Schmidt's Conjecture and Star Formation in Molecular Clouds

Author(s)

Charles J. Lada, Marco Lombardi, Carlos Roman-Zuniga, Jan Forbrich, João F. Alves

Abstract

We investigate Schmidt's conjecture (i.e., that the star formation rate

(SFR) scales in a power-law fashion with the gas density) for four

well-studied local molecular clouds (giant molecular clouds, GMCs).

Using the Bayesian methodology, we show that a local Schmidt scaling

relation of the form \Sigma _{*}({A}_{{K}}) = \kappa {A}_{{K}}^{\beta }

(protostars pc–2) exists within (but not between) GMCs.

Further, we find that the Schmidt scaling law does not by itself provide

an adequate description of star formation activity in GMCs. Because the

total number of protostars produced by a cloud is given by the product

of Σ*(A K) and S'(> A K), the

differential surface area distribution function, integrated over the

entire cloud, the cloud's structure plays a fundamental role in setting

the level of its star formation activity. For clouds with similar

functional forms of Σ*(A K), observed

differences in their total SFRs are primarily due to the differences in

S'(> A K) between the clouds. The coupling of

Σ*(A K) with the measured S'(> A

K) in these clouds also produces a steep jump in the SFR and

protostellar production above AK ~ 0.8 mag. Finally, we show

that there is no global Schmidt law that relates the SFR and gas mass

surface densities between GMCs. Consequently, the observed

Kennicutt-Schmidt scaling relation for disk galaxies is likely an

artifact of unresolved measurements of GMCs and not a result of any

underlying physical law of star formation characterizing the molecular

gas.

Organisation(s)

Department of Astrophysics

External organisation(s)

Harvard-Smithsonian Center for Astrophysics, Universidad Nacional Autonoma de Mexico, Università degli Studi di Milano-Bicocca

Journal

The Astrophysical Journal

Volume

778

No. of pages

DOI

https://doi.org/10.1088/0004-637X/778/2/133

Publication date

12-2013

Peer reviewed

Yes

Austrian Fields of Science 2012

103004 Astrophysics, 103003 Astronomy

Keywords

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