Autores
Dr.
Sharon Meidt
Fecha y hora
4 Nov 2012 - 11:30 Europe/London
Dirección
Aula
Idioma de la charla
Inglés
Número en la serie
1
Descripción
Gas kinematics on the scales of Giant Molecular
Clouds (GMCs) are essential for probing the framework that links the
large-scale organization of interstellar gas to cloud formation and
subsequent star formation. I will present an overview of results from the
PdBI Arcsecond Whirlpool Survey (PAWS, PI: E. Schinnerer), which has mapped
CO(1-0) emission over 9 kpc in the nearby grand-design spiral galaxy M51 at
40 pc resolution, and is sensitive to giant molecular clouds (GMCs) with
masses above 10^5 Msun. This unprecedented view challenges the
conventional picture of how molecular gas is structured and organized in
galaxies: clouds are not ‘universal’, but respond to their environment,
resulting in a diversity of cloud properties that not only depend on
(dynamical) environment but also vary from galaxy to galaxy. I will
discuss how this sensitivity to environment emerges, in consideration of
the stability of M51’s GMCs (including the effects of pressure, shear,
turbulence) and our view of non-circular motions in the gas disk. As a
result of the strong streaming motions that arise due to departures from
axisymmetry in the gravitational potential (i.e. the nuclear bar and spiral
arms), embedded clouds feel a reduced surface pressure, which can prevent
collapse. This dynamical pressure naturally leads to changes in the
efficiency of star formation and hence gas depletion time along the spiral
arms. I will show that local reductions to cloud surface pressure in M51
dominate over shear and star formation feedback-driven turbulence in
determining the observed radial variation the depletion time. I will also
describe how incorporating 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.