Massive Field Stars and the Stellar Clustering Law
M.S. Oey, N. L. King, & J. Wm. Parker
The distribution of N_*, the number of OB stars per association or
cluster, appears to follow a universal power-law form N_*^{-2} in
the local Universe. We evaluate the distribution of N_* in the Small
Magellanic Cloud using recent broadband optical and space-ultraviolet
data, with special attention to the lowest values of N_*. We find
that the power-law distribution in N_* continues smoothly down to
N_* = 1. This strongly suggests that the formation of field
massive stars is a continuous process with those in associations, and
that the field stars do not originate from a different star formation
mode. Our results are consistent with the model that field massive
stars represent the most massive members in groups of smaller stars,
as expected if the clustering law applies to much lower masses
as is expected from the stellar initial mass function (IMF). These
results are consistent with the simultaneous existence of a
universal IMF and a universal clustering law. Jointly, these laws
imply that the fraction of field OB stars typically ranges from about
35% to 7% for most astrophysical situations, with an inverse
logarithmic dependence on the most populous cluster, and hence, on
galaxy size and/or star formation rate. There are important
consequences for global feedback effects in galaxies: field stars
should therefore contribute proportionately to the volume of
the warm ionized medium, and equal relative contributions by
superbubbles of all sizes to the interstellar porosity are expected.
AJ, 127, 1632
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astro-ph/0312051
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