On the Star Formation Rates in Molecular Clouds (1009.2985v1)

Abstract: In this paper we investigate the level of star formation activity within nearby molecular clouds. We employ a uniform set of infrared extinction maps to provide accurate assessments of cloud mass and structure and compare these with inventories of young stellar objects within the clouds. We present evidence indicating that both the yield and rate of star formation can vary considerably in local clouds, independent of their mass and size. We find that the surface density structure of such clouds appears to be important in controlling both these factors. In particular, we find that the star formation rate (SFR) in molecular clouds is linearly proportional to the cloud mass (M_{0.8}) above an extinction threshold of A_K approximately equal to 0.8 magnitudes, corresponding to a gas surface density threshold of approximaely 116 solar masses per square pc. We argue that this surface density threshold corresponds to a gas volume density threshold which we estimate to be n(H_2) approximately equal to 10^4\cc. Specifically we find SFR (solar masses per yr) = 4.6 +/- 2.6 x 10^{-8} M_{0.8} (solar masses) for the clouds in our sample. This relation between the rate of star formation and the amount of dense gas in molecular clouds appears to be in excellent agreement with previous observations of both galactic and extragalactic star forming activity. It is likely the underlying physical relationship or empirical law that most directly connects star formation activity with interstellar gas over many spatial scales within and between individual galaxies. These results suggest that the key to obtaining a predictive understanding of the star formation rates in molecular clouds and galaxies is to understand those physical factors which give rise to the dense components of these clouds.

• The paper establishes a linear relationship between star formation rates and the mass of dense gas above an extinction threshold.
• It utilizes uniform infrared extinction mapping to correlate cloud structure with inventories of young stellar objects.
• The study indicates that dense, high-extinction regions drive star formation, underscoring the critical role of gas surface density.

Analysis of Star Formation Rates in Molecular Clouds

The research paper titled "On the Star Formation Rates in Molecular Clouds" by Charles J. Lada, Marco Lombardi, and João F. Alves provides a comprehensive examination of star formation activity within nearby molecular clouds. Utilizing uniform sets of infrared extinction maps, the paper evaluates cloud mass and structure and contrasts these with inventories of young stellar objects (YSOs).

Examination of Star Formation Variability

The investigation highlights considerable variability in star formation rates (SFRs) among local molecular clouds, which appears to be independent of mass and size. This variability is attributed to the surface density structure of the clouds. The paper reveals that star formation predominantly occurs in regions of high extinction (A$_K$ $\approx$ 0.8 magnitudes) and gas surface density ($\Sigma_{gas}$ $\approx 116$ M$_\odot$ pc$^{-2}$).

Linear Correlation between SFR and Cloud Mass

A key finding is the linear relationship between the SFR in molecular clouds and the cloud mass above a specific extinction threshold. Specifically, this relationship is expressed as SFR (M$_\odot$ yr$^{-1}$) = 4.6 $\pm$ 2.6 × 10$^{-8}$ $M_{0.8}$ (M$_\odot$). This correlation is consistent with previous observations in both galactic and extragalactic studies, suggesting it may represent a fundamental physical relationship linking star formation activity with interstellar gas.

Implications for Star Formation and Cloud Structure

The results indicate that understanding the factors leading to the formation of dense components within clouds is essential for developing a predictive understanding of star formation rates. The analysis confirms the existence of a column density threshold for active star formation and underscores the role of high-density gas in this process.

The paper observes that variations in star formation activity and efficiencies are significant among local clouds, exhibiting more than an order of magnitude difference. This underscores the notion that total cloud mass alone is not the primary determinant of star formation rates; rather, the content of dense, high-extinction material plays a crucial role.

Future Research Directions

The findings suggest that future research should focus on elucidating the mechanisms that produce high-density gas within molecular clouds and the factors leading to the observed variations in SFRs. Further examination of the transition from turbulent to gravitationally dominated gas in clouds may also provide insights into the processes governing star formation.

Conclusion

This research provides a nuanced understanding of the relationship between star formation rates and molecular cloud structure through a robust empirical analysis. By establishing a direct correlation between the mass of dense gas and star formation activity, the paper contributes to the development of predictive models for star formation, with implications for both theoretical frameworks and observational studies of galactic evolution.