The State of the Gas and the Relation Between Gas and Star Formation at Low Metallicity: the Small Magellanic Cloud
Year: 2011
Type: article
Abstract: We compare atomic gas, molecular gas, and the recent star formation rate (SFR) inferred from Hα in the Small Magellanic Cloud (SMC). By using infrared dust emission and local dust-to-gas ratios, we construct a map of molecular gas that is independent of CO emission. This allows us to disentangle conversion factor effects from the impact of metallicity on the formation and star formation efficiency of molecular gas. On scales of 200 pc to 1 kpc (where the distributions of H 2 and star formation match well) we find a characteristic molecular gas depletion time of τ mol dep ∼ 1.6 Gyr, similar to that observed in the molecule-rich parts of large spiral galaxies on similar spatial scales. This depletion time shortens on much larger scales to ∼0.6 Gyr because of the presence of a diffuse Hα component, and lengthens on much smaller scales to ∼7.5 Gyr because the Hα and H 2 distributions differ in detail. We estimate the systematic uncertainties in our dust-based τ mol dep measurement to be a factor of ∼2–3. We suggest that the impact of metallicity on the physics of star formation in molecular gas has at most this magnitude, rather than the factor of ∼40 suggested by the ratio of SFR to CO emission. The relation between SFR and neutral ( ) gas surface density is steep, with a power-law index ≈2.2 ± 0.1, similar to that observed in the outer disks of large spiral galaxies. At a fixed total gas surface density the SMC has a 5–10 times lower molecular gas fraction (and star formation rate) than large spiral galaxies. We explore the ability of the recent models by Krumholz et al. and Ostriker et al. to reproduce our observations. We find that to explain our data at all spatial scales requires a low fraction of cold, gravitationally bound gas in the SMC. We explore a combined model that incorporates both large-scale thermal and dynamical equilibrium and cloud-scale photodissociation region structure and find that it reproduces our data well, as well as predicting a fraction of cold atomic gas very similar to that observed in the SMC.
Source: The Astrophysical Journal
Authors: Alberto D. Bolatto, Adam K. Leroy, Katherine Jameson, Eve Ostriker, Karl Gordon, Brandon Lawton, Snežana Stanimirović, Frank P. Israel, Suzanne C. Madden, Sacha Hony, Karin M. Sandstrom, Caroline Bot, Mónica Rubio, P. Frank Winkler, Julia Roman-Duval, Jacco Th. van Loon, Joana M. Oliveira, Rémy Indebetouw
Institutions: University of Maryland, College Park, National Radio Astronomy Observatory, Space Telescope Science Institute, University of Wisconsin–Madison, Leiden Observatory, Centre National de la Recherche Scientifique, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Astrophysique, Instrumentation et Modélisation, Université Paris Diderot, Max Planck Institute for Astronomy, Observatoire astronomique de Strasbourg, Université de Strasbourg, University of Chile, Middlebury College, Keele University, University of Virginia
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
Awards: Astrophysics at Keele: the formation and evolution of galaxies, stars and planets., G143343982, Project support for the Wide Area Search for Planets, Collaborative Research: Astronomy with CARMA, From Galactic Centers to Galactic Fringes: Control of Star Formation in the Dynamic Interstellar Medium, Project support for WASP (Keele), supplement., CAREER:Steps Toward a Physical Understanding of the Star Formation Law, G6675224407, SEES Fellows: Recyclable Solid Supports as a Sustainable Platform Technology
OpenAlex ID: W2085640743