Dynamical effects of the radiative stellar feedback on the H I-to-H2 transition

Abstract

The atomic-to-molecular hydrogen (H/H2) transition has been extensively studied as it controls the fraction of gas in a molecular state in an interstellar cloud. This fraction is linked to star-formation by the Schmidt-Kennicutt law. While theoretical estimates of the column density of the H I layer have been proposed for static photodissociation regions (PDRs), Herschel and well-resolved ALMA (Atacama Large Millimeter Array) observations have revealed dynamical effects in star forming regions, caused by the process of photoevaporation. We extend the analytic study of the H/H2 transition to include the effects of the propagation of the ionization front, in particular in the presence of photoevaporation at the walls of blister H II regions, and we find its consequences on the total atomic hydrogen column density at the surface of clouds in the presence of an ultraviolet field, and on the properties of the H/H2 transition. We solved semi-analytically the differential equation giving the H2 column density profile by taking into account H2 formation on grains, H2 photodissociation, and the ionization front propagation dynamics modeled as advection of the gas through the ionization front. Taking this advection into account reduces the width of the atomic region compared to static models. The atomic region may disappear if the ionization front velocity exceeds a certain value, leading the H/H2 transition and the ionization front to merge. For both dissociated and merged configurations, we provide analytical expressions to determine the total H I column density. Our results take the metallicity into account. Finally, we compared our results to observations of PDRs illuminated by O-stars, for which we conclude that the dynamical effects are strong, especially for low-excitation PDRs.

Accepted by Astronomy & Astrophysics on September, 11th 2021. 18 pages, 16 figures

References in corpus (24)

• Dust Masses, PAH Abundances, and Starlight Intensities in the SINGS Galaxy Sample
• The Atomic to Molecular Transition in Galaxies. II: HI and H_2 Column Densities
• The VLA Galactic Plane Survey
• The Dynamics of Radiation Pressure-Dominated HII Regions
• HI-to-H2 Transitions and H I Column Densities in Galaxy Star-Forming Regions
• The Atomic to Molecular Transition in Galaxies. I: An Analytic Approximation for Photodissociation Fronts in Finite Clouds
• Compression and ablation of the photo-irradiated cloud the Orion Bar
• Dust and Gas in the Magellanic Clouds from the HERITAGE Herschel Key Project. II. Gas-to-Dust Ratio Variations across ISM Phases
• Evolution of the dust-to-metals ratio in high-redshift galaxies probed by GRB-DLAs
• Physical Properties of Molecular Clouds at 2 parsec Resolution in the Low-Metallicity Dwarf Galaxy NGC 6822 and the Milky Way
• The penetration of FUV radiation into molecular clouds
• Cold and warm atomic gas around the Perseus molecular cloud I: Basic Properties
• Aromatic emission from the ionised mane of the Horsehead nebula
• Three-Dimensional Dynamical Instabilities in Galactic Ionization Fronts
• The Orion HII Region and the Orion Bar in the Mid-Infrared
• On the (in)variance of the dust-to-metals ratio in galaxies
• VALES: I. The molecular gas content in star-forming dusty H-ATLAS galaxies up to z=0.35
• HI-to-H2 Transition Layers in the Star-Forming Region W43
• Dynamical cloud formation traced by atomic and molecular gas
• Resolving the Dust-to-Metals Ratio and CO-to-H${}_2$ Conversion Factor in the Nearby Universe
• Proximate Molecular Quasar Absorbers: Excess of damped H2 systems at zabs~zQSO in SDSS DR14
• HI-to-H${}_2$ Transitions in Dust-Free Interstellar Gas
• Herschel PACS and SPIRE spectroscopy of the Photodissociation Regions associated with S 106 and IRAS 23133+6050
• HD/H${}_2$ ratio in the diffuse interstellar medium

Cited by in corpus (12)

• High angular resolution near-IR view of the Orion Bar revealed by Keck/NIRC2
• The KOSMA-$\tau$ PDR Model -- I. Recent updates to the numerical model of photo-dissociated regions
• Interpreting molecular hydrogen and atomic oxygen line emission of T Tauri disks with photoevaporative disk-wind models
• The extremely sharp transition between molecular and ionized gas in the Horsehead nebula
• PDRs4All. XII. FUV-driven formation of hydrocarbon radicals and their relation with PAHs
• JWST observations of the Horsehead photon-dominated region I. First results from multi-band near- and mid-infrared imaging
• Multiline observations of hydrogen, helium, and carbon radio-recombination lines toward Orion A: A detailed dynamical study and direct determination of physical conditions
• High Resolution Observations of HI in the IC 63 Reflection Nebula
• Multi-line Observations, Models, and Data Needed to Understand the Nature of UV-irradiated Interstellar Matter
• H3+ in irradiated protoplanetary disks: Linking far-ultraviolet radiation and water vapor
• PDRs4All XVIII. JWST-NIRCam Photometric properties of protoplanetary disks in the Orion Nebula Cluster
• Spatial distribution of organics in the Horsehead nebula: Signposts of chemistry driven by atomic carbon