HII Regions in Spiral Galaxies:
Size Distribution, Luminosity Function, and New Isochrone
Diagnostics of Density Wave Kinematics,
M.S. Oey, J.S. Parker, V.J. Mikles, & X. Zhang
We investigate the relationship of the HII region luminosity
function (HII LF) to the HII region size distribution and density wave
triggering in grand-design spiral galaxies. We suggest that the
differential nebular size distribution is described by a power law of
slope ~ -4, , with flattening at radii below ~130 pc. This contrasts
with the conventional exponential
description, but it is physically and quantitatively consistent with the
typical observed value of -2 for the HII LF slope.
We have developed an interactive code that computes
spatial isochrones for the evolving loci of spiral density waves
in disk galaxies. This allows comparison of the nebular spatial
distribution with the spatial isochrones for simple rotation curve
parameters. Our comparisons for four grand-design galaxies suggest
that the corotation radius r_co coincides with the outer ends of the
star-forming arms. This value for r_co yields the best spatial
correspondence between the HII regions and the isochrones, and also
appears to yield a coincidence between the Inner Lindblad Resonance
with the radial onset of star formation in the arms. Thus, we
suggest that isochrones offer a new, simple, and effective technique for
determining r_co , and thus the spiral pattern speed. However,
application of the isochrones also demonstrates that evolution of the
nebular population is difficult to spatially isolate in these galaxies.
AJ, 126, 2317
Table of Contents
Journal article via ADS
astro-ph/0307230
(color figures)
PostScript preprint (color figures)
|