Molecular Cloud Evolution. II. From Cloud Formation to the Early Stages of Star Formation in Decaying Conditions

By E. Vázquez-Semadeni, Gilberto C. Gómez, A. Jappsen, J. Ballesteros-Paredes, R. F. González, Ralf Klessen. 2006

270 citations recorded by the source corpus.

We study the formation of giant dense cloud complexes and of stars within them using SPH numerical simulations of the collision of gas streams (``inflows'') in the WNM at moderately supersonic velocities. The collisions cause compression, cooling, and turbulence generation in the gas, forming a cloud that then becomes self-gravitating and begins to collapse globally. Simultaneously, the turbulent, nonlinear density fluctuations induce fast, local collapse events. The simulations show that (1) The clouds are not in a state of equilibrium. Instead, they undergo secular evolution. During its early stages, the cloud's mass and gravitational energy |Eg| increase steadily, while the turbulent energy Ek reaches a plateau. (2) When |Eg| becomes comparable to Ek, global collapse begins, causing a simultaneous increase in |Eg| and Ek that maintains a near-equipartition condition |Eg| ~ 2Ek. (3) Longer inflow durations delay the onset of global and local collapse by maintaining a higher turbulent velocity dispersion in the cloud over longer times. (4) The star formation rate is large from the beginning, without any period of slow and accelerating star formation. (5) The column densities of the local star-forming clumps closely resemble reported values of the column density required for molecule formation, suggesting that locally molecular gas and star formation occur nearly simultaneously. The MC formation mechanism discussed here naturally explains the apparent ``virialized'' state of MCs and the ubiquity of H I halos around them. Also, within their assumptions, our simulations support the scenario of rapid star formation after MCs are formed, although long (≳15 Myr) accumulation periods do occur during which the clouds build up their gravitational energy, and which are expected to be spent in the atomic phase.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/69d79b79b2d471d00f2c39488aaf246f7fb96c75

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Citations in the corpus

Gravity or turbulence? Velocity dispersion–size relation (2010, methodology): “3 Note that in Vázquez-Semadeni et al. (2007), the absolute value of the gravitational energy is a few times that of the kinetic energy.”
Cooling, Gravity, and Geometry: Flow-driven Massive Core Formation (2007, methodology): “Several numerical studies relevant to this problem have now been undertaken (see the discussions of the literature in Heitsch et al. 2006 and Vázquez-Semadeni et al. 2007).”
Clump morphology and evolution in MHD simulations of molecular cloud formation (2008, methodology): “(1) Concerning the cooling, we use the procedure described in Vázquez-Semadeni et al. (2007), which is based on the chemistry and cooling calculations of Koyama & Inutsuka (2000) and the analytic fits to them by Koyama & Inutsuka (2002).”
From the warm magnetized atomic medium to molecular clouds (2008, methodology): “Recently large multi-dimensional non-magnetic numerical simulations have been performed (Hennebelle & Audit 2007, Vázquez-Semadeni et al. 2007, Heitsch et al. 2008, the last two including self-gravity) with the aim of studying in detail the formation of dense gas from a large flow of warm neutral…”
Theory of Star Formation (2007, background): “Indeed, in simulations that do not include energy injection, the contraction eventually evolves into free-fall collapse (cf. Vázquez-Semadeni et al., 2007, who simulated the formation of molecular clouds in colliding flows, as discussed above), which is generally not observed.”
Gravity or turbulence? II. Evolving column density PDFs in molecular clouds (2011, background): “…of a giant molecular cloud involves timescales of a few tens of Myr, of which the “molecular stage” may represent a small final fraction (Hartmann, Ballesteros-Paredes & Bergin 2001; Bergin et al. 2004; Vázquez-Semadeni et al. 2007, 2010) as well as the so-called core-to-core velocity dispersion.”
Numerical simulations of compressively driven interstellar turbulence. I. Isothermal gas (2008, methodology): “Typical examples for the first approach are the simulations of colliding flows by Heitsch et al. (2006), Vázquez-Semadeni et al. (2007) and Hennebelle & Audit (2007).”
Global hierarchical collapse in molecular clouds. Towards a comprehensive scenario (2019, background): “…a few), implying that in general it is insufficient to prevent the cloud from quickly engaging in global gravitational collapse, at which point the nonthermal kinetic energy becomes “locked” to the gravitational energy, but is never capable of retarding the collapse (Vázquez-Semadeni et al. 2007).”
Is molecular gas necessary for star formation (2011, methodology): “…in complexity, from a simple two-parameter cooling function introduced by Koyama & Inutsuka (2002) and used in a number of later works (e.g. Vázquez-Semadeni et al. 2007; Banerjee et al. 2009), to the more detailed treatment used in e.g. Audit & Hennebelle (2005) that accounts explicitly…”
Accretion-driven turbulence as universal process: galaxies, molecular clouds, and protostellar disks (2009, background): “…accretion energy is converted into turbulent energy we resort to numerical simulations of converging flows (e.g. Audit & Hennebelle 2005; Heitsch et al. 2005, 2006a; Folini & Walder 2006; Vázquez-Semadeni et al. 2006, 2007; Hennebelle et al. 2008; Banerjee et al. 2009; Audit & Hennebelle 2010).”
Dynamic star formation in the massive DR21 filament (2010, background): “High velocity compressive flows form dense structures at stagnation points that may collapse to form stars/clusters (Ballesteros-Paredes et al. 2003, Vazquez-Semadeni et al. 2007, 2009, Heitsch et al. 2008).”
FILAMENTARY STRUCTURE OF STAR-FORMING COMPLEXES (2009, background): “Parsec-scale regions of cloud gas can be compressed by large-scale flows (Vazquez-Semadeni et al 2007), or by stellar wind bubbles, expanding H II regions, or supernova remnants (Whitworth 2007, Elmegreen 1998).”
SDC13 infrared dark clouds: longitudinally collapsing filaments? (2013, background): “During the collapse of the filaments, the gravitational energy of the gas is converted into kinetic energy (e.g. Peretto et al. 2007; Vázquez-Semadeni et al. 2007).”
Molecular Clouds in the Milky Way (2015, background): “F or p er so na l u se o nl y. basis of evidence for rapid star formation (Elmegreen 2000, Hartmann et al. 2001) and numerical simulations of cloud formation (Vázquez-Semadeni et al. 2007).”