Synthetic Spectral Signatures from Isothermal Collapsing Gas and the Interpretation of Infall Profiles

Loughnane, Robert M.; Vázquez-Semadeni, Enrique; Naranjo-Romero, Raúl

doi:10.48550/arxiv.1808.04792

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“…A common argument against the possibility of cores being in the process of dynamical contraction already during their prestellar stage is that the final parts of this stage produce supersonic infall speeds at the core's envelope, while typical estimators of the infall speed, such as blue-excess line profiles of moderately optically thick transitions often imply subsonic infall velocities (e.g., Lee et al 2001;Campbell et al 2016). However, as shown by Loughnane et al (2018), the fact that the largest infall speeds in collapsing cores occur at radii where the density is already decreasing (see eq. 24) may cause a systematic underestimation of the infall speed by these indicators.…”

Section: The Difference Between the Pre-and Protostellar Collapse Reg...mentioning

confidence: 99%

“…( 24). Moreover, the decrease of the infall speed towards the core's center (i.e., the outside-in nature of the profile) implies that the densest parts of the core do not have very large infall speeds during the prestellar stage, while the largest speeds occur at radii where the density is already decreasing, and therefore those speeds are downweighted in line profiles, giving the appearance that the cores have smaller infall speeds than they actually do (Loughnane et al 2018). This may help reconcile the supersonic nature of the actual infall speed with the apparently subsonic values often derived from blue-skewed molecular line profiles (Zhou 1992;Evans 1999;Lee et al 2001;Campbell et al 2016), as well as explain the observed BE-like column density profiles in spite of the configurations not being in equilibrium.…”

Section: Dynamical Contraction With Bonnor-ebert-like Density Profile...mentioning

confidence: 99%

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Global Hierarchical Collapse In Molecular Clouds. Towards a Comprehensive Scenario

Vázquez-Semadeni,

Palau,

Ballesteros-Paredes

et al. 2019

Preprint

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We present a unified description of the scenario of global hierarchical collapse (GHC). GHC constitutes a flow regime of (non-homologous) collapses within collapses, in which all scales accrete from their parent structures, and small, dense regions begin to contract at later times, but on shorter timescales than large, diffuse ones. The different timescales allow for most of the clouds' mass to be dispersed by the feedback from the first massive stars, maintaining the cloud-scale star formation rate (SFR) low. MCs, clumps, and cores are not in equilibrium, but rather are either undergoing contraction or dispersal. The main features of GHC are: 1) The gravitational contraction is initially very slow, and begins when the cloud still consists of mostly atomic gas. 2) Star-forming MCs are in an essentially pressureless regime, causing filamentary accretion flows from the cloud to the core scale to arise spontaneously.3) Accreting objects have longer lifetimes than their own free-fall time, due to the continuous replenishment of material. 4) The clouds' total mass and its molecular and dense mass fractions increase over time. 5) The clouds' masses stop growing when feedback becomes important. 6) The first stars appear several megayears after global contraction began, and are of low mass; massive stars appear a few megayears later, in massive hubs. 7) The minimum fragment mass may well extend into the brown-dwarf regime. 8) Bondi-Hoyle-Lyttleton-like accretion occurs at both the protostellar and the core scales, accounting for an IMF with slope dN/dM ∝ M −2 . 9) The extreme anisotropy of the filamentary network explains the difficulty in detecting large-scale infall signatures. 10) The balance between inertial and gravitationally-driven motions in clumps evolves during the contraction, explaining the approach to apparent virial equilibrium, from supervirial states in low-column density clumps and from subvirial states in dense cores. 11) Prestellar cores adopt Bonnor-Ebert-like profiles, but are contracting ever since when they may appear to be unbound. 12) Stellar clusters develop radial age and mass segregation gradients. We also discuss the incompatibility between supersonic turbulence and the observed scalings in the molecular hierarchy. Since gravitationally-formed filaments do not develop shocks at their axes, we suggest that a diagnostic for the GHC scenario should be the absence of strong shocks in them. Finally, we critically discuss some recent objections to the GHC mechanism.

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Section: The Difference Between the Pre-and Protostellar Collapse Reg...mentioning

confidence: 99%

Section: Dynamical Contraction With Bonnor-ebert-like Density Profile...mentioning

confidence: 99%

Global Hierarchical Collapse In Molecular Clouds. Towards a Comprehensive Scenario

Vázquez-Semadeni,

Palau,

Ballesteros-Paredes

et al. 2019

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

Synthetic Spectral Signatures from Isothermal Collapsing Gas and the Interpretation of Infall Profiles

Cited by 1 publication

References 0 publications

Global Hierarchical Collapse In Molecular Clouds. Towards a Comprehensive Scenario

Global Hierarchical Collapse In Molecular Clouds. Towards a Comprehensive Scenario

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