The Role of the Multi-Phase Interstellar Medium in Star Formation: From Clouds to Galaxies
Final Report Abstract
The studies and publications enabled by this DFG project allowed us to advance our understanding of molecular and atomic gas in nearby spiral galaxies. In particular, we studied the distribution of the different gas phases, different molecular spectral lines and their ability to trace different dynamical environments (for instance central bars, spiral arms) or gas density in spiral galaxies. Another focus was to understand what regulates the conversion of the warm, atomic hydrogen gas, ultimately the raw material “fueling” stellar mass growth in galaxies, to the much colder and denser molecular gas out of which stars eventually form. One highlight was the analysis of the super high-resolution molecular line survey in the center of the nearby spiral galaxy NGC 6946, where even several more exotic lines could be identified for the first time in this galaxy, such as C₂H(1−0), HC₃N(10−9), or HC₃N(16−15). These and other detected molecular lines show distinctly different patterns for instance in the dynamically very active central bar, in regions of enhanced shocks from colliding gas flows or depending on the local star formation activity. Other than expected, HCO⁺(1−0) shows the strongest correlation with star formation. Another striking set of results evolves around the extremely extended distribution of atomic hydrogen gas around the spiral galaxy M83, extending to nearly 50 kpc (more than 160,000 lightyears), with complex gas motions. These also include radial inflows (not just orbiting gas), which hints at a mechanism supplying fresh fuel for star formation in the inner part of galaxies. Follow up investigations using data from the new MeerKAT telescope in South Africa and ALMA in Chile focused on what regulates the conversion of atomic hydrogen into star forming molecular gas in eight local spiral galaxies. The key finding is a strong correlation between the fraction of molecular gas and hydrostatic pressure in these galaxy disks, leading to a relatively universal transition from atomic to molecular dominated gas about half-way through the stellar disk. The calibration, reduction, and imaging of the IRAM NOEMA Large Project SWAN (Surveying the Whirlpool at Arcsecond with NOEMA) has been a major achievement. This program covered the inner third of the famous M51 spiral galaxy on the northern sky in eventually nine detected molecular emission lines and for the first time on scales of individual molecular clouds or star forming regions. This allows for an unprecedented view on the density structure of the molecular gas and provides probes to excitation mechanisms such as radiation and (large-scale) shocks. The high-significance detections of N2H+ across the SWAN field of view was a major surprise and enabled the first study with robust statistics between this Milky Way gold standard for inferring (molecular) gas density and the extragalactic workhorse line HCN on cloud-scales showing an overall good correlation between both lines. Two environments could be identified where the correlation deviates — one is the central region affected by the central black hole, the second is associated to regions of highest gas density. These results are also highlighted in the press release “The birthplaces of stars in the Whirlpool Galaxy” by IRAM and MPIA in December 2023. This whole dataset with derived science-ready data products is being made publicly available via IRAM and described in an associated publication. Several further studies from the wider team are underway — all highlighting the (scientific) richness of this unique dataset.
Publications
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A 2–3 mm high-resolution molecular line survey towards the centre of the nearby spiral galaxy NGC 6946. Astronomy & Astrophysics, 659, A173.
Eibensteiner, C.; Barnes, A. T.; Bigiel, F.; Schinnerer, E.; Liu, D.; Meier, D. S.; Usero, A.; Leroy, A. K.; Rosolowsky, E.; Puschnig, J.; Lazar, I.; Pety, J.; Lopez, L. A.; Emsellem, E.; Bešlić, I.; Querejeta, M.; Murphy, E. J.; den Brok, J.; Schruba, A. ... & Williams, T. G.
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Proceedings of the IRAM Workshop “Multi-line Diagnostics of the Interstellar Medium”, Nice, France, Edited by Bouscasse, L.; Kramer, C., Gueth, F., EPJ Web of Conferences, Volume 265, id.00010
Schinnerer E., Pety J., Beslic I., et al.
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Kinematic analysis of the super-extended H I disk of the nearby spiral galaxy M 83. Astronomy & Astrophysics, 675, A37.
Eibensteiner, C.; Bigiel, F.; Leroy, A. K.; Koch, E. W.; Rosolowsky, E.; Schinnerer, E.; Sardone, A.; Meidt, S.; de Blok, W. J. G.; Thilker, D.; Pisano, D. J.; Ott, J.; Barnes, A.; Querejeta, M.; Emsellem, E.; Puschnig, J.; Utomo, D.; Bešlić, I.; den Brok, J. ... & Winkel, B.
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Proceedings of the 7th Chile-Cologne-Bonn Symposium, Puerto-Varas, Chile. Edited by V. Ossenkopf-Okada et al. ISBN: 978-3-00-074740-3. Published by Universitäts- und Stadtbibliothek Köln, 2023, 57, "Comparing physical properties of two extreme dynamical environments: The centers and outskirts of nearby disk galaxies"
Eibensteiner C., Bigiel F., Schinnerer E., et al.
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Surveying the Whirlpool at Arcseconds with NOEMA (SWAN). Astronomy & Astrophysics, 680, L20.
Stuber, Sophia K.; Pety, Jerome; Schinnerer, Eva; Bigiel, Frank; Usero, Antonio; Bešlić, Ivana; Querejeta, Miguel; Jiménez-Donaire, María J.; Leroy, Adam; den Brok, Jakob; Neumann, Lukas; Eibensteiner, Cosima; Teng, Yu-Hsuan; Barnes, Ashley; Chevance, Mélanie; Colombo, Dario; Dale, Daniel A.; Glover, Simon C. O.; Liu, Daizhong & Pan, Hsi-An
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Neutral atomic and molecular gas dynamics in the nearby spiral galaxies NGC 1512, NGC 4535, and NGC 7496. Astronomy & Astrophysics, 690, A169.
Laudage, Sebastian; Eibensteiner, Cosima; Bigiel, Frank; Leroy, Adam K.; Meidt, Sharon; Schinnerer, Eva; de Blok, W. J. G.; Querejeta, Miguele; Stuber, Sophia; Colombo, Dario; Rosolowsky, Erik; Pisano, D. J.; Utomo, Dyas; Levy, Rebecca C.; Klessen, Ralf; Cao, Yixian; Koch, Eric W.; Kurapati, Sushma; Sanchez-Blazquez, Patricia ... & Williams, Thomas G.
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PHANGS-MeerKAT and MHONGOOSE HI observations of nearby spiral galaxies: Physical drivers of the molecular gas fraction, Rmol. Astronomy & Astrophysics, 691, A163.
Eibensteiner, Cosima; Sun, Jiayi; Bigiel, Frank; Leroy, Adam K.; Schinnerer, Eva; Rosolowsky, Erik; Kurapati, Sushma; Pisano, D. J.; de Blok, W. J. G.; Barnes, Ashley T.; Thorp, Mallory; Colombo, Dario; Koch, Eric W.; Chiang, I.-Da; Ostriker, Eve C.; Murphy, Eric J.; Zabel, Nikki; Laudage, Sebstian; Maccagni, Filippo M. ... & Williams, Thomas G.
