Star Formation Efficiency in Low-Density Regions in Galactic Disksстатья
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Дата последнего поиска статьи во внешних источниках: 19 июля 2013 г.
Аннотация:The radial dependences of the star formation efficiency ΣSFE = ΣSFR/Σgas (per unit disk
surface area) in normal surface brightness spiral galaxies and low surface brightness (LSB) galaxies are
compared with the radial variations of the gas and stellar disk surface and volume densities. The volume
density of the components in the disk midplane is found through a self-consistent solution of the disk
equilibrium equations by taking into account the dark halo. The disk thickness variation with radius R is
calculated within the model of a galaxy with a marginally stable disk by taking into account the increase
stability parameter QT,c along the radius. We show that the star formation efficiency depends weakly
(for LSB galaxies, does not depend at all) on the gas density but correlates well with the disk surface and
volume density, with the normal and LSB galaxies forming a single sequence. The dependence vanishes
only at extremely low disk densities (σdisk ≤ (1−3) M pc−2, ρstars ≤ (1−3) × 10−24 g cm−3), where star
formation probably ceases to be related to disk properties. Estimations of the gas volume density allow us
to check the expected form of the ΣSFR–σdisk relationship that follows from the model by Ostriker et al.,
which relates the star formation rate to the pressure of the diffuse gas medium. For most of the galaxies
considered, there is satisfactory agreement with the model, except for the densest (of the order of several
hundredM pc−2) and least dense (severalM pc−2 or less) disk regions.