Abstract
We present the burst ages for young stellar populations in a sample of six
nearby (< 10 Mpc) spiral galaxies using a differential pixel-based analysis of
the ionized gas emission. We explore this as an alternative approach for
connecting large-scale dynamical mechanisms with star formation processes in
disk galaxies, based on burst ages derived from the Ha to far UV (FUV) flux
ratio. Images of each galaxy in Ha were taken with Taurus Tunable Filter (TTF)
and matched to FUV imaging from GALEX. The resulting flux ratio provides a
robust measure of relative age across the disk which we discuss in terms of the
large-scale dynamical motions. Systematic effects, such as a variable initial
mass function (IMF), non-solar metallicities, variable star-formation history
(SFHs), and dust attenuation, have been used to derive estimates of the
systematic uncertainty.
The resulting age maps show a wide range of patterns outside of those
galaxies with the strongest spiral structure, confirming the idea that star
formation is driven one by several processes, largely determined by the
individual circumstances of the galaxy. Generally, grand design spirals such as
M74, M100, and M51 exhibit age gradients across the main spiral arms, with the
youngest star formation regions along the central and inner edges. In M63 and
M74 galaxy-wide trends emerge, suggesting that although most star formation is
located along spiral arms, spiral density waves are not the only driver in
these cases. We argue that despite appearances, galaxy morphology is not an
absolute discriminator of the star formation history of an individual galaxy,
nor of the processes triggering it. We conclude that Ha-to-FUV flux ratios are
a relatively direct way to probe burst ages across galaxies and infer something
of their dynamical histories, provided that sources of systematics are properly
taken into account.
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