The Phases of the Interstellar Medium in the Milky Way

A short overview

Project A4 studies the properties of star forming clouds in the Milky Way. These studies of the local ISM enable the detailed investigation of the clouds physics and chemistry, as they allow to resolve individual source components with their specific properties and environmental factors. Large mapping allows to study the cloud properties over any spatial scales. These local studies are essential in order to fully understand the physical processes and to calibrate the modeling tools without averaging over different source components with a large range of properties. They form the basis for using the observed source averaged line intensity ratios and line/continuum ratios in nearby and far-out galaxies, averaged over whole star formation complexes in nearby galaxies and over whole galactic disks at large distances, as an astrophysical tools.

We focus on exploiting the unique possibilities that upGREAT/4GREAT offer on-board SOFIA. This includes large scale mapping of [CII] in different sources, but in particular mapping of [OI] in both the 63 μm and 145 μm transition. Both the [CII] 158 μm and [OI] 63 μm lines are the strongest cooling lines of the star forming ISM. The previous results have shown, that the velocity resolved line profiles show many unexpected features which imply, that the standard models and simple scenarios used to derive ISM properties from their integrated line intensities and intensity ratios are not applicable. The broader coverage of sources with different properties and morphology will be necessary to disentangle the various ISM components along the line of sight, to better understand the nature of the foreground gas affecting the emission, and to follow the variation of the line emission along the different evolutionary stages of the sources. The FIR-SOFIA data will be complemented by ground-based observations in the mm-wave (low-J) and submm-wave (mid-J) CO lines tracing the cloud cores and PDR surfaces, and in particular the [CI] fine structure lines. For the second half of the coming funding period onward, the new CCAT-prime telescope with the CHAI receiver will significantly improve the submm-mapping, in particular in the [CI] fine structure lines due to the excellent atmospheric conditions at CCAT-prime’s high site. The 28 μm extension of 4GREAT will, for the first time, allow fully velocity-resolved observations in the ground-state line of the most abundant molecular in space, H2, namely the J = 2 → 0 quadrupole transition.

With the detailed observations of star forming cloud complexes and individual cloud cores in the Milky Way, project A4 (together with A6) presents the “low” end of the sequence of scales at which the CRC 956 studies star formation. The detailed observations possible in the Milky Way are important to constrain the dependence of the observable line strengths of star forming clouds in different environments. They give the basis on which the global emission from star forming complexes and whole galaxies at larger distance (A1, A2) can be interpreted. The large scale mapping projects provide important input for the modeling projects  C5 and C6: the relevance of the feedback mechanisms studied there and how they shape the clouds in which the stars formed, as well as validity of the modeling approximation, need to be judged by the comparison with observational data. Similarly, the interaction with C1 is essential in order to “calibrate” the PDR-modeling tool by comparing the predicted and observed variation with physical cloud parameters. The unique observation opportunities provided by the SOFIA FIR-fine-structure line mapping and line-of-sight absorption studies are enabled by the instrumentation development in project area D and project S.

Selected Publications

• 2022

• Schneider, N., Ossenkopf-Okada V., Clarke S., Klessen R.S., Kabanovic S., Veltchev T., Bontemps S., et al., “Understanding star formation in molecular clouds. IV. Column density PDFs from quiescent to massive molecular clouds”, Astronomy and Astrophysics, vol. 666, 2022
• Tiwari, M., Wolfire M., Pound M.W., Tarantino E., Karim R., Bonne L., Buchbender C., et al., “SOFIA FEEDBACK Survey: PDR Diagnostics of Stellar Feedback in Different Regions of RCW 49”, The Astronomical Journal, vol. 164, no. 4, 2022.
• Bonne, L., Schneider N., Garcia P., Bij A., Broos P., Fissel L., Guesten R., et al.,  “The SOFIA FEEDBACK Legacy Survey Dynamics and Mass Ejection in the Bipolar H II Region RCW 36”, The Astrophysical Journal, vol. 935, no. 2, 2022. 
• Beuther, H., Schneider N., Simon R., Suri S., Ossenkopf-Okada V., Kabanovic S., Röllig M., et al., “FEEDBACK from the NGC 7538 H II region”, Astronomy and Astrophysics, vol. 659, 2022.

