Dense gas and the nature of the outflows

TL;DR

This study investigates the physical properties of dense gas in star-forming regions with outflows using ammonia observations, revealing correlations between gas dynamics, temperature, and stellar luminosity, and suggesting an evolutionary sequence.

Contribution

It provides new observational evidence linking ammonia emission characteristics with outflow types and stellar evolution stages in star-forming regions.

Findings

NH3 emission is stronger in molecular outflow regions.

Higher line widths correlate with greater mass and temperature.

NH3 emission decreases as outflows evolve from molecular to optical.

Abstract

We present the results of the observations of the (J,K)=(1,1) and the (J,K)=(2,2) inversion transitions of the NH3 molecule toward a large sample of 40 regions with molecular or optical outflows, using the 37 m radio telescope of the Haystack Observatory. We detected NH3 emission in 27 of the observed regions, which we mapped in 25 of them. Additionally, we searched for the 6{16}-5{23} H2O maser line toward six regions, detecting H2O maser emission in two of them, HH265 and AFGL 5173. We estimate the physical parameters of the regions mapped in NH3 and analyze for each particular region the distribution of high density gas and its relationship with the presence of young stellar objects. From the global analysis of our data we find that in general the highest values of the line width are obtained for the regions with the highest values of mass and kinetic temperature. We also found a correlation between the nonthermal line width and the bolometric luminosity of the sources, and between the mass of the core and the bolometric luminosity. We confirm with a larger sample of regions the conclusion of Anglada et al. (1997) that the NH3 line emission is more intense toward molecular outflow sources than toward sources with optical outflow, suggesting a possible evolutionary scheme in which young stellar objects associated with molecular outflows progressively lose their neighboring high-density gas, weakening both the NH3 emission and the molecular outflow in the process, and making optical jets more easily detectable as the total amount of gas decreases.