Applying a one-dimensional PDR model to the Taurus molecular cloud and its atomic envelope

Heiner, J. S.; Vázquez‐Semadeni, Enrique

doi:10.1093/mnras/sts645

Cited by 10 publications

(8 citation statements)

References 65 publications

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“…This means that, while the HISA strength maps do not corre- Figure 11. Left column: HISA strength maps at the three timesteps we study (with time increasing from top to bottom), where the HISA strength is defined as the maximum difference between values of the second derivative of the brightness temperature profile as in Heiner & Vázquez-Semadeni (2013). Middle column: the HISA mask, or 'real HISA', defined as the set of pixels in a projection of the simulation where local minima in the Hi line profile coincide with peaks in the optical depth.…”

Section: Strength Of the Hisa Features Compared To The 'Real' Hisamentioning

confidence: 99%

Molecular cloud formation as seen in synthetic H i and molecular gas observations

Heiner¹,

Vázquez‐Semadeni²,

Ballesteros-Paredes³

2015

Mon. Not. R. Astron. Soc.

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We present synthetic Hi and CO observations of a numerical simulation of decaying turbulence in the thermally bistable neutral medium. We first present the simulation, which produces a clumpy medium, with clouds initially consisting of clustered clumps. Self-gravity causes these clump clusters to merge and form more homogeneous dense clouds. We apply a simple radiative transfer algorithm, throwing rays in many directions from each cell, and defining every cell with A v > 1 as molecular. We then produce maps of Hi, CO-free molecular gas, and CO, and investigate the following aspects: i) The spatial distribution of the warm, cold, and molecular gas, finding the well-known layered structure, with molecular gas being surrounded by cold Hi and this in turn being surrounded by warm Hi. ii) The velocity of the various components, finding that the atomic gas is generally flowing towards the molecular gas, and that this motion is reflected in the frequently observed bimodal shape of the Hi profiles. This conclusion is, however, tentative, because we do not include feedback that may produce Hi gas receding from molecular regions. iii) The production of Hi self-absorption (HISA) profiles, and the correlation of HISA with molecular gas. In particular, we test the suggestion of using the second derivative of the brightness temperature Hi profile to trace HISA and molecular gas, finding significant limitations. On a scale of several parsecs, some agreement is obtained between this technique and actual HISA, as well as a correlation between HISA and the molecular gas column density. This correlation, however, quickly deteriorates towards sub-parsec scales. iv) The column density PDFs of the actual Hi gas and those recovered from the Hi line profiles, finding that the latter have a cutoff at column densities where the gas becomes optically thick, thus missing the contribution from the HISA-producing gas. We also find that the powerlaw tail typical of gravitational contraction is only observed in the molecular gas, and that, before the power-law tail develops in the total gas density PDF, no CO is yet present, reinforcing the notion that gravitational contraction is needed to produce this component.

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Section: Strength Of the Hisa Features Compared To The 'Real' Hisamentioning

confidence: 99%

Molecular cloud formation as seen in synthetic H i and molecular gas observations

Heiner¹,

Vázquez‐Semadeni²,

Ballesteros-Paredes³

2015

Mon. Not. R. Astron. Soc.

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“…3) We compute illustrative mass loss rates for the Guilloteau et al (2011) disc parameters in Taurus, finding that around half of those discs are expected to be undergoing significant photoevaporation in a 10 G 0 field (the field strength argued for in Taurus by Heiner & Vázquez-Semadeni 2013). These estimates are based on dust disc radii which, since the gas is more extended, make the mass loss rate estimates conservative.…”

Section: Discussionmentioning

confidence: 99%

The FRIED grid of mass-loss rates for externally irradiated protoplanetary discs

Haworth

Clarke

Rahman

et al. 2018

Monthly Notices of the Royal Astronomical Society

118

172

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We present an open access grid of 3930 calculations of externally evaporating protoplanetary discs. This spans a range of disc sizes (1-400 AU), disc masses, UV field strengths (10-10 4 G 0 ) and stellar masses (0.05-1.9 M ). The grid is publicly available for download, and offers a means of cheaply including external photoevaporation in disc evolutionary calculations. It can also be queried using an online tool for quick estimates of instantaneous mass loss rates (e.g for convenient evaluation of real observed systems). fried itself illustrates that for discs around stars ≤ 0.3 M external photoevaporation is effective down to small radii (< 50 AU) down to UV fields at least as weak as 10 G 0 . At the other end of the scale, in a 10 4 G 0 environment photoevaporation is effective down to 1 AU even for stellar masses at least as high as 1.9 M . We also illustrate in which regimes CO survives in the photoevaporative outflow for significant mass loss rates; marking a system a good candidate to detect external photoevaporation in weak-intermediate UV environments through sub-Keplerian rotation. Finally we make illustrative mass loss rate estimates for discs in Taurus based on the Guilloteau et al. (2011) star-disc parameters, finding that around half are expected to have both significant mass loss and retain CO in the photoevaporative outflow.

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“…As we discuss in Section 4.1, observations show that GMCs are ubiquitously surrounded by extended envelopes of atomic gas (see e.g. Wannier et al, 1983;Elmegreen & Elmegreen, 1987;Lee et al, 2012;Heiner & Vázquez-Semadeni, 2013;Motte et al, 2014) and so the observational "edge" of a GMC -the point at which we cease to be able to detect CO emission -more likely represents a chemical transition in the gas (see Section 5.1), rather than any sudden change in the density. In addition, a considerable fraction of the molecular gas of a galaxy seems to be in an extended diffuse component, rather than in discrete clouds (see e.g.…”

Section: Molecular Cloud Formation In a Galactic Contextmentioning

confidence: 97%

Physical Processes in the Interstellar Medium

Klessen

Glover

2015

Star Formation in Galaxy Evolution: Connecting Numerical Models to Reality

160

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Interstellar space is filled with a dilute mixture of charged particles, atoms, molecules and dust grains, called the interstellar medium (ISM). Understanding its physical properties and dynamical behavior is of pivotal importance to many areas of astronomy and astrophysics. Galaxy formation and evolution, the formation of stars, cosmic nucleosynthesis, the origin of large complex, prebiotic molecules and the abundance, structure and growth of dust grains which constitute the fundamental building blocks of planets, all these processes are intimately coupled to the physics of the interstellar medium. However, despite its importance, its structure and evolution is still not fully understood. Observations reveal that the interstellar medium is highly turbulent, consists of different chemical phases, and is characterized by complex structure on all resolvable spatial and temporal scales. Our current numerical and theoretical models describe it as a strongly coupled system that is far from equilibrium and where the different components are intricately linked together by complex feedback loops. Describing the interstellar medium is truly a multi-scale and multi-physics problem. In these lecture notes we introduce the microphysics necessary to better understand the interstellar medium. We review the relations between large-scale and small-scale dynamics, we consider turbulence as one of the key drivers of galactic evolution, and we review the physical processes that lead to the formation of dense molecular clouds and that govern stellar birth in their interior.

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Applying a one-dimensional PDR model to the Taurus molecular cloud and its atomic envelope

Cited by 10 publications

References 65 publications

Molecular cloud formation as seen in synthetic H i and molecular gas observations

Molecular cloud formation as seen in synthetic H i and molecular gas observations

The FRIED grid of mass-loss rates for externally irradiated protoplanetary discs

Physical Processes in the Interstellar Medium

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