Probing the evolution of molecular cloud structure: From quiescence to birth

By Jouni Kainulainen, H. Beuther, Th. Henning, R. P. M. F. Astronomy, U. Calgary. 2009

326 citations recorded by the source corpus.

Context. Probability distribution of densities is a fundamental measure of molecular cloud structure, containing information on how the material arranges itself in molecular clouds. Aims. We derive the probability density functions (PDFs) of column density for a complete sample of prominent molecular cloud complexes closer than d < 200 pc. For comparison, additional complexes at d ≈ 250−700 pc are included in the study. Methods. We derive near-infrared dust extinction maps for 23 molecular cloud complexes, using the nicest colour excess mapping technique and data from the 2MASS archive. The extinction maps are then used to examine the column density PDFs in the clouds. Results. The column density PDFs of most molecular clouds are well-fitted by log-normal functions at low column densities (0. 5m ag< AV < 3− 5m ag, or−0.5 < lnAV /AV < 1). But at higher column densities prominent power-law-like wings are common. In particular, we identify a trend among the PDFs: active star-forming clouds always have prominent non-log-normal wings. In contrast, clouds without active star formation resemble log-normals over the whole observed column density range or show only low excess of higher column densities. This trend is also reflected in the cumulative forms of the PDFs, showing that the fraction of high column density material is significantly larger in star-forming clouds. These observations agree with an evolutionary trend where turbulent motions are the main cloud-shaping mechanism for quiescent clouds, but the density enhancements induced by them quickly become dominated by gravity (and other mechanisms), which is in turn strongly reflected by the shape of the column density PDFs. The dominant role of the turbulence is restricted to the very early stages of molecular cloud evolution, comparable to the onset of active star formation in the clouds.

Subfields: Astronomy and Astrophysics, Fluid Flow and Transfer Processes

View Paper: https://www.semanticscholar.org/paper/454a6fe3fa37e7ce5ed107c1fe3fc0c94f985a38

