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Title: HIGH- AND LOW-MASS STAR-FORMING REGIONS FROM HIERARCHICAL GRAVITATIONAL FRAGMENTATION. HIGH LOCAL STAR FORMATION RATES WITH LOW GLOBAL EFFICIENCIES

Abstract

We investigate the properties of 'star-forming regions' in a previously published numerical simulation of molecular cloud formation out of compressive motions in the warm neutral atomic interstellar medium, neglecting magnetic fields and stellar feedback. We study the properties (density, total gas + stars mass, stellar mass, velocity dispersion, and star formation rate (SFR)) of the cloud hosting the first local, isolated 'star formation' event and compare them with those of the cloud formed by the central, global collapse event. In this simulation, the velocity dispersions at all scales are caused primarily by infall motions rather than by random turbulence. We suggest that the small-scale isolated collapses may be representative of low- to intermediate-mass star-forming regions, with gas masses (M{sub gas}) of hundreds of solar masses, velocity dispersions sigma{sub v} approx 0.7 km s{sup -1}, and SFRs approx3 x 10{sup -5} M{sub sun} yr{sup -1}, while the large-scale, massive ones may be representative of massive star-forming regions, with M{sub gas} of thousands of solar masses, sigma{sub v}approx a few km s{sup -1}, and SFRs approx3 x 10{sup -4} M{sub sun} yr{sup -1}. We also compare the statistical distributions of the physical properties of the dense cores appearing in the central regionmore » of massive collapse with those from a recent survey of the massive star-forming region in the Cygnus X molecular cloud, finding that the observed and simulated distributions are in general very similar. However, we find that the star formation efficiency per free-fall time (SFE{sub ff}) of the high mass region, similar to that of OMC-1, is low, approx0.04. In the simulated cloud, this is not a consequence of a 'slow' SFR in a nearly hydrostatic cloud supported by turbulence, but rather of the region accreting mass at a high rate. Thus, we find that measuring a low SFE{sub ff} may be incorrectly interpreted as implying a lifetime much longer than the core's local free-fall time, and an SFR much slower than that given by the free-fall rate, if the accretion is not accounted for. We suggest that rather than requiring a low value of the SFE{sub ff} everywhere in the Galaxy, attaining a globally low specific SFR requires star formation to be a spatially intermittent process, so that most of the mass in a giant molecular cloud (GMC) is not participating in the SF process at any given time. Locally, the specific SFR of a star-forming region can be much larger than the global GMC's average.« less

Authors:
; ;  [1];  [2];  [3]
  1. Centro de RadioastronomIa y AstrofIsica, Universidad Nacional Autonoma de Mexico, Apdo. Postal 3-72, Morelia, Michoacan 58089 (Mexico)
  2. School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA (United Kingdom)
  3. Zentrum fuer Astronomie der Universitaet Heidelberg, Institut fuer Theoretische Astrophysik, 69120 Heidelberg (Germany)
Publication Date:
OSTI Identifier:
21392603
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 707; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/707/2/1023; Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMPUTERIZED SIMULATION; DISTRIBUTION; FEEDBACK; FRAGMENTATION; GALAXIES; LIFETIME; MAGNETIC FIELDS; MASS; RANDOMNESS; STARS; TURBULENCE; VELOCITY; SIMULATION

Citation Formats

Vazquez-Semadeni, Enrique, Gomez, Gilberto C, Ballesteros-Paredes, Javier, Jappsen, A -Katharina, and Klessen, Ralf S. HIGH- AND LOW-MASS STAR-FORMING REGIONS FROM HIERARCHICAL GRAVITATIONAL FRAGMENTATION. HIGH LOCAL STAR FORMATION RATES WITH LOW GLOBAL EFFICIENCIES. United States: N. p., 2009. Web. doi:10.1088/0004-637X/707/2/1023.
Vazquez-Semadeni, Enrique, Gomez, Gilberto C, Ballesteros-Paredes, Javier, Jappsen, A -Katharina, & Klessen, Ralf S. HIGH- AND LOW-MASS STAR-FORMING REGIONS FROM HIERARCHICAL GRAVITATIONAL FRAGMENTATION. HIGH LOCAL STAR FORMATION RATES WITH LOW GLOBAL EFFICIENCIES. United States. https://doi.org/10.1088/0004-637X/707/2/1023
Vazquez-Semadeni, Enrique, Gomez, Gilberto C, Ballesteros-Paredes, Javier, Jappsen, A -Katharina, and Klessen, Ralf S. Sun . "HIGH- AND LOW-MASS STAR-FORMING REGIONS FROM HIERARCHICAL GRAVITATIONAL FRAGMENTATION. HIGH LOCAL STAR FORMATION RATES WITH LOW GLOBAL EFFICIENCIES". United States. https://doi.org/10.1088/0004-637X/707/2/1023.
@article{osti_21392603,
title = {HIGH- AND LOW-MASS STAR-FORMING REGIONS FROM HIERARCHICAL GRAVITATIONAL FRAGMENTATION. HIGH LOCAL STAR FORMATION RATES WITH LOW GLOBAL EFFICIENCIES},
author = {Vazquez-Semadeni, Enrique and Gomez, Gilberto C and Ballesteros-Paredes, Javier and Jappsen, A -Katharina and Klessen, Ralf S},
abstractNote = {We investigate the properties of 'star-forming regions' in a previously published numerical simulation of molecular cloud formation out of compressive motions in the warm neutral atomic interstellar medium, neglecting magnetic fields and stellar feedback. We study the properties (density, total gas + stars mass, stellar mass, velocity dispersion, and star formation rate (SFR)) of the cloud hosting the first local, isolated 'star formation' event and compare them with those of the cloud formed by the central, global collapse event. In this simulation, the velocity dispersions at all scales are caused primarily by infall motions rather than by random turbulence. We suggest that the small-scale isolated collapses may be representative of low- to intermediate-mass star-forming regions, with gas masses (M{sub gas}) of hundreds of solar masses, velocity dispersions sigma{sub v} approx 0.7 km s{sup -1}, and SFRs approx3 x 10{sup -5} M{sub sun} yr{sup -1}, while the large-scale, massive ones may be representative of massive star-forming regions, with M{sub gas} of thousands of solar masses, sigma{sub v}approx a few km s{sup -1}, and SFRs approx3 x 10{sup -4} M{sub sun} yr{sup -1}. We also compare the statistical distributions of the physical properties of the dense cores appearing in the central region of massive collapse with those from a recent survey of the massive star-forming region in the Cygnus X molecular cloud, finding that the observed and simulated distributions are in general very similar. However, we find that the star formation efficiency per free-fall time (SFE{sub ff}) of the high mass region, similar to that of OMC-1, is low, approx0.04. In the simulated cloud, this is not a consequence of a 'slow' SFR in a nearly hydrostatic cloud supported by turbulence, but rather of the region accreting mass at a high rate. Thus, we find that measuring a low SFE{sub ff} may be incorrectly interpreted as implying a lifetime much longer than the core's local free-fall time, and an SFR much slower than that given by the free-fall rate, if the accretion is not accounted for. We suggest that rather than requiring a low value of the SFE{sub ff} everywhere in the Galaxy, attaining a globally low specific SFR requires star formation to be a spatially intermittent process, so that most of the mass in a giant molecular cloud (GMC) is not participating in the SF process at any given time. Locally, the specific SFR of a star-forming region can be much larger than the global GMC's average.},
doi = {10.1088/0004-637X/707/2/1023},
url = {https://www.osti.gov/biblio/21392603}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 707,
place = {United States},
year = {2009},
month = {12}
}