Abstract

Context. Understanding the effect of feedback from young massive stars on the star-forming ability of their parental molecular clouds is of central importance for studies of the interstellar medium and star formation. Aims. We observed the G305 star-forming complex in the J = 3−2 lines of 12CO and 13CO to investigate whether feedback from the central OB stars was triggering star formation in G305 or actually disrupting this process. Methods. The region was decomposed into clumps using dendrogram analysis. A catalog of the clump properties such as their positions, luminosities, masses, radii, velocity dispersions, volume densities, and surface mass densities was created. The surface mass densities of the clumps were plotted as a function of the incident 8 μm flux. A mask of the region with 8 μm flux > 100 MJy sr−1 was created and clumps were categorized into three classes based on their extent of overlap with the mask, namely mostly inside (>67% overlap), partly inside (>10 and <67% overlap), and outside (<10% overlap). The surface mass density distribution of each of these populations was separately plotted. This was followed by comparing the G305 clumps with the Galactic average taken from a distance-limited sample of ATLASGAL and CHIMPS clumps. Finally, the cumulative distribution functions (CDFs) of the clump masses in G305 and their L∕M ratios were compared to that of the Galactic sample to determine which mechanism of feedback was dominant in G305. Results. The surface mass densities of clumps showed a positive correlation with the incident 8 μm flux. The data did not have sufficient velocity resolution to discern the effects of feedback on the linewidths of the clumps. The subsample of clumps labeled mostly inside had the highest median surface mass densities followed by the partly inside and outside subsamples. The difference between the surface mass density distribution of the three subsamples were shown to be statistically significant using the Kolmogorov–Smirnov test. The mostly inside sample also showed the highest level of fragmentation compared to the other two subsamples. These prove that the clumps inside the G305 region are triggered. The G305 clump population is also statistically different from the Galactic average population, the latter approximating that of a quiescent population of clumps. This provided further evidence that redistribution was not a likely consequence of feedback on the giant molecular cloud. The CDFs of clump masses and their L∕M ratios are both flatter than that of the Galactic average, indicating that clumps are heavier and more efficient at forming stars in G305 compared to the Galactic average. Conclusions. Feedback in G305 has triggered star formation. The collect and collapse method is the dominant mechanism at play in G305.

Highlights

  • G305 is one of the most massive and luminous star-forming giant molecular clouds (GMCs) in the Milky Way (Clark & Porter 2004, Fig. 1)

  • Inside and outside the feedback zone The analysis described in the previous subsection motivated us to follow an approach similar to that presented in Paper I

  • A Kolmogorov– Smirnov (KS) test on the masses of the two populations resulted in a p-value 0.0013 for masses of G305 clumps compared to the Galactic sample indicating that the G305 clumps are significantly different from the Galactic average

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Summary

Introduction

G305 is one of the most massive and luminous star-forming giant molecular clouds (GMCs) in the Milky Way (Clark & Porter 2004, Fig. 1). As is the case in G305, these stars exist in massive clusters located inside GMCs (Motte et al.2018) They inject energy and momentum into their natal clouds via very strong stellar winds, ionizing radiation and eventually supernovae (Krumholz et al 2014). Dispersion: in high mass star-forming regions feedback is very strong and can disperse most of the molecular material via various mechanisms (Krumholz et al 2014, and references therein), thereby suppressing the ability of the GMC to form stars If triggering is dominant, we expect to see more massive clumps when compared to the Galactic average and, in case of an increased star-forming efficiency, a higher luminosity-to-mass ratio.

Observations and data reduction
Findings
Extracting clumps
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