A Reexamination of Phosphorus and Chlorine Depletions in the Diffuse Interstellar Medium

By Keith Cowing
Status Report
January 25, 2023
Filed under , , , , ,
A Reexamination of Phosphorus and Chlorine Depletions in the Diffuse Interstellar Medium
High-resolution STIS spectra in the vicinity of the P ii λ1532 and λ1301 lines toward HD 24534 (left panels) and HD 90087 (right panels). Upper panels show the unnormalized spectra with dashed lines indicating the adopted continuum fits. Lower panels show the normalized spectra with solid red lines representing fits to the P ii absorption profiles. — astro-ph.GA

We present a comprehensive examination of interstellar P and Cl abundances based on an analysis of archival spectra acquired with the Space Telescope Imaging Spectrograph of the Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer.

Column densities of P II, Cl I, and Cl II are determined for a combined sample of 107 sight lines probing diffuse atomic and molecular gas in the local Galactic interstellar medium (ISM). We reevaluate the nearly linear relationship between the column densities of Cl I and H2, which arises from the rapid conversion of Cl+ to Cl0 in regions where H2 is abundant. Using the observed total gas-phase P and Cl abundances, we derive depletion parameters for these elements, adopting the methodology of Jenkins.

We find that both P and Cl are essentially undepleted along sight lines showing the lowest overall depletions. Increasingly severe depletions of P are seen along molecule-rich sight lines.

In contrast, gas-phase Cl abundances show no systematic variation with molecular hydrogen fraction. However, enhanced Cl (and P) depletion rates are found for a subset of sight lines showing elevated levels of Cl ionization.

An analysis of neutral chlorine fractions yields estimates for the amount of atomic hydrogen associated with the H2-bearing gas in each direction. These results indicate that the molecular fraction in the H2-bearing gas is at least 10% for all sight lines with logN(H2)≳18 and that the gas is essentially fully molecular at logN(H2)≈21.

Adam M. Ritchey (Eureka Scientific), J. M. Brown (Univ. of Toledo), S. R. Federman (Univ. of Toledo), Paule Sonnentrucker (Space Telescope Science Institute)

Comments: 43 pages, 21 figures, submitted to ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2301.09727 [astro-ph.GA] (or arXiv:2301.09727v1 [astro-ph.GA] for this version)
Submission history
From: Adam Ritchey
[v1] Mon, 23 Jan 2023 21:34:22 UTC (436 KB)
Astrobiology, Astrochemistry

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