| Description |
Studies of evolved systems like AM0644-741 and Cartwheel find
the ISM in the starburst rings to be overwhelmingly atomic despite
conditions (e.g., pressure and ambient far-UV fields)
clearly favoring a dominant molecular component. Moreover, the
local molecular fraction anti-correlates with SFR/area, yielding
unusually high star formation efficiencies (SFE) and a highly
peculiar star formation law. AM0644-741s starburst ring
moreover appears mostly stable gravitationally (Q = 2-6). We
have argued that these all follow naturally from the ISMs
>100 Myr confinement time in the ring, which amplifies the
destructive effects of embedded OB stars and SNe, producing an
``over-cooked ISM, i.e., one characterized by small H2 clouds,
and a large photo-dissociated HI background. Due to reduced
dust columns, H2 is poorly traced by CO rotational lines, and we
expect a large ``dark molecular component in the ring. We
will use PACS and SPIRE photometry with existing IRAC and MIPS
data to (1) construct infrared-submillimeter SEDs for the rings of
AM0644-741 and Cartwheel to determine the total mass and
distribution of H2 by its dust emission following Israel (1996)
and Leroy et al. (2009), (2) re-evaluate their peculiar SFE,
non-Schmidt star formation laws, and gravitational stability.
Not finding a large hidden H2 component would imply that
star formation is triggered by other processes (e.g., collisions)
at unusually high SFE. |