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Citations in the corpus

THE MAGELLANIC MOPRA ASSESSMENT (MAGMA). I. THE MOLECULAR CLOUD POPULATION OF THE LARGE MAGELLANIC CLOUD (2011, background): “Detailed mapping of Galactic clouds, however, has revealed evidence for departures from the lognormal distribution in star-forming clouds, with a power-law tail appearing at large column densities (Kainulainen et al. 2009; Froebrich & Rowles 2010).”
Filaments and ridges in Vela C revealed by Herschel: from low-mass to high-mass star-forming sites (2011, unknown): “Kainulainen et al. (2009) find that the shape of their observed column density distributions changes with the star formation status, clouds with active star formation develop a power-law tail at high column densities, in agreement with some numerical simulations including gravity (e.g.…”
THE RELATION BETWEEN GAS AND DUST IN THE TAURUS MOLECULAR CLOUD (2010, background): “Kainulainen et al. (2009) found that high–AV tails are only present in active star–forming molecular clouds while quiescent clouds are well fitted by a log–normal.”
A NEW JEANS RESOLUTION CRITERION FOR (M)HD SIMULATIONS OF SELF-GRAVITATING GAS: APPLICATION TO MAGNETIC FIELD AMPLIFICATION BY GRAVITY-DRIVEN TURBULENCE (2011, background): “…1994; Padoan et al. 1997; Passot & VázquezSemadeni 1998; Lemaster & Stone 2008; Federrath et al. 2008b; Price & Federrath 2010), and in turbulent systems including self-gravity (e.g., Klessen 2000; Federrath et al. 2008a; Kainulainen et al. 2009; Cho & Kim 2011; Kritsuk et al. 2011).”
The CO-to-H2 Conversion Factor (2013, background): “In the Milky Way, the fraction of cloud mass in high column density lines of sight can vary dramatically from cloud to cloud (e.g., Kainulainen et al. 2009; Lada, Lombardi & Alves 2010).”
Modelling CO emission – I. CO as a column density tracer and the X factor in molecular clouds (2010, background): “These signature high density tails have been found in column density PDFs obtained from observations of evolved clouds (Kainulainen et al. 2009).”
The density variance–Mach number relation in supersonic turbulence – I. Isothermal, magnetized gas (2012, background): “In this instance, the PDF exhibits a power-law tail at high densities (Klessen 2000; Federrath et al. 2008a; Kainulainen et al. 2009; Cho & Kim 2011; Kritsuk, Norman & Wagner 2011).”
On the relationship between molecular hydrogen and carbon monoxide abundances in molecular clouds (2010, background): “Finally, our neglect of the effects of self-gravity is important if one is concerned with the structure of the cloud on the scales of individual dense clumps (e.g. Klessen 2001; Kainulainen et al. 2009).”
VERTICAL STRUCTURE OF A SUPERNOVA-DRIVEN TURBULENT, MAGNETIZED INTERSTELLAR MEDIUM (2012, background): “Kainulainen et al. (2009) found that PDFs of column densities in nearby molecular clouds are generally lognormal, suggesting that turbulent motions dominate.”
Turbulent molecular clouds (2012, methodology): “Kainulainen et al. (2009) obtain the column density of 23 nearby molecular clouds.”
Is molecular gas necessary for star formation (2011, background): “There is also now observational evidence for the presence of power-law tails in the density PDFs of active star-forming regions in real molecular clouds (Kainulainen et al. 2009; Lombardi, Lada & Alves 2010; Kainulainen et al. 2011).”
Dispersal of molecular clouds by ionizing radiation (2012, result): “This is in good agreement with recent observational (Kainulainen et al. 2009, 2011; Lombardi et al. 2010) and theoretical (Kritsuk et al. 2011; Girichidis et al. 2012) findings.”
Herschel-Planck dust optical-depth and column-density maps - I. Method description and results for Orion (2014, background): “Although this behavior has been observed in the past, especially in star-forming clouds (Kainulainen et al. 2009), we are now in the position to demonstrate that the power-law regime dominates most ranges of column-densities and generally characterizes the cloud structure above AK ∼ 0.1 mag.”
A census of dense cores in the Aquila cloud complex: SPIRE/PACS observations from the Herschel Gould Belt survey (2015, background): “Similar column density PDFs have already been reported in the literature for other star-forming complexes based on near-infrared extinction data (e.g., Kainulainen et al. 2009) and Herschel observations (e.g., Schneider et al. 2013).”
Star Formation in the Milky Way and Nearby Galaxies (2012, background): “In fact, it is the clouds with the power-law tails that have active star formation (Kainulainen et al. 2009).”
THE STAR FORMATION RATE OF TURBULENT MAGNETIZED CLOUDS: COMPARING THEORY, SIMULATIONS, AND OBSERVATIONS (2012, background): “…VázquezSemadeni et al. 2008; Cho & Kim 2011; Kritsuk et al. 2011a; Ballesteros-Paredes et al. 2011; Collins et al. 2012; Safranek-Shrader et al. 2012), which has been observed in the column density PDFs of clouds that have already formed stars (Kainulainen et al. 2009; Schneider et al. 2012).”
Molecular Clouds in the Milky Way (2015, background): “These simple, single-point statistics are effective tools to distinguish different dynamical components within molecular clouds (Kainulainen et al. 2009; Lada et al. 2010, 2012; Schneider et al. 2011, 2015; Kainulainen & Tan 2013).”
WHAT DETERMINES THE DENSITY STRUCTURE OF MOLECULAR CLOUDS? A CASE STUDY OF ORION B WITH HERSCHEL (2013, methodology): “…et al. (2010)) data provides column density maps that are superior to those obtained from extinction using near-IR data (Lombardi et al. (2006), Kainulainen et al. (2009), Froebrich & Rowles (2010), Schneider et al. (2011)) that have angular resolutions of ≈2′ and suffer from saturation at…”
ON THE STAR FORMATION RATES IN MOLECULAR CLOUDS (2010, background): “Surveys by Kainulainen et al. (2009), Lombardi et al. (2008; 2010) and Froebrich & Rowles (2010) have found that the frequency distribution of extinctions in clouds can be well described by log-normal functions at low extinctions where most (90 - 99”