HyGAL: Characterizing the Galactic Interstellar Medium with Observations of Hydrides and Other Small Molecules. I. Survey Description and a First Look Toward W3(OH), W3 IRS5, and NGC 7538 IRS1
Year: 2022
Type: article
Abstract: The HyGAL Stratospheric Observatory for Infrared Astronomy legacy program surveys six hydride molecules—ArH+, OH+, H2O+, SH, OH, and CH—and two atomic constituents—C+ and O—within the diffuse interstellar medium (ISM) by means of absorption-line spectroscopy toward 25 bright Galactic background continuum sources. This detailed spectroscopic study is designed to exploit the unique value of specific hydrides as tracers and probes of different phases of the ISM, as demonstrated by recent studies with the Herschel Space Observatory. The observations performed under the HyGAL program will allow us to address several questions related to the life cycle of molecular material in the ISM and the physical processes that impact the phase transition from atomic to molecular gas, such as: (1) What is the distribution function of the H2 fraction in the ISM? (2) How does the ionization rate due to low-energy cosmic rays vary within the Galaxy? (3) What is the nature of interstellar turbulence (e.g., typical shear or shock velocities), and what mechanisms lead to its dissipation? In this overview, we discuss the observing strategy, the synergies with ancillary and archival observations of other small molecules, and the data reduction and analysis schemes we adopted; and we present the first results obtained toward three of the survey targets, W3(OH), W3 IRS5, and NGC 7538 IRS1. Robust measurements of the column densities of these hydrides—obtained through widespread observations of absorption lines—help address the questions raised, and there is a very timely synergy between these observations and the development of theoretical models, particularly pertaining to the formation of H2 within the turbulent ISM. The provision of enhanced HyGAL data products will therefore serve as a legacy for future ISM studies.
Source: The Astrophysical Journal
Authors: A. M. Jacob, D. A. Neufeld, P. Schilke, H. Wiesemeyer, W.-J. Kim, S. Bialy, M. Busch, D. Elia, E. Falgarone, M. Gerin, B. Godard, R. Higgins, P. Hennebelle, N. Indriolo, D. C. Lis, K. M. Menten, A. Sanchez-Monge, T. Möller, V. Ossenkopf-Okada, M. R. Rugel, D. Seifried, P. Sonnentrucker, S. Walch, M. G. Wolfire, F. Wyrowski, V. Valdivia
Institutions: Johns Hopkins University, Max Planck Institute for Radio Astronomy, University of Cologne, University of Maryland, College Park, Institute for Space Astrophysics and Planetology, National Institute for Astrophysics, Centre National de la Recherche Scientifique, Université Paris Cité, Université Paris Sciences et Lettres, École Normale Supérieure - PSL, Sorbonne Université, Laboratoire de Physique de l'Ecole Normale Supérieure, Observatoire de Paris, Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Université Paris-Saclay, Astrophysique, Instrumentation et Modélisation, Sorbonne Paris Cité, Université Paris Diderot, Space Telescope Science Institute, Jet Propulsion Laboratory, European Space Agency, CEA Paris-Saclay - Etablissement de Saclay, Nagoya University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
OpenAlex ID: W4221151114