Lifetime Of Massive Stars Research Articles

NH$_{3}$ Survey Observation of Massive Star-Forming Region W 43

Abstract We consider the properties of giant molecular cloud complexes in the star-forming region W 43 with a resolution of several pc scale, and discuss their relations to the evolutionary stages of massive star formation. We performed a NH$_{3}$ ($J$, $K$) $=$ (1, 1), (2, 2), and (3, 3) inversion-line survey with the Hokkaido University 11-m telescope. Among 51 observed positions, selected based on integrated intensity maps of $^{13}$CO ($J$$=$ 1–0), these three emissions were detected from 21, 8, and 5 positions, respectively. The integrated intensity of the NH$_{3}$ ($J$, $K$) $=$ (1, 1) line was found to be proportional to the far-infrared luminosity, estimated from IRAS data. The rotation temperatures were deduced to be $\sim\ $15–20 K at eight observed positions. In addition, the upper limits were estimated for 13 positions, which include the relatively low temperatures below 14 K at two positions with a relatively high fractions of NH$_{3}$ for $^{13}$CO and with a low far-infrared luminosity. We derived the ortho-to-para abundance ratio of NH$_{3}$. From the population distribution between the ortho- and para-levels of NH$_{3}$, we also derived temperatures of $\sim\ $6–12 K, which may be interpreted as the temperatures when NH$_{3}$ molecules were formed. We discuss the relevance of the present results of our observations to the massive star-formation process and the current status of the W 43 region while taking into account previous observations of other indicators of massive star formation. It is shown that the complexes contain several regions in different evolutionary stages, or with the distinct characteristics of star formation within a timescales shorter than the lifetime of massive stars.

Early Metal Enrichment by Pregalactic Outflows. II. Three‐dimensional Simulations of Blow‐Away

Supernova (SN)-driven pregalactic outflows may be an efficient mechanism for distributing the product of stellar nucleosynthesis over large cosmological volumes prior to the reionization epoch. Here, we present results from three-dimensional numerical simulations of the dynamics of SN-driven bubbles as they propagate through and escape the grasp of subgalactic halos with masses M = 108 h-1 M☉ at redshift z = 9. Halos in this mass range are characterized by very short dynamical timescales (and even shorter gas cooling times) and may therefore form stars in a rapid but intense burst before SN quenches further star formation. The hydrodynamic simulations use a nested grid method to follow the evolution of explosive multi-SN events operating on the characteristic timescale of a few times 107 yr, the lifetime of massive stars. The results confirm that if the star formation efficiency of subgalactic halos is 10%, a significant fraction of the halo gas will be lifted out of the potential well (blow-away), shock the intergalactic medium, and pollute it with metal-enriched material, a scenario recently advocated by Madau, Ferrara, & Rees. The volume filling factor of the ejecta is of order unity. Depending on the stellar distribution, we find that less than 30% of the available SN energy gets converted into kinetic energy of the blown-away material, the remainder being radiated away. It appears that mechanical feedback is less efficient than expected from simple energetic arguments, as off-nuclear SN explosions drive inward-propagating shocks that tend to collect and pile up cold gas in the central regions of the host halo. Low-mass galaxies at early epochs may survive multiple SN events and continue forming stars.