HI-to-H2 Transitions in the Perseus Molecular Cloud

Abstract

We use the Sternberg et al. (2014) theory for interstellar atomic to molecular (HI-to-H${}_2$) conversion to analyze HI-to-H${}_2$ transitions in five (low-mass) star-forming and dark regions in the Perseus molecular cloud, B1, B1E, B5, IC348, and NGC1333. The observed HI mass surface densities of 6.3 to 9.2 M${}_{\odot }$ pc${}^{-2}$ are consistent with HI-to-H${}_2$ transitions dominated by HI-dust shielding in predominantly atomic envelopes. For each source, we constrain the dimensionless parameter $\alpha G$, and the ratio $I_{\mathrm{UV}}/n$, of the FUV intensity to hydrogen gas density. We find $\alpha G$ values from 5.0 to 26.1, implying characteristic atomic hydrogen densities 11.8 to 1.8 cm${}^{-3}$, for $I_{\mathrm{UV}}\approx 1$ appropriate for Perseus. Our analysis implies that the dusty HI shielding layers are probably multiphased, with thermally unstable UNM gas in addition to cold CNM within the 21 cm kinematic radius.

5 pages, 2 Figures. Minor improvements suggested by the referee. Accepted for publication in the Astrophysical Journal

References in corpus (5)

• The Atomic to Molecular Transition in Galaxies. II: HI and H_2 Column Densities
• The COMPLETE Survey of Star-Forming Regions: Phase I Data
• The Large and Small Scale Structures of Dust in the Star-Forming Perseus Molecular Cloud
• HI-to-H2 Transitions and H I Column Densities in Galaxy Star-Forming Regions
• Cold and Warm Atomic Gas around the Perseus Molecular Cloud. II. The Impact of High Optical Depth on the HI Column Density Distribution and Its Implication for the HI-to-H2 Transition

Cited by in corpus (25)

• A Simple and Accurate Network for Hydrogen and Carbon Chemistry in the ISM
• On the Three-Dimensional Structure of Local Molecular Clouds
• Analytic HI-to-H2 Photodissociation Transition Profiles
• Discovery of a Perseus-like cloud in the early Universe: HI-to-H2 transition, carbon monoxide and small dust grains at zabs=2.53 towards the quasar J0000+0048
• The HI-to-H2 Transition in a Turbulent Medium
• The Razor's Edge of Collapse: The Transition Point from Lognormal to Powerlaw in Molecular Cloud PDFs
• The Lognormal Probability Distribution Function of the Perseus Molecular Cloud: A Comparison of HI and Dust
• GASKAP-HI Pilot Survey Science I: ASKAP Zoom Observations of HI Emission in the Small Magellanic Cloud
• Molecular gas and star formation in an absorption-selected galaxy: Hitting the bull's eye at z = 2.46
• HI-to-H2 Transition Layers in the Star-Forming Region W43
• Chemical Abundances in a Turbulent Medium -- H${}_2$, OH${}^{+}$, H${}_2$O${}^{+}$, ArH${}^{+}$
• The Galactic Census of High- and Medium-mass Protostars. IV. Molecular Clump Radiative Transfer, Mass Distributions, Kinematics, and Dynamical Evolution
• How chemistry influences cloud structure, star formation, and the IMF
• Proximate Molecular Quasar Absorbers: Excess of damped H2 systems at zabs~zQSO in SDSS DR14
• Simulating the atomic and molecular content of molecular clouds using probability distributions of physical parameters
• The Metallicity Dependence of the HI Shielding Layers in Nearby Galaxies
• The role of neutral hydrogen in setting the abundances of molecular species in the Milky Way's diffuse interstellar medium. I. Observational constraints from ALMA and NOEMA
• Study Turbulence and Probe Magnetic Field Using Gradients Technique: Application to HI-to-H2 Transition Regions
• The Catalogue for Astrophysical Turbulence Simulations (CATS)
• Dynamical effects of the radiative stellar feedback on the H I-to-H2 transition
• Metallicity dependence of the CO-to-H${}_2$ and the [CI]-to-H${}_2$ conversion factors in galaxies
• Exploring the interplay of dust and gas phases in DustPedia star-forming galaxies
• A High Resolution Study of Carbon Radio Recombination Lines towards Cassiopeia A
• Herschel 158$\mu$m [CII] Observations of "CO-dark" Gas in the Perseus Giant Molecular Cloud
• HI-to-H2 transitions in the Perseus Molecular Cloud