• 2021

• Luisi M, Anderson LD, Schneider N, Simon R, Kabanovic S, Güsten R, Zavagno A, Broos PS, Buchbender C, Guevara C, Jacobs K, Justen M, Klein B, Linville D, Röllig M, Russeil D, Stutzki J, Tiwari M, Townsley LK, Tielens AGGM. “Stellar feedback and triggered star formation in the prototypical bubble RCW 120”, SCIENCE ADVANCES: EABE9511 (2021)
• Higgins, R., Kabanovic S., Pabst C., Teyssier D., Goicoechea J.R., Berne O., Chambers E., et al., “Observation and calibration strategies for large-scale multi-beam velocity-resolved mapping of the [CII] emission in the Orion molecular cloud”, Astronomy and Astrophysics, vol. 652, 2021. 
• Kabanovic, S., Schneider N., Ossenkopf-Okada V., Falasca F., Güsten R., Stutzki J., Simon R., et al.,“Self-absorption in [C II], ¹²CO, and H I in RCW120. Building up a geometrical and physical model of the region”, Astronomy and Astrophysics, vol. 659, 2022

• 2020

• Schneider, N., Simon R., Guevara C., Buchbender C., Higgins R.D., Okada Y., Stutzki J., et al., “FEEDBACK: a SOFIA Legacy Program to Study Stellar Feedback in Regions of Massive Star Formation”, Publications of the Astronomical Society of the Pacific, vol. 132, no. 1016, 2020.
• Bonne, L., Schneider N., Bontemps S., Clarke S.D., Gusdorf A., Lehmann A., Steinke M., et al.,  “Dense gas formation in the Musca filament due to the dissipation of a supersonic converging flow”, Astronomy and Astrophysics, vol. 641, 2020.

• 2017

• C. Glück, J. Stutzki, M. Röllig, E. Chambers, and C. Risacher, “SOFIA/GREAT [CII] observations in nearby clouds near the lines of sight towards B0355+508 and B0212+735”, A&A 600, A94 (2017)
• J. Harju, O. Sipilä, S. Brünken, S. Schlemmer, P. Caselli, M. Juvela, K. Menten, J. Stutzki, O. Asvany, T. Kamiński, Y. Okada, and R. Higgins, “Detection of Interstellar Ortho-D 2 H + with SOFIA”, ApJ 840, 63 (2017)
• Z. Nagy, Y. Choi, V. Ossenkopf-Okada, F. van der Tak, E. Bergin, M. Gerin, C. Joblin, M. Röllig, R. Simon, and J. Stutzki, “Herschel/HIFI spectral line survey of the Orion Bar. Temperature and density differentiation near the PDR surface”, A&A 599, A22 (2017)
• C. H. M. Pabst, J. R. Goicoechea, D. Teyssier, O. Berné, B. B. Ochsendorf, M. G. Wolfire, R. D. Higgins, D. Riquelme, C. Risacher, J. Pety, F. Le Petit, E. Roueff, E. Bron, and A. G. G. M. Tielens, “[C II] emission from L1630 in the Orion B molecular cloud”, A&A 606, A29 (2017)

• 2016

• A. Breier, T. Büchling, R. Schnierer, V. Lutter, G. Fuchs, K. Yamada, B. Mookerjea, J. Stutzki, and T. Giesen, “Lowest bending mode of 13 C-substituted C 3 and an experimentally derived structure”, J. Chem. Phys. 145, 234302 (2016)
• H. Wiesemeyer, R. Güsten, S. Heyminck, H. Hübers, K. Menten, D. Neufeld, H. Richter, R. Simon, J. Stutzki, B. Winkel, and F. Wyrowski, “Far-infrared study of tracers of oxygen chemistry in diffuse clouds”, A&A 585, A76 (2016)

