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We present a fully sampled C^{18}O (1-0) map towards the southern giant molecular cloud (GMC) associated with the HII region RCW 106, and use it in combination with previous ^{13}CO (1-0) mapping to estimate the gas column density as a…

Conjunction assessment requires knowledge of the uncertainty in the predicted orbit. Errors in the atmospheric density are a major source of error in the prediction of low Earth orbits. Therefore, accurate estimation of the density and…

Earth and Planetary Astrophysics · Physics 2020-04-24 David J. Gondelach , Richard Linares

We investigate general aspects of molecular line formation under conditions which are typical of prestellar cores. Focusing on simple linear molecules, we study formation of their rotational lines by radiative transfer simulations. We…

Astrophysics · Physics 2009-11-13 Ya. Pavlyuchenkov , D. Wiebe , B. Shustov , Th. Henning , R. Launhardt , D. Semenov

Much of what we know about molecular clouds, and by extension star formation, comes from molecular line observations. Interpreting these correctly requires knowledge of the underlying molecular abundances. Simulations of molecular clouds…

Astrophysics of Galaxies · Physics 2023-08-02 F. D. Priestley , P. C. Clark , S. C. O. Glover , S. E. Ragan , O. Fehér , L. R. Prole , R. S. Klessen

(abridged) In this work we have a closer look at the gas content or fraction and the associated star formation rate in main sequence and starburst galaxies at z=0 and z~1-2 by applying an analytical model of galactic clumpy gas disks to…

Astrophysics of Galaxies · Physics 2017-06-28 B. Vollmer , P. Gratier , J. Braine , C. Bot

We present a new, approximate method of calculating the column density of ammonia in mapping observations of the 23 GHz inversion lines. The temperature regime typically found in star forming regions allows for the assumption of a slowly…

Instrumentation and Methods for Astrophysics · Physics 2015-06-04 L. K. Morgan , T. J. T. Moore , J. Allsopp , D. J. Eden

We carry out three-dimensional MHD simulations of star formation in turbulent, magnetized clouds, including ambipolar diffusion and feedback from protostellar outflows. The calculations focus on relatively diffuse clouds threaded by a…

Astrophysics · Physics 2009-11-13 Fumitaka Nakamura , Zhi-Yun Li

Due to our vantage point in the disk of the Galaxy, its 3D structure is not directly accessible. However, knowing the spatial distribution, e.g. of atomic and molecular hydrogen gas is of great importance for interpreting and modelling…

Astrophysics of Galaxies · Physics 2023-09-26 Laurin Söding , Philipp Mertsch , Vo Hong Minh Phan

{It is necessary to understand the dynamics of the atomic gas to use complex modeling and to carry out detailed comparisons between theoretical models and observations.}{In a companion paper, we present high resolution bidimensional…

Astrophysics · Physics 2007-05-23 P. Hennebelle , E. Audit , M. -A Miville-Deschenes

Motivated by oceanographic observational datasets, we propose a probabilistic neural network (PNN) model for calculating turbulent energy dissipation rates from vertical columns of velocity and density gradients in density stratified…

We develop a theory for filamentary molecular clouds including the effects of ordered magnetic fields, and external pressure. We first derive a form of the virial equation appropriate for filamentary clouds. By comparing with observational…

Astrophysics · Physics 2007-05-23 Jason D. Fiege , Ralph E. Pudritz

We use a suite of 3D simulations of star-forming molecular clouds, with and without stellar feedback and magnetic fields, to investigate the effectiveness of different fitting methods for volume and column density probability distribution…

Astrophysics of Galaxies · Physics 2023-05-22 Avery Kiihne , Sabrina M. Appel , Blakesley Burkhart , Vadim A. Semenov , Christoph Federrath

We study the formation of giant dense cloud complexes and of stars within them by means of SPH numerical simulations of the mildly supersonic collision of gas streams (``inflows'') in the warm neutral medium (WNM). The resulting…

We develop a new method to constrain the physical conditions in the cool (~10^4 K) circumgalactic medium (CGM) from measurements of ionic column densities, by assuming that the cool CGM spans a large range of gas densities and that small…

Astrophysics of Galaxies · Physics 2016-10-26 Jonathan Stern , Joseph F. Hennawi , J. Xavier Prochaska , Jessica K. Werk

Stars form within molecular clouds but our understanding of this fundamental process remains hampered by the complexity of the physics that drives their evolution. We review our observational and theoretical knowledge of molecular clouds…

Astrophysics of Galaxies · Physics 2015-06-12 Patrick Hennebelle , Edith Falgarone

We investigate the possibility to search for metal-poor high column density (> 10^{23} cm^{-2}) clouds at high redshift (z) by using gamma ray burst (GRB) afterglows. Such clouds could be related to primeval galaxies which may cause a burst…

Astrophysics · Physics 2009-11-11 Hiroyuki Hirashita , Hiroshi Shibai , Tsutomu T. Takeuchi

Emission line profiles of tracer molecule H$_2$CO 140 GHz transition from gravitational core collapsing clouds in the dynamic process of forming protostars are calculated, using a simple ray-tracing radiative transfer model. Three…

Solar and Stellar Astrophysics · Physics 2015-05-13 Yang Gao , Yu-Qing Lou , Kinwah Wu

Molecular hydrogen (H$_2$) formation and dissociation are key processes that drive the gas lifecycle in galaxies. Using the SImulating the LifeCycle of Molecular Clouds (SILCC) zoom-in simulation suite, we explore the utility of future…

Interstellar medium widely exists in the universe at multi-scales. In this study, we introduce the {\it Multi-scale Decomposition Reconstruction} method, an equation-based model designed to derive width maps of interstellar medium…

Astrophysics of Galaxies · Physics 2025-12-23 Mengke Zhao , Guang-Xing Li , Duo Xu , Keping Qiu

The $^{13}$CO molecule is often used as a column density tracer in regions where the $^{12}$CO emission saturates. The $^{13}$CO column density is then related to that of $^{12}$CO by a uniform isotopic ratio. A similar approximation is…

Astrophysics of Galaxies · Physics 2016-04-25 László Szűcs , Simon C. O. Glover , Ralf S. Klessen