Evidence of a Cloud–Cloud Collision from Overshooting Gas in the Galactic Center
The Milky Way is a barred spiral galaxy with bar lanes that bring gas toward the Galactic center. Gas flowing along these bar lanes often overshoots, and instead of accreting onto the Central Molecular Zone (CMZ), it collides with the bar lane on the opposite side of the Galaxy. We observed G5, a cl...
| 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/ad01be |
| _version_ | 1797397076096581632 |
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| author | Savannah R. Gramze Adam Ginsburg David S. Meier Juergen Ott Yancy Shirley Mattia C. Sormani Brian E. Svoboda |
| author_facet | Savannah R. Gramze Adam Ginsburg David S. Meier Juergen Ott Yancy Shirley Mattia C. Sormani Brian E. Svoboda |
| author_sort | Savannah R. Gramze |
| collection | DOAJ |
| description | The Milky Way is a barred spiral galaxy with bar lanes that bring gas toward the Galactic center. Gas flowing along these bar lanes often overshoots, and instead of accreting onto the Central Molecular Zone (CMZ), it collides with the bar lane on the opposite side of the Galaxy. We observed G5, a cloud that we believe is the site of one such collision, near the Galactic center at ( ℓ , b ) = ( +5.4, −0.4) with the Atacama Large Millimeter/submillimeter Array/Atacama Compact Array. We took measurements of the spectral lines ^12 CO J = 2 → 1, ^13 CO J = 2 → 1, C ^18 O J = 2 → 1, H _2 CO J = 3 _03 → 2 _02 , H _2 CO J = 3 _22 → 2 _21 , CH _3 OH J = 4 _22 → 3 _12 , OCS J = 18 → 17, and SiO J = 5 → 4. We observed a velocity bridge between two clouds at ∼50 and ∼150 km s ^−1 in our position–velocity diagram, which is direct evidence of a cloud–cloud collision. We measured an average gas temperature of ∼60 K in G5 using H _2 CO integrated-intensity line ratios. We observed that the ^12 C/ ^13 C ratio in G5 is consistent with optically thin, or at most marginally optically thick ^12 CO. We measured $1.5\times {10}^{19}\,{\mathrm{cm}}^{-2}\,{({\rm{K}}\,\mathrm{km}\,{{\rm{s}}}^{-1})}^{-1}$ for the local X _CO , 10–20× less than the average Galactic value. G5 is strong direct observational evidence of gas overshooting the CMZ and colliding with a bar lane on the opposite side of the Galactic center. |
| first_indexed | 2024-03-09T01:04:47Z |
| format | Article |
| id | doaj.art-786d0b96efc14c1296467e42eccc1383 |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-09T01:04:47Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-786d0b96efc14c1296467e42eccc13832023-12-11T11:39:11ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-0195929310.3847/1538-4357/ad01beEvidence of a Cloud–Cloud Collision from Overshooting Gas in the Galactic CenterSavannah R. Gramze0https://orcid.org/0000-0002-1313-429XAdam Ginsburg1https://orcid.org/0000-0001-6431-9633David S. Meier2https://orcid.org/0000-0001-9436-9471Juergen Ott3https://orcid.org/0000-0001-8224-1956Yancy Shirley4https://orcid.org/0000-0002-0133-8973Mattia C. Sormani5https://orcid.org/0000-0001-6113-6241Brian E. Svoboda6https://orcid.org/0000-0002-8502-6431Department of Astronomy, University of Florida , Gainesville, FL 32611 USA ; savannahgramze@ufl.eduDepartment of Astronomy, University of Florida , Gainesville, FL 32611 USA ; savannahgramze@ufl.eduNew Mexico Institute of Mining and Technology , 801 Leroy Place, Socorro, NM 87801 USA; National Radio Astronomy Observatory , P.O. Box O, Socorro, NM 87801 USANational Radio Astronomy Observatory , P.O. Box O, Socorro, NM 87801 USASteward Observatory, University of Arizona , 933 North Cherry Avenue, Tucson, AZ 85721, USAUniversität Heidelberg , Zentrum für Astronomie, Institut für theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg, Germany; Department of Physics, University of Surrey , Guildford GU2 7XH, UKNational Radio Astronomy Observatory , P.O. Box O, Socorro, NM 87801 USAThe Milky Way is a barred spiral galaxy with bar lanes that bring gas toward the Galactic center. Gas flowing along these bar lanes often overshoots, and instead of accreting onto the Central Molecular Zone (CMZ), it collides with the bar lane on the opposite side of the Galaxy. We observed G5, a cloud that we believe is the site of one such collision, near the Galactic center at ( ℓ , b ) = ( +5.4, −0.4) with the Atacama Large Millimeter/submillimeter Array/Atacama Compact Array. We took measurements of the spectral lines ^12 CO J = 2 → 1, ^13 CO J = 2 → 1, C ^18 O J = 2 → 1, H _2 CO J = 3 _03 → 2 _02 , H _2 CO J = 3 _22 → 2 _21 , CH _3 OH J = 4 _22 → 3 _12 , OCS J = 18 → 17, and SiO J = 5 → 4. We observed a velocity bridge between two clouds at ∼50 and ∼150 km s ^−1 in our position–velocity diagram, which is direct evidence of a cloud–cloud collision. We measured an average gas temperature of ∼60 K in G5 using H _2 CO integrated-intensity line ratios. We observed that the ^12 C/ ^13 C ratio in G5 is consistent with optically thin, or at most marginally optically thick ^12 CO. We measured $1.5\times {10}^{19}\,{\mathrm{cm}}^{-2}\,{({\rm{K}}\,\mathrm{km}\,{{\rm{s}}}^{-1})}^{-1}$ for the local X _CO , 10–20× less than the average Galactic value. G5 is strong direct observational evidence of gas overshooting the CMZ and colliding with a bar lane on the opposite side of the Galactic center.https://doi.org/10.3847/1538-4357/ad01beInterstellar line emissionInterstellar mediumInterstellar cloudsthe Milky Way physicsGalactic barGalactic Center |
| spellingShingle | Savannah R. Gramze Adam Ginsburg David S. Meier Juergen Ott Yancy Shirley Mattia C. Sormani Brian E. Svoboda Evidence of a Cloud–Cloud Collision from Overshooting Gas in the Galactic Center The Astrophysical Journal Interstellar line emission Interstellar medium Interstellar clouds the Milky Way physics Galactic bar Galactic Center |
| title | Evidence of a Cloud–Cloud Collision from Overshooting Gas in the Galactic Center |
| title_full | Evidence of a Cloud–Cloud Collision from Overshooting Gas in the Galactic Center |
| title_fullStr | Evidence of a Cloud–Cloud Collision from Overshooting Gas in the Galactic Center |
| title_full_unstemmed | Evidence of a Cloud–Cloud Collision from Overshooting Gas in the Galactic Center |
| title_short | Evidence of a Cloud–Cloud Collision from Overshooting Gas in the Galactic Center |
| title_sort | evidence of a cloud cloud collision from overshooting gas in the galactic center |
| topic | Interstellar line emission Interstellar medium Interstellar clouds the Milky Way physics Galactic bar Galactic Center |
| url | https://doi.org/10.3847/1538-4357/ad01be |
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