• 2015

• J. Goicoechea, D. Teyssier, M. Etxaluze, P. Goldsmith, V. Ossenkopf, M. Gerin, E. Bergin, J. Black, J. Cernicharo, S. Cuadrado, P. Encrenaz, E. Falgarone, A. Fuente, A. Hacar, D. Lis, N. Marcelino, G. Melnick, H. Müller, C. Persson, J. Pety, M. Röllig, P. Schilke, R. Simon, R. Snell, and J. Stutzki, “Velocity-resolved [CII] Emission and [CII]/FIR Mapping along Orion with Herschel”, ApJ 812, 75 (2015)
• V. Ossenkopf, E. Koumpia, Y. Okada, B. Mookerjea, F. F. S. van der Tak, R. Simon, P. Pütz, and R. Güsten, “Fine-structure line deficit in S 140”, A&A 580, A83 (2015)
• J. Pérez-Beaupuits, J. Stutzki, V. Ossenkopf, M. Spaans, R. Güsten, and H. Wiesemeyer, “Detection of a large fraction of atomic gas not associated with star-forming material in M17 SW”, A&A 575, A9 (2015)

• 2014

• Beuther, H, Ragan, SE, Ossenkopf, V, Glover, S, Henning, T, Linz, H, Nielbock, M, Krause, O, Stutzki, J, Schilke, P, and Güsten, R, “Carbon in different phases ([CII], [CI], and CO) in infrared dark clouds: Cloud formation signatures and carbon gas fractions”. A&A 571, A53 (2014 [Corrigendum)”, A&A 574, C2 (2015)]
• Brünken, S, Sipilä, O, Chambers, ET, Harju, J, Caselli, P, Asvany, O, Honingh, CE, Kaminski, T, Menten, KM, Stutzki, J, and Schlemmer, S.. “H2D+ observations give an age of at least one million years for a cloud core forming Sun-like stars”, Nature 516, pp. 219–221 (2014)

• 2013

• Burton, M.G., C. Braiding, C. Glueck, P. Goldsmith, J. Hawkes, D.J. Hollenbach, et al., The Mopra Southern Galactic Plane CO Survey. PASA, 2013, 30.
• Carlhoff, P., Nguyen, O., Schilke, P., et al., Large scale IRAM 30 m CO-observations in the giant molecular cloud complex W43, A&A, 2013, 560, 24.
• Stutzki, J., Graf, U.U., Simon, R., Colgan, S.W.J., Guan, X., Güsten, R:, Honingh, C.E., Large column densities and [12 CII] 158 μm self-absorption in Orion B, 2013, IAU Symp. 292, 57

• 2012

• Graf, U.U., R. Simon, J.M. Stutzki, S.W.J. Colgan, X. Guan, R. Güsten, et al., [12 CII] and [13 CII] 158 μm emission from NGC 2024: Large column densities of ionized carbon. A&A, 2012, 542, L16.
• Mookerjea, B., V. Ossenkopf, O. Ricken, R. Gusten, U.U. Graf, K. Jacobs, et al., The structure of hot gas in Cepheus B. A&A, 2012, 542.
• Okada, Y., R. Gusten, M.A. Requena-Torres, M. Rollig, P. Hartogh, H.W. Hubers, et al., Dynamics and photodissociation region properties in IC 1396A. A&A, 2012, 542.
• Perez-Beaupuits, J.P., H. Wiesemeyer, V. Ossenkopf, J. Stutzki, R. Gusten, R. Simon, et al., The ionized and hot gas in M17 SW SOFIA/GREAT THz observations of [C II] and (CO)-C-12 J=13-12. A&A, 2012, 542.
• Simon, R., N. Schneider, J. Stutzki, R. Güsten, U.U. Graf, P. Hartogh, et al., SOFIA observations of S106: dynamics of the warm gas, A&A, 2012, 542, L12.