Speaker
Matthew Hayes
(Stockholm University)
Description
I will present the first image of an individual extragalactic object in which the
coronal gas phase (T ~300,000 K) is both isolated and spatially resolved, by
targeting the O VI doublet at 1032,1037 Å in emission. The combination of HST UV
imaging and spectroscopy provides unique new insights into the mass, cooling,
kinematics, and ultimately the fate of gas that has been heated by feedback from star
formation. The O VI-bearing gas has the morphology of a significantly extended halo
that has an exponential scale length ten times larger than the ionizing stellar
population. COS spectroscopy confirms both the O VI nature of the gas in emission,
and in absorption shows the gas is outflowing with a velocity of ~350 km/s. I will
show how a large number of constraints can be placed on the conditions in the coronal
phase, that for the first time come with a significantly reduced assumptions: we
solve for the cloud sizes, electron density, pressure, cooling rate, and sound speed.
In this presentation I will demonstrate that: (A.) this phase contains only a small
amount of the mechanical energy returned by SNe explosions at any given instant, but
because of a short cooling time a significant fraction of the gas will have passed
through this phase over the star-forming episode; (B.) the coronal gas cannot have
been lifted from the star-forming regions - it will ultimately unbind from the galaxy
but will be neutral by the time it does, thereby joining and enriching the Ly-alpha
absorption systems; (C.) the pressure in the clouds observationally matches that in
the H II regions and, independently, the clouds must be pressure-confined in order to
remain visible. I will argue that we are observing outrushing gas that is compressed
- thereby undergoing rapid cooling - as it accelerates ambient gas in the galaxy halo.
These data represent the first stage in an ongoing study. I will present the status
of current observations of the first extended sample, that were selected to be the
analogues of galaxies at >2 that produced the bulk of the metals for early cosmic
enrichment. I will close with a discussion of how the results will be generalized to
provide new empirical insights for galaxy formation scenarios.
Primary author
Matthew Hayes
(Stockholm University)
