Probing the Conditions for the H i-to-H2 Transition in the Interstellar Medium
We investigate the conditions for the H i -to-H _2 transition in the solar neighborhood by analyzing H i emission and absorption measurements toward 58 Galactic lines of sight (LOSs) along with ^12 CO(1–0) (CO) and dust data. Based on the accurate column densities of the cold and warm neutral medium...
| Main Authors: | , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/ace164 |
| _version_ | 1797672364893274112 |
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| author | Gyueun Park Min-Young Lee Shmuel Bialy Blakesley Burkhart J. R. Dawson Carl Heiles Di Li Claire Murray Hiep Nguyen Anita Hafner Daniel R. Rybarczyk Snežana Stanimirović |
| author_facet | Gyueun Park Min-Young Lee Shmuel Bialy Blakesley Burkhart J. R. Dawson Carl Heiles Di Li Claire Murray Hiep Nguyen Anita Hafner Daniel R. Rybarczyk Snežana Stanimirović |
| author_sort | Gyueun Park |
| collection | DOAJ |
| description | We investigate the conditions for the H i -to-H _2 transition in the solar neighborhood by analyzing H i emission and absorption measurements toward 58 Galactic lines of sight (LOSs) along with ^12 CO(1–0) (CO) and dust data. Based on the accurate column densities of the cold and warm neutral medium (CNM and WNM), we first perform a decomposition of gas into atomic and molecular phases, and show that the observed LOSs are mostly H i -dominated. In addition, we find that the CO-dark H _2 , not the optically thick H i , is a major ingredient of the dark gas in the solar neighborhood. To examine the conditions for the formation of CO-bright molecular gas, we analyze the kinematic association between H i and CO, and find that the CNM is kinematically more closely associated with CO than the WNM. When CNM components within CO line widths are isolated, we find the following characteristics: spin temperature < 200 K, peak optical depth > 0.1, CNM fraction of ∼0.6, and V -band dust extinction > 0.5 mag. These results suggest that CO-bright molecular gas preferentially forms in environments with high column densities where the CNM becomes colder and more abundant. Finally, we confront the observed CNM properties with the steady-state H _2 formation model of Sternberg et al. and infer that the CNM must be clumpy with a small volume filling factor. Another possibility would be that missing processes in the model, such as cosmic-rays and gas dynamics, play an important role in the H i -to-H _2 transition. |
| first_indexed | 2024-03-11T21:28:59Z |
| format | Article |
| id | doaj.art-8a311c1fd3d64bea81dc8af932ad021b |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-11T21:28:59Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-8a311c1fd3d64bea81dc8af932ad021b2023-09-27T13:55:28ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-01955214510.3847/1538-4357/ace164Probing the Conditions for the H i-to-H2 Transition in the Interstellar MediumGyueun Park0https://orcid.org/0000-0002-7374-7864Min-Young Lee1https://orcid.org/0000-0002-9888-0784Shmuel Bialy2https://orcid.org/0000-0002-0404-003XBlakesley Burkhart3https://orcid.org/0000-0001-5817-5944J. R. Dawson4https://orcid.org/0000-0003-0235-3347Carl Heiles5https://orcid.org/0000-0002-7456-8067Di Li6https://orcid.org/0000-0003-3010-7661Claire Murray7https://orcid.org/0000-0002-7743-8129Hiep Nguyen8https://orcid.org/0000-0002-2712-4156Anita Hafner9https://orcid.org/0000-0001-6179-0606Daniel R. Rybarczyk10https://orcid.org/0000-0003-3351-6831Snežana Stanimirović11https://orcid.org/0000-0002-3418-7817Korea Astronomy and Space Science Institute , 776 Daedeok-daero, Daejeon 34055, Republic of Korea ; mlee@kasi.re.kr; Department of Astronomy and Space Science, University of Science and Technology , 217 Gajeong-ro, Daejeon 34113, Republic of KoreaKorea Astronomy and Space Science Institute , 776 Daedeok-daero, Daejeon 34055, Republic of Korea ; mlee@kasi.re.kr; Department of Astronomy and Space Science, University of Science and Technology , 217 Gajeong-ro, Daejeon 34113, Republic of KoreaDepartment of Physics, Technion—Israel Institute of Technology , Haifa, 3200003, IsraelDepartment of Physics and Astronomy, Rutgers University , Piscataway, NJ 08854, USA; Center