves, D.; Rodon, J.; Russeil, D.; Saraceno, P.; Sidher, S.; Spencer, L.; Swinyard, B.; Ward-Thompson, D.; White, G. J. and Zavagno, A. (2010). SPIRE spectroscopy of the prototypical Orion Bar photodissociation region. Astronomy & Astrophysics, 518, article no. L116.

DOI: https://doi.org/10.1051/0004-6361/201014654

Abstract

Aims. We present observations of the Orion Bar photodissociation region (PDR) obtained with the SPIRE instrument on-board Herschel.

Methods. We obtained SPIRE Fourier-transform spectrometer (FTS) sparse sampled maps of the Orion bar.

Results. The FTS wavelength coverage and sensitivity allow us to detect a wealth of rotational lines of CO (and its isotopologues), fine structure lines of C and N⁺, and emission lines from radicals and molecules such as CH⁺, CH, H₂O or H₂S. For species detected from the ground, our estimates of the column densities agree with previously published values. The comparison between ¹²CO and ¹³CO maps shows particularly the effects of optical depth and excitation in the molecular cloud. The distribution of the ¹²CO and ¹³CO lines with upper energy levels indicates the presence of warm (~100 - 150 K) CO. This warm CO component is a significant fraction of the total molecular gas, confirming previous ground based studies.

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