The initial conditions of star formation in the Ophiuchus main cloud: Kinematics of the protocluster condensations ,

By P. André, Arnaud Belloche, Fr'ed'erique Motte, Nicolas Peretto. 2007

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Context. The earliest phases of clustered star formation and the origin of the stellar initial mass function (IMF) are currently much debated. In one school of thought the IMF of embedded clusters is entirely determined by turbulent fragmentation at the prestellar stage of star formation, while in a major alternative view it results from dynamical interactions and competitive accretion at the protostellar stage. Aims. In an effort to discriminate between these two pictures for the origin of the IMF, we investigated the internal and relative motions of starless condensations and protostars previously detected by us in the dust continuum at 1.2 mm in the L1688 protocluster of the Ophiuchus molecular cloud complex. The starless condensations have a mass spectrum resembling the IMF and are therefore likely representative of the initial stages of star formation in the protocluster. Methods. We carried out detailed molecular line observations, including some N2H + (1−0) mapping, of the Ophiuchus protocluster condensations using the IRAM 30 m telescope. Results. We measured subsonic or at most transonic levels of internal turbulence within the condensations, implying virial masses which generally agree within a factor of ∼2 with the masses derived from the 1.2 mm dust continuum. This supports the notion that most of the L1688 starless condensations are gravitationally bound and prestellar in nature. We detected the classical spectroscopic signature of infall motions in CS(2–1), CS(3–2), H2CO(212−111), and/or HCO + (3–2) toward six condensations, and obtained tentative infall signatures toward 10 other condensations. In addition, we measured a global one-dimensional velocity dispersion of less than 0. 4k m s −1 (or twice the sound speed) between condensations. The small relative velocity dispersion implies that, in general, the condensations do not have time to interact with one another before evolving into pre-main sequence objects. Conclusions. Our observations support the view that the IMF is partly determined by cloud fragmentation at the prestellar stage. Competitive accretion is unlikely to be the dominant mechanism at the protostellar stage in the Ophiuchus protocluster, but it may possibly govern the growth of starless, self-gravitating condensations initially produced by gravoturbulent fragmentation toward an IMF, Salpeter-like mass spectrum.

Subfields: Astronomy and Astrophysics, Instrumentation, Physical and Theoretical Chemistry

View Paper: https://www.semanticscholar.org/paper/46433c8b0699f119704876308ea1bf937f34eec6

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Citations in the corpus

A census of dense cores in the Aquila cloud complex: SPIRE/PACS observations from the Herschel Gould Belt survey (2015, background): “…component of the velocity dispersion is neglected, is justified by observations of nearby cores in dense gas molecular tracers such as NH3 and N2H+ lines, which show that nonthermal motions are negligible in low-mass (and intermediate-mass) starless cores (e.g., Myers 1983; André et al. 2007).”
The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, background): “Both dense cores (André et al. 2007; Kirk et al. 2007; Rosolowsky et al. 2008a) and stars (Fűrész et al. 2008; Tobin et al. 2009) show systematically smaller velocity dispersions than the diffuse gas in the same region.”
Comparing the statistics of interstellar turbulence in simulations and observations - Solenoidal versus compressive turbulence forcing (2009, background): “Indeed, observations typically find that star-forming cores exhibit transonic to subsonic velocity dispersions (e.g., André et al. 2007; Ward-Thompson et al. 2007; Friesen et al. 2009).”
The initial conditions of stellar protocluster formation - I. A catalogue of Spitzer dark clouds (2009, background): “So far, the study of the earliest stages of the formation of protoclusters have mostly focussed on the closest objects such asρ-Oph(e.g. Motte et al. 1998; André et al. 2007), Perseus (Hatchell et al. 2005; Enoch et al. 2006), NGC2264 (e.g. Peretto et al. 2006; Teixeira et al. 2006).”
On the diversity and statistical properties of protostellar discs (2018, background): “Both numerical simulations (Bate et al. 2003) and recent observations (André et al. 2007; Foster et al. 2015; Rigliaco et al. 2016; Sacco et al. 2017) find the typical velocity dispersions in dense molecular gas, from which protostars form, are much lower than (typically ≈ 1/3) the velocity…”
Physical Processes in the Interstellar Medium (2014, background): “This indicates that the gas motions inside the cores are subsonic or at best transsonic, with Mach numbers less than ∼2 (Kirk et al. 2007; André et al. 2007; Rosolowsky et al. 2008).”
THE SPITZER c2d LEGACY RESULTS: STAR-FORMATION RATES AND EFFICIENCIES; EVOLUTION AND LIFETIMES (2008, background): “The issues connecting the core mass function and the initial mass function of stars are explored in a number of papers (Enoch et al. 2008b, Hatchell & Fuller 2008, Clark et al. 2007, Goodwin et al. 2008, André et al. 2007, and Swift & Williams 2008).”
The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X (2007, background): “This is particularly surprising since the lifetime of pre-stellar cores and condensations in nearby,lowmass star-forming regions is more than two orders of magnitude longer (1− 4 × 105 yr, e.g. Onishi et al. 2002; Kirk et al. 2005; André et al. 2007).”
An ALMA study of the Orion Integral Filament: I. Evidence for narrow fibers in a massive cloud (2018, background): “Similar networks of small-scale filaments are apparent in other nearby regions like rho-Oph (André et al. 2007), B59 (Román-Zúñiga et al. 2009), and L1517 (Hacar & Tafalla 2011).”
The Aquila prestellar core population revealed by Herschel (2010, background): “However, millimeter line observations in dense gas tracers such as N2H+ show that thermal motions generally dominate over nonthermal motions in starless cores (e.g., André et al. 2007).”
Analytical Theory for the Initial Mass Function: CO Clumps and Prestellar Cores (2008, background): “Given the low efficiency of star formation and the relatively high densities at which star formation is observed to take place, n̄ 104Y105 g cm 3 (Motte et al. 1998; André et al. 2007), it is not clear whether the Larson relations are representative of star formation regions.”
Accretion-driven turbulence as universal process: galaxies, molecular clouds, and protostellar disks (2009, background): “In ρ-Oph, for example, the typical core-to-core velocity dispersion is found to be less than 0.4 km s−1 (André et al. 2007).”
LIMITING ACCRETION ONTO MASSIVE STARS BY FRAGMENTATION-INDUCED STARVATION (2010, background): “…picture has been challenged, on the grounds that the kinematic structure observed in star-forming regions is inconsistent with the idea that protostars have time to interact with one another strongly before they completely accrete their parent cores (Krumholz et al. 2005; André et al. 2007).”
The stellar and sub-stellar IMF of simple and composite populations (2011, background): “Competitive accretion may govern the growth of starless, self-gravitating condensations initially produced by gravo-turbulent fragmentation towards an IMF-like mass spectrum (André et al. 2007).”