for Computational Astrophysics, Flatiron Institute , 162 Fifth Avenue, New York, NY 10010, USASchool of Mathematical and Physical Sciences and Macquarie University Astrophysics and Space Technologies Research Centre, Macquarie University , NSW 2109, Australia; Australia Telescope National Facility , CSIRO Space & Astronomy, PO Box 76, Epping, NSW 1710, AustraliaDepartment of Astronomy, University of California , Berkeley, CA 94720, USANational Astronomical Observatories, Chinese Academy of Sciences , Beijing 100101, People's Republic of China; NAOC-UKZN Computational Astrophysics Centre, University of KwaZulu-Natal , Durban 4000, South Africa; Research Center for Intelligent Computing , Zhejiang Laboratory, Hangzhou 311100, People's Republic of ChinaSpace Telescope Science Institute , 3700 San Martin Drive, Baltimore, MD 21218, USA; Department of Physics & Astronomy, Johns Hopkins University , MD 21218, USAResearch School of Astronomy and Astrophysics, The Australian National University , Canberra, ACT 2611, AustraliaAustralia Telescope National Facility , CSIRO Space & Astronomy, PO Box 76, Epping, NSW 1710, AustraliaDepartment of Astronomy, University of Wisconsin , Madison, WI 53706-15821, USADepartment of Astronomy, University of Wisconsin , Madison, WI 53706-15821, USAWe investigate the conditions for the H i -to-H _2 transition in the solar neighborhood by analyzing H i emission and absorption measurements toward 58 Galactic lines of sight (LOSs) along with ^12 CO(1–0) (CO) and dust data. Based on the accurate column densities of the cold and warm neutral medium (CNM and WNM), we first perform a decomposition of gas into atomic and molecular phases, and show that the observed LOSs are mostly H i -dominated. In addition, we find that the CO-dark H _2 , not the optically thick H i , is a major ingredient of the dark gas in the solar neighborhood. To examine the conditions for the formation of CO-bright molecular gas, we analyze the kinematic association between H i and CO, and find that the CNM is kinematically more closely associated with CO than the WNM. When CNM components within CO line widths are isolated, we find the following characteristics: spin temperature < 200 K, peak optical depth > 0.1, CNM fraction of ∼0.6, and V -band dust extinction > 0.5 mag. These results suggest that CO-bright molecular gas preferentially forms in environments with high column densities where the CNM becomes colder and more abundant. Finally, we confront the observed CNM properties with the steady-state H _2 formation model of Sternberg et al. and infer that the CNM must be clumpy with a small volume filling factor. Another possibility would be that missing processes in the model, such as cosmic-rays and gas dynamics, play an important role in the H i -to-H _2 transition.https://doi.org/10.3847/1538-4357/ace164Interstellar atomic gasMolecular cloudsInterstellar dust extinctionInterstellar moleculesInterstellar mediumRadio astronomy |
| spellingShingle | Gyueun Park Min-Young Lee Shmuel Bialy Blakesley Burkhart J. R. Dawson Carl Heiles Di Li Claire Murray Hiep Nguyen Anita Hafner Daniel R. Rybarczyk Snežana Stanimirović Probing the Conditions for the H i-to-H2 Transition in the Interstellar Medium The Astrophysical Journal Interstellar atomic gas Molecular clouds Interstellar dust extinction Interstellar molecules Interstellar medium Radio astronomy |
| title | Probing the Conditions for the H i-to-H2 Transition in the Interstellar Medium |
| title_full | Probing the Conditions for the H i-to-H2 Transition in the Interstellar Medium |
| title_fullStr | Probing the Conditions for the H i-to-H2 Transition in the Interstellar Medium |
| title_full_unstemmed | Probing the Conditions for the H i-to-H2 Transition in the Interstellar Medium |
| title_short | Probing the Conditions for the H i-to-H2 Transition in the Interstellar Medium |
| title_sort | probing the conditions for the h i to h2 transition in the interstellar medium |
| topic | Interstellar atomic gas Molecular clouds Interstellar dust extinction Interstellar molecules Interstellar medium Radio astronomy |
| url | https://doi.org/10.3847/1538-4357/ace164 |
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