The Molecular Cloud Life Cycle. I. Constraining H2 Formation and Dissociation Rates with Observations
Molecular clouds (MCs) are the birthplaces of new stars in galaxies. A key component of MCs are photodissociation regions (PDRs), where far-ultraviolet radiation plays a crucial role in determining the gas’s physical and chemical state. Traditional PDR models assume a chemical steady state (CSS), wh...
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2025-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/adb3a6 |
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| author | Shmuel Bialy Blakesley Burkhart Daniel Seifried Amiel Sternberg Benjamin Godard Mark R. Krumholz Stefanie Walch Erika Hamden Thomas J. Haworth Neal J. Turner Min-Young Lee Shuo Kong |
| author_facet | Shmuel Bialy Blakesley Burkhart Daniel Seifried Amiel Sternberg Benjamin Godard Mark R. Krumholz Stefanie Walch Erika Hamden Thomas J. Haworth Neal J. Turner Min-Young Lee Shuo Kong |
| author_sort | Shmuel Bialy |
| collection | DOAJ |
| description | Molecular clouds (MCs) are the birthplaces of new stars in galaxies. A key component of MCs are photodissociation regions (PDRs), where far-ultraviolet radiation plays a crucial role in determining the gas’s physical and chemical state. Traditional PDR models assume a chemical steady state (CSS), where the rates of H _2 formation and photodissociation are balanced. However, real MCs are dynamic and can be out of CSS. In this study, we demonstrate that combining H _2 emission lines observed in the far-ultraviolet or infrared with column density observations can be used to derive the rates of H _2 formation and photodissociation. We derive analytical formulae that relate these rates to observable quantities, which we validate using synthetic H _2 line emission maps derived from the SILCC-Zoom hydrodynamical simulation. Our method estimates integrated H _2 formation and dissociation rates with an accuracy ≈30% (on top of the uncertainties in the observed H _2 emission maps and column densities). Our simulations, valid for column densities N ≤ 2 × 10 ^22 cm ^−2 , cover a wide dynamic range of H _2 formation and photodissociation rates, showing significant deviations from CSS, with 74% of the MC’s mass deviating from CSS by a factor greater than 2. Our analytical formulae can effectively distinguish between regions in and out of CSS. When applied to actual H _2 line observations, our method can assess the chemical states of MCs, providing insights into their evolutionary stages and lifetimes. A NASA Small Explorer mission concept, Eos, will be proposed in 2025 and is specifically designed to conduct the types of observations outlined in this study. |
| format | Article |
| id | doaj-art-17ac54cdac6d4ab8801ea7f88fbbbe64 |
| institution | DOAJ |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj-art-17ac54cdac6d4ab8801ea7f88fbbbe642025-08-20T02:56:51ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-0198212410.3847/1538-4357/adb3a6The Molecular Cloud Life Cycle. I. Constraining H2 Formation and Dissociation Rates with ObservationsShmuel Bialy0https://orcid.org/0000-0002-0404-003XBlakesley Burkhart1https://orcid.org/0000-0001-5817-5944Daniel Seifried2https://orcid.org/0000-0002-0368-9160Amiel Sternberg3Benjamin Godard4Mark R. Krumholz5https://orcid.org/0000-0003-3893-854XStefanie Walch6https://orcid.org/0000-0001-6941-7638Erika Hamden7https://orcid.org/0000-0002-3131-7372Thomas J. Haworth8https://orcid.org/0000-0002-9593-7618Neal J. Turner9https://orcid.org/0000-0001-8292-1943Min-Young Lee10https://orcid.org/0000-0002-9888-0784Shuo Kong11https://orcid.org/0000-0002-8469-2029Physics Department, Technion—Israel Institute of Technology , Haifa 32000, Israel ; sbialy@technion.ac.ilDepartment of Physics and Astronomy, Rutgers University , 136 Frelinghuysen Rd, Piscataway, NJ 08854, USA; Center for Computational Astrophysics, Flatiron Institute , 162 Fifth Avenue, New York, NY 10010, USAI. Physics Institute, University of Cologne , Zülpicher Str. 77, 50937 Cologne, Germany; Center for Data and Simulation Science , 50937 Cologne, Germany 14Center for Computational Astrophysics, Flatiron Institute , 162 Fifth