Gas kinematics on giant molecular cloud scales in M51 with PAWS: Cloud stabilization through dynamical pressure
- Max-Planck-Institut für Astronomie/Königstuhl 17 D-69117 Heidelberg (Germany)
- Observatorio Astronómico Nacional - OAN, Observatorio de Madrid Alfonso XII, 3, E-28014 - Madrid (Spain)
- Institut de Radioastronomie Millimétrique, 300 Rue de la Piscine, F-38406 Saint Martin d'Hères (France)
- School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom)
- Instituto Radioastronomía Milimétrica, Avenida Divina Pastora 7, Nucleo Central, E-18012 Granada (Spain)
- National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)
- Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)
We use the high spatial and spectral resolution of the PAWS CO(1-0) survey of the inner 9 kpc of the iconic spiral galaxy M51 to examine the effects of gas streaming motions on the star-forming properties of individual giant molecular clouds (GMCs). We compare our view of gas flows in M51—which arise due to departures from axisymmetry in the gravitational potential (i.e., the nuclear bar and spiral arms)—with the global pattern of star formation as traced by Hα and 24 μm emission. We find that the dynamical environment of GMCs strongly affects their ability to form stars, in the sense that GMCs situated in regions with large streaming motions can be stabilized, while similarly massive GMCs in regions without streaming go on to efficiently form stars. We argue that this is the result of reduced surface pressure felt by clouds embedded in an ambient medium undergoing large streaming motions, which prevent collapse. Indeed, the variation in gas depletion time expected based on the observed streaming motions throughout the disk of M51 quantitatively agrees with the variation in the observed gas depletion time scale. The example of M51 shows that streaming motions, triggered by gravitational instabilities in the form of bars and spiral arms, can alter the star formation law; this can explain the variation in gas depletion time among galaxies with different masses and morphologies. In particular, we can explain the long gas depletion times in spiral galaxies compared with dwarf galaxies and starbursts. We suggest that adding a dynamical pressure term to the canonical free-fall time produces a single star formation law that can be applied to all star-forming regions and galaxies across cosmic time.
- OSTI ID:
- 22348515
- Journal Information:
- Astrophysical Journal, Vol. 779, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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