The LITTLE THINGS Science
The processes that lead to star formation on galactic scales are poorly
understood, even in the simplest systems in the universe,
dwarf galaxies. At best we have incomplete knowledge of certain processes in
certain environments. We are addressing this situation, starting with the simplest
systems Nature can provide, local dwarf irregular (dIm) galaxies.
Our approach begins with assembling a complete dataset on a sample of
dIm galaxies, tracing their stellar populations, gas content, dynamics,
and star formation indicators.
The LITTLE THINGS HI-line maps will reveal the gas from which
star-forming clouds are created and their kinematical context.
We will combine the HI data with our optical, UV, and IR data
to answer the following questions:
- What regulates star formation in small galaxies?
The standard large-scale gravitational instability model
does not work in dwarfs or the
outer disks of spirals where the gas density is below the critical
threshold and is stable to spontaneous perturbations.
Why do giant cloud complexes and stars form at all in sub-critical gas?
- What is the relative importance of sequential
triggering for star formation in small galaxies?
One generation of stars can trigger the formation of the next
by rearranging the gas through winds and supernovae explosions,
but how important is this process?
HI and optical observations of dwarfs show
a better correlation between the star formation rate and the
V-band surface brightness, which emphasizes ~Gyr old stars, than
any other measure.
This suggests that the existing stars are somehow
important for triggering new stars.
- What is the relative importance of triggering by random
turbulence compression in dwarf galaxies?
account for various phenomena that are indirectly related to star formation.
Is turbulence the key to allowing star
formation to proceed in a normal fashion in dwarfs even
though the gas density is sub-critical?
And, what regulates turbulence?
- What is happening in the far outer parts of dwarf galaxies,
where star formation continues in gravitationally stable gas?
Densities of gas in outer disks of dwarfs and spirals are
sub-critical by more than an order of magnitude.
Yet star formation is on-going out there.
Is turbulence the only remaining process to trigger star formation
- What happens to the star formation process at breaks
in the exponential light profiles?
There is a change in slope in the exponential surface brightness light profiles
of the outer disks of 20--40% of dIm and spiral galaxies
and disks at high z.
This break implies some sort of transition in the star formation process at the break radius.
- What happens in Blue Compact Dwarfs (BCD)?
BCDs are dIm galaxies in which the central star formation rates
jump by a factor of ~10, but not all BCDs show signs of a
galaxy-galaxy interaction on which to blame the starburst.
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