Avenue, New York, NY 10010, USA; Tel Aviv University , P.O. Box 39040, Tel Aviv 6997801, IsraelObservatoire de Paris, Universite PSL , Sorbonne Universite, LERMA, 75014 Paris, France; Laboratoire de Physique de l’Ecole Normale Superieure, ENS, Universite PSL , CNRS, Sorbonne Universite, Universite de Paris, F-75005 Paris, FranceResearch School of Astronomy and Astrophysics, Australian National University , Canberra ACT 2600, AustraliaI. Physics Institute, University of Cologne , Zülpicher Str. 77, 50937 Cologne, Germany; Center for Data and Simulation Science , 50937 Cologne, Germany 14Steward Observatory, University of Arizona , Tucson, AZ 85719, USAAstronomy Unit, School of Physics and Astronomy, Queen Mary University of London , London, E1 4NS, UKJet Propulsion Laboratory, California Institute of Technology , Pasadena, CA 91109, USAKorea Astronomy and Space Science Institute , 776 Daedeok-daero, Daejeon 34055, Republic of KoreaSteward Observatory, University of Arizona , Tucson, AZ 85719, USAMolecular clouds (MCs) are the birthplaces of new stars in galaxies. A key component of MCs are photodissociation regions (PDRs), where far-ultraviolet radiation plays a crucial role in determining the gas’s physical and chemical state. Traditional PDR models assume a chemical steady state (CSS), where the rates of H _2 formation and photodissociation are balanced. However, real MCs are dynamic and can be out of CSS. In this study, we demonstrate that combining H _2 emission lines observed in the far-ultraviolet or infrared with column density observations can be used to derive the rates of H _2 formation and photodissociation. We derive analytical formulae that relate these rates to observable quantities, which we validate using synthetic H _2 line emission maps derived from the SILCC-Zoom hydrodynamical simulation. Our method estimates integrated H _2 formation and dissociation rates with an accuracy ≈30% (on top of the uncertainties in the observed H _2 emission maps and column densities). Our simulations, valid for column densities N ≤ 2 × 10 ^22 cm ^−2 , cover a wide dynamic range of H _2 formation and photodissociation rates, showing significant deviations from CSS, with 74% of the MC’s mass deviating from CSS by a factor greater than 2. Our analytical formulae can effectively distinguish between regions in and out of CSS. When applied to actual H _2 line observations, our method can assess the chemical states of MCs, providing insights into their evolutionary stages and lifetimes. A NASA Small Explorer mission concept, Eos, will be proposed in 2025 and is specifically designed to conduct the types of observations outlined in this study.https://doi.org/10.3847/1538-4357/adb3a6Interstellar mediumMolecular cloudsUltraviolet spectroscopyMolecular gasAstrochemistryStar formation |
| spellingShingle | Shmuel Bialy Blakesley Burkhart Daniel Seifried Amiel Sternberg Benjamin Godard Mark R. Krumholz Stefanie Walch Erika Hamden Thomas J. Haworth Neal J. Turner Min-Young Lee Shuo Kong The Molecular Cloud Life Cycle. I. Constraining H2 Formation and Dissociation Rates with Observations The Astrophysical Journal Interstellar medium Molecular clouds Ultraviolet spectroscopy Molecular gas Astrochemistry Star formation |
| title | The Molecular Cloud Life Cycle. I. Constraining H2 Formation and Dissociation Rates with Observations |
| title_full | The Molecular Cloud Life Cycle. I. Constraining H2 Formation and Dissociation Rates with Observations |
| title_fullStr | The Molecular Cloud Life Cycle. I. Constraining H2 Formation and Dissociation Rates with Observations |
| title_full_unstemmed | The Molecular Cloud Life Cycle. I. Constraining H2 Formation and Dissociation Rates with Observations |
| title_short | The Molecular Cloud Life Cycle. I. Constraining H2 Formation and Dissociation Rates with Observations |
| title_sort | molecular cloud life cycle i constraining h2 formation and dissociation rates with observations |
| topic | Interstellar medium Molecular clouds Ultraviolet spectroscopy Molecular gas Astrochemistry Star formation |
| url | https://doi.org/10.3847/1538-4357/adb3a6 |
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